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The Origin of Biodiversity in Insects:

Phylogenetic Tests of Evolutionary Scenarios

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MEMOIRES DU MUSEUM NATIONAL D’HISTOIRE NATURELLE

TOME 173

ZOOLOGIE

The Origin of biodiversity in Insects:

Phylogenetic tests of Evolutionary Scenarios

Philippe GRANDCOLAS

E.P. 90 CNRS, Laboratoire d’Entomologie

Museum national d’Histoire naturelle

45 , rue Buffon

F -75005 Paris

EDITIONS

DU MUSEUM

PARIS

D97

Source: MNHN. Paris

CONTENTS

Pages

PREFACE .

1 The relevance of phylogenetic systcmatics to biology : examples from medicine and behavioral

ecology .

Laurence Packer

2. When is a phylogenetic test good enough?

John W. Wenzel

3. On the utility of mathematical models and their use in evolutionary biolog}

Yannis Michalakis, Eric Wajnberg& Carlos Bernstein

4. Testing evolutional*} processes with phylogenetic patterns: test power and test limitations

Philippe Grandcolas , Pierre Deleporte & Laure Desutter-Grandcolas

5. Comparative analyses of continuous data: the need to be phylogenetically correct

Serge Morand

6. Phylogenetic tests of evolutionary scenarios: the evolution of flightlessness and wing

polymorphism in insects.

Nils Moller Andersen

7. Habitat and ant-attendance in Hemiptera : a phylogenetic test with emphasis on trophobiosis in

Fulgoromorpha ......

Thierry BOURGOIN

8. Food choice and environment occupancy in Afrotropical dung beetles: a phylogenetic study of

two examples (Coleoptera, Scarabaeidae)

Yves Cambefort

9. Phylogenetic relationships among european Polities and the evolution of social parasitism

(Hymenoptera: Vespidae, Polistinae)

James M. Carpenter

10. Evolution of feeding and mating behaviors in the Empidoidea (Diptera : Eremoneura)

Christophc DAUGERON

11. Acoustic communication in crickets (Orthoptera: Grylloidea): A model of regressive evolution

revisited using phytogeny .

Laure Desutter-Grandcolas

12. Defense strategies in scale insects: phylogenetic inference and evolutionary scenarios (Hemiptera,

Coccoidea) .....

Imre Foldi

13 What did the ancestor of the woodroach Cryptocercus look like? A phylogenetic study of the

origin of subsociality in the subfamily Polyphaginae (Dictyoptera, Blattaria)

Philippe Grandcolas

. 9

109

125

135

163

183

203

231

PHYLOGENETIC TESTS OF EVOLU TIONARY SCENARIOS

14. Early evolution of the Lepidoptera+Trichoptera lineage: phylogeny and the ecological scenario ... 253

Niels Kristensen

15. Phylogeny and evolution of the larval diet in the Sciaroidea (Diptera, Bibionomorpha) since the

Mesozoic. 273

Loi'c Matile

16. The probabilistic inference of unknown data in phylogenetic analysis . 305

Andre Nel

17. The origin of Hexapoda: a developmental genetic scenario. 329

Jean S. Deutsch

18. Linking phylogenetic systematics to evolutionary biology: toward a research program in

biodiversity . 341

Philippe Grandcolas, Joel Minet, Laure Desutter-Grandcolas, Christophe Daugeron,

Loi'c Matile & Thierry Bourgoin

INDEX . 351

Source: MNHN. Paris

Preface

For several decades and since the development and

implementation of Hennigian methodology, phylogenetics

has been revitalized and is now more and more

incorporated into mainstream evolutionary biology. Beyond

the current use of buzzwords such as "biodiversity” or

"tree-thinking”, this shows that a new and promising

research field in comparative biology has arrived. Most

comparative studies of these last years may be considered

as either reconstructing parsimoniously past events or

modeling population processes and extrapolating them to

the past. This volume deals mainly with the first kind of

studies and emphasizes that both reconstruction and

modeling are specific and complementary fields which

should be kept independent and may thus test each other.

Comparative biology searches for evolutionary patterns

of descent with modification, which cannot be directly

ascertained in populations but only reconstructed from the

past. Comparative biology has been recently rejuvenated by

methodological advances in phylogenetic analysis. These

advances arose mainly by decreasing the use of a priori

hypotheses to infer more reasonable and more refutable

phylogenetic patterns. Because phylogenetic patterns are

constructed with minimization of a priori and ad hoc

hypotheses, they can test the scenarios predicted by

evolutionary' models of processes which are extrapolated

from population studies. In this way, phylogenetic patterns

do not provide direct estimates of the selective value of

traits or direct explanations of processes but can possibly

refute previous and lncongruent hypotheses of selection or

process.

To carry out phylogenetic tests of evolutionary scenarios,

it is thus necessary' to understand clearly what are the

respective aims and the pre-requisites of both phylogenetic

analysis and process modeling. Several contributions in

this issue deal with contrasting the methodologies of these

research fields. Packer stresses that using phvlogeny is a

highly heuristic task which may also help us to re¬

formulate evolutionary hypotheses. Wenzel characterizes

the extent to which phylogenetic patterns may be

themselves evaluated and may permit the test of

evolutionary models. Michalakis, Wajnberc. & Bernstein

comment on principles of modeling and stress that the

usefulness of models depends on their refutability.

Grandcolas, Deleporte & Desutter-Grandcolas

contrast phylogenetic patterns and evolutionary models and

emphasize that tests of congruence between them are

highly heuristic. Morand challenges the view that

modeling could not be used in phylogenetic analyses.

Phylogenetic patterns can be used to tell histories in

selected groups of organisms or to test formerly

hypothesized scenarios in these same groups. They can be

aiso used to test more general theories by repeatedly

testing evolutionary scenarios predicted by these theories.

This ultimate aim could be achieved using a large number

of phylogenetic case studies to confer a statistical value to

the addition of results of independent tests. This is why

"A major problem of contemporary evolutionary> theory

from an epistemological standpoint is not so much that its

propositions are untestable, but that its main practitioners

use theory to explain away pattern ...”

(ELREDGE & CRACRAFT, 1980: 14)

many studies of different groups with similar variation in

the trait of interest should be carried out Most

evolutionary models deal with hypotheses of stability and

complexification in some particular traits. These processes

imply particular patterns of stasis and polarity which can

be tested using phylogeny. Also, many evolutionary models

imply particular relations between traits. These process-

relations imply patterns of concentrated changes in traits

which can also be tested using phylogeny. Evolutionary

models are tested here using phvlogenies of water striders

(N. M. Andersen), leafhoppers and planthoppers (T.

Bourgoin), dung beetles (Y. Cambefort), vespid wasps

(J. M. Carpenter), flies (C. Daugeron, L. Matile),

crickets (L. Desutter-Grandcolas), scale insects (I.

Foldi), cockroaches (P. Grandcolas), moths and

caddisflies (N. P. Kristensen), sweat bees (L. Packer).

Evolutionary stability vs lability could also be tested with

respect to the paradigm of actualism in paleontological

studies. As many past taxa remain forever unknown,

probabilistic assumptions may be proposed to evaluate

actualistic hypotheses (A. Nel’s contribution).

Unexpectedly, most studies do not corroborate former

evolutionary hypotheses of stability and complexification.

Particular models of evolution were often shown to be

flawed: wasp social parasites are not closely related to their

hosts; the mutualism between ants and Homoptera is

homoplastic; ground-dwelling Exoporia (Lepidoptera) are

not primitive in this respect; predatory' habits and mating

swarms are not ancestral to empidoid flies; subsocial

cockroaches are not forerunners of eusocial termites. As far

as it can be reconstructed, evolution seems not to have

proceeded straightforwardly, and shows many

convergences and reversals. This homoplasy was not

predicted by models but is effectively detected using

parsimony. For example, social behavior in sweat bees,

flightlessness in water striders, or loss of acoustic behavior

in crickets all have reversed.

Regarding the neodarwinian paradigm, this could either

mean than genetic drift is more important than expected in

some cases or that the hypotheses of generalized selective

pressures are sometimes inaccurate. Disruptive selection or

genetic correlations could have influenced the evolution of

traits which w-ere hypothesized to be stable. This also

stresses the importance of studies in developmental

genetics (J. Deutsch's contribution): some traits could be

genetically determined in the way that they could have

been lost and regained, producing similar phenotypes. It

should also be taken into account that these results can be

biased regarding the whole history' of life. The ingroups

selected for phylogenetic studies are necessarily relatively

small and diverse and thus show probably more changes

than expected in the whole (Grandcolas et al.'s

contribution). Nevertheless, one major conclusion of this

volume is that homoplasy is detected even in supposedly

stable and complex traits and should be now taken into

account in the development of further evolutionary models.

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

Another important conclusion ot this volume could be a

methodological warning concerning phylogenetics and

modeling in evolutionary biology. It should be emphasized

that past reconstruction fundamentally remains conjectural.

Conjectures may become either sound and refutable

hypotheses, or gratuitous speculation. Only congruence

among independent data sets gathered using minimal

hypotheses permits us to propose sound evolutionary

hypotheses. The use of ad hoc models (by analogy, by

extrapolation,...) must be definitely checked using

appropriate “null” and minimal phylogenetic hypotheses.

The need for minimal null hypotheses has already been

emphasized in many research fields in evolutionary'

biology, with respect to hypotheses of adaptation (Gould &

Lewontin, 1979), biotic interaction (Quinn & Dunham,

1983), and biogeographv (Ball, 1975). It should be

stressed that this need also exists in comparative biology.

Comparative studies must take this need into accoimt, on

pain to have their results Hawed and refuted in the future.

This volume issued mainly from a Symposium (June

1996) organized by E.P. 90 CNRS (Laboratoire

d'Entomologie, Museum national d’Histoire naturelle) with

the support of Reseau national de Biosystematique

(financial support by Ministere de l'Enseignement

Superieur et de la Recherche, ACC-SV7). Many people

have contributed to the realisation of this Symposium,

thereby making possible the publication of this volume. I

would like to thank the persons who have accepted to give

talks and those who have provided moral and material

help, J. Najt, L. Desutter-Grandcolas, S. Tiller, C.

Caussanel, L. Packer, J. Boudinot, E. Guilbert, C.

DUaese, A. Souler-Perkjns, O. Montreue, A. Bendib.

Thanks also to Service des Publications of the Museum

national d’Histoire naturelle de Paris and to G. Hodebert

for his talented help concerning drawings. Referees have

kindly accepted to read the manuscripts and certainly

helped to improve them substantially: M. Akam, N. M.

Andersen, A. Bellido, J. M. Carpenter, J. Clobert, E.

Danchtn, P. Darlu, A. Deean, P. Deleporte, C.

Dietrich, R. J. Gagn£, P. J. Gullan, C. J. Hodgson, N.

Kristensen, D. McLennan, D. R. Maddison, S. Masaki,

J. Minet, C. M. Naumann, L. Packer, C. Plateaux-

Quenu, C. Scholtz, P. Tassy, B. Thorne, J. Van

Baaren, P. Vernon, J. Wenzel, B. Wegmann, S.

Wilson, D. Yeates.

Ball, I. R., 1975. — Nature and formulation of biogeographical hypotheses. Systematic Zoology\ 24: 407-430.

Eldredge, N. & Cracraft, J., 1980. — Phylogenetic patterns and the evolutionary process. Method and theory in

comparative biology. New' York, Columbia University Press: 1-349.

Gould, S. J. & Lewontin, R. C., 1979. — The spandrels of San Marco and the Panglossian paradigm. A critique of the

adaptationist programme. Proceedings of the Royal Society of London, B, 205: 581-598.

Quinn, J. F. & Dunham, A. E., 1983. — On hypothesis testing in ecology and evolution. The American Naturalist , 122:

602-617.

Philippe Grandcolas (Paris)

Source

The Relevance of Phylogenetic Systematics to Biology:

Examples from Medicine and Behavioral Ecology

Laurence Packer

Department of Biology and Faculty of Environmental Studies,

York University, 4700 Keele St., North York. Ontario, M3J 1P3. Canada

ABSTRACT

Results of phylogenetic analysis are frequently used to investigate the pattern of evolution of characteristics of interest. In

examples such as the evolution of spider webs, the number of horns on a rhinoceros or social behavior in halictine bees, the

results of phylogenetic tests may lead to traditional views being overturned. However, conclusions based upon phylogenetic

analyses of evolutionary pattern require careful consideration of character coding and taxonomic sampling as indicated by

studies of rhinos and HIV respectively. Phylogenetic results are less often used to direct further research, an area of their

application which remains underutilized. In this paper I concentrate on the application of phylogenetics to problems of social

evolution in halictine bees. There are seven genera/subgenera that are known to contain both solitary and social species and at

least 9 species which exhibit behavioral polymorphism with both solitary' behavior and eusociality found within the same or

different populations. A priori , these taxa would seem to be the best ones to use in tests of the selective advantages of

eusociality. However, results of phylogenetic analysis indicate that in the majority of cases ( Halictus , Seladonia,

Augochlorella and Augochlora) it is solitary behavior that is the recent evolutionary innovation and eusociality is ancestral.

Use of the non-phvlogenetic approach to the comparative method in each of these instances would not provide information on

origins of eusociality. In contrast, eusociality appears to be derived in both the subgenera Lasioglossum (in the species L

aegyptiellum for which the limited field-collected data are presented for the first time) and Evylaeus. Overall, of the nine

species for w'hich both eusociality and solitary’ behavior have been recorded, solitary’ behavior is the recent acquisition in at

least 6 cases, and the only probable case of recent origin of eusociality exhibited by behaviorally polymorphic species

(Lasioglossum (Evylaeus) comagenense and L (E.) J'rate Hum) refers to origin of delayed eusociality. The application of

phylogenetic methods to the study of evolutionary pattern suggests both which taxa are deserving of further field work and

which require additional phylogenetic analysis.

RESUME

L'interet de la systematique phylogenetique pour la biologie : quelques exemples issus de la biologie medicale et

I'eco-ethologie

Les resultats des analyses phylogenetiques sont frequemment utilises pour inferer les sequences devolution de caracteres

d'interet particular. Dans des exemples tels que revolution des toiles d'araignees, du nombre des comes de rhinoceros, ou du

comportement social des abeilles halictes, les resultats des tests phylogenetiques peuvent conduire a refuter des schemas

traditionnels devolution. Dependant, les conclusions basees sur l'analyse phylogenetique des sequences evolutives sont

dependantes du codage des caracteres et d'un echantillonnage taxonomique suffisant, comme cela est montre a propos des

etudes concemant les rhinoceros et le virus HTV. Les resultats phylogenetiques peuvent etre aussi utilises pour orienter de

futures recherches, ce qui constitue un domaine de recherche encore trop peu explore. Cette article conceme principalement

Packer, L., 1997. — The relevance of phylogenetic systematics to biology: examples from medicine and behavioral

ecology. In: Grandcolas, P. (ed.). The origin of biodiversity in Insects: phylogenetic tests of evolutionary' scenarios. Mem.

Mus. natn . Hist, fiat., 173 : 11-29. Paris ISBN : 2-85653-508-9.

L. PACKER : RELEVANCE OF PHYLOGENETIC SYSTEM AT ICS TO BIOLOGY

1'applicalion de la systematique phylogenetique aux problemes d'evolution sociale chez les Abeilles Halictes. II y a sept

genres/sous-genres qui sont eonnus pour regrouper non seulement des especes solitaires et des especes sociales mais aussi au

moins neuf especes dont le polymorphisme coniportcraental englobe des comportements solitaires et eusociaux trouves dans

les memes populations ou dans des populations diflerentes. A priori, ces taxa devraient done parfaitement convenir au test des

avantages que confererait l’eusocialite en regard de la selection naturelle. Cependant, les resultats de 1 analyse phylogenetique

indiquent que dans la majorite des cas ( Halictus , Sela/Ionia , Augochlorella et Augochlora), e'est le comportement solitaire qui

est l’innovation evolutive et Peusocialite qui est ancestrale. Dans chacun de ces cas, une approche non-phylogenetique de

biologie comparative n'aurait pas foumi d'information sur les origines de Peusocialite. L'approche phylogenetique indique que

Peusocialite est derivee a la fois dans deux des sous-genres de Izisioglossum (chez l'espece L. aegyptiellum pour qui des

donnees de terrain sont presentees ici pour la premiere fois) et dans le genre Evylaeus. Globalement, des neufs especes chez

qui Peusocialite et le comportement solitaire ont ete tous deux rapportes, le comportement solitaire est l'acquisition recente

dans au moins six cas. Le seul cas probable d'origine recente de Peusocialite chez des especes au comportement

polymorphique ( Lasioglossum (Evylaeus) comageneuse et L. (E.) fratellum ) conceme une origine de Peusocialite differee.

L'application de la methode phylogenetique a Petude de Pevolution permet de determiner a la fois quels taxa requierent des

etudes de terrain et quels taxa necessitent des etudes phylogenetiques supplementaires.

INTRODUCTION

In this paper I wish to explore the utility of phylogenetic systematics in providing answers

to two questions: i) what are we studying? and ii) what should we be studying? It may seem that

answers to these questions are self evident - surely we always know what it is that we are

investigating and are always confident that this is indeed what we should be studying. However,

recent reanalyses indicate that the confidence with which we approach our studies is often

misplaced.

What are we studying?

When biologists make comparisons of some feature of interest which varies between taxa

we generally rely upon “common sense” arguments as to the adaptive value of the differences we

observe. Species A has some condition which is a result of adaptation to its environment whereas

species B has some other state which is similarly adaptive. We study how both characteristics

function in their respective species/environments and understand both states to be adaptive.

However, the minimal requirement for a characteristic to be considered to be an adaptation is

that it is a derived feature (CODDINGTON, 1988, 1995; GRANDCOLAS et a/., 1994; CARPENTER,

1997, this volume). In comparing states between the species one of them is likely ancestral to the

other. It is the evolutionary change between states that represents the results of selection and

hence provides evidence for adaptation. Consequently, we need to know the polarity of

evolutionary change between character states; only then will we know what the direction of

evolutionary change in the character of interest has been: i.e., only then will we really know what

it is that we are studying.

Results of phylogenetic analysis indicate that common sense approaches to polarity are

often wrong. For example, consider spider webs of the cob and orb varieties. It is common sense

to suggest that the rather untidy cobwebs made by some spiders served as an antecedent to orb

webs, after all, they are apparently simpler in design and are constructed in places where it seems

easier for spiders to negotiate web building. However, phylogenetic analysis demonstrates the

reverse to be true: the orb web is ancestral to cobwebs with the latter arising several times

independently in different spider lineages (CODDINGTON, 1988). Thus, in comparing cob and orb

webs we would be answering questions about the selective advantage of cob versus orb webs

Source:

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

whereas the common sense, non-phylogenetic, approach suggests we would be looking at the

converse - the benefits of orb over cob webs.

Another classic example, the evolution of horn number in rhinoceroses, has recently

become more complex and illustrates the importance of careful character coding (DELEPORTE,

1993). A “common sense" argument is that as i) the protorhino condition would have zero as the

number of horns along the midline of the head and ii) rhinos come with one or two horns, then

the evolution of horn number must have followed the mathematically simple sequence of 0, to 1,

to 2. However, a morphological phylogeny (GROVES, 1983) indicated unambiguously that one

horned rhinos have evolved from 2 homed ancestors (CODDINGTON, 1988). Conversely, a recent

molecular phylogeny (MORALES & MELNICK, 1994) is consistent with the 0 to 1 to 2 scenario in

that one-horned rhinos form the first branch in the ingroup Combined data in a total evidence

analysis (PACKER, unpublished) leads to various possible interpretations of evolutionary change

in this character depending upon how horn number is coded. If treated as an ordered character

then there are two equally parsimonious resolutions of horn number evolution: i) from 0 to 2

(through 1) in the common ancestor, with a reduction to one horn in Rhinoceros (Fig. 1A) or ii)

from 0 to 1 in the ancestor followed by a change from 1 to 2 horns on two separate occasions

(Fig. IB). As an unordered character, 0 to 2 to 1 is the single most parsimonious result (Fig.

1A). This illustrates the problems that can arise as a result of alternative coding methods for the

characteristics of interest, a point that will be returned to later. However inclusion of fossil

genera demonstrates clearly that among extant rhinoceros, loss of the frontal horn has occurred

and so the polarity of change in horn number among extant rhinos is indeed from 2 to 1

(Packer, unpublished).

A B

Fig- 1- — Evolution of horn number in extant rhinoceros. A: If treated as an unordered character then two evolutionary

changes are required - from 0 to 2 in the ancestor and from 2 to 1 in Rhinoceros. If treated as an ordered character,

then three changes are required, from 0 to 2 (through 1) in the common ancestor and from 2 to 1 in Rhinoceros or B:

from 0 to 1 in the ancestor with two independent derivations of the second horn.

In much of modern evolutionary biology “common sense” is replaced by more complex

models based upon population genetics or evolutionary ecology. However, scenarios predicted

L. PACKER : RELEVANCE OF PHYLOGENETIC SYSTEMATICS TO BIOLOGY

by these sophisticated approaches can also be shown to be false using phylogenetic methods

(Andersen, 1997, this volume).

Although these examples stand out because their conclusions are counterintuitive, it is

precisely this point that I wish to make - in the absence of a phylogenetic test of some a priori

notion, one is likely to make mistakes by relying upon common sense biological “knowledge”.

These mistakes may lead to researchers spending a considerable amount of time (and money)

asking the wrong question; a research program aimed at answering the question “what selection

pressures caused the evolution of orb webs from cob webs?” would, at best, be doomed to

inadequacy from the outset. For excellent accounts of the use of phylogenetic approaches and

definitions and tests of adaptation see Grandcolas et al. (1994) and Coddington (1995).

What should we he studying?

Whereas mapping characters onto a phylogeny to verify or refute a scenario is becoming de

rigeur in evolutionary biology (see most of the papers in this volume), the use of a cladogram to

direct future research seems underutilized. Not only does phylogenetic analysis permit us to

know the polarity of evolutionary change between character states, it also locates the position of

the transition between states on the phylogeny. Clearly, comparisons of taxa on either side and in

close proximity to this juncture are most likely to provide clues as to causation. These are the

organisms that we should be studying; the comparisons that can most fruitfully be made.

The trouble is that our information is rarely complete. Phylogenetic studies of

characteristics of interest usually cannot include all taxa because not all species are known for the

traits of interest, phylogenetic information is incomplete, or both. There are several ways to

overcome these limitations.

It may be possible to make an educated guess as to the state of some character of interest if

a species is unknown behaviorally or ecologically but its position phylogenetically is known. For

example, BROOKS et al (1992) used phylogenetic analysis as a guide to field research and as a

result discovered the breeding site of Etheostoma wapiti , an endangered fish species whose

habitat requirements were not known. It is probable that discovery of the breeding site

requirements of this species would have been delayed if it weren't for the application of

phylogenetics to this problem. Thus, phylogenetic results can be used to guide field work.

Another approach is to produce a phylogeny for those species for which data of interest are

available. With a phylogeny based upon a restricted sample of taxa it is still possible to trace the

approximate position of a character state change of interest. Further systematic research can then

add taxa to the phylogeny, concentrating upon those species thought to lie close to the transition

point in the phylogeny. The results of this second phylogenetic iteration may then be used as a

guide to which species should be the subjects of field research. This procedure greatly simplifies

the problem of phylogenetic reconstruction, especially for speciose groups, although there is

some potential for loss of accuracy when large proportions of a group are left out of a

phylogenetic analysis. A more insidious cause of potential error with this approach is biased

sampling of taxa. Consider some character state to be of great interest in comparison to the

alternative condition: it is more likely that information on species possessing the interesting

condition will be reported than data on the absence of the feature of interest. Species within

higher level taxonomic groups will then have an unrealistic preponderance of the interesting

condition and the results of mapping character traits onto the phylogeny will be biased in favor of

Source:

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

optimizing the interesting character state as ancestral. I will return later to an example of this in

bees, but will first turn to a medical example.

The Evolution of HIV

I will illustrate my point with reference to the evolution of HIV both because of the clear

alternatives suggested by a phylogenetic approach and because it does serve as a great example

for use in the classroom - never will a class being taught the rudiments of phylogenetic

methodology be so attentive as when the evolution of HIV is being considered.

The classic story, that may be read in medical texts, is that HIVI and HIV2 spread from

non-human primates into the human population in Africa at some comparatively recent point in

time and that they did this independently of each other yet more or less simultaneously (e.g.

MYERS et al., 1993), this pattern is referred to as the simian hypothesis. Figure 2A shows a

phylogeny consistent with dual transfer to humans. The assumption that this disease is recent in

humans is supported by the classic epidemiological dogma that diseases evolve from levels of

high virulence to more benign relationships with their hosts. The high virulence of FIIV (HIV1 at

least) is taken by many as being the result of relatively recent introduction of the virus into

human populations by cross-species infection Combine several a priori notions into one logical

argument and it is not likely that one will meet much opposition. Fortunately, some researchers

step aside from these assumptions and test the logical bases upon which they rest. Here I will

concentrate upon the potential role that different taxonomic sampling protocols may have played

in this story. For details concerning the history of other criticisms of the standard dogma over

HIV see Grmek (1990).

MlNDELL et al. (1995) have published a phylogenetic analysis of immunodeficiency viruses

based upon sequence data (Fig. 2B). The most parsimonious mapping of hosts onto the viral

phylogeny suggests that the common ancestor of HIV1 and HIV2 was a virus that infected

human beings and that, in addition to an initial colonization event into humans, there have been

multiple independent interspecies transfers from human beings to other primates. This suggests

that HIV has had humans as hosts for at least several hundred years and that something other

than a recent transfer into the human population is responsible for the extreme virulence of HI VI

(EWALD, 1994; MASSAD, 1996).

It is evident that analyses that leave out much of the diversity found within HIV1 and HIV2

are likely to bias the results in favor of the simian hypothesis. MlNDELL et al. (1995) took into

consideration a great diversity of HIV and SIV lineages in comparison to previous analyses (e.g.

MYERS et al., 1993) If one were to remove all but one of the HI VI strains and all but two of the

HIV2 strains from Figure 2B, using the same phylogenetic mapping logic, one would conclude

that the common ancestor of HIVI and HIV2 did indeed occur in a non-human primate and the

simian hypothesis would thereby garner support simply as a result of biased sampling! This is

precisely the taxon sampling protocol used by MYERS et al. (1993).

The currently available analyses do not suggest that a stable phylogenetic pattern for

HIV/SIV evolution and evolutionary changes in host use has not been attained by HIV

researchers. Nonetheless, it is clear that when a wide range of taxa are available, choice among

them will influence the phylogenetic results obtained.

L. PACKER : RELEVANCE OF PHYLOGENETIC SYSTEMATICS TO BIOLOGY

Sykes

HIV2d205

HIV2rod

smmpbj

smmh4

mne

mm142

mm251

Agm3

Agmtyo

Agm155

Agm49

Agm9

Agm40

Agm692

Agm677

mndgbl

HIVImn

Cpz

FIV14

SIVsyk

SIVmndgb

HIV2nihz

HIV2st

HIV2rod

HIV3ben

HIV2d194

SIVstm

SIVmm239

SIVmne

SIVsmm9

SIVsmmh4

HIV2d205

HIV2uc1

SIVagm677

SIVagm155

SIVagm3

SIVagmtyo

i HIV1mvp5180

i HIV1ant70

SIVcpz

i HIVImal

i HIVIrf

i HIVIeli

i HIVIndk

> HIVIlai

■ HIVIjrcsf

p IG 2 . _Two scenarios for the evolution of host association for primate immunodeficiency viruses. Pale grey patterns

represent non-human primates as hosts, black ones refer to human hosts, dark grey ones represent leline

immunodeficiency virus and dashed patterns represents ambiguous resolution. A: the simian hypothesis is supported

by Myers et al (1993) who used only two strains of IHV2 and one of HIV 1 in their analysis. B: a human ancestral

host, a more ancient ancestry and multiple infection into non-human primates are suggested by Mindell et al. (1995).

Note that in both phvlogenies different non-human primate hosts are not differentiated in cladogram shading.

Phylogenies redrawn from both sources.

THE EVOLUTION OF SOCIAL BEHAVIOR IN HAL1CTINE BEES

Eusociality involves a reproductive division of labor between generations, archetypally

between a mother queen and her worker daughters (WILSON, 1971; MlCHENER, 1974). Among

the Hymenoptera it is found in ants, vespid and sphecid wasps and various groups of bees.

There have been many theoretical treatments aimed at explaining the origins of worker

sterility (partial or complete) of which the kin selection (or haplodiploidy) hypothesis has

received the most attention. A fundamental prediction of this hypothesis is that female nestmate

relatedness be high. But, most analyses indicate this not to be the case (Gadagkar, 1991).

However, the vast majority of tests have concerned ants and vespine wasps, taxa which have

been eusocial since the Cretaceous (Brandao et al , 1989; WENZEL, 1990). Testing a hypothesis

Source: MNHN. Pans

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

of origins of eusociality with these organisms is then somewhat too late, approximately 100

million generations too late Consequently, it has been stated that halictine bees are more suitable

candidates for testing hypotheses of eusocial origins (Packer, 1991; PACKER & OWEN, 1994).

One reason for this is that all halictines exhibit primitive eusociality ( i.e. they lack a marked

morphological disparity between the castes) and with few exceptions (Plateaux-Quenu, 1959;

Sakagami & PACKER, 1994), their societies are annual. Another reason for such optimism is the

spotty taxonomic distribution of eusociality among the Halictinae. Not only are there seven

genera/subgenera that contain both solitary and eusocial species (Table 1), there are at least 9

species which are known to have both solitary and social behavior as a behavioral polymorphism

Table 1. — Genera and subgenera of halictines which contain solitary and eusocial species. Species which are both eusocial

and solitary are listed under both categories. Data from a variety of sources including Yanega (1997) and Moure &

Hurd (1987).

Genus/subgenus

solitary

Number of species

eusocial

unstudied

Hal ictus

Seladonia

>30

Lasioglossum

>60

Evylaeus

>60

DiaUctus

many

100s

Augoch/orel/a

Table 2. — List of halictine species known to exhibit behavioral polymorphism either in the same, or different population *:

delayed eusociality and the normal annual eusocial colonies have both been reported. **: eusociality known only as

delayed eusociality.

Ha!ictus rubicundus

different

Seladonia confusus

same

Seladonia tumulorum

same?

Evylaeus calceatum*

different

E. albipes*

different

E. /rate Hum**

same

E. comagenense**

same

Dial ictus problematicum * *

same

Augochlorella striata

same

Yanega (1997); Eickwort et al. (in press)

Tuckerman (pers. com.)

Stockhert (1933); Sakagami & Ebmer (1979)

Sakagami & Munakata (1972)

PLATEAUX-QufeNU (1993)

von der Heide (1992); Field (1996)

Packer (unpubl. obs.)

Sakagami & Packer (1994)

Packer (1991)

(Table 2). By behavioral polymorphism I refer to a situation in which more than one type of

behavior is routinely found within the species/population under normal conditions, it does not

refer to a situation in which accidents of mortality cause a change in social structure (for

L. PACKER : RELEVANCE OF PHYLOGENETIC SYSTEMATICS TO BIOLOGY

example, if occasional early worker mortality leaves a foundress with no option but to act as a

solitary female). If a population exhibits some eusocial colonies but there is a large proportion of

foundresses that produce a brood with females none of which work then that would be

considered an example of behavioral polymorphism. Similarly if a species has populations that

are social and others that are solitary it would also be considered to be socially polymorphic. It

should be noted that in no cases have these polymorphisms been unambiguously determined as

having a genetic basis, although in one case bees from solitary and eusocial populations have

been shown to retain their behavioral differences when reared under identical conditions

(PLATEAUX-QUENUe/a/., submitted).

Arguments for both the frequency and recency of eusocial origins in the Halictinae rest on

the assumption that in each (or at least most) of the examples of intraspecific behavioral

polymorphism or behavioral variation within a genus/subgenus, it is eusociality that is the derived

condition. But for each variable taxon this common sense approach to evolutionary polarity is a

hypothesis that requires testing.

Below I will outline what we know of halictine phylogeny for each of the groups that are

behaviorally variable. In all cases our knowledge is doubly incomplete - no single genus or

subgenus has been subjected to a thorough phylogenetic analysis involving all species and for

none of them is the behavior of all species known (Table 1). Given the large number of species in

each genus/subgenus, it is doubtful that either of these areas of inquiry will be completed for any

taxon in the near future. Nonetheless, phylogenetic analysis can be useful in determining which

taxa are likely to be most suitable for further study both in the field and phylogenetically.

Methods

I have obtained phylogenies from the literature or from my own studies. Wherever the

example illustrates a point of general procedural interest, this is noted in the subheading.

All phylogenies were either verified or obtained using Hennig86 and whenever multiple

equally parsimonious trees resulted, successive approximations character weighting (Carpenter,

1988) was invoked. Inclusion of the social behavioral data in the matrix used to produce the

phylogenies is not recommended in all but one case because of the difficulties associated with

including polymorphic attributes (GRANDCOLAS et a/., 1994; DELEPORTE, 1993) in such

analyses, especially when one might want to code behavioral polymorphism as an intermediate

stage between solitary and social behavior (as would seem logical).

The examples

Total evidence and character coding in Halictus and Seladonia. PESENKO (1985) provided

a morphology-based phylogeny of species groups (as named subgenera) of Halictus and

RICHARDS (1994) used allozyme electrophoresis to construct a phylogeny of many of the

behaviorally known species in the subgenus and also some species of the subgenus Seladonia.

The former analysis is more complete in terms of the number of taxa included although it is now

suspected that Seladonia (and Vestitohalictus) should be included within the ingroup ( Halictus)

rather than among the outgroups (PESENKO, personal communication). Clearly, behavioral data

are not available for all of the included species and not even all of the species groups that

PESENKO (1985) defines. Nonetheless, mapping behavioral traits (Fig. 3) onto the phylogeny

Source: MNHN, Paris

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

yields the conclusion that social behavior is ancestral and solitary behavior has arisen

independently at least three times (Packer, 1986).

The electrophoretic data of Richards (1994) yielded two subsets of equally parsimonious

trees and in both sets it is more parsimonious to treat eusociality as ancestral with solitary

behavior and social behavioral polymorphism as being derived character states.

parallelus

farinosus

rubicundus

quadricinctus

latisignatus

tsingtsouensis

patellatus

maculatus

ligatus

cochlearitarsis

fulvipes

resurgens

scabiosae

sexcinctus

Fig. 3. — Mapping behavioral characters onto a phylogeny for Halictus provided by Pesenko(1985) suggests eusociality to be

ancestral with multiple independent origins of solitary behavior (from Packer. 1986). Pale grey patterns refer to

solitary behavior, dark grey ones represent behavioral polymorphism and black bars indicate eusociality, dashed

patterns represents ambiguity. Polymorphism coded as a third state in an unordered transformation series.

I have combined these data sets and added morphological data on Seladonia to produce a

very preliminary “total evidence” phylogeny for the group. In the analyses presented below, the

electrophoretic variables were considered as unordered and the morphological ones were ordered

where possible. A smaller morphological data set than presented by PESENKO is used here as I

have included only those characters whose polarity can be determined without reference to

Seladonia as an outgroup and where character states for this subgenus could be homologized

readily with those of Halictus. I have taken advantage of some more recent behavioral research

(ElCKWORT et ai, 1996; TUCKERMAN, personal communication) in assigning behavioral

character states to terminals.

The results provided here are clearly far from complete even in terms of the representation

of socially known species. Nonetheless, they do indicate the importance that choice among

alternative coding schemes may have upon deduced evolutionary scenarios. Twelve equally

parsimonious trees resulted from the analysis of the raw data matrix, each had a length of 159, a

Cl of 0.81 and RI of 0.77. One round of successive approximations character weighting led to

one tree, the various statistics of which stabilized. This tree retains both subgenera Seladonia and

Halictus as monophyletic groups.

Three coding methods were employed for the social behavior data: i) treating

polymorphism as a third character state in an ordered transformation series ii) treating

polymorphisms as a third character state in an unordered transformation series and iii) treating

L. PACKER : RELEVANCE OF PHYLOGENETIC SYSTEMATICS TO BIOLOGY

polymorphic species as having eusociality. These three coding protocols suggest different

phylogenetic patterns for social evolution. When polymorphism is treated as an ordered

intermediary character state social polymorphism is optimized as ancestral for Halictus +

Seladonia and from this, solitary behavior is lost two or three times and eusociality is lost twice

(Fig. 4A). When treated as an unordered three state character with polymorphism as the third

state there is still substantial ambiguity (Fig. 4B). If the presence of eusociality is coded whether

' 10 4 ., The f C T 10S !" r social edition in Halictus and Seladonia combined with phytogenies based upon a combined

data matrix from Pesenko (1985) and Richards (1994). Pesenko's characters 1 -6, 8-11, 17-23, 25-28, 35 37 and 38

were included in the analysis with all multi-slate characters coded as ordered except 1, 20 and 37 Note that

.4gaposlemon is listed as the outgroup as this was the taxon used as such in the electrophoretic study, a much wider

range ol taxa were used to polarise the ingroup characters for the morphological analysis. A: Behavior optimized with

polymorphism as a third, intermediary' state. B: polymorphism treated as a third state in an imordered character

C: polymorphism treated as presence of eusociality. For explanation of cladogram shading see legend to figure 3.

Source: MNHN. Paris

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

polymorphic or not, then eusociality is ancestral with reversal to solitary behavior occurring at

least twice (Fig. 4C).

The genus Lasioglossum. Lasioglossum aegyptiellum (Fig. 5) has been recorded as being

eusocial based upon one nest excavated by KNERER. I have had the opportunity to inspect the

preserved contents of this nest, although KNERER's original field notes and dissection data have

been lost. The nest was excavated on August 1st, 1977 in the Camargue region of France. Five

adults were found within the nest (Table 3), all had well worn wings and mandibles although the

largest individual had much the greatest amount of mandibular wear and, based upon the

Fig. 5. — Habitus drawing of female Lasioglossum aegyptiellum , the species for which recent evolution of eusociality seems

most readily documentable.

coloration of the wings, is the oldest individual among them, this individual is probably the

queen. All individuals had well developed ovaries, although deterioration and previous dissection

of the specimens makes it impossible to provide accurate ovarian development indices or to

establish which among them was mated. Three male and one female pupae, five fully grown

larvae and an unknown number of smaller larvae and pollen balls were also found. The female

L. PACKER : RELEVANCE OF PHYLOGENETIC SYSTEMATICS TO BIOLOGY

pupa had the same head width as the largest adult female. These meager data are consistent with

eusociaiity with poor ovarian suppression in the workers.

There is only this one species of Lasioglossum s.slr. which may considered to be eusocial

and at least 6 are known to be solitary (YANEGA, 1997) and so it is a priori probable that this

represents a recent origin of eusociaiity (as also suggested by the high degree of ovarian

development among the smaller adult females). Nonetheless, phylogenetic corroboration is

needed. There are currently no phytogenies for Old World Lasioglossum . However, McGlNLEY

(1986) has produced a phylogeny for the New World species, two of which ( leucozonium and

zonal urn) are holarctic. Lasioglossum aegyptiellum belongs to the leucozonium group

(WARNCKE, 1975; PESENKO, 1986).

I have added L aegyptiellum to the phylogeny by looking at its states for the 48 characters

in McGim.EY’s (1986) data matrix. As expected, /.. aegyptiellum falls within the leucozonium

group (Fig. 6) based upon the synapomorphy of long male mandibles (a character which varies

homoplastically elsewhere among New World species).

As both L. leucozonium (ATWOOD, 1933; STOCKHERT, 1933; PACKER, unpublished

observations) and L. zonulum (STOCKHERT, 1933; KNERER & ATWOOD, 1962; PACKER,

1ABLE l , D . a , tU lr T a ^^‘Oglossum aegyptiellum. *: mandible wear is scored from 0 (unworn) to 6 (worn down to

below the subapical tooth), wing wear is scored as the number of nicks in the wing margin, "tattered ' refers to the

entire margin being abraded, "very tattered" refers to the entire margin worn away such that wing length cannot be

Female

Head width (mm)

Wing length (mm)

Degree of abrasion of*

Mandible Wing

2.8

6.9

tattered

2.7

6.5

2.7

6.6

tattered

2.7

very tattered

2.6

6.1

tattered

unpublished observations) are solitary, as are all other Lasioglossum s.slr for which data are

available (Yanega, 1997), it is clear that eusociaiity in L. aegyptiellum is a derived condition

(F'g- 6).

Taxonomic sampling and Evylaeus. Packer (1991) provided a phylogeny of eight species

ot the subgenus Evylaeus based upon electrophoretic data. Only one of the included species was

known to be solitary and, at that time, another was known to exhibit behavioral polymorphism

he results were unambiguous in demonstrating that the polymorphic species represented a

, ecent t0 solltary behavior in a montane population in Japan (Sakagami & Munakata,

7_). W hether solitary or eusocial behavior was ancestral to the subgenus as a whole remained

Source: MNHN. Paris

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

Fig. 6. — Phylogeny for three species in the leucozonium group of the genus Lasioglossum demonstrating that L. aegyptiellum

has recently evolved sociality. Data from McGinley (1986) with additional information forL. aegyptiellum which has

indentical character states to those of L zonulum for all characters used by McGinley that could be assigned character

states unambiguously.

fulvicome

boreale

tricinctum

new species

i comagenense

i pauxillum

i marginatum

i cinctipes

i calceatum

i albipes

i laticeps

i lineare

malachurum

Fig. 7. — Phylogeny for some species of the subgenus Evylaeus based upon a total evidence analysis (redrawn from Taylor,

1994). For cladogram shading refer to legend for figure 3.

Source:

L. PACKER : RELEVANCE OF PHYLOGENETIC SYSTEMATIC^ TO BIOLOGY

undetermined, partly because the outgroup contained both solitary and social species. Note that

the fact that only one purely solitary species could be included in the analysis biased the result in

favor of finding that eusociality is ancestral: with only one solitary species in the ingroup and

ambiguity as to the outgroup' condition it is not possible to optimize solitary behavior as

ancestral, this indicates the importance of taxon sampling when incomplete phylogenies and

behavioral information are available. Inclusion of the behavioral data into the data matrix used in

phylogenetic analysis made no difference to the tree topology although Cl and RI were reduced

(Packer, unpublished).

In order to resolve this situation additional information was required for taxa close to the

root of the tree. Several North American species are allied with L. (E.) fulvicorne (Svensson et

a/., 1977) and so some of these (and other species) were sampled and added to the phylogeny by

Taylor (1994). In this case the results differ depending upon whether the behavioral data are

used in tree construction or not. The behavioral data considered appropriate to include in the

phylogenetic data matrix are those that do not vary within species. Thus, whether queen and

worker size distributions overlap or not, whether fewer than one percent of the workers mate or

not and three nest architectural variables were included whereas solitary versus eusocial

behavior, multiple foundress associations and the number of worker broods were not included as

these three features are attributes which vary within taxa. One species (L. (E.) cinctipes ) changes

position between electrophoretic and total evidence analyses. The latter approach is preferred

both philosophically (KLUGE & WOLF, 1993) and empirically: total evidence places this taxon in

a more reasonable position as judged by synapomorphies of the male genitalia (Packer

unpublished data).

Four equally parsimonious trees were obtained with the total evidence data set with lengths

of 125, Cl of 0.84 and RI of 0.77. One round of successive approximations character weighting

reduced the number of trees to three and the tree statistics stabilized at the second round to a

length of 850, Cl of 0.94 and RI of 0.92. The resulting Nelson consensus tree is shown in

figure 7.

Mapping behavior onto the total evidence phylogeny (Fig. 7) leads to the following

conclusions: i) Solitary behavior is ancestral in Evylaeus with eusociality arising in the

pauxillum malachurum clade and also, as delayed eusociality (in which founding females become

queens in their second year of life after their first brood daughter(s) overwinter), in the lineage

leading to comagenense. ii) Social polymorphism is ancestral to the albipes/calceatum species

pair (see Plateaux-Quenu, 1989, 1993 for data on the former species), (social polymorphism -

with delayed eusociality and solitary behavior is also known from comagenense and it's sibling

spec.es/ (E.)fratellum (yonderHEIDE, 1992; Field, 1996)). iii) It remains probable that the

perennial societies of L. marginatum are derived from an annually eusocial ancestral condition

However, given the increasing documentation of delayed eusociality (a phenomenon which

requires unusually detailed field work). This last conclusion may need to be revised. This is

because delayed eusociality is clearly a likely intermediate condition between annual and

perennial colony cycles and it seems to occur, at least as a polymorphic attribute fairly

commonly. ’ J

As there are many more species in this subgenus that remain unknown behavioraliy, a more

broadly based phylogenetic study is required. Once a more complete phylogeny including more

of the taxonomic diversity in Evylaeus is available, it should be possible to predict which taxa

Source: MNHN. Paris

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

should be studied in the field in order to narrow down more closely the precise phylogenetic

position of the origins of eusociality in these bees.

The genus Dialictus. Many species in this subgenus are known to be social and many

solitary (PACKER, 1992, 1994; WCISLO et a /., 1993). These small bees are morphologically

monotonous and very difficulty to identity, let alone analyze phylogenetically. Nonetheless,

molecular approaches to Dialictus phylogeny are underway (Danforth, personal

communication). At present, it is not possible to say anything about the phylogenetic

interrelationships among those Dialictus species whose behavior has been studied. Nonetheless,

it appears highly likely that recent transitions from solitary to eusocial behavior (as well as the

reverse) can be documented within Dialictus.

The genera Augochlorella and Augochlora. A recent phylogeny of genera of the tribe

Augochlorini demonstrates that the genera containing eusocial species form a monophyletic clade

(Fig. 8; DANFORTPI & ElCKWORT, 1997). Augochlorella is the sister group to the remaining

genera and one of its species, A. striata , is behaviorally polymorphic at the northern edge of its

range (PACKER et a/., 1989; PACKER, 1990) but only eusocial further south in New York

(MUELLER, 1991) and Kansas (ORDWAY, 1966). As i) the Augochlorini are largely tropical

American, ii) only 3 genera reach temperate North America, iii) A. striata achieves a higher

latitude than any other species and iv) other species of Augochlorella are eusocial (Yanega,

Fig. 8. — Phylogeny of genera of augochlorine bees (redrawn from Danforth & Eickwort, 1997). For cladograin shading,

refer to legend for figure 3. Note that for simplicity a clade of eight genera/subgenera, the sister group to the lineage

containing the eusocial taxa, is replaced here simply by the “Megalopla clade" Also, there are an additional 13

genera/subgenera more basal to the portion of the phylogeny shown here. Redrawn from Danforth & Eickwort

(1997).

1997), it seems safe to assume that the solitary aspect of this locally polymorphic species is the

derived condition and is presumably the result of the short summers experienced at the northern

latitude on the edge of the species' range (PACKER, 1990).

The subgenus Augochlora includes the solitary wood-nesting A. pura (STOCKHAMMER,

1966). It is clearly nested well within the eusocial clade of augochlorines and thus is an example

of the loss of eusociality.

L- PACKER : RELEVANCE OF PHYLOGENETIC SYSTEMATICS TO BIOLOGY

DISCUSSION

It is now no longer acceptable to make statements concerning the pattern of evolution in

some characteristic of interest without reference to a phylogeny that corroborates that pattern

(Grandcoi.as el a/., 1994). It is also clear that the incorporation of phylogenetic tests of the

polarity of evolutionary change in specific characters often overturns dearly held convictions

based upon a priori common sense biological “knowledge”. This paradigm shift influences not

only classifications (the original arena for the application of phylogenetic results) but also

evolutionary scenarios.

Cladistic methods provide a means of testing hypotheses of character evolution. If the

results indicate that the direction of evolutionary change in the character of interest differs from

that traditionally held, then a lot of effort which would have been misdirected can be refocussed

and events which actually happened can be investigated, rather than patterns which arose only as

a result of the preconceived notions of biologists. However, the utility of phylogenetics goes

much further than this. Particularly for the more speciose groups of organisms, basic biological

data are generally not available for all species yet the sparse information that does exist can be

placed within a phylogenetic framework. If a phylogenetic analysis includes taxa for which

information on the feature of interest is not available, the results may indicate clearly which taxa

occupy crucial transitional positions in the phylogeny and are thereby those which should be

studied in the field. If both phylogenetic and behavioral/ecological information are fairly

complete, then mapping the traits of interest onto the phylogeny will permit the pattern of

evolutionary change(s) in the characteristic of interest to be discovered. Thus, in addition to

aiding in the interpretation of field research, through the establishment of polarity, phylogenetics

can help us frame testable hypotheses as to how evolutionary changes took place and, throush

resolution of important areas of the cladogram, suggest to us which species are deserving of

further study. Thus, I would argue that phylogenetics is even more fundamental to many areas of

biology than is statistics: whereas statistics can tell us how to design experiments and analyze

their results, phylogenetics can tell us precisely what changes have occurred in evolutionary

history and which characteristics in which organisms are worthy of further study in the field or

laboratory.

, t< In thls P a P er 1 have plotted evolutionary changes between the character states “solitary”

and eusocial for all groups of Halictine bees for which suitable information is available. For the

6 genera/subgenera studied (no phylogeny is available for Dialictus ), the solitary species are

clearly derived from eusocial ancestors for four of them (Ha/ictus, Seladonia , AugochloreUa

ugociilora). There are four behaviorally polymorphic species known from among these taxa

(I able - and for each of them, solitary behavior is likely the recent evolutionary innovation

Thus, with respect to my first question: “what are we studying?” any comparison of solitary and

eusocial behavior within polymorphic species or between monomorphic species in these four

genera would be analyzing those factors that promote solitary behavior.

In h\ylaeus all the primarily or purely eusocial species included here share eusociality from

a common ancestor. This represents a switch from solitary to eusocial behavior within Evylaeus

although the number of species derived from the social common ancestor is quite large!

Source: MNHN , Paris

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

Phylogenetic study of this subgenus also indicates that two of the behaviorally polymorphic

species have solitary behavior as the recent evolutionary innovation. The remaining change to

eusociality in Evylaeus occurs in the comagenenselfratellum species pair, both of which are

behaviorally polymorphic within single populations which exhibit solitary, semisocial and delayed

eusocial behaviors (VON DER HEIDE, 1992; FIELD, 1996). This is probably a comparatively recent

evolutionary change. Thus, comparisons among comagenense , fratellum and their solitary

relatives could address the question of origins of delayed eusociality. In the genus Lasiog/ossum ,

the only known eusocial species represents a recent evolutionary origin of eusociality.

Thus, with respect to my second question “what should we be studying?” the following

research directions are suggested. First, phylogenetic and behavioral studies of additional species

in the L . leucozonium group would be desirable. Secondly, further phylogenetic and behavioral

studies of relatively basal lineages within Evylaeus would be useful. Thirdly, phylogenetic

analysis of behaviorally known Dialictus species may be particularly important. Furthermore, if

research on the origins of eusociality is to be done, the genera Halictus and Seladonia , and the

tribe Augochlorini (and vespine wasps, apine bees and ants) are best ignored.

ACKNOWLEDGEMENTS

I am grateful to Philippe Grandcolas for organizing the symposium at which a verbal version of this paper was

presented and to him and Roseau National de Biosystematique for arranging and providing funding. I have benefited from

discussions with Michael Bressalier and Dr. Yuriy PESENKOand from the comments of two anonymous reviewers on earlier

versions of this paper. Phillip Schappert, Enore Gardonio and Gilbert Hodebert helped me generate the figures. My

research is funded by the Natural Sciences and Engineering Research Council of Canada.

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Source: MNHN , Paris

When Is a Phylogenetic Test Good Enough?

John W. Wenzel

Department of Entomology. Ohio State University . Columbus. OH., 43210. USA

ABSTRACT

Cladistic viewpoints have not been widely appreciated during the rapid growth of interest in phylogenetic tests of

evolutionary' scenarios. General opinion sometimes contrasts with cladistic perspectives with respect to the nature or severity

of certain problems. Cladistic views are straightforward, if somewhat counter-intuitive in certain constituencies The tree that

best summarizes the data is always the most parsimonious tree (or consensus of most parsimonious trees) and nodes on this

tree should not be dissolved based on low numerical support, such as bootstrap values. Resolution of the consensus tree can be

a problem when data are inadequate. Successive approximations weighting to derive better resolution is consistent with the

cladistic paradigm in that congruence among characters determines the relative weights of the characters. This process is

recursive, but not circular. In contrast, techniques such as maximum likelihood should not be used to derive a more resolved

tree because that tree will not be based upon the data alone, results are biased according to (sometimes extensive) a priori

dictations of the probable path of evolution and they will not reveal patterns incongment with the initial assumptions.

Construction of maximum likelihood trees relies on process theories unrelated to, and perhaps uninformative for, adaptive

traits of interest. The characters of interest should be included in the final analysis because they are the data most relevant to

the analysis. Claims that eliminating them improves independence or that including them leads to circular reasoning are

incorrect both logically and empirically. Eliminating characters because they are expected to show high homoplasy is an

unacceptable ad hoc protection of an hypothesis from a legitimate test. Most statistical treatments require unnecessary and

often unsupportable assumptions regarding the process ot evolution and expected distribution ol traits. Character data and

their appearance on the most parsimonious tree are preterred because they are the most free of assumptions and remain the

most closely tied to the actual data.

RESUME

Qu'est ce qu'un bon test phylogenetique?

Le point de vue de la cladistique n'a pas ete suffisamment pris en compte a I'occasion de I’interet croissant manifesto pour

les tests phylogenetiques de scenarios evolutifs. L'opimon generate est souvent en disaccord avec les perspectives cladistes au

sujet de la nature ou de l'importance de certains problemes. Les points de vue cladistes sont clairs, meme si ils paraissent aller

a l'encontre de l'intuition dans certains domaines. L’arbre qui rend compte le mieux des donnees est toujours l’arbre le plus

parcimonieux (ou le consensus des arbres les plus parcimonieux) et des noeuds de cet arbre ne doivent pas etre abandonees

parce qu'ils presented de faibles valeurs de parametres numeriques, telles que des valeurs de bootstrap. La resolution d'un

arbre consensus peut consumer un probleme quand les donnees sont inadequates. La ponderation successive appliquee a

l'amelioration de la resolution est en accord avec le paradigme cladistique c’est bien la congruence entre les caracteres qui

determine les poids relatifs de ces caracteres. La procedure est recursive et non pas circulaire. A l’oppose, les techniques telles

que le maximum de vraisemblance ne devraient pas etre utilisees pour obtenir un arbre mieux resolu parce que cet arbre nest

plus base sur les seules donnees ; les resultats incorporent alors de maniere parfois importante des opinions a priori sur le

Wenzel, J. W . 1997. — When is a phylogenetic test good enough? In. Grandcolas, P. (ed.). Hie Origin ot

Biodiversity in Insects: Phy logenetic Tests of Evolutionary Scenarios. Mem. Mus. natn. Hist. not. 173 : 31-45. Paris ISBN : 2-

85653-508-9.

J. W. WENZEL : WHEN IS A PHYLOGENETIC TEST GOOD ENOUGH?

voies evolutives les plus probables et ils ne reveleront plus des schemas incongruents avec les hypotheses de depart. La

construction d'arbres de maximum de vraisemblance repose sur des processus theonques sans rapport, voire non ‘^rmat.ft

avec les traits adaptatifs a l'etude. Les caracteres a l'etude doivent etre mclus dans 1 analyse finale parce que ce sont les

donnees les plus pertinentes en regard de cette analyse. Certains ont pretendu que leur elimination ameliorerait

l'mdependance ou que leur inclusion conduirait au raisonnement circulaire : ces assertions sont mcorrectes a la tois

logiquement et empiriquement. Eliminer des caracteres parce qu'ils sont supposes etre hautement homoplasiques constitue

une entravc ad hoc inacceptable au test legitime d'une hypothese. La plupart des traitements statistiques requierent 1 adoption

inutile et souvent injustifiee dhypotheses portant sur les processus evolutifs et la distribution attendue des traits. L utilisation

des seuls caracteres et leur appantion sur l'arbre le plus parcimonieux leur sont preferces parce que ce sont les procedures les

plus independantes d'hypotheses a priori et qui demeurent au plus pres des donnees reelles.

INTRODUCTION

The modern systematist has a peculiar place in the natural sciences. His discipline might be

characterized as stuffing itself with data while trying to limit general theory. The systematist

collects information on morphology, development, genetics, phenology, behavior, ecological

associations, biogeographic patterns; indeed, just about anything he can find is potentially useful

for deducing hierarchical relationships of species and higher taxa. But as for general theory, there

is little more than the process of descent with modification, at least among Hennigian

systematists (ELDREDGE & CRACRAFT, 1980: 6). By contrast, nested or intertwined theories

about the evolutionary process form the foundation of other fields, such as those concerned with

competition or succession ecology, food web structure, sexual selection, or sociobiology. In this

light, it is interesting and ironic to see how recent enthusiasm for the primacy of phylogenetic

perspectives has revitalized studies of theories about the process of evolution. "Adaptation”, one

of the central features of Darwinian evolution, has earned the most attention. The papers

included in this volume are the result of a symposium that brought together a variety of

systematists and others to discuss phylogenetic perspectives on certain evolutionary scenarios.

What distinguished this symposium from one that might have been on the systematics of many

interesting organisms is that the speakers generally regarded the phylogenetic hypotheses as tools

for understanding the process of adaptation (see also EGGLETON & VANE-WRIGHT, 1994,

Martins, 1996). This method of examination leads to an improvement over the adaptive story¬

telling of old, but it also carries with it special hazards.

The literature regarding phylogenetic tests of evolutionary scenarios is growing rapidly, but

there seems to be a lack of proportional response from a Hennigian perspective on what are the

procedures and problems in such an enterprise (but see CARPENTER, 1992b; CODDINGTON, 1994;

WENZEL & CARPENTER, 1994). This paper may help to fill that void, or at least draw attention to

certain issues that seem to deserve special consideration in this context. One such issue concerns

the intent of the study in the first place. A systematist would generally make arguments about

various character definitions, states, additivity, etc., and then derive a tree, but in the

phylogenetic tests of adaptive hypotheses the process is reversed, producing a tree for the sake

of deciding the details of transformations of chosen characters. The phylogeny is only a tool, not

a endpoint. The relationships among taxa are the anvil upon which the traits of interest (and any

conclusion regarding the process of evolution) are worked into shape. This produces two

problems which will be discussed in turn.

Source: MNHN, Paris

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

HOW GOOD IS THIS TREE?

The first and most obvious problem is that the best phylogenetic hypotheses are generally

produced by those who see the phylogeny itself as the end product, but these are often not the

people generating the hypotheses for the study in question. Taking care not to sound cynical, we

should be cautious when someone who is not very interested in the phylogeny starts producing

the hypotheses as a way to get on with his real work (hammering out those interesting traits). Of

course, the hypothesis may be quite sound, but one cannot tell simply by reading that the

relationships illustrated were derived by analysis with an approved computer program. Even if

the primary data are beyond question, issues such as taxon sampling or character coding can

have a great impact on tree topology, and even the best computer programs cannot overcome the

errors introduced by a researcher’s weak understanding of these issues. This problem is

particularly important in these days when generating a few DNA sequences for a few taxa and

making a tree from them is commonly done by people with no formal education in the sometimes

deep problems of phylogenetic reconstruction. The solution, of course, is education.

Support

The simplest rule is to choose the optimal tree for the data in question. This approach has

the advantage of logical consistency because all other trees are less well supported. This

perspective leads us to the most parsimonious tree, or a consensus of equally most parsimonious

trees (Farris, 1983; Wiley, 1981; Brooks & McLennan, 1991)(some non-parsimony based

techniques will be discussed in Resolution , below). The strict consensus of several equally most

parsimonious trees cannot be better resolved than any of the original trees, but the consensus

should be considered highly supported anyway because all of the clades that appear are included

in all of the multiple, competing trees. Whenever there is homoplasy, some parts of the tree may

be more decisively reinforced by the data than others, but this is not a concern with respect to the

optimality criterion of parsimony. By analogy, if we examined the relationship between body

length and mass for humans, some points would be better predicted by a straight line than others,

but we would nonetheless choose the least squares regression because it is optimal for the

complete data set. The homoplasy in a most parsimonious tree can be compared to points that

are displaced from a least squares regression line. Each represents an exception to the

relationships we expect, but we use our optimum solution anyway.

Even when there is only one most parsimonious tree, measuring support is not

straightforward. Ultimately, whether or not a clade is well supported depends on the characters

that unite it. While experience and intuition are sometimes sufficient to make assumptions

concerning the strength of morphological characters uniting a clade, DNA sequence data usually

is not easily evaluated in a straight character by character comparison. What is the relative value

of a change from “A” to “G” versus anything else 9 Also, the relative merits of alternative

resolutions of homoplasy in DNA data are often not as logically interpretable as alternative

resolutions of morphological homoplasy. The most widely used technique to measure support in

this situation is the bootstrap (FELSENSTEIN, 1985), in which the original data are resampled

randomly with replacement, new trees are generated from this new matrix, and the clades from

the original tree are scored as present or absent on the new tree. This process is repeated and a

score is produced for how often such original clades appear, with high scores (100% is perfect)

suggesting that the clade is well supported, low scores suggesting it is not I hen clades with low

Source J\ANHN, Paris

J. W. WENZEL : WHEN IS A PHYLOGENETIC TEST GOOD ENOUGH?

scores (90% might be a cut off point) are dissolved and only strong clades are retained on the

“bootstrapped tree”.

Objections to the bootstrap include that the statistics generated this way are not

comparable to the normal probability estimates people want to use (SWOFFORD et al., 1996:

509); that competition for inclusion in the simulated matrices dictates that uninformative

characters (such as autapomorphies) degrade clades when they ought to have no effect

(Carpenter, 1992a; Kluge & Wolf, 1993); similarly, that strong support in one part of the

tree is interpreted as weak support in another part; that asymmetrically branching clades derive

higher bootstrap values than symmetrically branching clades even if the relative support for all

clades is identical (M. SlDDALL, pers. com ); and that clades with higher empirical content (more

taxa) are penalized even when they have the same amount of support as a smaller clade (M.

SlDDALL, pers. com.). It is also important to note that the ordinary application of bootstrapping

procedures is to derive a confidence interval for the estimate of a parameter of a distribution

(Manly, 1991: 28), and that statistical mean and variance do not apply to unique historical

identity of the phylogeny (WENZEL & CARPENTER, 1994: 80 ff). So, although the bootstrap

values mean something, it is not clear what they mean exactly, and it is clear that they do not

mean the same thing when compared across different trees. It would seem that these objections

would suffice to exile the bootstrap from its current place of honor.

An alternative to the bootstrap is BREMER support (Bremer, 1988), a technique that also

gives values for each clade, but these are not intended to serve as statistical confidence tools.

Although the calculations are tedious, the principle is simple: start with the most parsimonious

tree and then find the shortest trees that do not contain each of the clades in the most

parsimonious tree. Because all other trees will be longer, steps will be added when a clade in the

most parsimonious tree is broken up. Each clade is then recorded as having support according to

the minimum number of steps it costs to break it up. A high value is better support, meaning

many characters are less parsimonious on the shortest tree that does not contain the clade, a low

value means few steps are added by interrupting the clade. The problem with documenting

BREMER support is that calculations can be prohibitive because of the necessity of calculating so

many less-than-optimal trees. The advantage of BREMER support is that values are more easily

interpreted than the bootstrap values because they relate directly to how far away from optimal

(most parsimonious) the tree would be if it did not contain the clade in question. Interested

readers will find a more thorough discussion of the relationship between these measures and

short cuts to Bremer support in Davis (1995).

A common refrain in studies where trees are used to judge the validity of evolutionary

scenarios is "maybe the tree is not good enough”, or “maybe some of the branches are not well

supported’ From a Hennigian perspective, the most parsimonious tree (or consensus of

parsimonious trees) is the best tree according to the data. We may want to see values for

bootstraps or BREMER support, but we should not change the tree based on these measures.

IS THE TREE GOOD ENOUGH?

The second problem is related to the first one, but it is much older because it surrounds the

merits of the phylogenetic hypothesis itself. Phylogenies built for their own sake are usually

compared to our previous understanding of the group with the intention of showing that we now

know more than we did before. Any increase in understanding is good. However, if such

Source: MNHN , Paris

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

hypotheses are to serve as tools in another context, then a different kind of evaluation is

necessary. Gross polytomies may not matter depending on where they fall, so a phytogeny that

says very little about relationships may still be “good enough” to answer some questions. Figure

1A illustrates a case in which poor resolution of eight ingroup taxa has no effect on character

argumentation. In other cases, character distributions and exact topology can conspire to make

even detailed understanding of relationships “not good enough” to answer the question. Figure

1B shows a situation in which we cannot decide whether a character state was derived one, two,

three, or four times among seven ingroup taxa, despite having a completely resolved tree.

A ABABA BAB

X XYXYX YXY

0 10 10 110

Fig. 1. — A: A poor tree that is good enough to answer the question. Two characters exist in two states, (A or B) and (X or

Y). There are many ways in which the three polytomies can be resolved and the two characters optimized, but all

require at least three separate derivations of the association of AX and BY. This poor tree is good enough to answer

the question of multiple origins and convergence B: A complete resolution of seven ingroup taxa that is inadequate to

establish character argumentation. The pattern of character states can be explained by four steps, but it is ambiguous

as to whether they represent one, two, three, or four derivations of state “1”. One scenario has all “1” states derived

convergently (open boxes), another scenario has “1” states as two convergent synapomorphies for clades (solid tick

marks) followed by two reversals (X). We can combine different halves of these scenarios to get two different ways of

having three derivations and one loss (white boxes on one side combined with black ticks and X on the other).

Another possibility has“1” as a unique synapomorphy for the ingroup taxa (o) with three subsequent reversals (X and

o). Our interpretation of the significance of character state “1" will change greatly depending on w'hich optimization is

chosen, but this excellent tree by itself is not good enough to resolve the problem.

Resolution

One reason strict cladistic techniques seem to be out of favor among many people is that a

consensus of equally parsimonious trees often fails to resolve a polytomy. Techniques can

improve resolution, such as successive approximation weighting (Farris, 1969; CARPENTER,

1988), by which the characters acquire the weights suggested by their congruence with other

characters (stability on the cladogram), a new tree is generated with the newly weighted

characters, and the process is repeated until a stable solution is obtained. This method provides a

way to move from the initial set of trees to the local optimum (which may differ from the global

optimum if the original search was too restricted.) Critics have described these methods as

J. W. WENZEL . MIEN IS A PHYLOGENETIC TEST GOOD ENOUGH?

circular (SWOFFORD & OLSEN, 1990: 499), but such an appraisal is clearly wrong because the

weight of a character is determined by the degree to which it is coherent with other characters,

and some analyses produce topologies that were not in the original set of trees (BROTHERS &

Carpenter, 1993), hence novel endpoints. The process is recursive, but not circular.

Other reconstruction techniques that do not rely on parsimony, such as neighbor joining or

maximum likelihood, may produce one fully resolved tree when parsimony doesn’t.

Unfortunately, the great shortcoming of these techniques is often the same as their strength:

I hey produce only one tree. For example, when data support several alternative relationships

equally, neighbor joining techniques (SAITOU & NEI, 1987) choose one arbitrarily based on the

order in which taxa appear in the matrix (KLUGE & WOLF, 1993; Farris et al., 1996). This

means the tree is not strictly determined by the data. Neighbor joining is strictly an algorithm and

has no optimality criteria at all, meaning there is no basis for a justification that the tree derived

from a given study is somehow the best it can be. In this case, basing additional work on one

fully-resolved tree will be at least suspect and perhaps wrong. In contrast, the multiple, equally

parsimonious cladograms should not be seen as the failure of a divining rod in the search for

water, but rather as the success of a child-proof top on a medicine bottle: if you can’t handle this,

then you should go no further. Cladistic analyses do not produce a definitive solution when data

are ambiguous or lacking, and this result is most consistent with the general principles of the

scientific method. Unfortunately, the importance of multiple trees will not be widely appreciated

as long as influential publications on phylogenetic methods simply ignore the issue entirely ( e.g.

Swofford & Olsen, 1990; Swofford et al., 1996).

Judging from several conferences I attended recently, maximum likelihood is rapidly

growing to be a popular method of tree-building, and it too can produce resolution or topology

that is not present in the data matrix. Many varieties of maximum likelihood estimates are used in

modern statistical analyses, and more detailed discussions of their application to phylogenetic

hypotheses are available elsewhere (Swofford et a/., 1996); here I will approach only the issue

of how the tree reflects the data used to produce it. The basic operation, regardless of which

maximum likelihood model is used, is that lessons about evolution learned in other studies are

applied to the data in question to "improve’’ our understanding. If other studies have shown that

there is an evolutionary bias in the direction of mutation among nucleotide bases, then perhaps

we should create a model of the process of evolution that will allow us to build a tree that

accounts for this bias. Supporters see this as a strength in that we are using our general

knowledge to resolve some local problem, but cladists see this as a very serious flaw. Maximum

likelihood models favor some schemes over others a priori, and thereby dictate the path that

evolution is expected to follow (hence, “likelihood”), and then evaluate the degree of likelihood

according to that path. Although most proponents of maximum likelihood readily acknowledge

this, the severity of this shortcoming seems too easily overlooked. Several critics have attacked

maximum likelihood methods based on a number of weaknesses (Farris, 1986; WENZEL &

Carpenter, 1994), but here I will propose an additional flaw: such methods are self-fulfilling

and do not provide independent evidence of their legitimacy. Trees built according to a given

model cannot reflate the model, and therefore it is clear that the model (which determines to

some degree what we will find) is beyond testing. If we decide in advance how evolution is likely

to occur, we cannot later declare that we have discovered how evolution occurred. Claims to

special knowledge (say, that third positions evolve faster than the rest of the codon) become

Source: MNHN . Paris

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

dictations of pattern, the same pattern that is the point of the inquiry (WENZEL & CARPENTER,

1994). Indeed, arguing in favor of maximum likelihood, SWOFFORD et a/. (1996: 428, 429)

demonstrate that parsimony does not resolve placement of an ambiguous taxon, whereas

maximum likelihood does based on the assumption that adding another step to a long branch

costs less than adding a step to a short branch (that is, an expectation that more evolution

probably occurs on a branch that is already “long” versus one that is already “short”). Thus, the

fact that parsimony equivocates when data are equivocal is regarded as a flaw, but that branches

that are already short (according to other data) are made to stay short (in the face of new data) is

an advantage in maximum likelihood. Such logic would appear to condemn us to a science free

from discovery. Some might say that weighting according to branch length is like successive

approximations weighting according to homoplasy, but this is correct only superficially.

Successive approximations takes over after all of the many parsimonious resolutions have been

discovered, but maximum likelihood weighs things differently to get the first tree. Whereas

parsimony allows all data to compete among themselves in whatever alliances form, maximum

likelihood declares a priori that some data are favored and others not. Maximum likelihood can

never contribute to the business of discovery as meaningfully as does parsimony.

Resisting attacks like that above, some argue that parsimony reconstruction contains its

own assumptions. A recent incarnation of this view is that parsimony procedures assume at a

minimum that the data are probably generated by a process that would allow parsimony to

reconstruct the phylogeny correctly (SWOFFORD et ah, 1996: 426). Although this seems almost

tautological, it is false nonetheless. Seeking the most parsimonious explanation for data at hand is

a fundamental scientific principle and does not represent any statement or assumption about the

process that produced the data. There is no assurance that the “truth” is obtained, only that there

are infinity less parsimonious explanations, so we accept the optimal one and leave questions of

“truth” out of it. If the data are misleading, parsimony will yield a misleading answer, and this is

as it should be. Garbage in, garbage out. It begs at the margins of clairvoyance to claim that any

method can be expected to give good answers from bad data. Strangely, SWOFFORD et a/. (1996:

426) dismiss in a footnote the argument that parsimony is a fundamental aspect of scientific

method, whereas they devote the next 50 pages to non-parsimony methods.

Despite how dismissive they can be about parsimony, proponents of maximum likelihood

have been surprisingly forgiving of their method’s grave flaws with regard to logical circularity,

and quite generous in their acceptance of demonstrations purported to reflect problems in

phylogenetic reconstruction. The current school arose, for example, from a model of highly

variable rates of evolution with an absolute minimum number of taxa (FELSENSTEIN, 1978).

Although some critics have argued that the variable rates of evolution are not an accurate

reflection of what most data represent, it is even more obvious that the majority of

reconstructions do not consider only four taxa, two of which are very different from the others,

and therefore the exercise is highly contrived rather than representative. But, allowing themselves

grace, the authors generate data from this model and then show that using this model to interpret

the data gives the correct tree whereas parsimony does so less often. Thus, the demonstration is

fundamentally circular in addition to being nonrepresentative of general problems in

reconstruction. As an example, HULSENBECK (1995) generated artificial DNA sequence data, of

lengths from 100 bases to infinity, for four (!) taxa to compare 26 reconstruction techniques.

Data were generated from two models, JUKES-CANTOR (using equal base frequencies and one

J. W. WENZEL : WHEN IS A PHYLOGENETIC TEST GOOD ENOUGH?

substitution probability) and Kimura Two Parameters, (using equal base frequencies, but two

substitution rates as when transitions and transversion are unequal), and HULSENBECK measured

the relative accuracy of different techniques for reconstructing the “true” tree. As an example,

when Hulsenbeck used the Kimura model to generate the data, Kimura gave the best result,

thus establishing the perfection of circularity. The closely related JUKES-CANTOR model (see

S WOFFORD el a/., 1996, p. 434 for relationship among these and six other models) was second

best, demonstrating that logic that is nearly circular discovers itself almost as well (see summary

in Hillis el a/., 1996, fig. 5). Despite demonstration that the parsimony methods performed well

under all circumstances, and despite the fact that parsimony includes no elements of the model

used to generate the data, and despite the fact that real evolutionary history is often not

stochastic like his models, HULSENBECK concluded that maximum likelihood methods are

preferred because they performed best. Other than circular demonstrations of extraordinary

problems, there is little to support maximum likelihood as the preferred alternative to parsimony.

Eager to displace parsimony, proponents of maximum likelihood have been slow to

produce the necessary studies of how their methods fare when data are not derived from the

model used to reconstruct them (or more pointedly, not from any model at all), and comparing

closely related models (as Hulsenbeck did, above) hardly counts as a serious trial. With respect

to this charge, and much more relevant to the point of the current paper, maximum likelihood

models are based on molecular evolutionary processes that have little relevance to the behavioral,

ecological, or life history characters that people want to examine phylogenetically. Ignoring the

tautological (maximum likelihood) statement that more evolution is expected to occur on long

branches, what assurance is there that the characters associated with the evolution of a new diet,

or phenology, or habitat preference should obey the models of evolution based on, say, ribosomai

DNA sequences? If defenders argue that maximum likelihood is better at finding the best tree, we

should respond that the best tree will be found by including all the data, especially the characters

of interest regarding diet, etc. (see Independence , below), and then we will be including different

kinds of data that can only be combined in a parsimony analysis. Parsimony performs well at

reconstructing histories in the absence of any knowledge of the evolutionary model, which is to

say H Wl11 Perform well even when we know no more about our characters than that they have

evolved.

Occasionally we will see a presentation in which the researcher has done both parsimony

and maximum likelihood analyses to build trees to answer a particular question, perhaps “are

po ygamous males flamboyant”. The two trees usually have similar branching patterns which

increases our feeling that they are valid. The parsimony tree, typically less well resolved, may not

be adequate to provide a definitive answer, and so a plea is made to consider the maximum

likelihood tree. Such a proposal, although born of necessity, is naive in the extreme. If the

parsimony tree shows that there are inadequate data to resolve the problem at this time, then that

is the appropriate answer. Defining a tree that is not specified by our data just to use it to answer

t te external question is irresponsible and dangerous. Certainly, the researcher would not think of

Th u 8 T P t ie ? thCr d f ta (declann §’ wit hout any information, that a male was both polygamous

and flamboyant), so why should he settle for a tree that is not determined by the data?

Source: MNHN. Paris

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

INDEPENDENCE

There will always be problems regarding the independence of data used in phylogenetic

analyses. The most obvious problem is that characters are used to make trees, trees are used to

evaluate characters. This problem reduces in part to questions of homology and character

definition that are too large for this short paper. Recent treatments from a cladistic perspective

are available for the general issue (DE PINNA, 1991), and for morphological (PATTERSON, 1982),

behavioral (WENZEL, 1992) or ecological (MILLER & WENZEL, 1995) data. Here we will examine

a subset of the general problem: should we include the characters of interest in the phylogeny we

will use to evaluate the evolution of those characters? I will argue that we should include the

characters, and that intuitive fears of “circularity” are unfounded.

The best test of an evolutionary scenario starts with having the best tree, a tree that relies

on as much relevant data as possible. What could be more relevant to the scenario than the

characters in question? These characters would be considered useful data if the question was

about other characters, so why should they be excluded now? This “total evidence” approach

(also known as “combined” or “simultaneous” analysis), favored by many strict cladists, is

rejected by some because of the idea that it is preferable to have an “independent” test,

comparing the traits in question to a tree that was built without their contribution. This

widespread opinion has a strong pedigree (CODDINGTON, 1988; Baum & Larson, 1991;

Brooks & McLennan, 1992; Vane-Wright et al, 1992) but it is wrong anyway. As

DELEPORTE (1993) states nicely, any problem of circularity is restricted to character coding

(dictating transformations), not character choice, and therefore flaws are introduced prior to the

analysis rather than through analysis itself. This important point deserves more attention than it

has received: If our character coding is valid, then combined analysis will introduce no new error.

Ki.uge & WOLF (1993) argued that the assumption of independence is the same whether

comparing across data matrices or within a matrix. No special independence is obtained by

partitioning data into different sets, and so there is no circularity created by including all data in a

single analysis. Alternatively, if someone can partition any data set into two groups that disagree,

are we then obliged to keep them separate forever? Clearly not. Readers uninterested in

epistemology might be convinced by reviews of the effects of combined analysis, often producing

novel results not found in the partitioned data sets (BARRETT et al., 1991, ClTlPPrNDALE &

Wiens, 1994). Such novel results constitute empirical demonstrations that including all data does

not result in circularity.

Even in the spirit of independent sampling, there is no need to exclude the original

observations that first suggested a relationship By analogy, when the first tew male students

enter a room and sit near the window, and the first few females sit near the door, it is not

necessary to exclude these observations from the test to see if this is a general pattern. 1 he

students who suggested the relationship are good data, as are the students who have not yet

entered the room. With this in mind, consider a more relevant problem: several species of cave

crickets are white, blind, and without circadian rhythm. Perhaps they share these traits by descent

(the hypothesis of homology), or perhaps these represent independent adaptation (rejection of

homology). Combine these data with other characters and allow them to compete among

themselves to build a tree. If the cave species come out together, then this means that there is not

enough information to reject the proposal that they are alike due to synapomorphy. An obvious

J - w - WENZEL : WHEN IS A PHYLOGENETIC TEST GOOD ENOUGH?

question is “what if we get a different phylogeny when the characters of interest are left out?”

Then we are still in the position of having an hypothesis of synapomorphy that is not rejected

because it still emerges in the combined analysis. The hypothesis of synapomorphy survived the

challenges of all our data, which is a strong test if we have a lot of other data. In the absence of

much other data, we may be subject to statistical Type II error (failure to disprove a false

hypothesis), but that is different from circularity.

Some readers may be critical of the cave cricket scenario presented above because

synapomorphy is the null hypothesis, and failure to reject the null hypothesis is a weak statement.

Such critics may think that adaptation is likely to explain these traits, and that convergence is a

more likely explanation than synapomorphy. From this perspective, the null hypothesis would be

that the common aspects of the cave crickets are independently derived. Of course, the way to

test this proposal is to return all data to the combined analysis and see if we find evidence for

synapomorphy. If the commonalties can be plotted as a unique synapomorphy, then we would

have to reject the hypothesis of multiple convergent origins. There is no logical way to avoid the

combined analysis.

Excluding the characters of interest produces the image of independence when we imagine

that the other characters are a repetition of the phenomenon in question. But they are not

because they are other characters evolved from other pressures, and it is rare to see any two

characters share precisely the same distribution among all taxa. A tree built on other characters

cannot be considered an independent “replicate” of the question we want to examine

Statistically, eliminating the characters of interest is actually more like a jacknife procedure, in

which we exclude some data to derive a pattern for the others. Although jacknifing is useful and

respected in general, it is not designed for the purpose of providing an estimate of the data that

are excluded , and it is hard to imagine that anyone would recommend that the way to make sense

of certain particular data is to exclude them from the analysis. If the study centers on certain

data, then they should be included in the analysis.

Sometimes critics of the cladistic approach want to exclude the characters of interest

because these characters are expected to be misinformation, as when independent origins are

concealed by extensive convergence. For example, West-Eberhard (1996) endorsed a

traditional hypothesis that social parasitism was derived multiply in the genus Polistes. Evidence

in tavor of the hypothesis of separate origins relies on observations of facultative parasitism

(stealing nests) in ordinary species. Such variation within original species could become extreme

and permanent, eventually resulting in a new species, a social parasite. To defend her position

against a strong challenge (CHOUDHARY et a /., 1994; Carpenter et a/., 1993), WEST-

Eberhard argued that covariation of morphological traits of interest, (heavy cuticle, square

head, powerful mandibles) supply a false indication of synapomorphy (and a single derivation of

parasitism) because these traits are expected be convergent adaptations and should have

developed independently in each parasitic lineage. Even if parsimonious reconstruction of

characters indicates a single origin because the parasites are all closest relatives in a monophyletic

c ade, this interpretation is ruled out because it conflicts with the theory that parasites should

evolve convergently (West-Eberhard, 1996: 315). In this case we must ask ourselves “What

in formation would suffice to disprove the hypothesis of convergence?” If not the patterns among

relevant data, then what? There is no good reason to ignore evidence offered by the characters of

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

interest, and exclusion of them constitutes special protection of the hypothesis from a legitimate

test. Such a procedure is not within the scientific method.

The example above demonstrates a widespread view opposing combined analysis on the

general grounds that “bad” data will lead us away from the better answer we could have had with

the “good” data alone. Most of these authors are proponents of maximum likelihood, which may

explain why I do not agree with them. For example, HULSENBECK et al. (1996) offer a brief

review and promote a method (HULSENBECK & BULL, 1996) to identify “pathological” data

during reconstruction of the phytogeny for the four (!) taxa lizard, alligator, chicken, and mouse.

They argue that 18S rRNA sequence is more in conflict with other genes than is expected by

pure sampling error, and that we should then keep the 18S data separate from the other data and

come up with explanations about why the 18S data are different. Aside from questions about

how relevant such a study is to real phylogenetic reconstruction, one might well ask what we

expect to achieve by combining (good) partitions that agree and separating (bad) partitions that

don’t (see also Brower, 1996, for additional criticism of the method). The struggle between

“good” and “bad” data is hard for me to understand because of the difficulty in knowing which

data are “good” and which are “bad”. As argued above, the business of discovery seems to be

associated with patterns that were not expected (hence “discovery”) which means they are "bad

data according to the maximum likelihood method. More to the point, when carefully-examined

“adaptive” traits are plotted on a phylogeny, it seems that they are relatively well behaved (see

other papers in this volume), which demonstrates that adaptation does not confuse the larger

pattern of evolution, and that cautious homology statements recognize independent origins of

similar traits. DELEPORTE (1993) is supported empirically: if we are careful judging our

characters, we do not create problems in reconstruction. In situations where evidence indicates

separate origins for a character of interest, it is appropriate to reexamine that character and see

what differences might be found in the similar (but non-homologous) states. Recursive

examination is the best way to make use of information that was not available at the beginning of

the study. From the point of view of the phylogenetic analysis itself, such reappraisal commonly

identifies homoplasy that is due to coding problems rather than real evolutionary problems,

which is a necessary step to better understanding (MILLER & WENZEL, 1995). From the point of

view of character of interest, reappraisal deepens our understanding of the nature and limits of

similarity among separately derived states. Character reexamination should be an integral part of

all phylogenetic studies, whether focused on ecological transitions or not, or the process of

discovery will be crippled pointlessly.

STATISTICS

Many people become scientists because they like the idea of discovering things,

knowing the answers to important questions, and deciding which of competing ideas is true.

Nature however, does not always let us find a clear path to truth. Some solutions to this

problem were developed by early geneticists, who were forever presented with measurement

errors of various sorts, and biology in general followed them to become more statistical

Statistics is not only a way to summarize data, but a way to decide in favor of A or B when faced

with some uncertainty. It is only logical that the science of statistics has become associated with

the uncertainty of phylogenetic reconstruction as it has with nearly all else m biology. The

problem with this new development is that a phylogeny is unique, it is an historical event that

Source:

J. W. WENZEL : WHEN IS A PHYLOGENETIC TEST GOOD ENOUGH?

happened once and cannot be resampled. Whereas statistical analysis is good for predicting what

sort of distribution or expectation we should get from tossing a coin (because we can sample and

resample those events), it is poor for saying whether the fourth toss was heads or tails (because

that happened only once). History is not a sampling problem, and efforts to make it become one

are pseudoscientific at best. In the context of phylogenetic tests of adaptation, WENZEL &

Carpenter (1994) and LEROI et a/. (1994) discussed the inapplicability of certain procedures to

phylogenetics, and readers would do well to review those arguments. What is most relevant here

is that a researcher can always make a phylogenetic test or reconstruction highly statistical, but

would that actually make it better? The cladistic viewpoint is to rely upon the primary

observations as much as possible.

"Statistics As Truth" is a motto of many researchers who despise the idea of indecision.

There may be an overt advertisement for an artificial decision rather than an examination of

natural data, as with this endorsement of arbitrary values substituted for real observations: it

does allow analysis of the data now, rather than waiting for actual phylogenetic information to

become available” (Garland et a/., 1992: 19; see WENZEL & Carpenter, 1994, for treatment

of other examples). Other researchers substitute statistics to produce an image of quantification

when none is necessary. LOSOS (1992) presented a statistical approach in which lizard ecomorphs

from different island radiations were separated by principle component analysis (PCA) on

morphometric values. Then a phylogeny was used to reconstruct the PC scores for hypothetical

ancestors and decide what ecological transitions occurred in the separate clades. For this to be

valid, the covariance matrix of all characters must remain the same through evolutionary time,

which appears to me to rule out a lot of evolution, such as the evolution of species (whether

ancestral or terminal) that are allometrically unique with respect to other species. This

assumption should be a source of concern, but for now let us overlook it. In two radiations

(Jamaica versus Puerto Rico) the transitions through PC space were from a twig-resting form to

a tree-crown form to a trunk form, with grass and bush forms derived most apically, and it is

reported that this is significant at P<0.04 (LOSOS, 1992: 412). It is not discussed whether there

would have been a different answer if we just reconstructed “twig”, “crown”, “trunk”, and

grass , which seems to be the first thing to try. Such a reconstruction would be based on the

actual data of interest and would be free of assumptions about the process we are trying to

discover. It the patterns the author found are not supported by optimization of “twig”, “crown”,

trunk , and grass , but rather due to the statistical reconstruction of hypothetical ancestors,

then there is no evidence supporting his theory other than that it is consistent with the

assumptions he made about the evolutionary process; that is to say it is not supported by the

primary data. If the patterns are supported by the primary data, then there is no point in all the

statistical manipulation. An example of completely needless statistics giving a clearly wrong

answer can be found in COGNATO et a/. (1997). Examining the sex pheromone mixture of ten

species of beetles, the authors asked it the pheromone variation is congruent with phylogenetic

history or not. The test consisted of a resampling of data from the original matrix (excluding the

characters ot interest) and evaluating the average homoplasy for these when plotted on a

cladogram. When the average homoplasy for the characters of interest proved to be higher than

the average for the other characters, it was decided that they were not congruent with

phylogenetic history. Yet, four of nine pheromone components plot with no homoplasy, and

three require only one additional step (COGNATO et al ., 1997: fig. 1). Only two components seem

Source: MNHN. Paris

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

to be “poor”, trans-verbenol and verbenone, both of which are suspected to be artifacts of

unrelated chemical processes. So, whereas the answer from plotting data on a tree is that at least

four and perhaps seven components are congruent with phylogeny, the authors confused

themselves into rejecting that proposal. Fortunately, some researchers are content to plot data on

a tree and let these patterns speak for themselves with no appeal to probability values (BasOLO,

1996; Emerson, 1996; McLennan, 1996).

EPILOGUE

It is inspiring to see that biologists of all sorts are interested in using phylogenetic

perspectives to illuminate their evolutionary studies. We must see that rigorous scientific

methods are satisfied during the difficult task of discovering phylogenetic patterns. Cladistic

perspectives have been ignored sometimes because genera! eagerness to include phylogenies has

produced a demand for single, well resolved trees, and unambiguous tests that are easily

interpretable. Unfortunately, these things cannot be delivered simply because we desire them.

Many methods or opinions that enjoy broad support among widespread researchers were not

derived from careful consideration of their consequences or implications about how we do

science. Hennigian methods remain the most well-founded and will produce the results best

suited to serve as the foundation of future research.

ACKNOWLEDGEMENTS

I thank P. Grandcolas and the Museum National d'Histoire Naturelle for hosting the symposium from which this

paper came. I thank J. M. Carpenter, P. Grandcolas, M. E. Siddall, D. W. Wenzel, and an anonymous referee for

comments on the manuscript. S. A Teale kindly shared unpublished work.

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Kluge, A. G. & Wolf, A. J., 1993. — Cladistics: Whaf s in a word? Cladistics , 9: 183-199.

Leroi, A. M., Rose, M. R. & Lauder, G. V., 1994. — What does the comparative method reveal about adaptation? The

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Manly, B. F. J., 1991. — Randomization and Monte Carlo Methods in Biology. New' York, Chapman & Hall.

McLennan, D. A., 1996. — Integrating phylogenetic and experimental analyses: The evolution of male and female nuptial

coloration in the stickleback fishes (Gasterosteidae). Systematic Biology, 45: 261-277.

Martins, E. P., (ed), 1996. — Phylogenies and the Comparative Method in Animal Behavior. New' York, Oxford University

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Miller, J. S. & Wenzel, J. W., 1995. — Ecological characters and phylogeny. Annual Review of Entomology, 40: 389-415.

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Phylogenetic Reconstruction. London, Academic Press: 21-74.

Saitou, N. & Nei, M., 1987. — The neighbor-joining method: A new method for reconstructing phylogenetic trees. Molecular-

Biology and Evolution , 4: 406-425.

Swofford, D. L. & Olsen, G. J., 1990. — Phylogeny reconstruction. In: D. M. Hillis & C. Moritz, Molecular Systematics.

Sunderland, Massachusetts, Sinauer Associates: 411-501.

Swofford, D. L., Olsen, G. J., Waddell, P. J. & Hillis, D. M., 1996. — Phylogenetic inference. In: D. M., Hillis, C.

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Vane-Wright, R. I., Schultz, S. & Boppre, M., 1992. — The cladistics of Amauris butterflies: congruence, consensus and

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101 .

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1-439. ’

On the Utility of Mathematical Models and their Use in

Evolutionary Biology

Yannis Michalakis *, Eric Wajnberg ** & Carlos Bernstein ***

* Laboratoire d'Ecologie. URA 258 CNRS. Universite P. & M. Curie. CC237.

7. quai Saint Bernard. 75252 Paris Cedex 05. France

** Centre de Recherche d'Antibes. Laboratoire dc Biologic des Invertebres.

Unite de Biologic des Populations. I.N.R.A.. 37. Boulevard du Cap. 06600 Antibes. France

*** Biometric. Genetique et Biologie des Populations. UMR 5558 CNRS. Universite Lyon 1.

43. boulevard du 11 Novembre 1918. 69622 Villeurbanne Cedex, France

ABSTRACT

Mathematical modeling is a powerful tool used in almost any kind of scientific endeavor. Mathematical models are as

diverse as the problems we tackle with them because different problems call for different methods. The recent spectacular

development of computing capacity has dramatically increased the number of potential applications of mathematical models,

since many more problems are now tractable numerically. Models can be characterized accordmg to three essential properties:

generality, realism and precision (Levins, 1966). These properties often trade-off and only the questions to which the model is

supposed to give an answer, ( i.e . evolutionary questions in the case of evolutionary biology), can guide the choice of the

relevant degree of generality, precision or realism. Mathematical models can be a very useful tool in several respects. For

instance, where intuition may be a poor guide, they can be used as guides to study qualitatively the behavior of very complex

systems. They often help to clarity' our ideas, and their results can be used to build null hypotheses. Some caution is needed,

however, in their use, because it is often the case that several different models (or different combinations of parameter values

of the same model) yield similar results compatible to biological observations. Considering alternative hypotheses is necessary

and essential.

RESUME

A propos de I'utilite des modeles mathematiques et de leur utilisation en biologie evolutive

La modelisation mathematique est un outil puissant utilise quasiment dans tout champ d’activite scientifique. II existe une

grande diversity de modeles mathematiques, des problemes differents necessitant l'utilisation de methodes differentes. Le

recent et spectaculaire developpement des capacites de calcul en informatique a augments radicalement le nombre de

problemes auxquels on peut essayer de repondre. Les modeles mathematiques onl trois proprietes essentielles : generality,

realisme et precision (Levins, 1966). En general il existe un antagonisme entre ces propnetes. Le degre de pertinence de

chacune ne pourrait etre guide que par des considerations liees aux questions auxquelles le modele est cense repondre. Les

modeles mathematiques peuvent etre utiles a plusieurs titres. Ils peuvent servir pour etudier le comportement qualitatif de

systemes complexes dans des cas ou l'intuition est im guide peu liable. Ils aident souvent a clarifier les idees, et leurs resultats

peuvent constituer des hypotheses nulles. Cependant. ils doivent etre utilises avec precaution. En eftet, il arrive souvent que

des modeles qualitativemenl differents (ou bien des combinaisons differentes des valeurs de parametres du meme module)

Michalakis, Y., Wajnberg, E. & Bernstein, C. 1997. — On the utility of mathematical models and their use in

evolutionary biology. In: Grandcolas, P. (ed.). The Origin of Biodiversity in Insects: Phylogenetic Tests of Evolutionary'

Scenarios. Mem. Mus. natn. Hist. not.. 173 47-52. Paris ISBN : 2-85653-508-9.

Y. MCHALAKIS, E. WAJNBERG & C. BERNSTEIN : THE UTILITY OF MATHEMATICAL MODELS

produisent des resultats similaires et compatibles avec les observations biologiques. Ainsi, la prise en compte d'hypotheses

alternatives est non seulement essentielle mais aussi necessaire.

INTRODUCTION

Mathematical modeling is a very powerful tool used in almost any kind of human activity.

The nature of mathematical models is highly diverse because different problems require different

methods. The recent spectacular development of computing capacities and of software for

mathematical computation has radically increased the number of potential applications of

mathematical models, since many more problems are now tractable either by numerical

calculations or by stochastic simulations.

In this paper, we first give some reasons on why to build models, we then outline some

characteristics of models and finally discuss some applications of mathematical models, especially

in population and evolutionary biology. Before proceeding any further we would like to warn the

reader on several accounts. First, none of us was trained neither as a philosopher nor as a

mathematician, but rather as a population biologist. This text should therefore be regarded only

as a personnal account and opinion on what has become our main everyday activity. We, by no

means, intend to represent the orthodoxy or establish rules on how or why mathematical models

should be built or applied, nor do we seek to be exhaustive. Should the style of what follows

seem dogmatic in some places, we would like to present our apologies to the reader in advance.

Such authoritative-like expressions just reflect our wish to avoid overloading the text with

continuous repetitions of the fact that this text reflects only our opinion. Second, we take it for

granted that the reader is convinced of the utility of Theory in Science, actually of the

impossibility to do Science without a theoretical framework. Finally, citations to models or

theories mentioned here should be solely regarded as illustrations of a particular point we want to

make, and should by no means be viewed as a judgement, be it positive or negative, of their

scientific merit.

WHY BUILD/USE MODELS?

There are several good reasons to build mathematical models. We will concentrate on the three

that we think are most important in evolutionary biology. Usually, models are built in order to

test the effect of some changes in biological processes which can be evaluated this way. In this

respect, models often allow a conceptual synthesis. A very good example is the development of

theoretical population genetics in the first half of the 20th century by FlSHER, FlALDANE and

Wright (PROVINE, 1971). These three scientists, by developing mathematical models, managed

to make the large majority of biologists accept Darwin's theory of evolution, by showing that

natural selection of random mutations was indeed able to account for observed patterns of

adaptation. What is really remarkable is that the development of this impressive body of theory

took place while most of the underlying mechanisms concerning the way genes function or even

what genes are, were largely unknown.

While allowing a conceptual synthesis, mathematical models very often generate new

hypotheses. Such hypotheses can be subsequently theoretically or experimentally evaluated. It is

very often the case that the potential role of a particular mechanism has been ignored until

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PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

revealed by a modeling exercise. In other cases the relevance of a given mechanism as an

explanation of a particular set of observations cannot be easily assessed experimentally. A model

can suggest simpler ways to test this mechanism or at least help to explore its relevance.

Finally mathematical models, in that they are often quantitatively predictive, can be very

useful as aids to decision making and constitute null hypotheses against which predictions can be

tested. For instance, the development of the neutral theory of molecular evolution would have

been impossible without the mathematical models developed by Motoo Kimura and his

colleagues (Kimura, 1983). The mathematical models, in conjunction with statistical tests based

on these models and developed by others, not only substantiated the plausibility of this theory,

but provided a null hypothesis against which observations of molecular polymorphism are

compared.

PROPERTIES AND KINDS OF MODELS

It is possible to classify models with respect to three properties: generality, realism and

precision. As LEVINS (1966) noted, there is usually a sort of trade-off between these properties.

For example, to be qualified as “precise” a model would have to take into account many detailed

conditions and processes which apply to the situation modeled, most probably to the expense of

other processes which do not apply to the modeled situation. By doing so, the model would very

likely be quite “realistic” as well, but it is highly unlikely that it would be “general” in the sense

that it will probably not be applicable to a different situation without modification.

Fig. 1. — Schematic representation of a tritrophic food chain involving a herbivorous insect (represented by its various

developmental stages), its host plant (represented by its leaves) and its predators.

The optimal mixture of these three properties can be defined only by the question

addressed and the generality that one wishes the answer to have. A given model will be very

precise, perhaps too precise, to answer a given question and too general to answer another one.

To illustrate this point, consider the model depicted in figure 1: this model represents a tritrophic

system consisting of host plants, herbivorous insects feeding on these plants, and predators

feeding on the insects. This model could be considered adequate to study the evolution of

50 Y. MICHALAKIS, E. WAJNBERG & C. BERNSTEIN : THE UTILITY OF MATHEMATICAL MODELS

herbivorous insect populations. It would be too detailed, however, if one wanted to address

questions on tritrophic systems in general, since many tritrophic systems involve organisms

which, for instance, do not have as many distinct developmental stages as insects. On the other

hand this model is probably too general for other questions one might want to address on

herbivorous insect tritrophic systems. For example, plants are only represented by the amount of

leaves produced, assuming that all leaves are equivalent. This is probably an oversimplification as

quality of leaves of a given plant typically changes with leave age, while the quality of leaves of

different plants can be very different. Exactly the same arguments apply to the predators.

STEPS IN MODEL BUILDING

The most important step in mathematical modeling in evolutionary biology is the very

beginning: identify an interesting biological question. If the biological question is not relevant,

then, obviously, anything that will follow will be equally irrelevant from a biological perspective

(though may still be relevant from an applied mathematics perspective). Once the relevant

biological question has been identified, one has to think of the different processes that might

contribute to generate the observed patterns. The next step would be the formalization in

mathematical terms of the interactions of the various processes identified in the previous step.

This implies important decisions about which are the appropriate simplifications to be made.

Then, the mathematical model can be analyzed, analytically or by computer simulations, and the

results interpreted and discussed. Quite often the result of this analysis and discussion generates

new hypotheses, most frequently due to the examination of fUrther observations and the

emergence of processes that might be involved and which had not be taken into account so far.

The activity of model building resembles to the construction of a spiral, where one starts with an

initial idea which is reexamined in the light of the mathematical analysis and then expands to

another idea by the incorporation of new elements.

A step often discussed is the “validation” of a model. What is at stakes is not whether a

mathematical model is mathematically correct (such cases are “relatively” easily resolved), but

rather how does it apply to the biological question it is supposed to answer. Such situations may

arise for several reasons. First, some relevant mechanisms may not be taken into account by the

specific model. In this case, the model as such cannot answer the question it was supposed to,

but requires, at least, modifications. We would like to express at this point the view that such

failures are equally valuable for the process of scientific knowledge as “negative” experiments,

i.e. experiments which fail to find statistically significant effects of the factors they have

examined, and should therefore deserve equal attention. A second reason for which a model may

not answer a biological question is because some specific parameter values used to produce

quantitative predictions with the model are wrong. In this case, the problem is not actually due to

the model but to its applications. This kind of problem can be “easily”, at least from the model's

perspective, solved by implementing the model with new parameter values and does not require

the modification of the model itself.

In practice, of course, things are much more complicated than what would appear from the

previous argumentation. The first, and probably most important problem, is how one decides that

a given model does not satisfactorily explain the observed patterns. The answer to this problem is

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PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

clearly question-specific. If the question requires a quantitative answer one can conduct

experiments and actually empirically measure the variables whose behavior the model is designed

to predict. Because quantitative variables can be easily accompanied by confidence intervals one

may compare the values predicted by the model using the observed confidence intervals. For

questions requiring qualitative answers, however, it is much more difficult to decide whether a

specific model provides a satisfying answer. The main difficulty lies in the fact that the way the fit

of the model is ascribed as “good” or “bad” remains largely subjective. For instance, would a

model designed to explain the evolution of dioecy in Angiosperms and which actually explains

about 70% of the data be considered as validated or invalidated 9 Furthermore, the fact that

models are not a single hypothesis but rather a full set of them makes it difficult to decide

whether to just reject an unsatisfactory model or modify it.

Another problem arises because many models may lead to the same patterns, at least for a

particular variable. Therefore the fact that a particular pattern can be satisfactorily explained by a

given model should not be viewed as a confirmation of the model, but rather as the absence of an

information. The only way to avoid such caveats is to examine the alternative models and force

them to produce contradicting predictions with respect to at least one experimentally measurable

variable. In saying this, we do not want to imply that scientists should not publish papers with

mathematical models unless they have examined all alternative models. We just suggest that until

such an examination is done by somebody the question should still be considered open.

CONCLUDING REMARKS

Mathematical modeling is a very powerful tool, which is necessary in almost any research

program. Models are necessary because they allow to build quantitative null hypotheses. As

evolutionary biology progresses towards the study of problems of increasing complexity the use

of mathematical models becomes indispensable, simply because the increasing complexity of the

questions addressed renders intuitive expectations untrustly and in some cases even impossible.

Mathematical modeling offers a relatively inexpensive way to contrast alternative

hypotheses and thus allow the evaluation of the relative importance of several mechanisms. For

such a parallel examination to be possible, alternative hypotheses should be forced to produce

opposite predictions. The interested reader can find more information on mathematical modeling

applied in biology in BROWN & ROTHERY (1993) and in PROVINE (1971).

“Models” are used in many areas of human activities though they do not always bear the

same meaning. In the arts, a “model” is “what really exists”, what the Artist wants to represent

by her/his work. In biology a “model” is meant to be a simplified representation of “what really

exists”. Such representations will only fulfill their role if they are guided by natural history, so

that the final object of investigation remains clear in the mind of all actors.

ACKNOWLEDGEMENTS

We would like to thank Denis CouvETand Philippe Grandcolas and an anonymous referee for helpful comments.

REFERENCES

Brown, D. & Rothery P., 1993. — Models in Biology: Mathematics, Statistics and Computing. Chichester, John Wiley &

Sons: 1-708

Kimura, M., 1983. — The Neutral Theory of Molecular Evolution. Cambridge, Cambridge University Press: 1-367

Y. MICHALAKIS, E. WAJNBERG & C. BERNSTEIN : THE UTILITY OF MATHEMATICAL MODELS

Levins, R., 1966. — The strategy of model building in population biology. The American Scientist , 54: 421-431.

Murray, J. D., 1993. — Mathematical Biology. Berlin, Springer Verlag, 2 nd edition: 1-768

Provine, W. B., 1971. — The Origins of Theoretical Population Genetics. Chicago, Chicago University Press: 1-202

Testing Evolutionary Processes with Phylogenetic Patterns

Test Power and Test Limitations

Philippe Grandcolas * Pierre Deleporte **

& Laure Desutter-Grandcolas *

* E.P. 90 CNRS. Laboratoirc d'Entomologie. Museum national d'Histoire naturelle,

45. rue Buffon. 75005 Paris. France

** UMR 6552 CNRS. Laboratoirc de Primatologie - Biologie evolutive. Station Biologique,

Universite de Rennes I. 35380 Paimpont. France

ABSTRACT

Using parsimony, phylogenetic patterns may be inferred with cladistics, and may validate predictions issued from models of

evolutionary processes. The use of parsimony is needed - whatever the evolutionary model implied - to minimize the number

of unwarranted hypotheses, according to the elementary rules of comparative biology. Following this minimization, patterns

are less hypothetical and more independent, and a higher number of evolutionary processes may be tested. One should be

aware of possible biases in the comparison of the results provided by several tests in different clades, biases related to

delineation of characters and ingroups.

RESUME

Le test des processus evolutifs par les sequences phvlogenetiques : puissance et limitations du test

La phylogenie cladistique permet d'etablir par eeonomie d'hypotheses des sequences devolution des caracteres. Ces

sequences peuvent valider les predictions issues de modeles de processus evolutifs concemant ces memes caracteres. L'usage

de la parcimonie se justifie dans ce domaine, quelque soit le modele evolutif qui y corresponde, par la necessity de minimiser

les hypotheses gratuites en biologie comparative. II permet d'une part de ne pas rendre les resultats trop hypothetiques, et

d'autre part de ne pas oberer le test d'hypotheses supplementaires par manque d independance. II est recommande de prendre

en compte les biais possibles dans la comparison de resultats de plusieurs tests dans des clades differents, biais pouvant

decouler de la definition des caracteres et des groupes a l’etude.

INTRODUCTION

Phylogenetic tests of evolutionary scenarios formally existed since approximately twenty

years (ANDERSEN, 1979). Following the development of cladistics, many people were interested

in taking into account phylogenetic information for testing evolutionary hypotheses, as

emphasized by several seminal papers (BROOKS, 1985; GREENE, 1986; Coddington, 1988,

1990; Carpenter, 1989). More recently, a large number of reviews dealt with this research field

Grandcolas, P. Deleporte, P. & Desutter-Grandcolas, L., 1997. — Testing evolutionary processes with

phylogenetic patterns: test power and test limitations. In Grandcolas, P. (ed ). The Origin ol Biodiversity in Insects:

Phylogenetic Tests of Evolutionary Scenarios. Mem Mus. naln. Hist, nat., 173 : 53-71 Paris ISBN 2-85653-508-9.

P. GRANDCOLAS, P. DEI.EPORTE & L. DESUTTER : TESTING EVOLUTIONARY PROCESSES

(Funk & Brooks, 1990; Wanntorp etal., 1990; Brooks & McLennan, 1991, 1993; Baum&

Larson, 1991; Coddington, 1994; Eggleton & Vane-Wright, 1994a; Maddison, 1994;

Spence & Andersen, 1994; Miller & Wenzel, 1995; Desutter-Grandcolas, 1996). The

goal of these studies in comparative biology is to use phylogenetic patterns either to infer an

evolutionary history per se or to test previous hypotheses of evolutionary processes (ELDREDGE

& Cracraft, 1980; Grandcolas el al. , 1994).

The number of available methods using phylogenetic information in the study of processes

has also greatly increased (e.g. Harvey & Pagel, 1991; Miles & Dunham, 1993; Harvey et

<*l; 1995; MARTINS, 1996) generally without clear distinction of their respective pre-requisites or

uses (Carpenter, 1992; GRANDCOLAS et al., 1994). Only some empirical modeling studies have

been carried out to evaluate and to compare these methods, and they did not settle general issues

in this respect (e.g. GlTTLEMAN & HANG-KWANG, 1994; WESTNEAT, 1995; BJORKLUND, 1995).

Several works have also criticized the reliability of phylogenetic tests. Regarding some specific

evolutionary models, tests are supposed to be flawed either because parsimony is used or

because adaptation is circumstantially detected (LEROI et al., 1994; FRUMHOFF & REEVE, 1994;

GRETHER, 1995; SCHLUTER, 1995).

The phylogeny user who compares taxa and builds phylogenies for inferring or testing

evolutionary histories could now wonder which method is the most powerful and relevant in his

case study, the more likely to provide him with robust and reliable results. He could also ask

what are the limitations of these methods. We try to answer these questions, focusing mainly on

the phylogenetic tests of evolutionary scenarios which seem to us of prime importance regarding

the aim of comparative biology.

TEST POWER

A test results from the contrast of two independent sets of data: for instance, statistical

tests compare an observed distribution and an expected distribution. The phylogenetic tests of

evolutionary scenarios compare phylogenetic patterns and patterns implied by evolutionary

processes (i.e. evolutionary scenarios), to infer sound hypotheses of evolution (ELDREDGE &

Cracraft, 1980; Carpenter, 1989; Grandcolas et al ., 1994). As in any test, if expected and

observed data sets are incongruent, the hypothesis under test (which has been obtained using

unwarranted hypotheses) is rejected as unsatisfactory. Conversely, the congruence of the two

data sets provides independent support (i.e. corroboration) for the unwarranted hypotheses used

for obtaining one of the data sets. By unwarranted, we mean hypotheses which are not

substantiated directly but made by extrapolation or by logical reasoning.

Phylogenetic tests may be ranked relative to other methods of extracting historical

information, according to their respective testing power. This testing power may be estimated

with respect to the range of different situations in which the tests can be performed, and with

respect to the ratio and the reliability of refutations which they can produce. Estimating the

testing power makes necessary to assess critically the kind of items to be compared in the test,

the intrinsic properties of these items and thus the way to contrast them maximally. Both the

phylogenetic patterns and the evolutionary scenarios should be examined in this perspective, in

order to draw the guidelines for carrying out the tests.

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PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

Lessons from the phylogenetic patterns

Minimizing the burden of hypotheses. Evolution is a historical and unique phenomenon

which occurred in the past and produced similarities and differences between taxa. The aim of

comparative biology is to fill the gaps existing between the taxa to understand their differences,

using the principle of descent with modification (Fig. 1). Consequently, comparative biology

deals mainly with hypotheses, i.e. the basic hypotheses of descent patterns which link the

respective characters’ states in the different taxa (NELSON, 1970; FARRIS, 1983). These

hypotheses will never be ascertained totally, because gaps in knowledge still remain (PATTERSON,

1994). Neither fossils nor additional taxa could provide anything other than hypotheses because

these additional taxa could only insert themselves between other taxa without totally filling the

gaps. Consequently, any methodological advance in comparative biology should consist in

decreasing as much as possible the number of hypotheses. For reconstructing the past, one

should not add any extra-hypothese ( e.g. ad hoc hypotheses sensu Farris, 1983) to the basic

and necessary descent hypotheses linking character states in taxa. Any additional ad hoc

hypothesis will remain unwarranted (unsupported by the data) and thus decrease the reliability of

Trait

time

General

Biology

Taxon

Comparative

Biology

Trait

Taxa

•

descent with

modification

•*— ? — ►

•

Fig. 1. — General biology deals with comparisons of different states of a trait (XI and X2) in a same taxon “A" at two

different moments. Comparative biology 1 deals with comparisons of different states of a trait “X” (XI and X2) in two

different taxa “A” and “B” In comparative biology, one relies on an assumption of descent, which will remains

hypothetical ultimately (here quoted with a question mark).

the results. A usual argument for adding hypotheses that we called here “unwarranted” is to

make analogy with previous case studies, in the way: “it is well-known that evolution proceeds in

the way ...” For example, “it is well-known that transversions are more frequent than

transitions”. This kind of argument seems to us clearly inappropriate in science in the absence of

directly supporting evidence.

Taking into account the principle of independence. There is another reason to decrease the

number of ad hoc hypotheses. To test evolutionary processes with phylogenetic patterns, it is

P. GRANDCOLAS, P. DELEPORTE & L. DESUTTER : TESTING EVOLUTIONARY PROCESSES

Predictive power

v -■/ •' -^y^4»r - *>_ r y«.

Explanatory power

Model

Process

Implied

scenario

Heuristic power

(test: corroboration or refutation)

. — Hie phylogenetic test of evolutionary scenarios compares two independent issues: a pattern issued from a

phylogenetic analysis (maximizing explanatory power) and a pattern issued from a model of evolutionary process

(maximizing predictive power). The test itself has a maximal heuristic power, whether it provides a refutation or a

corroboration as a result.

necessary to follow the principle of independence (DELEPORTE, 1993; GRANDCOLAS et a!.,

1994). One should not test hypotheses of evolutionary processes with phylogenetic patterns

which would have been inferred using these same hypotheses. The more ad hoc hypotheses used

to infer phylogenetic patterns, the less validly evolutionary processes can be tested, i.e. tested

with truly independent evidence.

The testing power of phylogenetic tests is inversely related to the number of ad hoc

hypotheses made for reconstructing phylogenetic patterns. Using a lesser number of ad hoc

hypotheses, one could test and refute a higher ratio of evolutionary processes with a higher

reliability. This explicit principle is reminiscent of the earlier characterization of cladistics during

the discussions among the different taxonomic schools. HENNIG (1950) himself already

distinguished phylogenetic systematics from evolutionary systematics on the basis of the use of

fewer a priori assumptions, as quoted by DlJPUlS (1984).

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PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

Lessons from the evolutionary processes

The plea concerning this particular minimization of ad hoc hypotheses does not concern

studies in general biology and especially in population biology. These kinds of biological studies

mainly deal with processes rather than patterns, and they study them in a diachronic way but in

the same taxa: the progress of a process can be observed along the time and the different states

of a trait during a process may be put directly into relation without making too many hypotheses

(Fig. 1). Along the time, several parameters can also be monitored to study their influence on the

process. In this way, comparing a trait in the same species (or even in the same population of the

same species) at different moments allows control of most influential parameters. The

comparison of two different states of the trait under study at two different moments does not

necessarily increase the number of uncontrolled parameters. This consequently does not decrease

the number of degrees of freedom for these comparisons, as opposed to studies of comparative

biology which compare different states of a trait in distinct taxa differing by many other

characters.

Population biology can thus develop fairly directly testable models. Models formalize the

relationships between several parameters on the basis of previous population studies. Models

make predictions which can be validated by further observations on populations. The empirical

validation of models is thus possible using complementary observations carried out at different

moments on the same phenomenon (Levins, 1966; Michalakis et al, 1997, this volume). In

general biology, predictions of models can be checked directly, while this is impossible for the

same hypotheses in comparative biology. Many models in general biology are predictive

regarding evolutionary processes in populations and are considered only secondarily as predictive

in different situations, at a macroevolutionary level and in different taxa. These models acquire by

extrapolation an heuristic value in comparative biology because their predictions can be

addressed secondarily at a macroevolutionary level. The validity of models at this level can no

longer be assessed empirically because the observations are no longer repeatable in the same

taxa. It has been sometimes argued that validation may be possible however, using antagonistic

models with opposite predictions (LEMEN & FREEMAN, 1989; MICHALAKIS et al, 1997, this

volume). But an identical prediction can be produced by several different models and thus cannot

be validated solely by refutation of an opposite prediction generated by an antagonistic model

(DUNBAR, 1989).

An evolutionary model at macroevolutionary level can only be validated by a comparison

with the independent patterns which can be collected using phylogenetic analysis. This is an

important methodological justification of the usefulness of phylogenetic tests of evolutionary

scenarios.

Phytogenies versus models: explanatory power versus predictive power

Both approaches, phylogenetic analysis and process modeling, are obviously valuable for

different reasons and they are complementary. There is an opportunity to compare the models of

processes in general biology and the phylogenetic patterns in comparative biology. In this

comparison, the patterns are testing the processes because patterns minimize ad hoc hypotheses

at a macroevolutionary level while the models are ad hoc constructions at this level (Fig. 2).

Analyses of patterns and processes have contrasting powers (Figs 2, 3). Phylogenetic patterns

have a high explanatory power (FARRIS, 1979, 1983), because available data are explained by

Source:

P. GRANDCOLAS, P. DELEPORTE & L. DESUTTER : TESTING EVOLUTIONARY PROCESSES

themselves without any ad hoc additional hypothesis (Figs 2-3). Models of processes have a high

predictive power, because they are designed to make predictions (Figs 2-3). The comparison of

these two contrasted analyses has a higher heuristic power than each separate analysis (Fig. 2)

because conclusions obtained when maximizing explanatory power are compared with

conclusions obtained when maximizing predictive power.

PHYLOGENY

EVOLUTIONARY

MODEL

Concern

Pattern

Process

Object

Clade

Population / Clade

Power

Explanatory

Predictive

Level

Unique

Statistic

Reliability

Robustness

Validation

Pre-requisites

Descent with

Additional

modification

Hypotheses

I' 1G - 3. Contrasted characteristics of phytogeny and model, including respective concern, object, power, level, reliability

and pre-requisites.

With respect to these principles, parsimony is not used as a particular model of evolution

but as a logic for reasoning using as few ad hoc hypotheses as possible (Farris, 1983). This

point has particularly been misunderstood (e.g. Pagel & Harvey, 1989; Pagel, 1994) and has

been a blind alley in discussions for several decades as noticed by RlEPPEL (1988) and EGGLETON

& VANE-WRIGHT (1994b). Parsimony must be used as a logical principle and it has inevitable

consequences concerning the reconstruction of evolution. However, any other method would be

less valuable, because of the use of more ad hoc and unwarranted hypotheses. Parsimony in data

analysis for phylogeny reconstruction is like democracy in the popular joke “the worst system,

but nobody has ever found a better one". Assertions such as “in this case, parsimony does not

work” are soundless because one does not know how evolution has proceeded in a given case

and one cannot propose a model - to mitigate parsimony use - which is free of additional and

costly assumptions.

It is sometimes asserted that phylogeny has also a predictive power (RlEPPEL, 1988;

SYSTEMATICS Agenda 2000, 1994), because it supplies parsimonious hypotheses of character

states when one state is unknown within part of an ingroup. This assertion is misleading because

it confounds the causation and the effect of parsimony use. Parsimony is used to provide

hypotheses of phylogenetic patterns, even though some character states are unknown in some

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PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

taxa, because a phylogenetic explanation is needed even with incomplete data. But parsimony is

primarily not used for predicting the value of missing data, such as unknown character states.

Used in this exclusive way, parsimony would be nothing else than a model, and a poor one, of

phylogenetic inertia through extrapolation of character states present in the sister taxa. The use

of the term “predictive” should be restricted to modeling; it is misleading in the case of

phylogenetic analysis and was probably mistaken for “heuristic”, “informative”, or better-

conceived “explanatory”.

TEST LIMITATIONS

Limitations can be intrinsic or extrinsic to the methodology of tests. Some intrinsic

limitations have been emphasized in recent criticisms and are the product of unwarranted

predictions by particular models of evolution. As these models cannot be validated, these

hypotheses of limitations are not testable and are refuted in a first step. Other intrinsic limitations

deal with the very nature of cladistic phylogenetic hypotheses and should be taken into account.

A first limitation is related to the robustness of phylogenetic trees on which phylogenetic tests are

based. Many authors have stressed that phylogenetic trees are not necessarily correct and that

studies based on phylogenies should consider carefully this point ( e.g. EGGLETON & Vane-

WRJGHT, 1994c). Although this point must be obviously a matter of concern, it could not justify

rejection of phylogenetic tests based on phylogenetic trees which have been correctly assessed

even according to only one set of data (either morpho-anatomical, or behavioral, or molecular,

etc ). As in any scientific study, a reasonable amount of evidence must be taken into

consideration, even if additional evidence can possibly change the results in the future, provided

that these results are refutable (Quin & Dijnham, 1983). It could be far less hazardous to use

phylogenies even if they are young hypotheses still not much discussed in the literature than to

use many ad hoc hypotheses to test evolutionary hypotheses. Cladistic phylogenies and related

phylogenetic tests - even based on limited evidence - can be refuted contrary to ad hoc

hypotheses of macroevolution. By the way, a further examination of the problem of tree

robustness may be found in this volume (WENZEL, 1997)

A second intrinsic limitation deals with the absence of temporal scales when dealing with

cladistics. Minimizing unwarranted hypotheses such as “evolutionary clocks” precludes any

possible absolute dating in cladistics (except minimal age estimates using fossils, which is

evidence independent of cladistics per se). This is particularly detrimental to the comparisons

between clades for testing hypotheses of niche displacement, coevolution, etc. Conversely,

studies which do not use this principle increase the burden of hypotheses. For instance, the

validity of the conclusions of OWENS & BENNET (1995) relies on their hypothesis of an

evolutionary clock in bird clades, a hypothesis less than reliable (CRACRAFT, 1992; MlNDELI.,

1992; O’Hara, 1991).

Most other limitations stay far beyond the tests and are related to the general and statistical

significance of the addition of the results of several tests (Fig. 4). They are extrinsic to the tests

but will undoubtedly become an important matter of concern when many phylogenetic tests are

achieved in the future. The addition of their results will allow generalizations (Grande, 1994),

provided that tests are carried out without sampling bias. These possible biases will be discussed

in a second step.

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60 P. GRANDCOLAS, P. DELEPORTE & L. DESUTTER : TESTING EVOLUTIONARY PROCESSES

Model-based criticisms

Recently, several authors have criticized phylogenetic tests, considering that parsimonious

reconstructions do not work under the assumptions of particular evolutionary models (LEROI el

al , 1994; FRUMHOFF & REEVE, 1994; GRETHER, 1995; SCHLUTER, 1995).

A first criticism was based on a misunderstanding of phylogenetic tests. According to

LEROI et al. (1994), pattern and process would be confused in phylogenetic tests and the pattern

would not be sufficient in itself to prove the existence of a corresponding process (for example,

polarity testing for the adaptive value of a trait). But, many phylogeneticists do not make the

assumption of an obligatory and reciprocal relationship between a kind of pattern and a kind of

process (CARPENTER, 1989; CODDINGTON, 1990; GRANDCOLAS et al , 1994). This point has

been clearly explained by CODDINGTON (1990) who showed that phylogenetic tests of

evolutionary scenarios contrast two patterns, one from the phylogeny and one implied by

evolutionary process (the scenario). In this way, the phylogenetic pattern is not taken as a direct

indication of the presence of a process but tests for its lack versus its possible presence. The

presence of this pattern in phylogeny is only a corroboration of the hypothesis of process. A

corroboration is always weaker than a refutation (BERNARD, 1865; POPPER, 1959); it cannot be

taken as a proof and thus it is necessary to substantiate the hypothesis of process by additional

Fig. 4. — The generalization of a pattern (1 -* 2) by the addition of phylogenetic analyses of three independent clades A, B

and C. This generalized parsimonious pattern must be compared to the underlying scenario of an evolutionary model.

population studies. For example, character polarity may corroborate an hypothesis of adaptation

but cannot prove directly the adaptive value of this character. The possible strong inference

issuing from a phylogenetic test comes in fact from the observation of a phylogenetic pattern

incompatible with the expected pattern, thus constituting a refutation of the tested process. More

precisely, it constitutes a refutation of the idea that the process would have existed and played a

major role in orienting macroevolution in the considered clade. The process is refuted by the

phylogenetic pattern and not the contrary because it comprises much more unwarranted

hypotheses at the macroevolutionary scale than the phylogenetic pattern. It is always possible to

imagine that the process existed and left no traces behind, but this is not a testable and scientific

proposition.

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PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

A second criticism deals with the possible genetic linkage between several traits

(Frumhoff & Reeve, 1994; LEROI et al., 1994; GRETHER, 1995). According to this criticism, a

strong genetic link could better explain the changes of certain characters than their own adaptive

value. This criticism is related to the misunderstanding commented upon above. Still, if the

phylogenetic pattern of a trait is incompatible with the pattern implied by a hypothetical process

concerning this trait, there is refutation of the process hypothesis, whatever any possible role of

genetic linkage. As previously mentioned, if there is corroboration, there is still additional work

to be achieved on populations before conclusion. This additional work should include genetic

studies of linkage (see also MORAND, 1997, this volume).

A third criticism, addressed more widely, concerns some general assumptions of

evolutionary models. Under specific evolutionary models dealing with rates or likelihoods of

transitions and speciations, FRUMHOFF & Reeve (1994) and Schllter (1995) imagined how

phylogenetic tests could become inefficient in reconstituting past events. This sort of model-

based assumptions are easily testable in populations but are unwarranted at a macroevolutionary

scale, a priori to any phylogenetic reconstruction (see Carpenter, 1997, this volume, and

SCHULTZ et al ., 1996 for arguing against the model of FRUMHOFF & RF.F.VE, 1994). Even if some

patterns constructed with cladistics are biased because of some particular modes of evolution,

there is a priori no other means to reconstruct them. The addition of the burden of any particular

model would only make results less reliable because one can never substantiate this particular

model concerning a past evolutionary phenomenon (analogy is not adequate in this respect to

build a particular model).

These three kinds of criticisms either are based on a misunderstanding of the procedure of

phylogenetic tests or do not follow a primary principle of comparative biology, that is to

minimize unwarranted hypotheses.

Actual limitations: beyond the individual tests

Particular as well as general hypotheses can be tested using phylogenetic patterns. When

dealing with general hypotheses, and to assess more strongly the conclusions, the phylogeny of

several monophyletic groups may be studied to perform as many tests. Monophyletic groups may

be considered as having evolved independently if they are not directly related (not sister-groups,

or one group not included in another). This assumption is only statistical as even if only a few

symplesiomorphic characters are shared, they can possibly determine evolutionary processes in

two clades which were hypothesized to be independent. Consequently, if several tests bearing on

different and independent groups provide the same results (refutation or corroboration of the

hypothesis), the hypothesis is tested by analogy more strongly and generally. In this way, a kind

of statistical significance may be assessed using the addition of several phylogenetic independent

tests (Fig. 4). Such independent tests are not often possible today because of lack of available

phylogenies. The opportunities of carrying out phylogenetic tests are still scarce. This should not

preclude anticipating the future statistical pitfalls and the biases which could occur, but should

incite to the realization of much more phylogenetic analyses.

Delineation of the trait under study. Depending on this delineation, the phylogenetic

pattern may vary. Trait delineation comprises the definition of the trait itself, the definition of its

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62 P GRANDCOLAS, P. DELEPORTH & L. DESUTTER : TESTING EVOLUTIONARY PROCESSES

states and the establishment of primary homology. A trait may be used in phylogenetic tests

either as a character for building the tree, or as an attribute optimized afterwards on the tree.

Considering the trait either as a character or as an attribute depends on the primary homology of

the trait (DE PINNA, 1991; GRANDCOLAS el a/., 1994), also named topographical correspondence

by RlEPPEL (1988). The establishment of primary homology is often neglected although it is a

Attribute

Character (Matrix)

Character (Tree)

Primary

Secondary

homology

Similarity

only

assumed evolved

assumed

by descent with

evolved

modification

by descent with

modification

Test of

Test of congruence

congruence

of the assumption

"descent with modification"

Fig. 5. — The different operations applied during phylogenetic analysis to traits being attribute, or character in a matrix, or

character in a tree. The attribute satisfies only to a statement of similarity, but not to a statement of homology; it is

submitted to a test of congruence. The character is firstly assessed primary homologous on the basis of its similarity

and on the basis ol an assumption ol descent with modification: it is secondly assessed secondarily homologous on the

basis of a test of congruence of the assumption of primary homology.

critical step in phylogenetic analysis (GRANDCOLAS, 1993; GRANDCOLAS et a/., 1994). The

primary homology of a trait is arbitrarily assessed by using statements of similarity which

themselves rely mainly on the heritability and the delineation of this trait (Fig. 5). For example,

traits such as geographical distributions may not be said to be strictly homologous because they

are not heritable sensu stricto (Dupuis, 1984). Also, macroecologica! traits such as “benthic”

cannot be said homologous because they are defined at a too large scale (Mickevich & WELLER,

1991) and thus poorly defined. Most disagreements concerning primary homology come from the

definition of primary homology itself. For example, all broadly similar traits could to be said to be

primarily homologous (DELEPORTE, 1993), even if they are not used to build a tree, because they

are similar and coded as such when mapped on the cladogram afterwards. This concept is

however equivocal, in that it does not take into account the fact that these so-called homologous

traits are not used as characters for building the tree, as all presumed a priori homologous traits

should be with respect to the principle of total evidence (KLUGE, 1989). According to

GRANDCOLAS et a/. (1994), only similar traits which are used for building the tree should be said

primarily homologous; they should be said to be only similar when optimized on the tree and

when this mapping is the only way to assess their homology. In other words, primarily

homologous traits - characters - are by definition similar traits which are postulated a priori to

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PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

be acquired by descent with modification and not to be homoplastic (Fig. 5). Conversely,

attributes are similar but are not a priori postulated acquired by descent with modification (Fig.

5), and this is why one does not treat them as characters supporting phylogeny construction (but

see in this volume: CARPENTER, 1997 for another distinction between characters and non¬

characters, or Wf.NZEL, 1997 for arguing in favor of all traits taken as characters).

00101

10010

Character versus Attribute

Primary homology

intrinsic vs extrinsic

(trait heritability)

large scale vs small scale

(trait delineation)

structural vs functional

(trait delineation)

Fig. 6. — The distinction between character and attribute by the mean of a primary homology statement. This statement

concerning a trait is based on the perception of its nature, intrinsic versus extrinsic (heritability), structural versus

functional (delineation) and the scale large or small at which it has been defined previously (delineation).

Increasing both the accuracy of the definition and the number of states improves primary

homology because the criteria of homology may be more easily applied to the trait (Fig. 6). In

this way, more available phylogenetic information existing in the traits is used. A trait the primary

homology of which is assessed can be used to build the tree and is thus submitted to an internal

test of congruence with other characters (Fig. 5). Increasing both the accuracy of the definition

and the number of states optimizes in turn the secondary homology of the trait. When the

primary homology of the trait has not been assessed, this trait can be optimized (as an attribute)

on the tree to discover its phylogenetic pattern. This pattern can be more precise if the definition

of both the trait and its states are accurate.

Concerning the problem of character delineation and especially the “character versus

attribute” alternative, one should be aware that primary homologies should not be indirectly

assessed. Unfortunately, homologies of behavioral or ecological traits are often based not really

on direct examination of the criteria of homology but on indirect considerations. For instance, the

homology of a behavioral trait is often assessed according to its neural or its anatomical

correlates. If homology of the neural scheme or anatomical structures are assessed, we would

better use neural schemes or anatomy as characters. Also, homology is often assessed using

circular reasoning, especially in broadly similar traits: behavioral trait is observed in two taxa

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P. GRANDCOLAS, P. DELEPORTE & L. DESUTTER : TESTING EVOLUTIONARY PROCESSES

known to be closely related, and so it is considered homologous, provided that they are related.

This is obviously circular. Homology is not independently assessed for the ethological trait itself

but by using a model of phylogenetic inertia. Determining the homology of behavioral traits is

however possible using the classical criteria of homology, but actually applied to behavior itself.

Most problems of plasticity and variability which are often said to prevent assessing behavior

homology must be solved by appropriate ethological studies (WENZEL, 1992).

Selection of the ingroup. This term refers here to the selection of a group of taxa

supposedly monophyletic, without any contingencies related to the sampling of taxa. The

ingroups are generally studied for a priori reasons of suitability for specific phylogenetic tests of

characters. Ingroups are often studied also according to some constraints of feasibility: are the

taxa well known, have their phylogeny or at least their characters been preliminarily studied 17 A

phylogenetic test deals with the evolution of one or several traits from an ancestral state toward

derived state(s), possibly including reversals; this means that the group on which the test is

carried out comprises taxa showing at least two states for each trait. Also, the groups under

study are generally relatively small, still because of constraints of feasibility. Phylogenetic studies

of larger groups are rarely carried out because many more character state occurrences must be

documented according to the increased number of terminal taxa. Ingroups are consequently most

often relatively small in size and diverse with respect to the trait under study. Consequently,

patterns inferred from these phylogenies will be submitted statistically to scale effects.

Comparing the results of several phylogenetic tests carried out on different clades could lead to a

bias which, in turn, could prevent a statistical estimate of the general prevalence of a pattern and

to assess the validity of the model corresponding to this pattern. For example, if someone wants

to study the evolution of flying kinematics and behavior in insects, he would probably focus on

Diptera, as this is the order which is currently very diverse and well-known in this respect. But he

would not analyze the whole order of Diptera because to examine hundreds of taxa in this group

will overwhelm his capacity to carry out phylogenetic studies within a few years. Thus, he would

select a few groups which are smaller , which have been already partly studied, and which are

diverse with respect to flying behavior. Selected groups should necessarily be diverse (character

diversity), otherwise no comparative study may be carried out for want of different states of

traits to be compared.

As they are statistically smaller and more diverse than if they were truly taken randomly in

the tree of life, ingroups may present a non-random selection of patterns which are used to test

evolutionary processes. In our example, our Dipterist would have certainly not selected very

large taxa with very few variation in flying behavior ( e.g . a monophyletic tribe comprising 500

species, of which 499 have a first kind of flight and only one another kind). These groups would

be excluded from the analyses. Afterwards, generalizations based on these studies would not take

into account patterns which could be more frequent in large and homogeneous groups. This non-

random selection may be expected to be particularly biased. Indeed, the diversity of a given

character should statistically increase with the size of a group. Thus, choosing small and diverse

groups excludes most of groups present in a given part of the tree of life, those which are larger

and moderately diverse, and those which are of the same size and which are not diverse.

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PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

The patterns and the relevant tested processes (Figs 7-8, see also GRANDCOLAS et a/.,

1994) are listed below with the possible bias induced by the choice of the ingroup. The biases are

mentioned below provided that all things are equal otherwise in the ingroup and in the tree of

life, except the ingroup size and the diversity of the character under study in this ingroup. These

biases may be expected statistically only ( i.e. for a large number of ingroups); it is obvious that a

unique and particular group may not conform to the statistical expectation.

- Polarity (testing for adaptation, Fig. 7): size and diversity of the ingroup may or may not

have particular scale effects regarding this pattem/process. Polarity cannot be expected to have a

particular value in a small and diverse group and only depends on the distribution of character'

states on the taxa and on the structure of the phylogenetic tree.

Process Pattern

Example

Adaptation Polarity

2 2 2 1 1

2 may be

adaptive

Convergence Homoplasy

3 2 2 3 3

L M N O P

2 in M is

convergent

with 2 in N

Fig. 7. — Two patterns relevant to the phylogenetic test of two processes (see Grandcolas et al. , 1994 for more details).

From left to right, the process to be tested, the pattern to be searched for testing, an example of phylogenetic test with

its issue.

- Homoplasy (testing for convergence, Fig. 7): small and diverse ingroups may present

statistically less homoplastic patterns because of the decrease of the number of subordinated

nodes after a change in character state. The bias concerning this pattern is only related to the size

of the ingroup: small ingroups do not allow to document as many reversals as could be expected

because small ingroups have statistically fewer nodes. If there is a change of states of a character

at a given node, there is simply more cases with no existing subordinated nodes which could

permit to document another subsequent change of state such as a reversal.

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66 P- GRANDCOLAS, P. DELEPORTE & L. DESUTTER : TESTING EVOLUTIONARY PROCESSES

- Time lag (testing for coadaptation-exaptation, Fig. 8): when testing for coadaptation or

exaptation, (relative) time lag between the changes of two traits or between a trait and its

function are searched for in phytogenies. Using smaller and diverse groups, there is a lower

number of nodes where changes can take place. This can bias the correlation studies between

two traits: after the change of a first trait, subsequent changes could take place in fewer places.

Consequently, a smaller number of changes will necessarily be observed. This will bias the

Process Pattern

Adaptive Differential

radiation cladogenesis

Example

2 2 2 2 1 1

A B C D E F

2 may be

an adaptation

which caused

radiation

Coadaptation Time lag

/ Exaptation

II II I I I

2 2 2 1 1

A B C D E

2 and II may be

coadapted /

2 may be

exaptive in A,B

Fig. 8. — Two other patterns relevant to the phylogenetic test of two other processes (see Grandcolas et al. y 1994 for more

details). From left to right, the process to be tested, the pattern to be searched for testing, an example of phylogenetic

test with its issue.

frequency of observed time lags and will provide us with fewer corroborations of coadaptation-

exaptation. This statement does not refer to a probabilistic approach for testing coadaptation-

exaptation, such as that presented by Maddison (1994) for challenging the views of Sillen-

Tullberg (1988). Probabilistic approaches deal with events occurring within the clades while

our statement concerns the statistical meaning of (in)congruent results obtained from several

clades.

- Differential cladogenesis (testing for radiation, Fig. 8): small ingroups with a high number

of evolutionary changes cannot show relatively differential cladogenesis concerning the trait

under study. Important differential cladogenesis can exist by definition only in very large

ingroups because they imply a high number of taxa in the subgroup where occurred the most

important cladogenesis. This can prevent to test for the importance of adaptive radiation which is

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PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

the process corresponding to the phylogenetic pattern of differential cladogenesis (GUYER &

SLOWINSKI, 1991). This can prevent conversely testing for the role of evolutionary stasis,

because the chosen small ingroups with a high number of evolutionary changes may not show

evolutionary stasis.

Smaller ingroups are also statistically and relatively more recent groups, compared to

larger ingroups, provided that both are taken in the same inclusive monophyletic group.

Depending on the stability of evolutionary rates, this could lead to study only the relatively more

recent evolutionary events. This is detrimental to the tests of evolutionary hypotheses which are

linked to particular climatic or geological periods (but we can note that using too large a group

could also lead to irrelevant correlations between a relatively old phylogenetic pattern and much

more recent geological or climatic events). It should be kept in mind that the relation between

ingroup size and age is not absolute but statistical. There also exist a few small and relatively old

groups among all possible ingroups taken in the same inclusive monophyletic group ( e.g . the so-

called “relict taxa”).

The last bias, but not the least, is related to the relevance of the ingroup for testing a

particular evolutionary model. The phylogenetic test is designed to refute or to corroborate the

prediction of an evolutionary model taking into account a number N of factors. The model could

not be tested correctly when only (N - I) factors are considered in the phylogenetic test. This

situation would occur if (N - !) factors are represented as apomorphies in the ingroup and if the

N th factor is represented by a symplesiomorphy of the ingroup. This factor/plesiomorphy could

make either trivial or extremely rare the pattern corroborating the model and could thus bias

strongly the test toward corroboration or refutation. A recent example may be found in studies of

Hymenoptera, where reversals of sociality were documented in Halictidae using phylogeny.

Packer et al. (1994) interestingly questioned why so many sociality reversals occur, while no

appearances were documented. Together with other reasons, the phylogenetic inertia may have

been quite important in biasing the tests. In Hymenoptera, most theories of social evolution put

forward the role of brood care for favoring sociality. Higher-level phylogenetic analysis shows

that brood care (the N th variable) is ancestral to Halictidae and this could bias the study toward

a minimization of appearance events. Only studies at a much wider phylogenetic scale could

adequately document appearances of sociality, for instance succeeding to the appearance of

brood care and not preceding it. Another example deals with the origin of complex reproductive

behaviors in cockroaches. These behaviors - ovoviviparity and viviparity - evolved following the

appearance of “deposition of ootheca after sclerotization ’, which is apomorphic in cockroaches,

relative to mantids and termites (GRANDCOLAS, 1996). If the females did not keep their ootheca

after sclerotization, they could not have evolved toward subsequent retraction and nutrition ol

oothecae in a brood sac (ovoviviparity and viviparity). Anyone who would like to study

subsequent evolution of reproductive behavior in a particular group of cockroaches should not

forget that the character “deposition of ootheca after sclerotization , plesiomorphic at this level,

is still influential (ROTH, 1989).

CONCLUSION

Comparative biology is still a young and growing research field, as was phylogenetics when

HENNIG (1965) published one of his last methodological accounts. Following the development of

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P. GRANDCOLAS, P DELEPORTE & L. DESUTTER : TESTING EVOLUTIONARY PROCESSES

phylogenetic methodology, it is now necessary to elaborate a cohesive methodology which can

take into account the possible interrelations of phylogenetic patterns with evolutionary processes

(and relevant models). This is generally made through the phylogenetic test of patterns which are

expected under some process hypotheses.

As a contribution to this methodology, three rules are proposed which could improve

phylogenetic analysis both intrinsically and extrinsically. These improvements should increase the

phylogenetic test power and decrease the test limitations.

First, the burden of hypotheses in phylogenetic analysis should be reduced by decreasing

the number of unwarranted hypotheses (with parsimony use). Comparative biology proceeds

using hypotheses only. Adding unwarranted extra-hypotheses is detrimental to the reliability of

the results.

Second, the independence of phylogenetic patterns relative to process hypotheses should

be enhanced the same way, by decreasing the number of ad hoc hypotheses used to infer them.

Particularly, to test an hypothesis of process, one should not use patterns inferred using this same

process hypothesis.

Third, statistical bias during the generalization of the tests should be minimized. When

several similar tests are carried out on different ingroups, their results may be compared to

generalize them. The possible peculiarities of ingroups should be taken into account to minimize

the possible bias in the generalization.

The first two rules deal with a general problem encountered in many research fields of

evolutionary biology. Minimal hypotheses (sometimes named null hypotheses or null models, e.g.

Patterson, 1994) are wanted in comparative studies as well as in population studies of

adaptation (GOULD & Lewontin, 1979) or in studies of biotic interactions (Quinn & DUNHAM,

1983). These minimal hypotheses are needed to check the validity of the ad hoc hypotheses used

to reconstruct the past. Both a lack of minimal hypotheses or an abuse of ad hoc hypotheses will

make the results flawed or unreliable. It is stressed that comparative studies should take this

principle into account, for consideration paid to previous methodological analyses in evolutionary

biology. We must not reinvent the wheel in comparative biology, disregarding methodological

advances in phylogenetics or in evolutionary biology.

ACKNOWLEDGEMENTS

We are pleased to thank James Carpenter and Pascal Tassy for their comments on our manuscript. The arguments of

this paper were presented during the Symposium '‘Phylogenetic tests of evolutionary scenarios’' and we are grateful to people

who questioned and commented on the ideas presented in this paper.

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Comparative Analyses of Continuous Data

the Need to Be Phylogenetically Correct

Serge Mgrand

Centre de Biologie et d'Ecologie Tropicale et Mediterraneenne. UMR 5555 CNRS

Universite de Perpignan. 66880 Perpignan Cedex. France

ABSTRACT

In this paper I focus on the problem of non incorporating phylogenetic information when doing a comparative analysis. A

review of the theory on this subject shows that not incorporating the phylogenetic information inflates the degree of freedom

and can increase the risk of type I and type A errors of statistic tests done on cross species data (non phylogenetically

controlled). The phylogenetic independent contrasts method (Felsenstein, 1985) has been developed to resolve the problem

of non-independence of data ( i.e ., traits measured across different species) in comparative studies. After a presentation of the

assumptions of this method, I provide one example on parasite species richness of mammals which shows the errors that lead

to false conclusions. For example, a non phylogenetic approach (cross species comparisons) would lead to the conclusion that

parasite diversity is linked to host body size, whereas a phylogenetic independent comparison shows no relationship between

host body size and parasite richness. A non phylogenetic approach would thus lead us to reject the null hypothesis when it is

false (Type I error). One assumption underlining the independent contrasts method is the random walk model (Brownian

motion), which is used as a null hypothesis. Many traits that are considered in comparative studies are unlikely to be well

described by a simple Brownian motion process. I propose to use Mantel tests to detect evolutionary trends in comparative

analyses. I performed a simulation that shows the efficiency of Mantel tests for detecting evolutionary' trends and for

measuring phylogenetic effects. Mantel tests could be one answer to the critical comments made on the independent

contrasts method.

RESUMfi

Analyse comparative des donnees continues : la necessite d’etre « phylogenetiquement correct »

Dans ce travail, je m'interesse aux problemes lies a la non prise en compte des informations phylogcnetiques quant on

realise une analyse comparative. Une revue de la theorie concemant ce sujet montre que de ne pas incorporer les informations

phvlogenetiques augmente le degre de liberte et accroit les risques d'erreur de type I et de type D des tests statistiques

effectues sur les donnees non controlees pour la phylogenie. La methode des contrastes independants (Felsenstein, 1985) a

ete developpee pour resoudre le probleme de la non-independance des donnees (les traits mesures chez les diflerents taxons)

dans les etudes comparatives. Apres une presentation des hypotheses de cette methode, je donne un exemple concemant les

richesses parasitaires des mammiferes terrestres qui montre les erreurs conduisant a des conclusions erronees. Ainsi, une

approche non phylogenetique aurait conduit a la conclusion que la diversite parasitaire est liee a la taille de 1 hole, alors que

la methode des contrastes independants montre V absence de relation entre ces deux variables. Une appri>che non

phylogenetique peut conduire a rejeter Phypothese nulle alors qu'elle est vraie (erreur de type I). Une des hypotheses de la

methode des contrastes independants est le modele de marche aleatoire (mouvement brownien). De nombreux traits, pris en

compte dans les analyses comparatives, ne sont pas bien decrit par le modele de mouvement brownien. Je propose d utiliser

Morand, S., 1997. — Comparative analyses of continuous data: the need to be phylogenetically correct. In:

Grandcolas, P. (ed.), The Origin of Biodiversity in Insects: Phylogenetic Tests of Evolutionary Scenarios. Mem. Mus. natn.

Hist, nat., 173 : 73-90. Paris ISBN : 2-85653-508-9.

Source: MNHN, Paris

S. MORAN!) : COMPARATIVE ANALYSES OF CONTINUOUS DATA

les tests de Mantel pour detecter les tendances evolutives dans les analyses comparatives. J’ai conduit une simulation qui

montre Pefficacite des tests de Mantel pour detecter les tendances evolutives et mesurer les effets phylogenetiques. Les tests

de Mantel peuvent etre une des reponses aux critiques effectuees sur la methode des contrastes independants.

INTRODUCTION

There are two ways for analyzing evolutionary processes. The first one, the population

approach, focuses on micro-evolutionary processes and tries to find adaptation at work, i.e. the

evolution of a specific character under natural selection or sexual selection. The second one, the

comparative method, tries to identify adaptation by studying the evolution of a specific character,

in different lineages, supposed to be driven by the same selection pressures. The development of

cladistic analyses has challenged the definition of adaptation. For example, CODDINGTON (1988)

has defined an adaptation as an apomorphic fiinction promoted by natural selection. I will

concentrate on the second approach.

First of all, we have to distinguish the differences between phylogenetic effects from

phylogenetic constraints. DERRICKSON & RiCKLEFS (1988) have drawn the attention on the fact

that numerous biologists do not make the difference between phylogenetic effects and

phylogenetic constraints. According to these authors, the phylogenetic effects are only the

expression of the tendency of related species to be similar because they share a common history.

They defined a phylogenetic constraint as the effect of history onto the changes in diversification

of a given clade or as the differences in evolutionary interactions between a phenotype and its

environment. However, as emphasized by McKlTRlCK (1993) such definition refers more to the

results than to the causes of a constraint. McKlTRlCK (1993) suggested that a constraint

highlights the absence of a given character or the lack of an expected evolution. She proposed

the following definition where a phylogenetic constraint is “any result or component of the

phylogenetic history of a lineage that prevents and anticipated course of evolution in that

lineage”. The lack of viviparity among birds is an example of phylogenetic constraint.

Very early, people have recognized several pitfalls linked with cross-species comparisons.

It has been recognized that taxonomic relationships greatly influence the correlation between the

analyzed traits (STEARNS, 1992). Interspecific comparison is a very common approach in ecology

(as well as in other branches of biology). Many recent studies, and even recent textbooks, in

ecology or evolutionary biology continue to ignore these statistical pitfalls and persevere to

ignore the importance of the phylogeny and the history of organisms.

Some evolutionary biologists use parsimony methods for inferring the evolution of a

particular character. GARLAND & ARNOLD (1994) argued that the application of parsimony

analyses can be justified only on methodological grounds but do not refer to any model of

evolution (but see SOBER, 1994 for the use of parsimony in evolutionary biology). FELSENSTEIN

(1988) challenged the view that reconstructing phylogenies is a statistical problem and implies an

explicit model of evolution. People interested in the evolution of discrete characters mostly use

parsimony analyses whereas those dealing with continuous characters use independent

comparative methods (but see Pagel, 1994).

It is not my aim to compare these two very different methods (parsimony versus

independent comparative method) for the analysis of adaptation. Rather, I focus deliberately on

the statistical approach in order: (1) to convince evolutionary ecologists about the need to

control for phylogeny when comparing different species, (2) to draw the attention of

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

phylogeneticists to models (and statistics) that underline every methods, (3) to propose Mantel

tests as a method to detect evolutionary trend.

HOW TO REVEAL PHYLOGENETIC EFFECTS? A FIRST APPROACH

FISHER & Chapman (1993) tried to answer to this question by analyzing the dispersal

mechanisms of plant fruit. The objectives of their study were to examine the degree to which

plants have evolved predictable, disperser-specific syndromes and to determine the consequences

of using different taxa as sampling units when analyzing comparative data to test for the

existence of dispersal syndromes. These authors recognized that using species as independent

sample units implies that the analyzed character (fruit morphology) should have evolved

independently in any clade, which is not self-evident. Furthermore, an analysis based on species

will dramatically inflate the number of events. In the absence of a fully resolved phylogeny,

Fisher & Chapman (1993) proposed to use genera as sample units. The hypothesis is that if the

apparition of a given trait is the result of convergent evolution then this correlation should always

be found when using genera as sample units. Because the correlation was lost using genera as

sample units, FISHER & Chapman (1993) concluded that a study based at the species level is not

unbiased. This example highlights two major problems. First, the use of taxonomic information is

arbitrarily and, second, the use of species as independent points may lead to false conclusion.

WHY USING PHYLOGENETIC INFORMATION IN COMPARATIVE ANALYSES?

Three pitfalls should be avoided in comparative analyses:

(1) not incorporating phylogenetic information may inflate the degrees of freedom,

(2) high risk of rejecting Ho when it is true (Type I error),

(3) high risk of accepting Ho when it is false (type II error).

Not incorporating phylogenetic information implies that we make the assumption of a true

case of multiway speciation events (“hard polytomies”; MADDISON, 1989), which refers to a star

phylogeny. However, most phylogenies are dichotomous even if some parts are unresolved (soft

phylogeny). Imagine the case of 5 species, a star phylogeny gives (5-2=3) degrees of freedom

while a dichotomous phylogeny gives (5-3=2) degrees of freedom or less (GARLAND & ARNOLD,

1994).

Figure 1, redrawn from GlTTLEMAN & LUH (1992), shows the problem of phylogenetic

relations. Suppose a known phylogeny with 2 genera and 6 species. By plotting trait variations

and ignoring phylogenetic pattern we might find a relationship whereas it is erroneous (type I

error: false rejection of H 0 ). Conversely, we might reject a relationship (type II error: false

acceptation of H 0 ) which actually exists.

I will give below an example showing both statistical errors.

THE INDEPENDENT CONTRASTS METHOD

The phylogenetic independent contrasts method (FELSENSTEIN, 1985; MARTINS &

Garland, 1991; PAGEL, 1992; Garland, 1992) has been developed to resolve the problem of

non-independence of data ( i.e. traits measured across different species) in comparative studies.

FELSENSTEIN (1985) suggested a procedure for calculating comparisons between pairs of taxa at

each bifurcation in a known phylogeny (Fig. 2).

Source MNHN, Paris

S. MORAND : COMPARATIVE ANALYSES OF CONTINUOUS DATA

Error type II Error type I

Fig. 1 — Ignoring phylogenetic relationships may lead to erroneous conclusions. A Type I error (false acceptation of the null

hypothesis) occurs when rejecting the extant correlations (dashed lines) whereas a Type II error (false rejection of the

null hypothesis) occurs when claiming correlation (solid line) when its actually false (dashed lines). The illustration is

after Gittleman & Luh (1992),

In a phylogenetic tree, the independent events (on which an analysis can be performed)

correspond to the nodes that give rise to daughter branches. For each branch of a node, values

for a given variable are obtained by averaging the values of its own daughter branches. Then the

difference for each variable between the two daughter branches of each node is calculated. In the

calculation of contrasts, the direction of subtraction is arbitrary. Multiple nodes can be treated in

a way that gives a single contrast (Purvis & Garland, 1993). Pairs of sister branches that

diverged a long time ago are likely to give greater contrasts than pairs of sister branches that

diverged recently. It is thus necessary to standardize each contrast through division by its

standard deviation where the standard deviation of a contrast is the square root of the sum of its

branch lengths (Garland el a/., 1992). In the absence of information on branch length, one can

assume each branch length to be equal to unity. Another method is proposed by Grafen (1989)

for assigning arbitrary lengths. In this method the age of a node is assigned as the number of

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

daughter groups descended from that node minus one. Nevertheless, GARLAND el al. (1992)

showed that using arbitrary or real branch lengths often leads to similar results. In order to check

that contrasts are properly standardized it is suggested to perform a regression of the absolute

values of standardized contrasts versus their standard deviations. In case of positive relationship

it is necessary to transform branch lengths before computing standard deviations (Garland el

al., 1992). All correlations between contrasts are forced through the origin (Fig. 2).

Regression forced through the origin

Fig. 2. — The independent contrasts method. The illustration is after Gittleman & Luh (1992) and Purvis & Rambaut

(1995).

The three main assumptions of independent contrasts are:

(1) a correct topology,

(2) branch lengths measured in units of expected variance of character evolution,

(3) a Brownian motion model of character evolution or random walk model (FELSENSTF.IN, 1985;

1988).

Under a Brownian motion model of evolution, a change in the mean phenotype is expected

to be non-directional and to occur at a constant rate. This rate can be described in terms of the

relation between the variance among species phenotypes and time as:

Vb = pt + s

Source:

S. MORAND : COMP.4R4TIl'E ANAL YSES OF CONTINUOUS DATA

As pointed out by MARTINS (1994), many traits that are considered in comparative studies

are thought to have been the subject to the action of natural or sexual selection. Thus, these traits

are unlikely to be well described by a simple Brownian motion process. The performances of the

independent contrasts under different models of character evolution have been tested (see

Martins & Garland, 1991; Martins, 1994; BjOrklund, 1994). Simulation studies indicate

that the independent contrasts method produces acceptable error rates. Moreover, the

independent contrasts method produces less error rates than other phylogenetic correction

methods, like nested ANOVA or phylogenetical autocorrelation (MARTINS & GARLAND, 1991;

Purvis et al., 1994; Diaz-Uriarte& Garland, 1996).

Three statistical assumptions must be tested when working with a real data set (GARLAND

el al., 1992; PURVIS & RAMBAUT, 1995):

(1) the random walk model can be tested by regressing the absolute values of the standardized

contrasts against the estimated nodal values,

(2) homogeneity of variances can be tested by regressing the absolute values of the standardized

contrasts against the height or ages of the corresponding nodes,

(3) and ANOVA can be used to test for heterogeneity of variances amongst multiple node

values.

However, one problem with the independent contrasts method is the accurate estimation of the

ancestral values at ancestral nodes (PAGEL, 1992). The method of averaging values can introduce

several biases. Excluding ancestral nodes from the analysis is one way to test if the relationship

remains identical with actual species (PAGEL, 1992).

PARASITE RICHNESS OF MAMMALS AS EXAMPLE

1 compiled data on nematodes recovered from 66 species of terrestrial mammals. These

data were collected from several sources based on a survey of 90 studies published over the last

30 years. Comparative analyses of parasite species richness should avoid 2 pitfalls: sample size

(Gregory, 1990; WALTHER et a /., 1995) and phylogenetic confounding effects (Harvey,

1996). As GREGORY (1990) and WALTHER et al. (1995) pointed out, investigations on parasite

species richness must take into account differential sampling effort. Differential sampling effort is

a consequence of both the researcher’s sampling procedure and of the geographical range of the

hosts, and both may affect host and researcher encounters, and thus directly influences the

observed number of parasite species.

The need to take the phylogeny into account is related to the coevolution between hosts

and parasites. Hence, host phylogeny may be important in determining the richness of a parasite

community (Holmes & Price, 1980; Brooks & McLennan, 1991). Furthermore, cross-species

comparisons performed using species values as independent data points may be confounded by

the phylogenetic relationship of the analyzed species (FELSENSTEIN, 1985; HARVEY & PAGEL,

1991, Martins & Garland, 1991). For example, a correlation between host body size and

parasite species richness may arise because a group of related and same-sized hosts have a high

parasite species richness because of their common phylogenetic origin and not because of

common ecological forces. Closely related species tend to be similar. Therefore, species values

cannot be treated as statistically independent points (Harvey & PAGEL, 1991).

I based the analysis on the working phylogeny of mammals (Fig. 3) proposed by POULIN

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

Didelphis rirginiana

Marmola monax

Sciurus carollnrnsts

Tamascturns hudsonicus

Thamomys talpoides

Thamomys bulbivorus

Dipodomys deseru

Dipodomys merrlami

Hydrochaerls hydrochaeris

Ondatra zibrlhica

Neofiber alleni

Sigmodon hispidus

Onychomys leucogaster

Oryzomys palustris

Podomys fioridanus

Peromyscus gossyptnus

Peromyscus polionotus

Clethrionomys glaerotus

Rattus rattus

Apodemus sylvaticus

Lepus americanus

Lepus ealifornicus

Oryetolagus cuniculus

Sytvilagus fioridanus

Ochotona princeps

Blarina brericaudata

Sorex araneus

Sorex min ulus

Ursus americanus

Ursus aretos

Procyon lotor

Lulra canadensis

Mephitis mephitis

Taxidea tax us

Maries americana

Martes pennanti

Mustela erminea

Music la rison

Canis familiaris

Cams latrans

Canis lupus

Urocyon cinerorargenteus

Vulpes vulpes

Felis canadensis

Felis cati

Felis concolor

Felis rufus

Equus burchelh

Equus caballi

Equus zebra

Giraffa Camelopardalis

A Ices alces

Cerrus axis

Cerrus elaphus

Dama dama

Ondocoileus hemionus

Ondocoileus virginianus

Rangi/er larandus

Bos taurus

Oris americana

Oris aries

Oris canadensis

Oris orientalis

5 us scro/a

Tayassu tajacu

Lama glama

Eptesicus fuse us

My otis luci/ugus

Nycticeius humerahs

Fig. 3. — Phytogeny of mammals used in the analysis (this phytogeny redrawn from Poulin, 1995 is based on various sources:

molecular and morphological data)

Source: MNHN, Paris

S. MORAND : COMPARATIVE .ANALYSES OF CONTINUOUS DATA

(1995). I used the C.A.I.C. program (Purvis & RAMBAUT, 1995). Data on parasite species

richness and host body lengths were logarithmically transformed (HARVEY, 1982). Because

parasite species richness can correlate with sampling effort, both variables were controlled for

host sample size before the analyses. All correlations between contrasts were forced through the

origin (GARLAND et a/., 1992).

Parasite richness and host body size

Cross species analysis and phylogenetic independent method gave rise to different results

(Fig. 4). A non phylogenetic approach (cross species comparisons) leads to the conclusion that

parasite diversity is linked to host body size. However, a phylogenetic independent comparison

of contrasts analysis showed no relationship between host body size and parasite richness. A non

phylogenetic approach would lead us to accept the null hypothesis when it is false (Type I error).

My results support those of POULIN (1995) who also did not find any relationship between

mammal body size and parasite species richness when correcting for host phylogeny.

(a) Cross-species' comparison (non-phylogenetic comparison)

Significant (P < 0.001)

False rejection of Hq

T ype I Error

(b) Independent contrasts

_ s

c ‘K

■ i

1.0 -

O '

1 . ..... 1 .

0.8 -

0.6 ■

0.4 -

O O 0 ° n

0.2 ■

o# ° ° 0°

O o .

0.0 •

° 9j COO o CP

-0.2

° O CL

®o 0°0 *

-0.4

°°

-0.6

;

-0.8

-1.0

• • r

-0.5 0 0.5 1.0 l.S 2.0 2!s 3.0

N.S. (P = 0.33)

Host bodv size (In k^)

corrected for sample size

Fig. 4. — A significant relationship between host body size and parasite diversity (nematodes) is found when using a non-

phylogenetic approach whereas it is false as detected by the independent contrasts method. Parasite species richness is

controlled for sampling effort.

Source:

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

(a) Cross-species' comparison (non-phylogenetic comparison)

2.0

1.5

-.2 1.0

e ’7.

| | «

.i 5 o

.Si u

* -2 - 0.5

s -g

a s -i.o

« t

8 -»- 5

- 2.0

o o

0 O . 0^0

OOO

• • I • I «

101 2345678

Biomass (In kg/ha)

N.S. (P=0.11)

° °

o o° 0 °o. 0 o 0 o Re¬

raise acceptation of Hq

T ype II Error

(b) Independent contrasts

1.0

~ a

■

« £

a -a

0.8 -

0.6 -

.0.4

0.2

- 0.2

-0.4

- 0.6

Significant (P= 0.038)

-0.2 0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8

Biomass (In kg/ha)

Fig. 5. — A lack of relationship between host biomass and parasite diversity (nematodes) is foimd using a non-phvlogenetic

approach whereas the independent contrasts method detects a positive relationship.

Parasite richness and host biomass

The results found by the two methods were also different. While a non-phylogenetic

approach did not detect any relationship between the two variables (Fig. 5), the independent

comparison allows to find a significant relationship between nematode diversity and host

biomass. Thus, a non phylogenetic approach will lead to accept the null hypothesis whereas the

null hypothesis is wrong (Type II error).

DETECTING EVOLUTIONARY TRENDS AND THE USE OF MANTEL TESTS

Analyzing evolutionary trends was the topic of the essay of MCKINNEY (1990), who

proposed time series analyses as a tool for detecting an evolutionary trend. For McKinney, trends

are persistent statistical tendencies in some variables (such as morphological) in an evolutionary

time span. De facto, random walk (Brownian motion) is used as a null hypothesis. McShea

( 1994) argued that large-scale evolutionary trends may be passive or driven. Whereas the passive

trend may correspond to a Brownian motion of character evolution (random walk), the driven

trend corresponds to a selection-driven system (McShea, 1994).

Source

S. MORAND : COMPARATIVE ANALYSES OF CONTINUOUS DATA

Both systems of evolution (passive or driven) yield to the conclusion that related species

share the same characters due to their phylogenetic proximities. However, in a passive system

distant species can share the same characters because of the random evolution of characters

(Brownian motion).

I performed a simulation study, to show that Mantel tests cannot detect pure Brownian

motion of character evolution (passive trends) but can detect driven evolutionary trends with

acceptable error rates. Mantel tests have been used to quantify phylogenetic effects (TAYLOR &

GOTELLI, 1994), and an extended version of this test has been proposed by LEGENDRE el al.

(1995). However, the robustness of the MANTEL test in comparative analyses has not yet been

evaluated.

the "true phylogeny"

1 ^

(Purvis et al., 1992)

Brownian Motion

Time

Brownian Motion + Driven Trend

Time

Fig. 6. — The "true phylogeny” used in the simulation study. The changes in variance among species phenotypes with time

are shown under a Brownian model of evolutionary change (with a 2 = 1 throughout clade) and under a Brownian + a

driven evolutionary trend.

Source:

PHYLOGENE TIC TESTS OF EVOLUTIONARY SCENARIOS

Methodology and examples

Using a modified version of Purvis el aid s methodology (1994) to take into account a

driven trend, values of pairs of characters, Y and X, were generated for the 32 species along the

phylogeny given in Fig. 6. For each branch segment, the changes of values of these traits are

given by:

AX = N(0,1)* yjbranch length + pi((3)

AY = a.AX + (l -<7).N(0,1)* yjbranch length

where N(0,1) is a normal pseudo-random number of mean 0 and variance 1, a is the input

correlation and pi(P) the probability of increase (see below). Each normal random number is

multiplied by the square root of the branch length (following PURVIS et al., 1994). Starting from

the root of the tree, where X = 0 and Y = 0, values at successive nodes i are computed as

X(/+l) = X(/) + AX

Y(/+l) = Y(/) + AY

The values of X and Y for the species, located at the tip of the branches, were calculated by

summing the changes along all branches of the phylogeny.

In a passive system (pure Brownian motion), pi = 0. In a driven system, the value b (10 in

my simulations) is added to AX according to a probability of increase pi (pi = 0.9; I used the

same value as in McShea, 1994). The passive system corresponds to the simulation method of

Purvis et al. (1994) whereas the driven system follows a similar methodology to that

exemplified by McSHEA (1994).

I calculated 1000 pairs of X variable with a = 0 and used them for detecting errors of

Mantel tests

X Y

and Phylogeny and Phylogeny

Pure Brownian

test of validy (Type I)

test of power (Type II)

p>0.05 p>0.05

Brownian + Driven trend

p>0.05

test of validy (Type I) p<0.05

test of power (Type II) p<0.05

Fig. 7. — Mantel test method. In Mantel tests, the X variable is transformed into distance matrix X, by computing the

"distance” among values (absolute value of the difference). The phylogeny is represented by a matrix P of patristic

distances among species. Patristic distances are computed as the lengths of segments along the evolutionary tree that

separate two species. The regression of the individual values in the matrices yields the regression coefficients

constructed by Monte Carlo simulation (Manly, 1991). The significance (p) was determined by Monte Carlo

simulation.

Source:

g 4 S. MORAND : COMPARATIVE ANALYSES OF CONTINUOUS DATA

Type II. Similarly, I used a further set of 1000 pairs with a value for a = 0.3 for detecting errors

of Type I (I used the same value as PURVIS e/ al 1994).

In Mantel tests, the X and Y variables are transformed into distance matrices X and Y, by

computing the “distance” among values (absolute value of the difference). The phylogeny is

Phylogeny

Matrix

of phylogenetic distances

Matrix

of Euclidean distances

Trait X

X a x b

X a = 2

X a

0 2-1

3-2

Xb=l

X„

3-1

X c = 3

X c

Fig. 8. — Results of the simulation study for a passive system (Brownian motion of character evolution) and a driven system

(phylogenetic trend). Test of validity (detection of type I errors) is carried out using a fixed input correlation of a = 0;

Test of power (detection of type II) is performed using a fixed input correlation of a = 3. Mantel tests were done

between variable X and the matrix of the phylogeny (999 permutations each for the Mantel test).

A. sylvalicus

M. musculus

R. rattus

K. norvrgicus

M. sprelus

P. duodecimcostalus

P. lusitanicus

M. agrestis

M. arvalis

M. cabrerae

C. nivalis

A. sapid us

A. terreslris

C. glareolus

—

Etiomys GLIRIDAE

Fig. 9. — Working phylogeny of rodents. Evolutionary divergences between rodents were obtained from various sources:

paleontological records, morphological and molecular data, (see Feliu et al., 1997).

Source: MNHN, Paris

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

represented by a matrix P of patristic distances among species. Patristic distances are computed

as the lengths of segments along the evolutionary tree that separate two species (Fig. 7).

I implemented the Mantel test according to Manly (1991). The regression of the

individual values in the matrices yields the regression coefficients constructed by Monte Carlo

simulation (SMOUSE et ai, 1986; MANLY, 1991). The significance (p) was determined by Monte

Carlo simulation (999 replications) (LEGENDRE et ai , 1995).

According to my hypothesis, Mantel tests cannot detect a passive trend but can detect a

driven trend based upon both validity (a = 0) and power tests (a = 0.3) (Fig. 8). The detection is

found only for the X variable, which was the variable affected by the driven trend. Based upon

these results, it may be possible to detect a phylogenetic trend in comparative analyses. This can

be seen in the following real data sets: the parasite species richness of Iberian rodents and the

parasite species richness of African cyprinids. Using data on parasites of rodents, collected over

an eighteen year period on the Iberian peninsula, FELIU el ai (1997) investigated the

determinants of parasite species richness in Iberian rodents. More than 70 species of helminth

parasites (nematodes, cestodes and digenes) were identified among fifteen species of rodents, for

which a working phylogeny has been proposed (Fig. 9). Parasites were classified into groups

according to their host specificity. Specificity corresponds to the number of infected host species

by a given parasite species: the larger the host species number, the lower the specificity. One

explanation of parasite species richness is linked to host phylogeny. A Mantel test shows that

richness of specific parasites (corrected for host sample size according to WALTHER et ai , 1995)

Fig. 10. — Relationship between rodents using parasites as characters in a parsimonious construction tree (Feliu el al., 1997).

Specific parasite species are coded as characters (values of bootstrap analysis are given on the figure, 100 replicates).

Note that major phylogenetic relationships are found.

Source:

S. MORAND COMPARATIVE ANALYSES OF CONTINUOUS DATA

is correlated with the phylogeny of their host (p = 0.001, R = 0.66). This pattern is clearly

illustrated when using parasite species as characters for a tree reconstructing host relationships

(Fig. 10). The obtained consensus tree reflects the major phylogenetic divisions of the host

group. Thus, the detection of a phylogenetic trend, the increase of parasite species richness

through the diversification of their hosts, is revealed by MANTEL tests and confirmed by tree

reconstruction.

GUEGAN el al. (1992) investigated the richness of monogeneans (ectoparasites) of cyprinid

fishes and found that host length is a major determinant of ectoparasite diversity. More recently,

GUEGAN & MORAND (1996) have shown using the independent contrasts method that parasite

species richness is correlated with changes in the level of host ploidy. Because of the loss of

explanatory power (percentage of variance) when using independent comparison, we may

suggest that history of the host group can partially explain parasite species richness. In this case,

I used a MANTEL test (Fig. 11) and found that phylogeny effectively explains a substantial

amount of variance of species richness (p < 0.001; R = 0.16). In other words, this finding

suggests that related species of hosts tend to have the same parasite species richness because

most of the parasites have been inherited from their common ancestors.

These two examples illustrate how Mantel tests can be applied in comparative analyses.

However, I would like to emphasize that the lack of detection of a phylogenetic correlation does

host species parasite number

. Raiamas senegalensis

. Raiamas nigeriensis

. Raiamas steindachneri

■ Lepiocyphs nilolicus

. Chelaethiops bibie

- Garra orn ala

. labeo alluaudi

- labeo parvus

- labeo obscurus

- Labto roseopunclatus

- lutbeo rouaneti

- Labeo coubir

- labeo senegalensis

- Barbus issenensis

. Barbus massaensis

- Barbus lepineyn

_ Barbus palaryi

_ Barbus figuiensis

- Barbus selivimensis

_ Barbus nasus

- Barbus moulouyensis

- Barbus magnianlalis

_ Barbus ksibi

- Barbus peliijeani

- Barbus sacralus

- Barbus wurtzi

- Barbus parawaldrom

Barbus b. occidentals

. Barbus b. waldroni

Fig. 11. — Phylogeny of African cyprinid fish based on isoenzymes data (from Guegan & Morand, 1996) with number of

parasite species.

Source:

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

not allow to the conclusion of the absence of phylogenetic effects. The simulation studies clearly

show that Mantel tests do not detect passive evolutionary trends (pure Brownian motion of

character evolution) and that comparative studies should always use the independent contrasts

method.

SKEPTICISM ABOUT COMPARATIVE METHODS?

Before concluding, it is necessary to mention some problems concerning the use of

comparative methods in evolutionary biology. Two different criticisms have been put forward,

one by LEROI et al. (1994) and the other one by WESTOBY et al. (1995a, 1995b).

LEROI et al. (1994) argued that comparative methods are “valuable for examining the

evolutionary history of traits but they will often mislead in the study of adaptive processes”.

Their major concern is that we know very little on the evolutionary genetic mechanisms

responsible for distributions of traits among species. They claimed that it is very difficult to

justify any evolutionary scenario without evidence of historical selection forces and, more

important, the genetic relations among traits. Some of their arguments concern mainly the

invocation of constraints in the explanation of either adaptation or phylogenetic conservatism.

However, the problem is more a problem of definition (what is a phylogenetic constraint) than a

problem of method (the use of comparative method). A second set of arguments addresses the

question of the evolution of continuous characters, the topic of this study. Using the example of

the scaling of brain and body size, described as a power function, they found at least two

problems of the comparative method. The first is that of confounding selection pressures. I

cannot see why this is a specific problem of the comparative method. A correlation constitutes no

proof whether the correlation is the result of the comparative method or any other methods. The

second criticism deals with “the confounding of the causal influence of selection with that of

genetic correlations”. This is a more serious critique but, again, the problem is more related to

the causes and correlations than to methods. Indeed, LEROI et al (1994) concluded their study

with the acknowledgment “that the methods of comparative biology and genetics might be

usefully combined”.

The second criticism came from WESTOBY et al. (1995a, 1995b). Their concern was that a

phylogenetic correction (i.e. phylogenetic analysis) is not a correction but rather a conceptual

decision which gives priority to one interpretation over another. In fact, they assumed that part

of variation of a given trait is correlated with phylogeny and other part correlated with ecology.

However, their arguments refer to the notion of phylogenetic niche conservatism. This process

can be described as follows: “the ancestor of a lineage possesses a constellation of traits, enabling

it to succeed in a particular habitat and disturbance regime, through a particular life history and

physiology. The lineage will therefore leave most descendants in similar niches. This niche

conservatism in turn will tend to sustain a similar constellation of traits in descendants of the

lineage (WESTOBY et al ., 1995a). Harvey et al. (1995) gave a clear answer to that questions by

emphasizing that the independent contrasts method does not remove phylogenetic effects but

produces plots in which all the variation of the data set in one variable is graphed against all the

variation in the other variable. In this way, phylogenetic niche conservatism means that

adaptations to different components of the niche will be correlated (Harvey et al., 1995), which

is what the contrasts method has been designed to detect.

S. MORAND : COMPARATIVE ANALYSES OF CONTINUOUS DATA

CONCLUSION

Within a multi-species study, species do not necessarily represent independent data points

(KELLY & Purvis, 1993; HARVEY, 1996). The recent debate involving WESTOBY et al. (1995a,

1995b) and Harvey et at. (1995) highlighted some misinterpretations of comparative methods.

Comparative biologists have drawn attention to all the biases which could arise when the

phylogenetic information are not taken into account (PAGEL & HARVEY, 1991; GARLAND et a /.,

1992; Martins, 1995; Harvey, 1996). Moreover, as emphasized by Garland & Arnold

( 1994), caution should be exerted to all comparisons involving only two species (there is no

degree of freedom!).

In this study, I have provided one example on parasite species richness of mammals which

showed these biases. Not incorporating phylogenetic information would have lead to false

conclusions.

The independent contrasts method remains the best method to avoid the phylogenetic

confounding effects (Harvey, 1996, but see BJORKLUND, 1994, for a comparison of this method

with character mapping by optimization on a cladogram). Even if the independent contrasts

method assumes a model of character evolution (the Brownian motion model or any other

models, see Martins, 1994), simulation studies showed that this method is very robust (low error

rates). However, without a correct phylogeny of the studied organisms it is impossible to test

evolutionary hypotheses. The main problem is the availability of a correct phylogeny. Recently

Losos (1994) proposed to use computer simulations to generate a large sample of possible

phylogenies in the absence of a correct topology and to calculate independent contrasts for each

generated tree. LOSOS (1994) gave two rules of thumb. First, if all analyses give the same result

(significant or not), then the result is independent of what the true phylogeny is. Second, if a

substantial minority of phylogenies yield different results from the majority, then the outcome of

the analysis will depend on the correct phylogeny.

There are some other methods in comparative analyses which solve the problem of non¬

independence (LYNCH, 1991), for example, the phylogenetic autocorrelation method

(GlTTLEMAN & KOT, 1990) or the permutation on distance matrices method (LEGENDRE et al.,

1995; MORAND, 1996; MORAND et al ., 1996). All these other methods have not been tested for

their power in a wide range of character evolution (but see PURVIS et al, 1994; MARTINS, 1995).

I carried a simulation study showing the efficiency of Mantel tests for detecting evolutionary

trends and for measuring the phylogenetic effect. I hope that Mantel tests will be an answer to

the questions of WESTOBY et al. (1995). Mantel tests done on the data set (each variable against

the phylogeny) will indicate if there is a trend in the changes of the values of each variable. We

should remember that the lack of correlation may not lead to the conclusion of the independence

of species. A correlation may indicate that the character does not evolve under a pure Brownian

motion. The Mantel tests reveals a phylogenetic niche conservatism or, in the case of parasite

diversity, a phylogenetic trend but they do not allow to avoid a phylogenetic independent

analysis.

ACKNOWLEDGEMENTS

I thank Antoine Danchin and Philippe Grandcolas for their comments that greatly improved the first version of this

manuscript. Pierre Legendre, Jean-Frai^ois Gu£gan, Robert Poulin, Gabriele Sorci, Claude Combes, Sandrine Trouve and

Pierre Sasal have contributed to this study by many discussions. 1 thank Philippe Grandcolas for his kind invitation to the

Source:

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

Symposium and Laure Desutter and Judith Najt for help during the preparation of the meeting. I would like to thank John

Wenzel for his stimulated ideas. Special thanks to Christine Muller-Graf.

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Phylogenetic Tests of Evolutionary Scenarios: the Evolution

of Flightlessness and Wing Polymorphism in Insects

Nils Me Her Andersen

Zoological Museum, University of Copenhagen, Universitetsparken 15,

2100 Copenhagen, Denmark

ABSTRACT

Secondary loss of the flight ability has occurred in nearly all winged orders of insects, many times within most orders, and

probably hundreds of times within the Hemiptera and Coleoptera. Loss of flight may be an attribute of all individuals of a

species, of only one sex (usually the female), or populations may be polymorphic, composed of both flying and flightless

individuals, eventually with a seasonal variation in frequencies. Since flightlessness is linked to a multitude of morphological,

physiological, and ecological components that are of great evolutionary significance, flight loss and wing polymorphism in

insects have received much attention in recent years. The present paper focus on the role phylogenetic inference can play in

clarifying evolutionary patterns of flightlessness in insects and possible causes of the loss of flight ability. This approach is

here exemplified using the orders of pterygote insects, the families of Hemiptera-Heteroptera (true bugs), the genera of the

heteropteran family Gerridae (water striders), and the species of the water strider genera Limnoporns , Aquarius , and Gerris.

Cladograms can be used to track associations between flightlessness and other factors as well as the relative evolutionary'

success of flying and flightless sister groups. However, phylogenetic inference applied to higher taxonomic levels presents

many problems as exemplified by the orders of pterygote insects and the families of Hemiptera-Heteroptera. hi many cases

obligatory loss of wings coincides with a significant change in way of life, e.g ., ectoparasitism or marine habit, but it is rarely

possible to tell which came first. It is argued that phylogenetic inference are most effectively applied at lower taxonomic

levels, in particular to monophyletic groups of species with varying expressions of wing polymorphism. In species of northern

temperate w'ater striders (Heteroptera, Gerridae), phylogenetic inference show's definite associations between flight loss and

durational stability of habitats. Contrary to previous hypotheses, the winged state is not the ancestral one. Surprisingly, the

ancestors are inferred to be predominantly flightless or permanently dimorphic, occupying relatively stable habitats.

Subsequent evolution of long-wingedness or seasonal dimorphism has allowed descendant taxa to colonize less stable

habitats.

RESUME

Tests phylogenetiques de scenarios evolutifs : revolution de la perte du vol et du polymorphisme alaire chez

les Insectcs

La perte secondaire de la capacite a voler a eu lieu dans presque tous les ordres ailes d'insectes, de nombreuses fois chez la

plupart des ordres, et probablement des centaines de fois chez les Hemipteres et les Coleopteres. La perte du vol peut etre un

attribut de tous les individus dime espece, ou de fun des sexes (le plus souvent les femelles), ou bien encore les populations

peuvent etre polvmorphes, c'est a dire composees d'individus capables ou incapables de voler, avec la possibility d'une

variation saisonniere de leur frequence. La perte du vol et le polymorphisme alaire chez les insectes ont ete 1'objet de

beaucoup d'interet ces demieres annees, parce qu'ils sont lies a une multitude de composantes morphologiques,

physiologiques, et ecologiques qui sont dime grande importance dans le domaine de 1'evolution. L'etude presente conceme le

Andersen, N. M., 1997. — Phylogenetic tests of evolutionary' scenarios: the evolution of flightlessness and wing

polymorphism in Insects. In: Grandcolas, P (ed.). The Origin of Biodiversity in Insects: Phylogenetic Tests of Evolutionary

Scenarios. Mem. Mus. natn. Hist, nat., 173 : 91-108. Paris ISBN : 2-85653-508-9.

N. M. ANDERSEN : EVOLUTION OF FLIGHTLESSNESS AND WING POLYMORPHISM

role de l'inference phylogenetique dans la clarification des sequences evolutives de la perte du vol chez les insectes et des

causes possibles de cette perte. Cette etude prend en compte les ordres d'insectes Pterygotes, les families d'i lemipteres-

Heteropteres (punaises), des genres d'Heteropteres Gerridae (patineurs), et des especes des genres de patineurs Limnoporus,

Aquarius , et Gems. Les cladograntmes peuvent etre utilises pour retracer non seulement les associations entre la perte du vol

et d'autres facteurs mais aussi le succes evolutif relatif de groupes-freres respectivement capables et incapables de voler.

Cependant, l'inference phylogenetique appliquee aux plus hauts niveaux taxonomiques pose de nombreux problemes comme

c'est le cas des ordres d'insectes Pterygotes et des families dTIemipteres-Heteropteres. La perte totale des ailes coincide de

nombreuses fois avec un changement important de mode de vie, e.g., 1'ectoparasitisme ou le mode de vie marin, mais il est

rarement possible de dire quel changement s'est fait en premier. II est done propose que l'inference phylogenetique soit utilisee

de maniere plus efficace et plus judicieuse a de plus bas niveaux taxonomiques, en particulier sur des groupes

monophyletiques d'especes montrant des types varies de polymorphisme alaire. Dans les especes de patineurs des zones

temperees de Hiemisphere Nord (Heteropteres, Gerridae), l'inference phylogenetique montre qu'il existe une nette association

entre « perte du vol » et « stabilite continue des habitats dans le temps ». L'etat aile n'est pas ancestral, ce qui est en

contradiction avec les hypotheses anterieures. De maniere inattendue, les ancetres sont inferes avoir ete en majorite

incapables de voler ou constamment diinorphiques, et avoir occupe des habitats relativement stables. Devolution subsequente

vers la possession d'ailes longues et fonctiomielles ou vers im dimorphisme saisonnier a pennis aux taxa descendants de

coloniser des habitats moins stables.

INTRODUCTION

Flight capability is without doubt one of the primary innovations governing the

evolutionary success of insects. However, secondary loss of this capability has occurred in nearly

all winged orders of insects, many times within most orders, and probably hundreds of times

within the large orders of Hemiptera and Coleoptera. The loss of flight may involve all kinds of

modifications of wings and flight musculature. Loss of flight may be an attribute of all individuals

of a species, of only one sex (usually the female), or populations may be polymorphic, composed

of both flying and flightless individuals and, eventually, with a seasonal variation in frequencies.

The largest variability in wing development is observed among water striders (Heteroptera,

Gerridae) as illustrated in Fig. 1.

Flightlessness in insects is linked to a multitude of morphological, physiological, and

ecological components that are of great evolutionary significance (e.g., HARRISON, 1980; ROFF,

1986, 1990; WAGNER & LlEBHERR, 1992; SPENCE & ANDERSEN, 1994). The production and

maintenance of the flight apparatus (wings, tlight musculature, etc.) is energetically expensive

and bound to compete with other, physiologically equally demanding processes such as the

production of oocytes (“oogenesis-flight” syndrome; JOHNSON, 1969). Therefore, one possible

advantage of wing loss is that it allows a female insect to divert energy normally used in wing

and wing muscle development to the production of more eggs. This could increase the female's

fitness more than the advantages associated with the ability to fly (Roff, 1986, 1990; ROFF &

FAIRBAIRN, 1991).

The most widely accepted explanation for loss of the flight ability in insects relates to

environmental heterogeneity. SoUTHWOOD(1962: 172) predicted “that within a taxon one should

find a higher level of migratory movement in those species associated with temporary habitats

than in those species associated with more permanent ones”. In his review of the evolution of

flightlessness in insects, ROFF (1990) assembled considerable evidence indicating that

flightlessness is strongly associated with habitat stability in all major groups of insects. Habitats

in which insects have a higher frequency of flightless forms than the average are: woodlands,

deserts, mountains, caves, ocean surfaces, termite and hymenopteran nests, and the body surfaces

of homeothermic vertebrates (ectoparasites). Flightlessness has also been related to habitat

Source:

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

Imago

Fig. 1. — Wing polymorphism in water striders (Heteroptera, Gerridae) and different ontogenetical pathways of wing

development through fourth (IV) and fifth (V) instar nymphs, and imago. Nymphs and imagines shown without

antennae and legs, not drawn to same scale. Further discussion in text. (Reproduced with modification from

Andersen, 1982).

isolation. Darwin's (1872) hypothesis that on oceanic islands a flightless morph would be more

fit than a winged morph because it would be less likely to be accidentally blown or fly from the

island was, however, questioned by ROFF (1990) who concluded that the proportion of flightless

insects on islands was no higher than in continental areas.

N M. ANDERSEN : EVOLUTION OF FLIGHTLESSNESS AND WING POLYMORPHISM

Phylogenetic inference

The convergent evolution of flightless adult forms in taxonomically widely separate,

primarily winged insect taxa suggests that the loss of flight ability and maintenance of wing

polymorphism is a consequence of adaptation through natural selection as first proposed by

Darwin (1872). Nevertheless, previous discussions of the evolution of flightlessness in

insects(e?.g. HARRISON, 1980; ROFF, 1986, 1990; R.OFF& FAIRBAIRN, 1991) have largely ignored

the historical perspective in explaining patterns of flightlessness in insects. The importance of

phylogeny in comparative biological studies is now widely recognized (BROOKS & McLennan,

1991; Harvey & Pagel, 1991; Eggleton & VanE-Wright, 1994; Grandcolas et al., 1994;

Miller & Wenzel, 1995) and this approach has recently been applied in studies of the evolution

of flightlessness in insects (ANDERSEN, 1993a; Roff, 1994).

What role can phylogenetic inference play in understanding the evolution of flightlessness

in insects? First, reconstructed phylogenies (cladograms) can be used to track the evolutionary

fate ( e.g ., relative rates of speciation and extinction) of flightless and winged sister groups (ROFF,

1994). Second, cladograms may provide the basis for making phylogenetically more relevant

comparisons among monophyletic groups (clades). Previously, correlation tests involving flight

loss have assumed that every species of a clade represents an independent datum. However,

species sharing a trait (e.g., wing loss) inherited from their most recent, common ancestor, do

not yield statistically independent data. Cladograms may also be used to predict which species

require further study in order to resolve a particular problem. Third and finally, by mapping

different states of wing development upon a cladogram, ancestral states can be reconstructed,

number of evolutionary transitions between states can be traced, and possible sequences of

change can be inferred (ANDERSEN, 1993a). If two attributes are considered at the same time

(e.g., wing morphism and type of habitat), the relative position of state changes for the two

attributes may be located. If the flight ability was lost after a significant change in habitat,

flightlessness may be an adaptation to the new habitat. If flight loss preceded the change in

habitat, flightlessness may be a prerequisite (exaptation) for the colonization of a new habitat. It

is important to remember, however, that in both cases flightlessness may be caused by other,

presently unknown factors.

Before using phylogenetic inference in comparative biological studies, the choice of

taxonomic level should be seriously considered. Ideally, the attribute(s) in question should vary

much between, but only little within the groups selected as terminal taxa. Within-taxon variability

presents a major problem in most studies involving higher taxa (families, orders) which are more

likely to show within-taxon variation than, e.g ., genera and species groups. As a rule, the only

solution to the problem of high within-taxon variability is to repeat the analysis with a more finely

resolved phylogeny.

MATERIAL AND METHODS

Phytogenies

'Hie phylogenetic relationships between the orders of winged insects (Insecta-Pterygota; Fig. 2) are chiefly based upon

Kristensen (1991/1994, 1995) with the following modifications: (1) Plecoptera (stoneflies) are placed as sister group to the

remaining Neopteran order (as suggested by Kristensen 1991/1994, p. 132, but not depicted in his cladogram, his Fig. 5.5);

(2) Hemiptera and Thysanoptera are treated as genuine sister groups (Superordcr Condylognatha) following a more widely

accepted hypothesis than joining the thysanopterans with psocodeans (Psocoptera + Phthiraptera); (3) Strepsiptera is placed as

sister group of Coleoptera following Kukalova-Peck & Lawrence (1993). The alleged sister group relationship between

Strepsiptera and Diptera (Whiting & Wheeler, 1994) has been seriously questioned by Kristensen (1995).

Source:

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

The primary source for the phylogeny of the Hemiptera-Heteroptera (Fig. 3) is the excellent monograph by Schuh &

Slater (1995) supplemented by Andersen (1982, 1995a), Schuh (1986), Schuh& Stys (1991). Wheeler ei al. (1993), and

Mahner (1993). The currently accepted classification of the Heteroptcra excludes the southern temperate family Peloriidae

(Coleorrhyncha) from the suborder and divides it into seven infraorders (listed by the same order of families as in Fig. 3):

Enicocephalomorpha (Aenictopecheidae, Enicocephalidae), Dipsocoromorpha (Ceratocombidae to Steinmocryptidae),

Gerromorpha (Mesoveliidae to Gerridae), Nepomorpha (Nepidae to Helotrephidae), Leptopodomorpha (Aepophilidae to

Leptopodidae), Crmocomorpha (Pachynomidae to Polyctenidae), and Pentatomomorpha (Aradidae to Rhopalidae). Tlie

relationships between these infraorders depicted in the cladogram (Fig. 3) follows Wheeler et al. (1993) and Schuh &

Slater (1995).

□

Wing polymorphism

winged

I I polymorphic

flightless

ILllllJ equivocal

EPHEMEROPTERA

ODONATA

PLECOPTERA

■ BLATTODEA

ISOPTERA

I MANTODEA

■ GRYLLOBLATTODEA

| DERMAPTERA

| ORTHOPTERA

| PHASMATODEA

EMBIOPTERA

ZORAPTERA

| PSOCOPTERA

| PHTHIRAPTERA

| HEMIPTERA

THYSANOPTERA

STREPSIPTERA

| COLEOPTERA

MEGALOPTERA

RHAPHIDIOPTERA

| NEUROPTERA

| MECOPTERA

| SIPHONAPTERA

| DIPTERA

| TRICHOPTERA

LEPIDOPTERA

HYMENOPTERA

Fig. 2. — Phylogeny and distribution of three states of wing development in the orders of pterygote insects. Further discussion

in text.

Source:

N. M. ANDERSEN : EVOLUTION OF FLIGHTLESSNESS AND WING POLYMORPHISM

The phvlogenetic relationships between the genera of the family Gerridae (Fig. 4) are primarily based upon Matsuda

(1960) and Andersen (1982, 1995b; and unpublished). Finally, phylogemes for species or species groups of the genera

Aquarius , Gems, and Limnoporus (Fig. 5) are compiled from Andersen (1990, 1993b) and Andersen & Spence (1992) with

modifications for the last mentioned genus as discussed by Sperling el al. (in press).

Wing polymorphism

l I winged

CZI3 polymorphic

WM flightless

fTTITTi equivocal

Aemctopecheidae

Emchocephalidae

Ceratocombidae

Dipsocoridae

Hypsipterygidae

Schizopteridae

Stemmocryptidae

Mesoveliidae

Hebridae

Paraphrynoveliidae

Macroveliidae

Hydrometridae

I Hermatobatidae

I Velndae

I Gerridae

Nepidae+Belostomatidae

Ochteridae+Gelastocoridae

Corixidae

Potamocondae

Naucoridae

Aphelocheindae

Notonectidae

Pleidae+Helotrephidae

I Aepophiiidae

Saldidae

I Omanudae

Leptopodidae

Pachynomidae

I Reduviidae

velocipedidae

Microphysidae

Joppeicidae

Thaumastocoridae

Miridae

Tingidae

Medocostidae

Nabidae

Lasiochilidae+2 fam

Anthocoridae

I Cimicidae+Polyctemdae

I Aradidae

I Termitaphididae

Acanthosomatidae+2 fam

Cydnidae

Pentatomidae*-8 fam

I Thaumastellidae

Piesmatidae

Berytidae* Malcidae

I Lygaeidae

Idiostolidae

Colobathristidae

I Largidae

Pyrrhocoridae

Stenocephalidae

Alydidae

■ Coreidae

Hyocephalidae

Rhopaiidae

Fig. 3. — Phytogeny and distribution of three states of wing development in the families of Hemiptera-Heteroptera. Further

discussion in text.

Source: MNHN , Paris

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

Wing morph frequencies

A complex terminology ( e.g ., Andersen, 1982; Schuh &. Slater, 1995) has been employed to distinguish various

degrees of wing modification in flightless and polymorphic insects (apterous, brachypterous, etc.)- For the sake of simplicity, I

here distinguish between three states of wing morphism in adult insect orders, Heteroptera, and the Gerridae (slightly

different states are used for Aquarius, Genis , and Limnoporus\ see below): (1) winged, all individuals of a species possess

fully developed and presumably functional wings; (2) polymorphic, ; natural populations composed of both winged and

flightless adult individuals, the latter sometimes restricted to only one sex; and (3) flightless ; all individuals of a species

flightless. Information on the distribution and frequencies of different wing morphs are chiefly compiled from the following

sources: Roff (1990) and CSIRO & Naumann (1991) for the orders of insects; Schuh & Slater (1995) lor the Hemiptera-

Heteroptera; and Andersen (1982, 1990, 1993a, 1993b; Andersen & Spence, 1992) for the Gerridae.

Optimization

The evolutionary changes between different states of wing development (treated as non-additive or unordered) were

optimized on the cladograms using the computer program MacClade, version 3.05 (Maddison & Maddison, 1992) with the

“show all most parsimonious states at each node” option. The results of this optimization are shown as different shading of the

branches ol the cladogram. lire shading for “equivocal” is used when the optimization is unable to resolve the state of wing

development on a particular branch.

RESULTS AND DISCUSSION

The orders of pterygote insects

In only 4 out of 27 orders of pterygote insects are the adult stage always winged. These are

the Ephemeroptera (mayflies) and Odonata (dragonflies, damselflies), previously united in the

Palaeoptera, and the small endopterygote orders Megaloptera (alderflies, dobsonflies) and

Rhaphidioptera (snakeflies, cameineckflies). Except for the last mentioned order, the immature

stage is aquatic in these groups. Flightless adult forms are rare in the Plecoptera (stoneflies),

Neuroptera (lacewings), Mecoptera (scorpionflies), and Trichoptera (caddisflies) the first and last

order with aquatic immature stages. Relative to the total number of species, flightless or wing

polymorphic species are also rare in the large orders Diptera, Lepidoptera, and Hymenoptera.

Obligatorily flightless orders are the Phthiraptera (sucking and chewing lice, Anoplura and

Mallophaga) and Siphonaptera (fleas), both ectoparasites on warm-blooded vertebrates, and the

small northern temperate order Grylloblattodea.

In the remaining orders, flightlessness or wing polymorphism (sex-bound or not) is

common or very common in the exopterygote orders Blattodea (cockroaches), Isoptera

(termites, but limited to the worker caste), Mantodea (praying mantids), Orthoptera

(grasshoppers, locusts, crickets), Dermaptera (earwigs), Phasmatodea (stick insects), Embioptera

(web-spinners), Zoraptera, Hemiptera, and Thysanoptera (thrips) Relative to the total number of

species, loss of the flight ability is uncommon in the Coleoptera, but because wing reduction

rarely affects the elytra, the flightless adult form is difficult to recognize and its frequency may

therefore be underestimated in beetles.

Because of the extremely diverse nature of wing development in most insect orders, the

results of the optimization of the three states on the phylogeny of pterygote insects are

ambiguous (Fig. 2). Because both palaeopteran orders are obligatorily winged, this undoubtedly

was the ancestral state for the Pterygota. The ancestral state for the neopteran orders is

equivocal (winged or polymorphic). However, this ambiguity disappears if the Strepsiptera is

treated as a subordinate group of Coleoptera (following Crowson, 1955, and later writings); the

winged state is then selected as the ancestral one. The Dictyoptera s.l. (Blattodea + Isoptera +

Mantodea) were probably primitively wing polymorphic and the Paraneoptera (Psocodea +

Hemiptera + Thysanoptera) likewise. It is very unlikely that the ancestors of these groups were

98 N. M. ANDERSEN : EVOLUTION OF FLIGHTLESSNESS AND WING POLYMORPHISM

obligatorily flightless since this requires that wings have evolved as (autapomorphic) character

reversals in some lineages. Finally, although the ancestral state for the Endopterygota is

equivocal, it is predicted that analyses with more finely resolved phylogenies will show, that

ancestral endopterygotes were winged like the ancestors of all endopterygote orders except the

Strepsiptera and Siphonaptera.

Wing polymorphism

CD winged

L-J polymorphic

flightless

mUTTl equivocal

□

Rhagadotarsus

□ ■ Rheumatobates

□

Metrobates

Rheumatometra

□

Metrobatopsis

Cryptobates

Ovatometra

Halobatopsis

□

Trepobates

□

Telmatometra

□

Trepobatoides

Hynesiorrella

Naboandelus

■ Rheumatometroides

■ Stenobates

□

Charmatometra

□

Eobates

Brachymetra

□

Cylindrostethus

Potamobates

Platygerris

Rheumatogonus

□

Potamometropsis

□

Ptilomera

Potamometra

□

Heterobates

□

Potamometroides

Rhyacobates

□

Pleciobates

□

Ventidius

□

Esakia

E urymetropsielloides

Eurymetropsis

□

Eurymetropsiella

MeTrocoris

i m

Eurymetra

■ Asclepios

■ Haiobates

i m

Chimarrhometra

i □

Eotrechus

Amemboa

i m

Onychotrechus

i □

Eurygerris

Tachygerris

1 u

Gerrisella

i □

Neogems

i □

Tenagogems

j □

Tenagogonus

Limnometra

i □

Tenagometra

) □

Umnogonus

J E3

Tenagometrella

) □

Gigantometra

Limnoporus

^□o

Aquarius

too

Gems

Pig. 4 . — Phylogeny and distribution of three states of wing development in the genera of Gerridae (Hemiptera-Heteroptera).

Further discussion in text.

Source: MNHN. Paris

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS 99

At the level of insect orders, phylogenetic inference leading to estimates of the causes

underlying patterns of flightlessness is difficult. However, orders with a gradual metamorphosis

( paurometabolous orders) and with immatures and adults occupying similar niches are more

frequently wing polymorphic or flightless than orders with complete metamorphosis and a

significant niche shift between the immature and adult stage (Roff, 1990). To the last category

belongs the hemimetabolous orders Ephemeroptera, Odonata, and Plecoptera, and most of the

holometabolous orders. Wing polymorphism and flightlessness are also more frequent in orders

where adult flight is not an “everyday” activity necessary for feeding, mating, or local dispersal

(as the Orthoptera, Hemiptera, and Coleoptera).

Wing polymorphism

I l winged

IZZ.] permanent dimorphic

1. .f- l seasonal dimorphic

1=1 equivocal

iivuicua

Limnoporus esaku

L canaliculatus

L. notabilis

L dissortis

L rufoscutellatus

L genitalis

Aquarius najas

A cinereus

A. ventralis

A. chilensis

A. remigis

A. anti gone

A. fabricn

B A paludum

■ A adelaidis

A conformis

A nebularis

A elongatus

Gerris lateralis

G asper

G brachynotus

G gracilicornis+4 spp

G cui

G gillettei

G. pingreensis

G incogmtus

G sphagnetorum

G nepalensis

G. costae

G thoracicus

G margmatus

I G. comatus

I G msperatus

I G. alacns

G latiabdommis

G argenticolhs

G gibbiter

G. maculatus

G. lacustns

G. argentatus

G babai

G odontogaster

G. buenoi

G. gobanus

G. swakopensis

Fig. 5. — Phylogeny and distribution of states of wing development in species belonging to Aquarius, Gerris, Gigantometra,

and Limnoporus (Heniiptera-Heteroptera, Gerridae). Further discussion in text.

Source:

100

N. M. ANDERSEN : EVOLUTION OF FLIGHTLESSNESS AND WING POLYMORPHISM

The families of Hemiptera-Heteroptera

The Hemiptera (true bugs, cicadas, plant- and treehoppers, plantlice, etc.) with about

82 000 described species is the largest of the hemimetabolous insect orders. Wing polymorphism

is very common and widespread in this order, in particular within the suborder Heteroptera or

true bugs where it occurs in 41 out of 75 families (Fig. 3). Flightlessness is especially common in

the infraorders Enicocephalomorpha, Dipsocoromorpha, Gerromorpha (semiaquatic bugs), and

in the large families Reduviidae (assassin bugs) and Miridae (plant bugs) belonging to the

Cimicomorpha, whereas it is relatively rare in the Nepomorpha (aquatic bugs),

Leptopodomorpha (shore bugs), and Pentatomomorpha except for the families Aradidae (bark

bugs) and Lygaeidae (seed bugs). Obligatorily flightless species are found in the

Paraphrynoveliidae, Cimicidae (bed bugs), and Polyctenidae (bat bugs), the last two families

being vertebrate ectoparasites, the Termitaphididae (termite inquilines), and in the small marine

families Hermatobatidae, Aepophilidae, and Omaniidae.

An optimization of the three states of wing development on the reconstructed phytogeny of

the Heteroptera (Fig. 3) unequivocally picks the winged state as the ancestral one for all major

lineages Thus wing polymorphism and flightlessness have seemingly evolved independently

numerous times in true bugs. The flightless state is inferred to be ancestral to the families of

Gerromorpha (except Mesoveliidae and Hebridae). The explanation for this result is the presence

of two small, obligatorily flightless families (Paraphrynoveliidae and Hermatobatidae) as well as

flightless taxa in the large families Veliidae and Gerridae.

At the level of heteropteran families, phylogenetic inference leading to estimates of

causality between flightlessness and other attributes is equally problematical. Flightless forms are

most frequent in predaceous bugs and in species inhabiting ground litter (Enicocephalidae, most

Dipsocoromorpha, the gerromorphan families Mesoveliidae, Hebridae, Paraphrynoveliidae,

Macroveliidae, some Leptopodomorpha and Cimicomorpha, and the Lygaeidae), semiaquatic

habitats (most Gerromorpha), marine habitats (Hermatobatidae, some Veliidae and Gerridae,

Aepophilidae, and Omaniidae), and in ectoparasites (Cimicidae, Polyctenidae, some Lygaeidae),

and in those bugs which live under bark (Aradidae and Lyctocoridae). Winged forms are

predominant in phytophagous bugs belonging to the family Miridae (Cimicomorpha) and most

families of the Pentatomomorpha.

The genera of Gerridae

The Gerridae (water striders) is one of the largest families of semiaquatic bugs

(Heteroptera, infraorder Gerromorpha), with about 600 described species. The vast majority of

species belonging to this group are wing polymorphic (Fig. 4). Only the genera Amemhoa

(Eotrechinae), Tachygerris , Limnometra, Limnoporus, Aquarius, and Gerris (Gerrinae) include

species which are monomorphic winged. Obligatorily flightless species are restricted to the

genera Rheumaiometra (Rhagadotarsinae), Nahoandelus, Rheumatometroides, Stenobates

(Trepobatinae), Asclepios, and Halobates (Halobatinae), all living in marine habitats (from

estuaries, mangroves, and intertidal coral reef flats to the open sea).

Ancestral gerrids were probably wing polymorphic (like most gerromorphan bugs, see Fig.

3) and the loss of the flightless form in some species is most likely secondary. Since all marine

water striders have polymorphic freshwater relatives, the complete loss of the winged form

associated with the extremely stable marine habitats is easily explained. Adult water striders only

Source: MNHN, Paris

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

101

use flight for dispersal among habitats and (in temperate regions) in connection with hibernation

which takes place on land (Andersen, 1982).

The species of Gerris and related genera

Northern temperate water striders belonging to the genera Aquarius , Gerris, and

Limnoporus (formerly united in the genus Gerris sd.) have been extensively used as model

organisms in studies of the relations between wing polymorphism, dispersal strategies, and life

history dynamics (ANDERSEN, 1973; VEPSALAINEN, 1978; SPENCE, 1989; SPENCE & ANDERSEN,

1994). The phylogeny of the three genera is relatively well understood (ANDERSEN, 1990, 1993b;

Andersen & Spence, 1992). The cladogram (Fig. 5) shows the relationships between most

species belonging to the genera Limnoporus, Aquarius, Gerris with the monotypic genus

Gigantometra added as outgroup (Andersen, 1995b).

W ater striders belonging to this group are either monomorphic winged or wing dimorphic.

Following Andersen (1993a), I distinguish between permanent dimorphism in which

populations usually include both winged adults (which may be rare) and adults with more or less

reduced wings and flight musculature, and seasonal dimorphism in which the flightless adult form

only occurs during summer, indicating a direct breeding second generation. The wing

development of the two types of flightless forms follow different ontogenetic pathways (Fig. 1).

In seasonally dimorphic species, the fourth (IV) and fifth nymphal instar (V) have the same size

of wing-pads as nymphs from which the winged adults emerge (a -» A' -* A). In permanently

dimorphic species, the fourth and fifth instar nymphs have distinctly reduced wing-pads

(f —> F —> F).

Optimization of the three states of wing development on the cladogram (Fig. 5) points to

the permanently dimorphic state as the ancestral one for the whole group as well as for Aquarius

and Gerris, while the wing morphism state is equivocal for the genus Limnoporus (one species

dimorphic, the rest always winged).

Flightlessness and the "oogenesis-flight ” syndrome

The concurrent development in insect ontogeny of the flight apparatus, the ovaries, and the

ancillary systems such as the fat-body has been termed the “oogenesis-flight” syndrome

(JOHNSON, 1969). The differential development of these systems in response to environmental

factors has produced a variety of different forms in insects, ranging from sexually immature,

migrant individuals, to various types of flightless, sexually mature, and eventually

parthenogenetic or paedogenetic individuals. The wing muscles are relatively massive structures,

comprising 10-20 % of the body mass in most insects and undoubtedly consuming a significant

proportion of an insect's energy budget (ROFF, 1990). Flightless female insects lack wing muscles

and are therefore able to divert more energy to the production of oocytes. In addition, winged

females commonly autolyse (self-digest) their flight muscles during egg production as well

documented in northern temperate water striders (ANDERSEN, 1973, 1982; FA1RBAIRN &

Desranlf.au, 1987; Kaitala& Hulden 1990).

In insects where adult flight is not an “everyday” activity necessary for feeding, mating, and

escaping from temporary or deteriorating habitats, it can be predicted that patterns of

flightlessness often will be compatible with the “oogenesis-flight” syndrome explanation. The

high incidence of flightless forms in the orders Orthoptera, Hemiptera, and Coleoptera, and the

102 N. M ANDERSEN : EVOLUTION OF FLIGHTLESSNESS AND WING POLYMORPHISM

distribution of flightless forms among and within the families of Heteroptera seem to meet this

prediction (SCHUH & SLATER, 1995).

Flightlessness and ectoparasilism

Ectoparasites on warm-blooded vertebrates belonging to the orders Phthiraptera,

Siphonaptera, Hemiptera-Heteroptera, and Diptera, are all obligatorily flightless. It has been

suggested (Lyal, 1985) that the chewing lice (Mallophaga; a paraphyletic group) and sucking

lice (Anoplura) evolved from some subgroup of the Psocoptera, namely the family Liposcehdae

which contains many flightless species (booklice). If this hypothesis is correct, the phylogeny

supports a scenario where loss of flight ability preceded ectoparasitism (Fig. 6). However, the

fact that some ectoparasitic Diptera (belonging to the family Hippoboscidae) are winged or

dimorphic points at the opposite sequence of evolution, where the parasitic way of life preceded

wing loss (Wagner & LIEBHERR, 1992). In the case of Siphonaptera, its presumed sister group,

the Mecoptera, contains both dimorphic and flightless forms. Since ancestral scorpionflies most

likely were winged, the loss of flight ability and ectoparasitism in fleas coincide and it is not

possible to tell which came first. The situation is the same for the heteropteran families Cimicidae

Fig. 6 — Presumed phylogeny and evolution of flightlessness and ectoparasitism in orders of Insecta-Psocodea. Both

Psocoptera and Mallophaga are paraphyletic in this phylogenetic hypothesis. Abbreviations: Di, wing dimorphic; F,

flightless; W, winged. Further discussion in text.

Source: MNHN, Paris

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

103

and Polyctenidae which form a monophyletic group related to the Anthocoridae.

Flightlessness and habitat stability

Phylogenetic tests of scenarios explaining the evolution of flightlessness in relation to

habitat are difficult to perform at the level of insect orders as well as the families of Heteroptera.

Roff (1990, 1994) found significant correlation between loss of flight ability with decrease in

environmental heterogeneity, with increasing altitude and latitude, but not with isolation ( e.g ., on

oceanic islands). However, the correlation tests performed by Roff (1990) did not take

phylogeny into consideration. In a subsequent paper, Roff (1994) tried to find methods for

correcting his analyses for “phylogenetic effects” using the Orthoptera of North America as

example. However, the success of this trial was modest due to a lack of adequate phylogenies for

this group of insects.

The currently accepted scenario for the evolution of flightlessness in insects (Southwood,

1962; VepsalAINEN, 1978; HARRISON, 1980; ROFF, 1986) assumes that winged monomorphism

EVOLUTION OF FLIGHTLESSNESS IN INSECTS

IN RELATION TO HABITAT

monomorphic

wing

predominantly

winged

polymorphic

flightless

populations

flightless morph

appears

selection favours

flightless morph

temporary

->■ permanent

Durational stability of habitats

Fig. 7. — Scenario for the evolution of wing polymorphism and tlightlessness in relation to durational stability of habitats

(from temporary to permanent). Evolutionary sequence from winged, through dimorphic, to predominantly flightless

populations/species. Further discussion in text.

104

N. M. ANDERSEN : EVOLUTION OF FLIGHTLESSNESS AND WING POLYMORPHISM

is the original (ancestral) state, and that flightlessness and/or wing polymorphism has evolved

through the combined effects of selection against dispersing winged individuals and presumed

higher fitness value of non-dispersing, flightless individuals (Fig. 7). In a changing environment

where habitats proceed from being relatively unstable (temporary) to increasingly more stable

(permanent), populations may change from being monomorphic winged to being wing dimorphic

or even purely flightless. If this scenario is applied to a monophyletic group of species which

show various degrees of adaptation on a scale of environmental stability, it is predicted that

winged species will occupy habitats placed towards the temporary end of the scale while wing

dimorphic or flightless species will occupy habitats towards the permanent end of the scale. A

hypothetical phylogeny which meets this prediction is shown in Fig. 8.

Although this scenario has intuitive appeal, it should be submitted to phylogenetic tests

using real insects before it is used as a general explanatory model for the evolution of

flightlessness in relation to habitat. Phylogenetic inference involving temperate water striders of

the genera Aquarius and Gerris (ANDERSEN, 1993a), confirmed that patterns of wing

polymorphism were related to habitat stability. However, contrary to the predictions (Fig. 8), the

winged state is not the ancestral one. Surprisingly, the ancestors are inferred to be predominantly

flightless or permanently dimorphic (Fig. 5), occupying relatively stable habitats. Subsequent

evolution of long-wingedness or seasonal dimorphism has allowed descendant taxa to colonize

less stable habitats. Thus, patterns of wing polymorphism in temperate water striders are more

compatible with the hypothetical phylogeny shown in Fig. 9.

It is relatively straightforward to extend this approach to encompass other biological

important traits beside the potential for dispersal, e.g., fecundity, length of reproductive period,

pressure from parasitoids and predators, reproductive strategies and mating systems (SPENCE,

1989; Andersen, 1993a, 1994, 1996; Spence & Andersen, 1994). Among other things, this

approach allows predictions about where mechanisms of determination of adaptive traits may

Durational stability

HABIT AT temporary - >■ permanent

WING MORPH W W Di Di Di F F

SPECIES 1 2 3 4 5 6 7

Fig. 8 . — Phylogenetical relationships between species 1-7 and patterns of wing morphism compatible with the scenario in

Fig. 7. Abbreviations: Di, wing dimorphic; F, flightless; W, winged adult morph. Further discussion in text.

Source:

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

105

HABITAT temporary

Durational stability

permanent

WING MORPH

SPECIES

W/Di W/Di W W Di F/Di F

Fig. 9. — Phylogenetical relationships between species 1-7 and patterns of wing morphism compatible with the observed

pattern ol wing polymorphism in northern temperate water striders belonging to the genera Aquarius and Gerris (see

Fig. 5). Abbreviations as in Fig. 8. Further discussion in text.

differ and thus enable us to select the taxa appropriate for generalizations about selective

processes leading to a particular kind of adaptation, like flightlessness and wing polymorphism in

insects.

CONCLUSIONS

Wing polymorphism and flightlessness are very widespread among the orders of pterygote

insects, in particular those orders where adult flight is not an “everyday” activity necessary for

feeding, mating, or local dispersal, as in the Orthoptera, Hemiptera, and Coleoptera.

Flightlessness is rare where there is a significant niche shift between the immature and adult

individual, as in the Ephemeroptera, Odonata, and Plecoptera, and the holometabolous orders

Diptera, Lepidoptera, and Hymenoptera. Because most orders of pterygote insects and many

families of Hemiptera-Heteroptera are highly variable with respect to wing morphism,

phylogenetic inference is not very helpful in disclosing the causes underlying the observed

patterns of flightlessness. In general, however, the patterns are compatible with the “oogenesis-

flight” syndrome explanation when viewed in a phylogenetic context.

At the generic level of the water strider family Gerridae, the ancestral mode of adaptation

was wing dimorphism, and the few cases of winged monomorphism are estimated to be results of

secondary loss of the flightless form. As an extension of permanent dimorphism in freshwater

species, marine water striders are obligatorily flightless.

Ectoparasites on warm-blooded vertebrates (Phthiraptera, Siphonaptera, some Hemiptera-

Heteroptera and Diptera) are all obligatorily flightless. If the chewing lice (Mallophaga) and

sucking lice (Anoplura) evolved from some subgroup of the Psocoptera, the phylogeny supports

106

N M. ANDERSEN : EVOLUTION OF FLIGHTLESSNESS AND WING POLYMORPHISM

a scenario where loss of flight ability preceded ectoparasitism whereas the opposite sequence of

evolution may apply to the Diptera-Hippoboscidae.

The currently accepted scenario for the evolution of flightlessness in insects assumes that

the winged state is ancestral and that wing polymorphism or flightlessness have evolved through

the combined effects of selection against dispersing winged individuals and presumed higher

fitness value of non-dispersing, flightless individuals. The present study suggests that this

scenario should be submitted to phylogenetic tests using real insects before it is used as a general

explanatory model for the evolution of flightlessness in relation to habitat. For example, patterns

of wing polymorphism in temperate water striders are more compatible with the reverse scenario,

where ancestors are predominantly flightless or permanently dimorphic, occupying relatively

stable habitats, and their descendants are long-winged or seasonally dimorphic, colonizing less

stable habitats.

Finally, the present study emphasizes the need for taking phylogeny into consideration for

further understanding of the evolution of flightlessness in insects. It also illustrates the

importance of choosing the right taxonomic level and phylogenetic resolution for analysis. When

correctly applied, phylogenetic inference applied to patterns of biologically important attributes

can make significant contributions towards understanding the causes underlying these patterns

and suggests possibilities for process. In the end, however, understanding process will depend on

studying process directly.

ACKNOWLEDGEMENTS

I thank Philippe Grandcolas and the organizers of the symposium “Phylogenetic tests of evolutionary scenarios» for

inviting me to present this paper at the meeting in Paris. I am further indebted to Philippe Grandcolas, Niels P. Kristensen,

and two anonymous referees for useful comments on earlier versions of the manuscript, rhis paper is part of a project

supported by the Danish Natural Science Research Council (Grant n°9502155).

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Habitat and Ant-Attendance in Hemiptera : a Phylogenetic

Test with Emphasis on Trophobiosis in Fulgoromorpha

Thierry BOURGOIN

E.P. 90 CNRS, Laboratoire d’Entomologie, Museum national d'Histoire naturelle,

45, rue Buffon, 75005 Paris, France

ABSTRACT

The biological attribute “ant-mutualism” is so widely distributed within the Hemiptera that Schaefer (1987) suggested that

the association of Hemiptera vrith ants represents the retention of an early way of life which originated on the ground and

always preceded a life up on plants. A phylogenetic test of Schaefer's scenario indicates that ant-mutualism cannot be

retained as ancestral for all major hemipteran clades but arose independently several times in groups for which habitat is

above ground. Causation between a ground habitat and ant-attendance is not corroborated. Special attention is paid to

trophobiosis in Fulgoromorpha. Although all planthoppers could theoretically be associated with ants only a few of them are

ant-attended, and mainly the Tettigometridae. Members of this family share morphological characteristics (no jumping

apparatus, no wax plates, no sensory pits, a long anal tube, no anal combs, no anal apodemes in adults) and particular

fulgoromorph behavior traits (subsociality, sessile behavior) that could have evolved under selection for trophobiosis. This

calls for a reanalysis of these morphological and behavioral characters that have been generally considered as plesiomorphic.

Durable fulgoromorphan-ant associations are observed when planthoppers are unable to escape or live with gregarious or

subsocial behaviors.

RESUME

Habitat et relations avcc les fourmis chez les Hemipteres (plus particulierement les Fulgoromorphes) : un test

phylogenetique.

L'attribut « mutualisme avec les fourmis » a ete si souvent observe chez les Hemipteres que Schaefer (1987) a suggere que

l'association Hemipteres-fourmis serait l'expression d'un mode de vie ancestral ayant pris place au niveau du sol avant que ces

insectes ne conquierent les strates superieures de la vegetation. Un test phylogenetique refute le scenario de Schaefer et

montre que le mutualisme avec les fourmis ne peut etre retenu comme un etat ancestral pour tous les grands clades

d'Hemipteres. Au contraire, il serait appam de maniere independante a plusieurs reprises chez des groupes occupant deja une

strate de vegetation superieure. La relation de causalite entre vie au niveau du sol et mutualisme avec les fourmis n’est done

pas retenue. La trophobiose chez les Fulgoromorpha est plus particulierement abordee. Bien que theoriquement tous les

Fulgoromorphes puissent maintenir des relations trophobiotiques avec les fourmis, seules quelques especes sont concemees,

et tout particulierement les Tettigometridae. Cette famille presente des caracteristiques morphologiques (pas d'appareil de

saut, pas de plaques cirieres ni de fossettes sensorielles, un tube anal allonge, absences des processus pectines et des

apodemes anaux chez l'adulte) et ethologiques (comportements subsocial et faible mobilite) qui auraient pu etre selectionnees

dans le contexte du comportement de trophobiose. Ceci plaide pour une nouvelle etude de ces caracteres morphologiques et

appelle a verifier leur homologie primaire supposee avec les etats plesiomorphes observes chez les Cicadomorphes. Seuls les

Bourgoin, T., 1997. — Habitat and ant-attendance in Hemiptera : a phylogenetic test with emphasis on trophobiosis

in Fulgoromorpha. In: Grandcolas, P. (ed.), The Origin of Biodiversity in Insects: Phylogenetic Tests of Evolutionary-

Scenarios. Mem. Mus. natn. Hist, nat., 173 : 109-124. Paris ISBN : 2-85653-508-9.

110

T. BOIJRGOIN : HABITAT AND ANT-ATTENDANCE IN HEMIPTERA

Fulgoromorphes qui sont subsociaux el/ou ne peuvent s'eloigner des fourmis semblent presenter des associations durables

avec les fourmis.

INTRODUCTION

One of the major problems in evolutionary biology is the impossibility of repeating

speciation experiment. Evolution is a historical process with a unique result, and the repetition of

an experiment which validates the scientific results is inapplicable in this field of study.

Evolutionary biologists thus have substituted for the repetition of experiment the repetition of

observation. How those observations are organized and studied are the object of comparative

biology, the purpose of which is a better understanding of “the extent and pattern of organic

diversity” (HUEY, 1987).

Until the last two decades, diversity of a biological trait was most often analyzed according

to a “horizontal analysis”: the different states of the trait were observed and a scenario was

inferred according to an a priori general idea of evolution of the group. In such a view the

proposed scenario took into account at the same time the observed states of the trait (pattern),

the mechanisms which select the trait and those involved for its maintenance (processes) and it

was impossible to distinguish between them. Patterns and processes were merged in the same

explanation Since then, one has seen increasing concern of taking into account the historical

dimension in comparative biology. Analysis of the diversity of a biological trait has now to be

rooted in the phylogeny according to a “vertical analysis”. The result of this has been the shift

from empirical methods to analyze a biological trait to more formalized ones. The former were

producing a “series of natural histories” incorporating ad hoc explanations which were difficult

to evaluate. The latter now result in refutable “evolutionary scenarios” directly linked with

phylogenetic patterns (FUNKS & Brooks, 1990; Brooks & McLennan, 1991; ...).

To study and compare biological traits (morphological, physiological, behavioral or

ecological) between different taxa, two main types of methodologies have been developed. The

first uses statistical techniques (RIDLEY, 1989; FELSENSTEIN, 1985; Harvey & PAGEL, 1991...);

the second consists of mapping the traits being studied onto cladograms (CODDINGTON, 1988;

Brooks & McLennan, 1991; Grandcoi.as el al., 1994; Andersen, 1995; ...). In this last

case, patterns of biological traits are produced and used to test proposed models of evolutionary

processes. If the model fits the pattern observed then it is corroborated. Indeed, such procedures

do not aim to explain how evolution has proceeded (processes) but seek to describe or to

account for what has happened (patterns). Patterns and processes provide each by themselves a

better understanding of evolution but any explanation by processes using models needs to fit with

what has happened as it is shown by patterns. In such a way, phylogenetic patterns test

evolutionary scenarios proposed by models or allow one to infer new evolutionary scenarios

waiting for models (ELDREDGE & CRACRAFT, 1980; CARPENTER, 1989; GRANDCOI.AS el a/.,

1994). All these methodologies provide new insights into the origin and the development of

biological traits and more generally they are concerned with the origin and the development of

biodiversity. Revisiting old well-established ideas using these new approaches has most often

raised new and sometimes unexpected interpretations about different aspects of evolution: e.g.

cave adaptation and return to epigean life, (Dhsij'ITER-Grandcolas, 1994) or social behavior

and return a solitary way of life (PACKER, 1991).

Source:

PI IYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

I 1 I

With special attention paid to the Auchenorrhyncha and the Fulgoromorpha within the

Hemiptera, the first aim of this paper is to revisit the interpretation of causation (GRANDCOLAS et

a/., 1994) given for two biological attributes (sensu MlCKEVICH and Weli.hr, 1990): “habitat”

and “ant-attendance”. Ant-attendance, or trophobiosis, is so widely distributed within the

Hemiptera that SCHAEFER (1987) has suggested that the association of Auchenorrhyncha with

ants represents the retention of an early way of life and is “a secondary consequence” of the

ancestral habitat (ground level) of the Auchenorrhyncha (SCHAEFER, 1981, 1987). The second

aim of this work is to provide the basis for new research directions on ant-lulgoromorph

mutualism with special attention paid to the Tettigometridae on both morphological and

behavioral particularities of this family.

MATERIALS AND METHODS

Methodology

Both “habitat” and "trophobiosis” are two traits for which homology is difficult to establish. They cannot be directly

used in constructing phylogenies where an hypothesis of primary homology has to be proposed first for the putative

synapomorphies (de Pinna, 1991). They are used here as “attributes”, according to the meaning of Mickevich and Weller

(1990). The mapping methodology has been used in this work. All trait states are unordered and Wagner parsimony (Farris,

1970) is used to optimize them onto the cladogram using MacClade, version 3.06, (Maddison and Maddison, 1992).

To test if there is any relation between the habitat and its changes and evolution of trophobiosis in the focal group, the

following protocol was employed:

/. Mapping the different habitats observed onto a phylogeny (Deleporte, 1993) and inferring historical changes to

determine the ancestral state.

2. Mapping trophobiosis onto the same phylogeny and inferring the ancestral state of this attribute.

3. Inferring from the changes observed at the different nodes how the two attributes, “ant-attendance” and "habitat”,

are linked onto the cladogram and whether there is any indication of causation or relationship (Grandcolas et al., 1994)

between the two traits.

Phylogenetic background

Hemipteran and Fulgoromorphan phylogenies have been widely recast in the last few years and differ substantially

from the classic view summarized by Evans (1963. 1977) and used by Schaefer (1987). This results from recent

phylogenetic works dealing with morphological (Asche, 1988; Emeljanov, 1987, 1990; Dietrich & Deitz, 1993; Bourgoin,

1993b) and/or molecular data (Wheeler et al. , 1993; Sorensen et al ., 1995; Campbell et al. , 1994, 1995; Von Dohlen and

Moran, 1995; Bourgoin et al ., 1997). Ilomoptera is no longer considered as a monophyletic group (Sorensen et al., 1995)

and even the monophyly of the Auchenorrhyncha is now questionable (Bourgoin, 1993b; Campbell et al ., 1995). Within

Fulgoromorpha, the basal position of the Tettigometridae has been recently debated: morphological and molecular evidence

now places this clade among more recent lineages (Bourgoin et al., 1997). The classical (e.g. Schaefer, 1987) and the

revised (represented by the consensus of these recent cladistic analyses) Hemiptera and Fulgoromorpha phylogenies have been

both tested in this study. According to Sorensen et al. (1995), Euhemiptera refers to the monophyletic group [Cicadomorpha

+ Neohemiptera] and Neohemiptera to [Fulgoromorpha + Coleorhvncha + HeteropteraJ.

Attributes: habitat and ant-attendance

The different stales of the attributes “habitat” and “ant-attendance” for the major taxa of Hemiptera and for the

Cicadomorpha and f ulgoromorpha families are provided in Table 1. Nymphal habits, when known, have been chosen first to

determine the state of the habitat attribute in the different lineages. This assumes that nymphs retain more specific

information ("more conservative”, Schaefer, 1987) than adults which are more likely to expand their habitat and their range

of host plants as also noted by Wilson et al. (1994). Most information comes from Schaefer (1987) w ith some modifications.

Data have been completed mainly for the Fulgoromorpha using Wilson et al.' s (1994) important paper for the habitat. For

Tettigometridae, it has been reported several times that they have been found underground attended by ants. This has led to

the idea that "tettigometrid nymphs typically live on plant roots” (Emeljanov, 1987), a view that has been widely accepted

(O'Brien & Wilson, 1985; Wilson et al., 1994) although, in fact, most nymph and adult tettigometrids live on and more

generally above ground (most Ilildinae and Egropinae, many Tettigometrinae, Bourgoin, unpublished data). Therefore

tettigometrid habitat has been coded as polymorphic. Even if some cercopoid nymphs are well known to occur in masses of

froth on low grasses or in fluid-filled tubes (Machaerotidae), such behavior is most probably derived (Boulard, 1991).

According to Maa (1963) and Schaefer (1987), Cercopoidea are considered as originally subterranean (many cercopid and

112

T BOURGOIN : HABITAT AND ANT-ATTENDANCE IN HEMIPTERA

Table 1. — General habitat and ant-attendance in major AuchenorThyncha taxa. Data sources m text.

Taxa

Habitat

Ant-attendance

Stemorrhvncha

above ground

not in basal

groups

Cicadomorpha:

above ground

Aetalionidae

Cercopoidea

in or on ground

Cicadoidea

in ground

Cicadellidae (other)

above ground

Eurvmelinac

in. on or above ground

some species

Macropsinae

above ground

some species

Melizoderidae

Membracidae

above ground

Fulgoromorpha:

Achilidae + Achilixiidae

above ground, under bark

Cixiidae

in ground

some species,

in ant nests

Delphacidae Ugvopini

on ground (plant crown)

Delphacidae Asiracini

on ground (plant crow n)

Delphacidae (other)

on ground (plant crown)

some species,

under ant shelters

Derbidae

above ground, under bark

Dictvopharidae

above ground

Eurybrachidac

above ground

Flatidae

above ground

Fulgoridae

above ground

Gengidae

Hypochthonel 1 idae

in ground

in ant nests

Issidae + Acanaloniidae

above ground

some species

Kinnaridac + Meenoplidae

in ground (kinnarids)

■

Lophopidae

above ground

Nogodinidae

above ground

Ricaniidae

above ground

Tettigometridae

in, on or most

often above ground

most often

outside ant nests

Tropiduchidae

above ground

Coleorhyncha

Heteroptera

on ground

not in basal groups

Source:

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

113

Dietrich & McKamey (1990), reporting the cases already known, have shown that although most of the species in which ant-

mutualism occurs belong to subfamilies generally thought to be old lineages (Nelson, 1985), their apparent taxonomic

disjunctions among Cicadellidae suggests multiple origins of these behaviors. Indeed, several cases of ant-mutualism are

reported in eurymeline and macropsine leafhoppers which are considered to have a relative basal place in the Cicadellidae

phylogeny This information has been incorporated into the study by including a polymorphic status for these two taxa in

regard to ant-attendance. The other Cicadellidae subfamilies (Agalliinae, lassinae, Hecalinae, Idiocerinae), in which only one

or two cases of ant-attendance have been reported, are not included in this study. Excepted for Tettigometridae, trophobiosis

in Fulgoromorpha is poorly documented (see further the second part of this study) and also scattered among different families.

Treating ant-attendance as a polymorphic attribute has been used for the Fulgoromorpha Cixiidae, Delphacidae and Issidae. In

Delphacidae where the phylogeny is best known the first divisions Ugyopini and Asiracini (sensu Asche, 1990, but see

Emeljanov, 1995) have been used. Trophobiosis in Stemorrhyncha and Heteroptera is restricted to non basal taxa

(Stemorrhyncha and Fleteroptera phylogenies according to Campbell el al. (1994) and Wheeler el al. (1993) respectively)

and thus without incidence possible on the ancestral state of this attribute which then has been considered as absent for these

groups in this study.

RESULTS AND DISCUSSION

Habitat

Mapping the attribute habitat onto the revised phylogeny (Fig. 1) leads to an equivocal

result for the Hemiptera and the three states in, on or above ground are equally parsimonious (7

steps each). Moreover, one cannot propose any ancestral state for the Euhemiptera, the

Cicadomorpha, the Neohemiptera or the Fulgoromorpha. In order to try to resolve these

equivocal results and because the sister group of the Hemiptera is still unclear (KRISTENSEN,

1995), a basal group to the Hemiptera has been added permitting a test of the three different

attribute states (Fig. 2, test 1, 2 ,3). All trees are equal with a five step length. An “above

ground” basal state does not resolve the equivocal results (Fig. 2a). An “on ground” basal state

provides a full resolution: the ancestral state for the Euhemiptera, the Neohemiptera and the

Fulgoromorpha is “on ground”, while it is in ground for the Cicadomorpha (Fig. 2b). With an “in

ground” basal state, the Neohemiptera and the Fulgoromorpha are left with an equivocal result

between on or in ground, while the ancestral state for Cicadomorpha remains “in ground” (Fig.

2c).

The putative sister groups for the Hemiptera are either the [Psocodea + Thysanoptera] or

the Thysanoptera alone (KRISTENSEN, 1995). Insects in these two lineages live generally on

ground (Psocodea, Terebrantia) but some live also above ground. This last state does not allow

to resolve the equivocal results. If one retains an ancestral state on the ground for the Hemiptera,

there is no equivocal result and one can suggest the following evolutionary scenario for the

changes of habitat (Fig. 2b). The ancestral habitat state for the Hemiptera was probably on

ground and each major lineage has evolved in its own direction, whether above ground in

Stemorrhyncha, in ground in Cicadomorpha (nymphs) or on ground in Neohemiptera. In

Cicadomorpha, the Membracoidea (sensu Dietrich & DEITZ, 1993) have evolved to an above

ground habitat for all instars. In Fulgoromorpha one lineage (Delphacidae, Cixiidae, Kinnaridae-

Meenoplidae) has moved to an underground habitat (Cixiidae and Kinnaridae-Meenoplidae

nymphs) and a second lineage has changed to a complete above ground life This evolutionary

scenario agrees with EMELJANOV (1987) rather than WILSON et al. (1994) who retain an

ancestral subterranean feeding for the Fulgoromorpha and Auchenorrhyncha as a whole.

114

T. BOURGOIN : HABITAT AND ANT-ATTENDANCE IN HEMIPTEM

F ig - * • Optimization of the habitat attribute (in, on or above ground) upon the phytogeny of the Hemiptera.

Ant-attendance

The ancestral state of this attribute corresponds to an absence of ant-attendance for all the

major lineages: Hemiptera, Cicadomorpha, Euhemiptera, Neohemiptera and Fulgoromorpha

(Fig. 3). Within these clades each subgroup exhibiting trophobiosis has acquired this behavior

independently except for the clade Aetalionidae + Membracidae. This last result needs however

to be confirmed. Several taxa of membracids are known to be unattended by ants and an

ancestral trophobiosis condition in Membracidae may not be retained if these taxa are confirmed

as basal taxa. Indeed, recent results of Dietrich & DEITZ's (1993) phylogeny combined with

Wood s observations (1984) show for instance that Stegaspidini in the basal Stegaspidinae are

unattended. Ant-attendance in Fulgoromorpha is scattered throughout the taxa.

Schaefer's scenario

Schaefer (1981) suggested that the original habitat of Hemiptera was on the ground. He

considered that, from a ground-dwelling hemipteran ancestors, two basic stocks emerged. One

became predacious and developed into the Heteroptera; the other lineage became phytophagous,

Source: MNHN, Paris

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

115

Fig. 2. — Tests for optimization of the habitat attribute upon the phytogeny of Hemiptera inferring each habitat state possible

at the base of the tree. Each cladogram is equally parsimonious to the others but only one (Test 2) allows a non

equivocal resolution for this attribute, a: Test 1: above ground; b: Test 2: on ground; c: Test 3: in ground.

Source: MNHN, Paris

116

T. BOURGOIN : H.ABIT AT AND ANT-ATTENDANCE IN HEMIPTERA

sucking plant juices (probably from roots), and developed into the Homoptera (SCHAEFER, 1987).

As many members of the Hemiptera, especially many evolutionarily older members, live in

ground debris, or on just below the surface of the ground, or associated with ground biota (such

as roots, ants, burrowing mammals), or in groundlike habitats ( e.g . in nests, under bark)”, this

type of habitat “represents the retention of an early way of life; [...] it is probable that the

association with ants originated on the ground, and always preceded a life up on plants”

(Schaefer, 1987).

Schaefer's scenario is thus built on three successive steps: 1. Hemiptera lived ancestrally

on the ground, 2. Ant attendance was an ancestral attribute for Auchenorrhyncha, and 3. Ant

attendance preceded change of habitat from in/on ground to above ground. However the last two

steps are refuted and ant-attendance has appeared several times independently after all clades

have moved above ground. Indeed and according to the phylogeny used by SCHAEFER (Fig. 4),

mapping and optimizing parsimoniously the different types of habitat observed shows that it is

impossible to decide if the state in, on or above ground (9 steps each) represents the ancestral

state in the Hemiptera. For the second attribute the ancestral state corresponds to an absence of

ant-attendance for all the major lineages: Hemiptera, Auchenorrhyncha, Cicadomorpha,

Neohemiptera, Fulgoromorpha.

Why do we obtain different results? To address this scenario SCHAEFER has clearly tried to

link his argument with the historical perspective according to three main points. The first one is

in accordance with the methodology used here: the phylogenetic pattern allows one to choose

between plesio-apomorphic states of the character under study using a parsimonious

optimization. However SCFIAEFER has added two more points to build his scenario: “ingroup

commonality criterion” and “older characters are primitive”. Unfortunately, these criteria are well

known to be inappropriate and should not be used to address character polarity (HENNIG, 1966;

Nelson & Platnick, 1981; Watrous & WHEELER, 1981; and reviews in BROOKS &

MacLennan, 1991 or Forey et a /., 1992). Using these criteria and adding ad hoc hypotheses

lead to build a scenario out from parsimony and to rend it unrefutable.

Ant-attendance and habitat in the Hemiptera

In conclusion, which scenarios can be proposed for these two attributes according to the

above analyses? A parsimonious account of the patterns observed for these two attributes is

proposed here with some hypotheses on the processes which could have been involved to explain

these patterns. These are not ad hoc arguments but just possible explanations that still need to be

tested.

With Schaefer (1987) one can retain a ground level habitat as an ancestral condition in

the Hemiptera as a whole. One may expect that for competitive reasons (?) each major lineage

has evolved by itself either on ground (Neohemiptera), above ground (Sternorrhyncha) or in

ground (Cicadomorpha). Probably with the evolution of lignophytes leading to angiosperms that

allowed new feeding strategies passing from non-phloem to phloem feeding (Campbell et at.,

1994, 1995), each group had the opportunity to radiate independently in an above ground level:

Source:

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

117

Fig. 3. — Optimization of the ant-attendance attribute upon the phytogeny of the Hemiptera.

recent Sternorrhyncha, Membracoidea, higher Fulgoromorpha and secondary phytophagous

Cimicomorpha and Pentatomorpha Heteroptera.

Ant-associations do not appear to be a ancestral condition in Hemiptera. Such a result

agrees with the fact that Formicidae is a recent taxon - the oldest known ant fossil is from Upper

Cretaceous, 80 millions of years old (HOLLDOBLER & WILSON, 1989; Boi.ton, 1994) - relatively

to Hemiptera which are known since the Permian (see review in SORENSEN et a/., 1995). Ant-

attendance occurred always after change of the habitat from on ground to above ground and

subterranean associations with ants appear to be derived But not all above ground clades are

ant-attended and there is no direct link (causation) between change of habitat and trophobiosis.

Probably changes of habitat to an above ground level occurred with changes of host plants. One

may expect that host plants mediate Hemiptera attractiveness and that some host plants are more

suitable for trophobiosis than others.

118

T. BOURGOIN : HABITAT AND ANT-ATTENDANCE IN HEMIPTERA

/V/ //A//

□ ■■□□□□□EH

Homoptera

Hemipiera

Habitat

unordered

1_I above ground

HI on ground

in ground

polymorphic

I 1 equivocal

Fig. 4. — Optimization of the habitat attribute (in, on or above ground) upon the phytogeny of the Hemiptera used by

Schaefer (1987). One cannot choose between the character states for the Hemiptera, the Homoptera, the

Auchenorrhyncha, the Cicadomorpha and the Fulgoromorpha.

In Fulgoromorpha, the cixiidian lineage retained the probable ancestral habitat on ground

(at least at nymphs) and within this lineage, the Kinnaridae and several Cixiidae taxa went in a

subterranean habitat (HOCH, 1994). From the paraphyletic Kinnaridae (BOURGOIN, 1993a) the

above ground Meenoplidae family arose. In the sister lineage, the first Derbidae-Achilidae-

Achilixiidae lineage specialized as fungal feeders (nymphs) under the bark of living and dead

trees (WILSON el a/., 1994) while its above ground sister group radiated successfully in number

(half of the known species in Fulgoromorpha) and in diversity (13 families). This success is

probably related to angiosperm diversification but also with vicariance events linked to the

breakup of Gondwana that led to the constrained distributions (absence in some biogeographical

areas) observed in some of these families. Within the Fulgoromorpha and with exception of some

scattered examples, the Tettigometridae is the only lineage which has developed strong

mutualistic relationships with ants. One may expect that radiation of Tettigometridae from

Tropiduchidae (BOURGOIN el a /., 1997) took place with change of host plants which have

influenced their attractiveness to ants either directly (quality of honeydew) or indirectly (plant ant

attractants).

Source:

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

119

Trophobiosis in Fulgoromorpha and the case of Teltigometridae. Prospectives

Theoretical studies (ROUGHGARDEN, 1975; WILSON, 1983; KEELER, 1985) suggest that

mutualism should be restricted to situations where the cost of maintaining the situation is low to

each participant, while the benefits are relatively great (BRISTOW, 1991). Fulgoromorpha-ant

associations would seem to fit these restrictions. Indeed, benefits/costs for both partners of such

associations are already well known in other Homoptera and are also valid for Fulgoromorpha

associations. Ants benefit in reduced search time for food (honeydew) and for prey pursuit by

direct predation on the hoppers, and in increased stability and quantity of the food resource.

Benefits for the fulgoromorphs include defense against predators which allows a relative

perennial site of food and non accumulation of honeydew on the substrate (Rozario et a/.,

1993). Cost for ants includes active defense against predators and active monopolization of

fulgoromorphan resources while a higher honeydew production by the hopper is requested.

However among Fulgoromorpha, ant-mutualism is only documented in few species of

Cixiidae (MYERS, 1929; THOMPSON, 1984), Delphacidae (DEJEAN et al., 1996), Issidae

(Dietrich & McKamf.y, 1990), Hypochthonellidae (China & Fennah, 1952) and in most

species of Tettigometridae (Bourgoin, in prep ). Why are so few Fulgoromorpha ant-attended?

Why do more than 70% of the records concern the Tettigometridae? Are there phylogenetic

constraints (morphological or behavioral adaptations) which could limit or favor ant-associations

and should be hypothesized to account for this pattern? What is the impact of ant-attendance on

such adaptations?

Although such generalizations should be approached with some caution (BRISTOW, 1991),

regularly ant-attended aphids show several characteristics: e.g. cornicle length reduced, leg

length reduced, not saltatorial, trophobiotic organ, ... (Way, 1963; SKINNER, 1980; SUDD,

1987,...) and placid behavior, gregariouness (DlXON, 1958; PIERCE et a/., 1987). These

characteristics seem to fit with those observed for the Tettigometridae within the

Fulgoromorpha. Indeed tettigometrid larvae share several unique morphological characteristics

(no jumping apparatus, no wax plates, no sensory pits, a long anal tube, absence of anal combs

and anal apodemes in adults) and particular behavioral traits (subsociality, sessile behavior).

Morphological characteristics. Considering the function of these structures and correlation

with myrmecophily, it appears legitimate to hypothesize an adaptive scenario that these

autapomorphic characters in Tettigometridae have evolved under selection for tettigometrid-ant

mutualism and thus may be secondarily simplified (versus showing a plesiomorphic state) or lost

(versus primary absence). From a phylogenetic standpoint, all these tettigometrid characters have

been considered plesiomorphic and homologous to the cicadomorphan state. But, with a new

careful and extended morphological analysis (thus independently with regard to this adaptive

scenario to avoid circular reasoning), can the primary homology of these characters a priori

hypothesized with the cicadomorphan state, be rejected? For instance, a new morphological

analysis of the characters “long anal tube” and “absence of anal combs” have shown that they are

in fact secondarily modified for the first, or reduced or secondarily absent for the second

120

T. BOURGOIN : HABITAT AND ANT-ATTENDANCE IN HEMIPTER4

Source: MNHN. Paris

PHYLOGENETIC TESTS OF EVOLU TIONARY SCENARIOS

121

(BOURGOIN & CAMPBELL, 1996). At least, these two misinterpreted characters may carry an

adaptive value for trophobiosis in ant-associations. The other characters need to be reanalyzed

according to this possibility.

Sessile and subsociality behavior. Four main types of ant-attendance have been reported in

Fulgoromorpha literature: 1. Opportunistic or occasional attendance by ants which collect on the

substrate the honeydew drops randomly deposited by the planthopper kicking; such associations

are generally limited in time (one flatid: PFEIFFER, 1996; some issids: O'BRIEN, 1988; DIETRICH

& McKamey, 1990). 2. Underground attendance in ant nests (some cixiids: MYERS, 1929;

Sheppard et al ., 1979; Thompson et a/., 1979; Tfiompson, 1984; hypochthonellids (China &

FENNAH, 1952), some tettigometrids). 3. Attendance of planthoppers under shelters build by ants

(some delphacids, reviewed in DEJEAN et al, 1996). 4. Long time attendance; ants collects

honeydew drops directly at the anal opening and regularly antennate the planthoppers (many

tettigometrids, Figs 5-10).

DIETRICH & McKamey (1990) have noted that all ant-attended Membracoidea and

Cicadelloidea are sessile (non-jumping) and exhibit subsocial behaviors. It is thus interesting to

note that (i) all durable fulgoromorphan-ant associations are observed when planthoppers are

either unable to escape (unground in ant galleries or under shelter) or sessile species

(Tettigometridae) and (ii) all durable fulgoromorphan-ant associations are observed when

planthoppers are either forced into gregariousness (cixiids kept in ant nests, delphacids kept

under ant shelters) or when they are subsocial (tettigometrids). Such close correlations are

noticeable and further studies are needed to elucidate the relationships between these different

attributes: ant-mutualistic, sessile, gregarious and subsocial behaviors.

In Fulgoromorpha, modalities of trophobiosis appear to be quite diverse while it is limited

to few species only. Although morphological and behavioral characteristics seem important for

mutualistic relationships between planthoppers and ants, one cannot forget that habitat and

particularly host plants may have had an important impact on formation and maintenance of these

associations. This makes the Fulgoromorpha a nice model to study ant mutualism. Mapping such

attributes within a parsimonious evolutionary framework will allow to move from an anecdotal

and descriptive natural history to a refutable evolutionary scenario of “how mutualistic

interactions evolve and are maintained” (BRISTOW, 1991).

ACKNOWLEDGEMENTS

This paper is a modified version of the talk presented during the symposium, “Tests phylogenetiques de scenarios

evolutifs - Phylogenetic tests of evolutionary scenarios”, Paris, 3-4 June, 1996, supported by the Reseau National de

Figs 5-10. — 5-9: Euphyonarlhex phvllostoma Schmidt (Fulgoromorpha Tettigometridae) attended by various species of ants

(Hvmenoptera, Fonnicidae) on Bridelia micrantha Baillon (Euphorbiaceae) in Cameroun. 5: Attended by Camponotus

brutus Forel; in the upper left part of the photograph one can also observe a dictvopharid (Fulgoromorpha,

Dictyopharidae) feeding. 6: Attended by Oecophyila longinoda Latreillc (in laboratory) 7: Attended by ( amponotus

acvapimensis Mayr. 8: Attended by Polyrhachis laboriosa Smith (in laboratory). 9: Nymphs attended by Myrmicana

opaciventris Emery 10: Hilda rubrospersa Fennah (Fulgoromorpha Tettigometridae) attended by Camponotus sp.

(brutus group) (Hvmenoptera, Formicinae) on Ficus vallis-choudae Delile (Moraceae), in Cameroun. Photographs by

A. Dejean.

Source: MNHN, Paris

122

T. BOURGOIN : HABITAT AND ANT-ATTENDANCE IN HEMIPTERA

Biosystematique (ACC-SV7). I am very grateful to A. Dejean who kindly provided the photographs and to the reviewers for

their comments on the manuscript.

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Source: MNHN, Paris

Food Choice and Environment Occupancy in Afrotropical

Dung Beetles: a Phylogenetic Study of two Examples

(Coleoptera, Scarabaeidae)

Yves Cambefort

E.P. 90 CNRS. Laboratoire d'Entomologie, Museum national d'Histoire naiurcllc,

45. rue BufTon. 75005 Paris. France

ABSTRACT

Phylogenetic studies of two genera of Afrotropical Scarabaeidae dung beetles (Euoniticellus and Milichus) have enabled to

clarify some points in their evolutionary history. The species of Euoniticellus which have experienced an early separation from

the rest of the genus live in forest and use non-ruminant mammals dung of the elephant type. Phylogenetic analyses enable to

assume that the ancestor had the same macrohabitat and microhabitat. In the course of evolution, the genus seems to have

gradually invaded savanna environments and ruminant mammals dung, when these new habitats were available. These

changes considerably enlarged the genus' ecological niche. The genus Milichus experienced the same change in food, but the

change in environment has been inverse and took place from savanna to forest.

RESUME

Regime alimentaire et utilisation de I’environnement chez des coleopteres coprophages afrotropicaux : etude

phylogenetique de deux exemples (Coleoptera, Scarabaeidae)

L'etude phylogenetique de deux genres de Scarabaeidae coprophages afrotropicaux (Euoniticellus et Milichus) a permis de

preciser certains elements de leur histoire evolutive. Pour ce qui est des Euoniticellus , les especes qui se sont separees

precocemcnt du reste du genre vivent dans des milieux de foret et exploitent les dejections de mammiferes non ruminants, du

type de l'elephant. La meme analyse permet de penser que 1’ancetre du genre avait les memes macrohabitat et nucrohabitat.

Dans le courant de 1'evolution, ie genre semble avoir envahi les milieux de savane et les excrements des mammiferes

ruminants au fur et a mesure que ces nouveaux habitats etaient disponibles. Ces changements ont considerablement agrandi la

niche ecologique du genre Euoniticellus. Le genre Milichus a connu le meme changement de nourriture, mais son changement

d'environnement s'est fait en sens inverse : de la savane vers la foret.

INTRODUCTION

The present environments of tropical Africa can be divided into two well-defined and

contrasted groups: tropical evergreen rainforest and both grasslands and woodlands, these two

latter environments or biomes constituting the “savanna” category (especially in West Africa.

Cambefort, Y., 1997. — Food choice and environment occupancy in Afrotropical dung beetles: a phylogenetic study

of two examples (Coleoptera, Scarabaeidae). In. Grandcolas, P. (ed.). The Origin of Biodiversity in Insects: Phylogenetic

Tests of Evolutionary Scenarios. Mem. Mus. natn. Hist, not., 173 : 125-134. Paris ISBN : 2-85653-508-9.

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Y. CAMBEFORT : FOOD CHOICE AND ENVIRONMENT OCCUPANCY IN DUNG BEETLES

Gha/.anfar, 1989). Most Afrotropical plants and animals live in either forest or savanna. This

division is clear-cut, at least as far as Scarabaeidae dung beetles are concerned: no forest species

inhabit savanna, and vice versa (CAMBEFORT, 1991c; CAMBEFORT & WALTER, 1991). However,

most of the generally recognized genera ( i.e . monophyletic ensembles of species - as far as

phylogenetic studies have established their monophyly) comprise forest and savanna species.

Therefore, in these monophyletic groups, some species must have changed from one environment

to another. In each case, it can be asked which was the ancestral environment, and what was the

influence of this change on the history of the genus.

The vegetal environment constitutes what could be called the “macrohabitat” of

populations. Within these macrohabitats, the Scarabaeoidea lineage experienced changes in diet

from a supposed mycophagy to such advanced diets as wood, flowers and dung (SCHOLTZ &

Chown, 1995). So-called dung beetles live in and around the “microhabitats” made up by the

excrements of animals, especially of mammals. Dung beetles also use these excrements as their

food. Although these insects are able to accept different sorts of dung, they seem to have rather

precise requirements for adult food, and especially for the making of brood balls which larvae eat

from inside and develop in (CAMBEFORT & Hanski, 1991). According to these preferences, it is

possible to divide dung beetles into omnivore dung specialists and herbivore dung specialists. In

this latter category, it is possible to distinguish between non-ruminant herbivore dung specialists

and ruminant herbivore dung specialists (CAMBEFORT, 1984, 1991c; TRIBE, 1976). In the second

case, most genera comprise both categories of specialists. In the course of each genus' history,

changes in food (microhabitat) can have occurred, as well as in macrohabitat. Therefore, it can

be asked how these changes have occurred, and what was their influence on the evolutionary

history of the genus. To test this two-fold problem (changes in macro- and microhabitat), two

genera of dung beetles have been selected: Euoniticellus and Milichus. Both are specialists of

large mammals' dung. But some of their species occur in forest, some others in savanna; some

species prefer the dung of Bovine mammals (including cattle), some others are found only in

elephant dung.

MATERIAL AND METHODS

The taxa

Genus Euoniticellus Janssens, 1954: The 19 species of the genus (habitus: Fig. 1) occur mostly in tropical Africa (14

species). There are 2 species in the Palaearctic region, 2 in the Oriental region (including one in common with the Palaearctic

region), and one Neotropical species, restricted to Cuba and Jamaica. These species are specialists of large herbivore

mammals' dung, especially elephant and Bovini (including cattle). Some species are among the most evolved and efficient

dung beetles, because they have developed optimal use of dung. Their larvae use the most nutritious part of this dung

(“coprobiontic” alimentation: Cambefort, 1991a), which allows the female to lay eggs a very short time after emergence

(down to 5 days: Halffter & Edmonds, 1982). A phylogenetic study of the genus, which will not be detailed here, has

produced the cladogram of Figs 3-4 (Cambefort, 1996b).

Genus Milichus Peringuey, 1901: The taxon (habitus: Fig. 2) is endemic of Afrotropical region. There are 15 described

species, all specialists of herbivore mammals' dung, which live both in savanna and forest. As for Euoniticellus , a

phylogenetic analysis of this genus has recently been published (Cambefort, 1996a).

Habitat choice

Habitat (both macro- and microhabitat) choices are here considered as “attributes'’ of the relevant species (see

following paragraph). These choices of most of the species of the genera Euoniticellus and Milichus have been established

from field works, especially the author’s ones (published or not), and according to other authors ( e.g . Kingston, 1977). As for

the environment (macrohabitat), there is no possible doubt: the species clearly occur either in forest or in savanna (grassland

and/or woodland). Food (microhabitat) choice is sometimes less clear-cut. It has been considered that, when more than 90 %

Source: MNHN, Paris

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

127

Figs 1-2. —Euoniticellus and Milichus : habitus. 1: E. capnus Cambefort, 1996; 2: M boucomonti Cambefort, 1996. (Scale

bars = 1 mm).

of the individuals occurred in either of the categories taken into account (elephant dung or cattle dung), the relevant species

was a specialist of this sort of excrement (Hanskj & Cambefort, 1991). When there was some doubt, the choice (the

attribute) has been considered as polytypic.

Evolution of attributes

The ecological traits have not been used for establishment of the relevant phytogenies, these traits are not considered

as characters but rather as attributes, according to the definition given by Grandcolas et al (1994): l 'an attribute is a trait of

yvhich primary homology is questionable, because it does not match the homology criteria; an attribute is empirically an

extrinsic or widely defined trait; it is not used for phylogeny construction but is studied in reference to an independent

phylogeny” For this reason, some consensus exists in favor of treating ecological aspects of the niche as attributes and not to

use them to construct the tree whose aim is to clarify their changes ( e.g . Brooks & McLennan, 1991).

For the present study, the program MacClade, version 3.04, was used. This program has a set of functions which

enable the study of the analysis of characters, including traits not used to construct the tree (Maddison & Maddison, 1992,

1993). These fimctions use the classical principles of character optimization according to Fitch parsimony (e.g. Kjtching,

1992).

RESULTS

Genus Euoniticellus

The phylogenetic study of the genus (CAMBEFORT, 1996b) shows that it can be divided

into two clusters of species: a paraphyletic cluster (from pemiger to parvus ), which comprises

smaller species (average length: 5 mm); a monophyletic group (from cubiensis to pal/ipes),

128

Y. C AMBEFORT : FOOD CHOICE AND ENVIRONMENT OCCUPANCY IN DUNG BEETLES

which comprises species whose average length is almost two times bigger (9.6 mm). The former

cluster consists of species close to the tree root, and which, in this hypothesis of phylogeny, can

be considered for this reason as “older”. They occur mostly in tropical Africa, with one species in

tropical Asia. In general, they are rare or very rare, with restricted geographical distribution, and

most of them have been described rather recently. The latter group represent a monophyletic

clade which consist of probably more recent species. They are more widespread than the former

species, with a vast geographical distribution. Most of them have been described a longer time

ago (XIXth or even XVIIIth century). Most of them occur in Tropical Africa, but some also

occur in Palaearctic and/or Oriental regions, with one Neotropical species. These 11 species are

the descendants of one ancestral species and constitute the sister-group of one species of the

former group: E. parvus. The ancestral species split from the stem of the “older” species at some

time during the evolution of the genus, and experienced an especially important cladogenesis

which gave rise to a clade of eleven species.

On the relevant phylogeny, the ecological attributes have been mapped: food or

microhabitat and environment or macrohabitat. There is a very clear difference between smaller

and larger species as far as food is concerned (Fig. 3): while the former prefer elephant dung

(only E. parvus occurs exclusively in cattle), most of the latter occur in cattle dung (only the twin

species E. kawanus-tibalensis prefer elephant dung). The difference is also clear in the case of

the environment (Fig. 4): most of the smaller, elephant specialist, basal species occur in forest;

most of the larger, cattle specialist, apical species occur in savannas.

Genus Milichus

The phylogeny of this genus (CAMBEFORT, 1996a) does not show such clear-cut species groups

as in the preceding case. Only the 4 species of the top of the tree, which form a monophyletic

group (with two pairs: dudleyaeldudleyi and inaequalisllecourti) are of a smaller size than the

other species. In the same way as Euonilicellus , two ecological attributes have been studied:

food and environment. As for food choice (Fig. 5), although it is unknown for 4 species out of

15, it seems clear that a mere minority of the species occurs in cattle dung (also 4 species out of

15). On the contrary, elephant dung seems to be the choice of 8 species. On the 15 described

species, 10 live in herbaceous environments, grasslands and/or woodlands (Fig. 6). A mere 5

species occur in evergreen rainforest, of which 4 constitute a monophyletic group, and the 5th

one seems to have diversified separately and specialized for this environment from a step living in

humid savanna of the Guineo-Congolian type (GHAZANFAR, 1989).

DISCUSSION

The ecological attributes which have been reported on the phylogenetic hypotheses of the

genera Euonilicellus and Milichus are recent. The past environments were probably not the same

as the present ones. Also, it is difficult to know which sort of dung was used as food by the

Figs 3-4. — Phylogeny of the genus Euoniticellus , with ecological attributes optimized. 3: food (microhabitat); 4:

environment (macrohabitat).

Source: MNHN , Paris

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

129

/////&////////*

Food

I_1 unknown

ISlII elephant dung

I bovine dung

illlilll polymorphic

Euoniticellus : food

Environment

1 1 forest

I savanna

Euoniticellus : environment

Source: MNHN, Paris

130

Y. CAMBEFORT : FOOD CHOICE AND ENVIRONMENT OCCUPANCY IN DUNG BEETLES

ancestors of the living species. But I assume that, in the early history of the genus, both macro-

and microhabitats were not very different from the present ones. In the phylogenetic tree of

Euoniticellus , ecological attributes show a clear-cut change both in food and environment.

Smaller, “primitive” species live(d) in forest environments and use(d) the dung of browser

mammals of the type of the elephant's. These are coarse dung types, small parts of which only

can be used by smaller dung beetles (TRIBE, 1976). At some time in the genus' history, one of

these species seems to have changed this diet for some grazer mammal dung, probably a

ruminant one. The question is open as to the time - in the genus' evolution - when this change

took place. In the present species, there is a “small” one (E. panrns) which feeds on cattle dung.

On the other hand, there is a pair of “large” species ( E. kawanus-tibatensis) feeding on elephant

dung. According to MacClade's optimization (Fig. 3), this change occurred before the

differentiation of E. parvus , and the specialization of the pair kawanus-tibatensis is of secondary

nature. In any case, this change was a very important innovation, which opened quite a new area

(or “niche”) to the genus, and made possible the cladogenesis which produced the more modern

species of the genus. It is possible that this cladogenesis was an adaptive radiation, which took

place to fill the new niche of grazer mammals' dung.

These grazers, perhaps ruminants, no longer lived in the forest. Food change of

Euoniticellus coincided with environment change: part of the forest which has originally covered

almost the whole tropical Africa, was gradually changed into savanna: woodlands in the more

humid areas, grasslands in dryer ones. This new environment, rich in grasses of the family

Graminaceae (Poaceae), induced the evolution of quite a new fauna of grazer mammals, among

which the Bovini possess the most evolved digestive adaptations. Their dung has a very fine

structure and allows an optimal use by dung beetles, both adults and larvae. The joint change in

micro- and macrohabitat, which possibly occurred almost at the same time (at the geological

scale), opened a new niche: ruminant-dung-in-savanna, which has been exploited by the

Euoniticellus species ancestor of the group cubiensis-pallipes. This new niche has proven more

successful than the older one (browser-dung-in-forest), enabling the adaptive radiation of modern

Euoniticellus , which have occupied all the environments of savanna, and even gone out the

tropical areas, probably following their mammalian sources of food. Moreover, cattle

domestication by man even enlarged this niche and geographical distribution of the genus. Up to

this point, the spreading of the taxon has been a natural one. Recently, the efficiency of some

Euoniticellus in recycling cattle waste, having been taken into consideration, one species ( E.

intermedius) has been introduced artificially into Australia. It is now one of the most successful

of the introduced species in this area (DOUBE et a /., 1991). The species has also been introduced

into other Oceanian areas: New Caledonia and Vanuatu (Guttierrez et at., 1988), and also in

(sub)tropical America (FINCHER, 1986).

Coming back to the adaptive radiation of the modern species of Euoniticellus, it is worth

remarking that their size is larger than for those using elephant dung. This is in contradiction with

a previously established “rule” ( e.g. CAMBEFORT, 1991c), according to which there is a

Figs 5-6. — Phytogeny of the genus Milichus, with ecological attributes optimized. 5: food (microhabitat); 6: environment

(macrohabitat).

Source: MNHN, Paris

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

131

Food

1 1 unknown

bovine dung

Milichus : food

Milichus : environment

Source: MNHN. Paris

132

Y. CAMBEFORT : FOOD CHOICE AND ENVIRONMENT OCCUPANCY IN DUNG BEETLES

correlation between average size of mammals and of dung beetles using their dung. Now, this is a

general rule, valid for the entire dung beetle fauna. In the case of the genus Euonilicellus,

optimal utilization of cattle dung, which is highly characteristic of the genus, and higher

alimentary value of this type of dung, possibly enabled the species having this diet to reach a

larger average size than those exploiting elephant dung. On the contrary, size ratio in the genus

agrees with another “rule” according to which savanna dung beetle species have an average size

larger than forest species (Cambefort & Walter, 1991).

Is it possible to give a minimum date, even approximate, of the change of habitats that lead

to the “modern" Euonilicellus ? First pollen grains of grass appear, in Africa, in the mid-Eocene

(Van Der Hammen, 1983), documenting the first grassland and woodland areas. During the

Cenozoic, grass formations evolved between forests and (sub)deserts, probably at the expense of

the former, and at least to some extent owing to the action of “megaherbivores” (Owen-Smith,

1988), i.e large herbivorous mammals of the elephant type, which seem to have been abundant in

Africa at least from Miocene to Holocene (Kalb, 1995). Due to their action, arboreal vegetation

disappeared on vast expanses of land, where grass was able to develop (Cambefort, 1991b,

1991c). But it was for the benefit of other mammals: the so-called grazers, including ruminants,

group of which the Bovini represent the more advanced branch. It is in the Pliocene that recent

Bovini began to appear in Africa, probably from Asia (e.g. Gentry, 1990, 1992; Geraads,

1992; Thomas, 1984; Vrba, 1985). It is from that time on that modern Euonilicellus , which

may have begun to settle in woodland areas in large mammal dung ( cf the E. kawanus-tibatensis

pair), must have started to use Bovini dung. More Bovini gained importance and number, more

modem Euonilicellus became widespread, in Africa first, then in Asia, and finally in America, of

which E. cubiensis is up to now the proof. Today, this species lives in grassland areas in Cuba

and Jamaica, where it uses cattle pats (Matthews, 1966). It is possible that its ancestors once

followed Bovini troops during their migration eastward. As Bovini have never reached the West

Indies, we must assume that this dung beetle has, for some reason, changed its diet and started to

use the dung of some large American mammals: Edentata (Xenarthria) of the group of terrestrial

sloths (Megalonychidae), for these were the only large mammals in Cuba (ITURRALDE-VINENT,

1988). The beetle then might have followed the mammals in their land or sea journey towards

Large Antilles. Finally, the mammals disappeared there, and the beetle turned back to Bovini

dung, when cattle was introduced into the islands, from XVIth century on. This is a rather

complicated history, but the real “scenario” may have been even more complicated. In any case,

the species is not very different from other “modern” Euonilicellus , and does not make a

particular section in the genus (contrary to MATTHEWS, 1966).

All the precedent paragraphs dealt with Euonilicellus. If we now consider the genus

Milichus, and first its microhabitat (food), it seems that there has been also a change from

elephant (“old’ species diet) to Bovini dung (“modern” species diet). In this case, change of

macrohabitat seems to have been from savanna to forest. Africa occupancy by Milichus species

seems to have been not “centrifugal” (i.e. from central forest to peripheral savannas, as in

Euonilicellus) but centripetal (i.e. from savanna to forest). Now, centrifugal dispersion (in

Africa) leads to a larger distribution than a centripetal one, due to the fact that the expanse of the

savannas are larger than that of the forest, and used to be even larger because the relative

extension of the forest versus savanna is now larger than average (Maley, 1996). Older species

of Milichus seem larger than more modern ones. These size relationships are less clear than in

Source: MNHN, Paris

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

133

the precedent genus. Moreover, if the spreading really took place from savanna to forest, it is

difficult to date it.

CONCLUSION

Study of evolution of two ecological attributes: food (microhabitat) and environment

(macrohabitat) in two genera of Afrotropical dung beetles enables one to formulate some

hypotheses concerning “evolutionary scenarios” of these genera. The shift from use of non¬

ruminant dung to ruminant (especially bovine) dung is assumed in the two cases in question. On

the other hand, the shift from forest to savanna seems to have taken place in one case out of two.

In any case, it is clear that those species whose evolution is in conformity with the double

scenario: “non-ruminant dung -» ruminant dung”, and “forest -> savanna” will be promoted by

all means, including human action. This last factor in turn can act at two levels:

- passive action: destruction of Afrotropical forest and of elephant; multiplication and

dissemination of domestic cattle;

- active action: introduction of dung beetle species into areas where they do not occur.

This is the case of some “modem” Euoniticellus, particularly of E. intermedins , which is

now one of the most abundant and widespread dung beetle on earth. On the contrary, older

species are “trapped” both in their macrohabitat and microhabitats. Coming back to the word

“scenario”, and giving it its proper meaning of “history”, it could be said that the older species

are not (or no longer) “in the sense of History”. The scenario can even be expanded in the future,

and it can be predicted - in the true meaning of the word, i.e. in the future - that the older

species will get extinct before the more modern ones, and lamentably perhaps in a short span of

time, together with the Afrotropical forest and elephant.

ACKNOWLEDGEMENTS

Thanks to Philippe Grandcolas, for fruitful discussions, and to the anonymous referees.

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Source:

Phylogenetic Relationships among European Polistes

and the Evolution of Social Parasitism

(Hymenoptera: Vespidae, Polistinae)

James M. Carpenter

Department of Entomology, American Museum of Natural History.

Central Park West at 79 th Street. New York. NY 10024. U S. A.

ABSTRACT

Cladistic analysis of the European species tit Polistes is used to investigate the evolution of social parasitism in the genus.

The three species of social parasites (formerly the genus Sulcopolistes) are all inquilines: lacking a worker caste, and

dependent on usurping tire colony of a host species to obtain a worker force. Emery's Rule states that social parasites are more

closely related to their hosts than to any other species. Previously published allozyme (Carpenter el al. 1993) and mtDNA

(Choudhary et al., 1994) data did not support this hypothesis, but did not resolve relationships among the species ol social

parasites Morphological characters are adduced which resolve the phylogenetic relationships among these three species, and

the combination of the morphological and molecular data sets largely resolves the relationships among a nine European

species Cladistic optimization of traits associated with social parasitism on the resulting cladogram shows. (!) Emery s Rule

is rejected. (2) the scenario proposed by Taylor (1939) for the evolution of social parasitism is not supported either. The

predatory behavior of the inquiline P. atrimandibularis , with separate "supply” and "nursery nests, is evidently secondary, as

is its initially passive invasion behavior.

RESUME

La phvlogenic des Polistes d'Europe et revolution du parasitisme social (Hymenoptera : Vespidae, Polistinae)

L'analyse cladistique des especes de Polistes europeennes est Utilisee pour etudier revolution du parasitisme social dans le

genre. Les trois especes de parasites sociaux (autrefois le genre Sulcopolistes ) sont toutes « inquilines » ^ elles nont pasde

caste ouvriere e. s'approprient celle de la colon,e d'une espece hole. Le regie d Emery affirme que es ^ de^rasites

sociaux sont plus proches parents de leurs holes que de toute autre espece Des analyses basecs sur les' all °f>™ c J•

e, al., 1993) et 1'ADN mitochondrial (Choudhary « al., 1994) n'ont pas conf.nne cette hypothese, nuns n<nt pajrfajumm

plus les relations entre les especes parasites. L'addilion de caracteres morphologiques et la combinaison des donnees

morphologiques et moleculaires ont pennis de resoudre respectivement les relations

et entre les neuf especes europeennes [.'optimisation sur le cladogramme de traits assoc.es au J^safement

(1) le reole d'EMFRY est refutee ; (2) le scenario devolution du parasitisme social propose par Taylor (1939) est egalement

predatem’ Je I'mquilme P. aMitulans, qui maintient aids separes pour les provisions et

pour le couvain, est a l’evidence secondaire, de meme que son comportement d invasion imtiale passive.

Carpenter J M 1997. - Phylogenetic relationships among european Polistes and the evolution of social parasitism

1 . . d r , } Cv Awnrm as P (e<i) The Origin of Biodiversity in Insects. Phylogenetic Tests ot

(Hymenoptera: Vespidae; Polistinae). In. Grandcolas, r . (ea j n e g

Evolutionary Scenarios. Mem. Mus. nan, Ilis,. not., 173 135-161. Pans ISBN . 2-85653-508-9.

136

J. M. CARPENTER : EVOLUTION OF SOCIAL PARASITISM WPOLISTES

INTRODUCTION

The social parasites known as inquilines are among the most intriguing outcomes of

evolution in paper wasps. Inquilines have no worker caste and cannot build nests; they must

invade the colony of a host species and supplant the queen to obtain workers to rear their brood.

Striking morphological differences occur between host and parasite (cf. Figs 1-2). This form of

behavior is rare in paper wasps, having been found in just three species in one genus, Po/isles.

Po/istes is a cosmopolitan genus, with more than 200 described species (Carpenter, 1996b);

the three social parasites ( atrimcmdibiilaris , semenowi and sulcifer) are found only in Europe and

the Mediterranean Region. The inquiline behavior has long been known (Weyrauch, 1937), but

recent years have seen a profusion of studies, particularly by workers at the University of

Florence (for a review see CERVO & Dani, 1996). These studies have revealed remarkable

phenomena, such as simultaneous domination by atrimcmdibularis of several colonies of the host

biglumis, only one of which serves for parasite brood rearing while the larvae of the other nests

serve as a source of food (Cervo el al., 1990c), or change in the composition of the chemical

signature of atrimcmdibularis to match that of biglumis at the time of emergence of host workers

(Bagneres el a /., 1996). This wealth of new information has stimulated intense interest in

evolutionary explanations of aspects of social parasitism.

In this paper I apply cladistic analysis to investigate the evolution of social parasitism in

Po/isles. I first review evolutionary explanations that have been advanced for the social parasites,

and how cladistic tests may be constructed for such hypotheses. I then present the first cladistic

analysis of interrelationships among the inquilines and related species to be based on

morphology. I'hese characters are also combined with previously published molecular data, and

analyzed simultaneously. Behavioral features associated with social parasitism are optimized on

the resulting cladogram, to test various evolutionary hypotheses.

Emery's Rule

The classical explanation that applies to the origin of socially parasitic species is the

hypothesis known as Emery's Rule (after Emery, 1909). Emery's Rule is that social parasites

are more closely related to their host species than to any other species. This is usually interpreted

to mean that social parasites evolved directly from their hosts, either by sympatric speciation

(e.g. West-Eberhard, 1986; BUSCHINGER, 1986, 1990; BOURKE & FRANKS, 1991) or not (e.g.

WILSON, 1971). Alternatively, social parasites may exploit similar recognition systems in closely

related species (CARLIN, 1988). However, previous cladistic analyses do not support Emery's

Rule in Po/istes. CARPENTER el al. (1993) presented an allozyme data set for the three species of

social parasites, their four host species (see Table 1) and two outgroup species. The 27 loci were

subjected to three different coding procedures, which led to different results for each method, but

under none of the codings were the social parasites most closely related to their hosts.

CHOUDHARY el al. (1994) analyzed a 386 base pair sequence from the mitochondrial 16S rRNA

gene. I heir cladistic results were less ambiguous, with two cladograms, differing only in the

interrelationships among the social parasites. The social parasites were a monophyletic group.

Thus, phylogenetic analysis of two independent sources of evidence, by rejecting close

relationship of parasite to host, rejected Emery's Rule.

Source: MNHN, Paris

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

137

Figs 1-2. — Frontal view. 1: Polistes dominulus ; 2: Polistes atrimandibularis. Hie magnification is 2lx.

Table 1. — Host-parasite relations among European Polistes species. Cervo & Dani (1996) report experimental introduction

of atrimandibularis into the nests of nimphus, but this is unknown to occur naturally.

Parasite

Host

atrimandibularis

biglumis, gallicus

semenowi

dominulus, nimphus

sulcifer

dominulus

Taylor's Scenario

Emery's Rule also played a role in development of an evolutionary scenario tor the origin

and elaboration of social parasitism in wasps, that of TAYLOR (1939). TAYLOR observed a case

of nest usurpation of the vespine species Vespula vidua by l. squamosa , then considered closely

related. He then suggested a sequence of behavioral changes from free living to mquilme. The

scenario consisted of four stages: (1) Intraspecific, facultative, temporary parasitism, U)

Interspecific, facultative, temporary parasitism, (3) Interspecific, obligate, temporary parasitism,

(4) Interspecific, obligate, permanent parasitism. .... -• .

Intraspecific nest usurpation thus evolved into inquiline behavior, with the loss of a worker

force produced by the usurping queen. The existence of intraspecific nest usurpation was well

known in vespines (JANET, 1903), as were inquilines (e.g WEYRAUCH 1937), and Taylors

scenario became generally accepted (e.g. Wilson, 1971; Matthews, 1982; Greene, 199').The

applicability of this hypothesis to polistine social parasites has been questioned by Carpe t

138

J. M. CARPENTER : EVOLUTION OF SOCIAL PARASITISM IN POLISTES

al. (1993) and CHOUDHARY et al (1994), who observed that whereas the first stage in Taylor's

scenario was common in paper wasps, the second stage was rarely reported, and the third stage

is unknown (see review in Cervo & Dani, 1996). Nevertheless, the general notion of evolution

of usurpation into inquilinism was accepted.

Recent hypotheses

The recent increase in knowledge of the behavioral ecology of the inquilines has been

accompanied by novel hypotheses on the evolution of features of their biology, some newly

reported. Notable examples discussed by Cervo & Dani (1996) include observations on the

distribution of parasites and length ot the colony cycle in one host, timing of usurpation by the

parasite, the tactics employed by the parasite in dominating the host queen, and the predatory

behavior of atrimandihularis. These ideas are briefly summarized here.

The Florence group has shown that inquilines are moderately abundant at the foot of

mountain ranges. The hosts nest mostly at low elevations, but biglumis nests high in the

mountains (800-2000+ m in Italy; see CERVO et al., 1990b). Obligate parasitism is suggested to

have evolved from such a high altitude species (Lorenzi & Turillazzi, 1986), because the

colony cycle is short (four months, vs. six in the low altitude hosts), which is correlated with a

high frequency of intraspecific usurpation. Synchronization of colony cycle, resulting in

availability of suitable host nests (WciSLO, 1987), may also explain the limitation of inquiline

behavior to temperate regions. Migratory behavior (between lowlands and mountain tops in both

inquilines and hosts in Italy) may be related to the origin of obligate parasitism, whether through

decreased kinship (CERVO & Dani, 1996) or through reduction in population size leading to

enhanced parasitic tactics (West-Eberhard, 1996).

Local nesting environment may also influence timing of invasion by the inquiline. Colonies

at higher altitudes are invaded earlier in the colony cycle, in the middle of the period before

worker emergence (pre-emergence phase), while those in the lowlands may be invaded early in

the period after workers have begun to emerge (post-emergence phase). Inquilines tend to prefer

larger nests in more advanced stages of development among available nests (Cervo et al. , 1993).

Early invasion by atrimandihularis in biglumis nests may be an adaptation to the shortened

colony cycle of the host, because usurpation while workers are emerging would entail delay in

production of inquiline offspring, jeopardizing reproductive success at high altitudes (CERVO et

a/., 1990c).

The inquilines differ in tactics employed during usurpation. In sulcifer , aggressive fighting

generally leads to the expulsion or death of the host queen (Scheven, 1958; DiSTEFANO, 1969;

Turillazzi et al, 1990). Aggressive tactics, when invading hosts at low altitudes, may occur

because the inquiline can afford to dispose of the host queen, and retain only individuals that

contribute to the worker force (Cervo et al., 1990b). The tactics of semenowi are also usually

aggressive (Scheven, 1958; Cervo et al, 1990b; Mead, 1991; Zacchi et al, 1996), but may

be passive, with the host queen remaining on the nest (DEMOLIN & MARTEN, 1980). The tactics

of atrimandihularis are variable. Initially it is passive, temporarily submissive when invading

biglumis (CERVO et al, 1990a), and the host queen of biglumis remains on the nest. When

invading gallicus nests the host queen is expelled (Cervo et al, 1992). But when invading

colonies of biglumis later in the season atrimandihularis employs violent, fighting tactics

(Scheven, 1958). It also is more aggressive on the secondary nests that serve as food supply

Source: MNHN, Paris

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

139

than on the primary nest (nursery nest) where brood is reared (Cervo et al. , 1990a). The tactical

flexibility of atrimandibularis is thus correlated with characteristics of the invaded nest, such as

number of foundresses present, length of colony cycle, and the point in the colony cycle where

invasion occurs (CERVO el al, 1990b; CERVO & DANI, 1996). The passive tactics of this

inquiline may be considered unexpected in a generalist (i.e., with several hosts; FISHER, 1984),

but may be explained if biglumis is the original host of atrimandibularis, for which

atrimandibularis has evolved specialized tactics (Cervo & Dani, 1996). Cohabitation of the

inquiline and host queen may indicate an advanced form of parasitism, for example involving

chemical control, or it may be a necessity if the inquiline is unable to inhibit ovarian development

of host workers (Cervo & LORENZI, 1994), and so would be a less advanced type of parasitism.

The outstanding feature of the behavior of atrimandibularis is the ability to dominate more

than one colony simultaneously (CERVO et al., 1990c). Females of the other two species, once

successfully established on a host nest, remain there, and depend entirely on the host workers to

rear the parasite brood. Females of atrimandibularis engage in extensive extra-colonial activity,

during which they usurp nests of the same host species, from which larvae and pupae are taken

to the primary (nursery) nest and fed to the brood. This behavior occurs with either host species,

and CERVO & Dani (1996) wonder whether it evolved originally on biglumis nests in response to

the short colonial cycle of that species, due to a necessity for collaborating with host to increase

fitness, or whether the behavior evolved independently of ecological conditions. This predatory

behavior may represent a different pathway to obligate parasitism, for example as a form of

cuckoo behavior, or it may be a secondary development, for example in response to reduced

colony productivity in hosts (CARPENTER et at., 1993).

Cladistic tests

Answers to questions such as those outlined in the preceding section require a cladistic

context. The justification and a general framework for the use of phylogenetic information in

evolutionary biology have been clearly stated by Grandcolas et al. (1994). These authors

outlined the correspondence between four types of phylogenetic patterns and the evolutionary

processes that can be tested with these patterns. All are relevant to paper wasp inquilines, to

greater or lesser degree, as will be seen.

The first correspondence concerns adaptation, which is tested by the phylogenetic pattern

of polarity. That determining the direction of character change (polarity) is necessary to test

whether a feature may be an adaptation is something that has long been understood by cladists

(HENNIG, 1966; EldrEDGF, & CRACRAFT, 1980). As formulated by CODDINGTON (1988, 1990),

adaptation is apomorphic (derived) function, therefore the change from the primitive to the

derived condition must be established. Direction of change is established by cladistic character

optimization, or mapping onto a cladogram. I have applied optimization to the question of

adaptation in various behavioral features in social wasps before (CARPENTER, 1987,1988a;

WENZEL & CARPENTER, 1994). In the present case, for example, the question whether the

predatory behavior of atrimandibularis represents a novel pathway to inquilmism, or is

secondary, is potentially answered by optimization showing the behavior to be ancestral, or

derived. . , , , . ,

The second correspondence concerns convergence, which is tested by the phylogenetic

pattern of homology and homoplasy. Again, the pattern is established by optimization. Features

140

J. M. CARPENTER : EVOLUTION OF SOCIAI. PARASITISM IN PGLISTES

shared by species and shown by optimization on a cladogram to be present in their common

ancestor are most parsimoniously inferred to be homologous, that is, to have been inherited from

their common ancestor (HENNIG, 1966). Convergence is demonstrated by homoplasy, that is,

multiple independent occurrences of a feature on a cladogram. A pertinent example is inquiline

behavior itself: is it homologous (CARPENTER el al., 1993; CHOUDHARY el ai, 1994;

CARPENTER, 1996a) or has it evolved as many as three times (West-EberharD, 1996)? If the

most parsimonious optimization shows a single origin for this feature, arguments that it has

evolved more than once are ad hoc (Farris, 1983), because there is then no positive evidence

for multiple origins. Specifically, the claim that a behavior is “labile” and so prone to

convergence is contradicted by showing that only a single origin is necessary to explain the

evolution of that behavior.

The third correspondence is between evolutionary causality and relative phylogenetic

appearance. Relations among features are often the object of study in comparative biology. The

relative positions among two or more features shown by optimization on a cladogram may allow

test of a causal relation. That is, the “time lag” (order of appearance) between origins of features

may support or reject a suggested evolutionary progression based on the association of those

features. I have previously applied this approach to testing a complex evolutionary scenario

(CARPENTER, 1989, 1991, 1992). West-Eberhard's (1978) model for the evolution of social

behavior in wasps was tested by simultaneously optimizing the different behavioral features onto

cladograms for social wasps. The relations among these features matched some of the stages in

West-Eberhard's model, and did not correspond to others. In the case of the evolution of

inquilines, a transition from intra- to interspecific usurpation and then obligate parasitism would

correspond to part of Taylor's (1939) scenario.

The fourth correspondence is between adaptive radiation and differential cladogenesis. A

feature suggested to promote diversification may be optimized onto a cladogram, and the relative

diversity of sister-groups compared. If the feature in question is ancestral to the larger of two

sister-groups, diversification occurred after the origin of the feature, according with the

suggestion of adaptive radiation. In the case of social parasites, the question is whether inquiline

behavior is associated with increased speciation.

All these questions on the evolution of social parasitism may thus be approached by

cladistic optimization. What is required is a cladogram for the taxa in question, and knowledge of

the distribution of behavioral features. This raises however the question as to the proper

treatment of these features. Specifically, should the behavioral data be used during construction

of the cladogram, or should they be optimized onto a cladogram constructed independently?

That is, would inclusion of these features during cladistic analysis lead to bias or circularity

(Brooks & McLennan, 1991)? Kluge & Wolf (1993) have argued strongly that features to be

interpreted phylogenetically should be used as evidence when inferring phylogeny, and behavioral

and ecological features have indeed been treated successfully as characters, that is, as evidence of

phylogenetic relationships (reviews in WENZEL, 1992; MILLER & WENZEL, 1995). DELEPORTE

(1993) has pointed out that circularity is avoided as long as the cladogram is independent of the

evolutionary hypothesis to be tested, not of the characters used. That is, the question is not

choice of characters, rather it is the rationale that has been used to code the characters. Character

polarity determined by the cladistic outgroup criterion is independent of hypotheses of direction

of change according to an evolutionary model

Source: MNHN. Paris

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

141

But some features are not typically treated as characters. As MICKEVICH & WELLER (1990:

139) put it: “Certain features of organisms are influenced by a large environmental component.

The features influenced by environmental factors provide doubtful evidence for phylogenetic

relationships”. MICKEVICH & WELLER (1990), DELEPORTE (1993) and GRANDCOLAS el al.

(1994) referred to such features as “attributes” and distinguished them from characters.

Attributes are to be interpreted by optimization, rather than used in constructing cladograms.

Grandcolas (1993) considered attributes to be features for which a priori homology statements

are so problematic that interpretation with reference to a pre-existing phylogeny is preferable.

Deleporte (1993) and Grandcolas ei al. (1994) applied de Pinna's (1991) distinction

between primary and secondary homology, suggesting that cladogram construction proceeds

only with characters, whose primary (a priori) homology may be confidently assessed, while

attributes be interpreted, with homology assessed by optimization (secondary homology).

However, the distinction between primary and secondary homology should not be maintained

dogmatically, because the process of reciprocal illumination (“checking, correcting and

rechecking,” Hennig, 1966) is an integral part of cladistics, and the critical test of homology is

congruence with other characters. I suggest that logical justification for excluding some features

from cladogram constaiction comes in the distinction between “traits” and characters made by

Nixon & WHEELER (1990: 217). These authors defined traits as “attributes that are not

universally distributed among comparable individuals within a terminal lineage " and characters as

“found in all comparable individuals in a terminal lineage”. In this terminology, traits are features

that are variably distributed within any grouping (population, species or higher taxon) that is

phylogenetically unresolved internally. So for example, features that vary within the genus

Polistes, such as male clypeal ridges, would be considered traits when the genus Polistes is

viewed a single terminal lineage. This same feature might diagnose a monophyletic group, and

therefore be viewed as a character, if analysis of species within the genus is undertaken. Variable

features within populations do not meet the constancy criterion for phylogenetically informative

characters. Species are the terminal lineages that are phylogenetically unresolved by definition,

because they consist of populations linked by tokogenetic (birth) relationships, to which cladistic

analysis is not applicable. Features variable within species are therefore traits by definition. I raits

only become phylogenetically informative when they become fixed in comparable semaphoronts

(Nixon & Wheeler, 1990; Davis & Nixon, 1992), which at the level of species occurs by

extinction of plesiomorphic states, that is, at speciation (Nixon & WHEELER, 1992). Features

variable within species are precisely those for which a priori homology assessment is (by

definition) problematic, and such traits should not be used to infer phylogenetic relationships.

To the extent, then, that the behavioral features associated with social parasitism in paper

wasps are variable within species, they are best treated as traits. Evolutionary interpretation may

be made by optimization on a pre-existing cladogram. Methodologically, the approach taken here

will treat all the behavioral features as traits. It will be seen, however, that there are reasons for

considering some of these features to be phylogenetically informative characters.

MATERIALS AND METHODS

Taxonomy

Some discussion of taxonomy is first warranted. The nomenclatural history of the European species of Polistes is quite

tangled (Table 2). Nine species are currently recognized (see Carpenter, 1996b), but four have been described within the

past 100 years, and five have gone under more than one name in this century. The type species ol the genus, gallicus, was

142

J. M. CARPENTER : EVOLUTION OF SOCIAL P.ARjiSITISM IN POLISTES

misidentified in the revision by Kohl (1898), and this was followed by other authors until Day (1979). As a result, the older

behavioral literature used the name gallicus (or gallica) for what is now known as dominulus, and foederala for what is now'

known as gallicus, including the landmark papers of Pardi (e.g. 1942), which first demonstrated dominance hierarchies in

social insects. Numerous subspecies have also been described, but none arc more than minor color variants, which do not

deserve taxonomic recognition (Carpenter, 1996b, and see MacLean et al ., 1978; Gusenleitner, 1985; and below).

I his nomenclatural instability has had its counterpart in the higher-level taxonomy of these species (Carpenter,

1996a). The distinctiveness of the social parasites was recognized on the basis of morphology before their behavior was

known (Zimmermann, 1930). Discovery of social parasitism led to the generic separation of these three species - under two

different names, first, but invalidly, as Pseudopolistes (Weyrauch, 1937) and then as Sulcopolistes (first as a subgenus,

Bluthgen, 1938; then as a genus, BlOthgen, 1943). The latter name was generally used until I (Carpenter, 1990, 1991,

1996a; van der Vecht & Carpenter, 1990; Carpenter el al., 1993) synonymized it with Polistes, on the grounds that

Table 2. — Taxonomic history of European Polistes species.

Author

Currently recognized species

biglumis

dominulus

nimphus

gallicus

associus

Saussure (1853)

Kohl (1898)

biglumis

dubia

gallica

opinabilis

gallica

foederata

associa

Zimmermann (1930)

dubia

gallica

opinabilis

foederata

chinensis

Weyrauch (1937)

dubia

gallica

opinabilis

foederata

chinensis

Bluthgen (1938)

kohli

gallicus

nimpha

foederatus

associa

associus

Weyrauch (1938)

kohli

gallica

opinabilis

foederata.

associa

Weyrauch (1939)

kohli

gallica

nympha

omissa

foederata ,

associa

Bluthgen (1943)

bimaculatus

gallicus

nimpha

omissa

foederatus ,

associus

Bluthgen (1955)

Day (1979)

Gusenleitner (1985)

biglumis

bimaculatus

dominulus

omissus

gallicus

Author

Currently recognized species

bischoffi

semenowi

sulcifer

atrimandibularis

Saussure (1853)

Kohl (1898)

semenowi

Zimmermann (1930)

semenowi

sulcifer

atrimandibularis

Weyrauch (1937)

bischoffi

semenowi

sulcifer

atrimandibularis

Bluthgen (1938)

semenowi

sulcifer

Weyrauch (1938)

bischoffi

semenowi

sulcifer

atrimandibularis

Weyrauch (1939)

bischoffi

semenovi

sulcifer

atrimandibularis

Bluthgen (1943)

bischoffi

semenowi

sulcifer

atrimandibularis

recognition ol Sulcopolistes rendered Polistes paraphyletic. Other generic ( Polistula : Weyrauch, 1938) and subgenenc

(Leptopohstes : BlOthgen, 1943) names have been proposed for the remaining European species, although they have not

always been accepted (Richards, 1973). The misidentification of the type species of Polistes means that these other names

are synonyms m any event. All of the European species, including the social parasites, are now placed in the subgenus Polistes

Source:

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

143

sensu stricto (Carpenter, 1996a, 1996b). Polistes is the sole member of the tribe Polistini (Carpenter, 1993), which is the

sister-group of the other Polistinae (Carpenter, 1991, 1993).

Morphological characters

Morphological characters for the European species of Polistes, and two outgroup species, are presented in Tables 3-4.

Morphological terminology is as in Carpenter (1996a). All species were examined, including dissection of male specimens

for study of genitalia. The literature was surveyed for characters to be examined, in particular keys, both published (e.g.

Guiglia, 1972) and unpublished (Starr & Luchetti, 1993). These keys, however, are largely based on color characters,

which may w'ork well for identification in a limited part of a species' range, but generally show considerable variation over the

entire range of widespread species. That was found to be true for the species studied here, particularly w hen material from,

e.g.. Western Europe was compared to material from Scandinavia or Turkey. Color variation was therefore concluded to be

microenvironmentally induced (see MacLean el al. , 1978), and w r as not included. Some of the morphological characters

discussed in the literature were also found to be more continuously variable than implied by their inclusion in keys (for

example, the characters used to separate foederatus and omissus . both now' considered synonyms). The character states listed

in Table 4 are those that could be consistently distinguished. Additivity of multistate characters w'as determined from

observed nested similarity.

Tables 3-4 also include characters establishing monophyly of the ingroup, namely those establishing monophyly of the

subgenus Polistes sensu stricto relative to the outgroups, both of which are species in the New World subgenus

Table 3. — Morphological characters for European Polistes species, and two outgroups. Multistate characters are treated as

additive except for character 18. See Table 4 for Matrix

1. Male antennae: tapered (0); coiled (1). This is a synapomorphv for the subgenus Polistes sensu stricto in

Carpenter (1996a).

2. Male antennal apex: rounded (0); pointed (1). A number of other distinctions in shape of the terminal article of

the male antenna have been made since the time of Kohl (1898), but do not appear to be tenable.

3. Scape: cylindrical (0); dorsobasally flattened (1).

4. Male interantennal ridge: raised (0); grooved (1).

5. Clypeal apex: convex (0); angular (1); broadly depressed (2). Depression of the clypeal apex diagnoses the

inquilines, and is variable among the species, being more extreme in sulcifer.

6. Male clypeal rim: smooth (0); angulate rim (1). Interpretation of this character is complicated: it appears to be

derived within the genus Polistes as a whole, in the European species, but then appears to have been lost in the

group of species related to gallicus (see Fig. 3).

7. Male clypeal ridges: absent (0); present (1); extending to clypeal apex (2). Hie angulate, black rimmed margin

of the clypeus seems to be an exaggeration of slight swellings commonly seen in males of the subgenus Polistes

sensu stricto, and fully developed ridges are seen in some ol the non-European species.

8. Male clypeal punctation: weak (0); macropunctures (1).

9. Male clypeal proportions: width > length to width = length (0); length > width (1). As the coding indicates, this

character shows some continuous variation, which does not seem to lend itself to further partitioning.

10. Malar space: gena tapering (0); gena quadrate (1). The enlarged malar space is diagnostic of the inquilines.

11. Mandible: smooth (0); shallow' groove (1); ridges pronounced (2); deeply grooved (3). Excavation of the external

surface of the mandible is diagnostic of the inquilines, and is variable among the species, showing a morphocline

in development. The groove is shallow' in atrimandibularis, and semenowi and sulcifer are more similar to one

another in having more perpendicular ridges, which are greatly exaggerated in sulcifer.

12. Male occiput: convex (0); straight (1). Temples convergent backwards is supposed to diagnose the species

formerly placed in Leptopolistes (viz., associus, bischoffi and gallicus non auct.) - but is found in non-European

species of the subgenus Polistes sensu stricto.

13. Mesepisternal punctation: fine (0); clathrate (1). This is a synapomorphy for the subgenus Polistes sensu

stricto in Carpenter (1996a).

14. Epicnemial carina: absent (0); present (1). This is a synapomorphy for the subgenus Polistes sensu stncto in

Carpenter (1996a). However, it is reduced to traces in bischoffi.

15. Scutal hairs: short (0); elongate, much longer than an ocellus diameter (1). This character appears to vary, but

some of this variation is evidently due to specimen wear

16. Parameral spine: straight (0), lobed (1).

1 7. Aedeagal teeth: Fme (0); robust (1).

18. Aedeagus medial lobes: small, sharp (0); large (1); square (2); pointed (3).

144

J. M. CARPENTER : EVOLUTION OF SOCIAL PARASITISM IN POLISTES

Table 4. — Morphological characters for European Polistes species, and two outgroups. Multistate characters are treated as

additive except for character 18.

111111111

Taxon 123456789012345678

exclamans

dorsalis

biglumis

dominulus

nimphus

gallicus

sulcifer

atrimandibularis

semenowi

associus

bischoffi

000000000000000111

000000000000000000

101101000000111111

111101010000110111

101101100000110111

101100101001110113

101121000130110112

101111010110110111

101111000120110111

101100201001110111

101100101001101111

Aphanilopterus , sister-group of Polistes sensu stricto (Carpenter, 1996a). The two outgroup species included, dorsalis and

exclamans , were selected because they were used in both the molecular analyses (Carpenter et al ., 1993; Choudhary et al.,

1994).

Cladistic Procedures

Cladistic analysis (Hennig, 1966) was implemented with the computer program Nona (Goloboff, 1996a). As pointed

out elsewhere (Coddington & Scharff, 1994; Carpenter, 1996a), Nona implements a more stringent requirement for

cladogram support than other available programs: cladograms are only reported if every branch is supported by all possible

optimizations of at least one character. Programs such as Hennig86 (Farris, 1988) report cladograms with branches supported

only by one of several possible optimizations for at least one character. Such optimizations can lead to the program reporting

cladograms that are not in fact supported by the data, with branches supported by optimizations that cannot simultaneously

coexist with other branches (examples are given in Lorenzen & Sieg, 1991; Coddington & Scharff, 1994; Wilkinson,

1995; Carpenter, 1996), even without missing values, which can also produce this misleading result (Platnick*/ a/., 1991).

Coddington & Scharff (1994) argued that branches supported only under some optimizations are desirable, but such

“semistrict” support is at best ambiguous, if not misleading (Nixon & Carpenter, 1996b).

The Nona program's implementation of “strict” support (Nixon & Carpenter, 1996b) is incomplete, because the

program does not optimize on multi furcations. Hence, it does not necessarily collapse all ambiguously supported branches.

Several methods of collapsing such branches may be implemented with current programs (Nixon & Carpenter, 1996b); with

Nona, use of the “ksv" command to save cladograms in collapsed form, reading them back into Nona, and issuing the “best

command will filter out semistrict support. That method is employed here. Output from Hennig86 is also reported, for

comparison. For both programs, exact calculations were made, using either the “inswap” command of Nona or the “ie'

command of Hennig86.

Character weighting was employed as a check of the reliability of the results, both successive weighting as

implemented in Hennig86, and implied weighting as implemented in the program Piwe (Goloboff, 1996b). A posteriori ,

recursive character weighting checks the self-consistency of results: a cladogram based on reliable characters should imply

weights that imply the same cladogram (see Carpenter, 1988b, 1994; Carpenter et al., 1993).

In the simultaneous analyses of the morphological characters, allozymes and mtDNA sequences, the allozyme data

were taken from tables 2-4 of Carpenter et al. (1993), while the mtDNA data of Choudhary et al. (1994) were provided by

J. E. Strassmann. Choudhary et ai. (1994) reported 79 polymorphic sites, of which 55 were potentially informative, out of

386 sites sequenced. Their aligned sequences were converted to files for analysis by Nona and Hennig86 by the program

Malign (Wheeler & Gladstein, 1995); due to differences in interpretation of ambiguity codes, this resulted in 93

polymorphic sites (of which 43 were informative). Tins difference was irrelevant to the results, as analysis produced the same

Source: MNHN, Paris

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

145

two cladograms reported by Choudhary et al. (1994). The program Dada (Nixon, 1995a) was used to calculate the

incongruence length ditTerence (Farris et al. , 1994) among the character sets, and to determine whether these values were

large, by performing the significance test of Farris et al. (1994). For the tests, 100 iterations were made using Hennig86 for

cladogram calculations on the random matrix partitions.

Optimizations of the behavioral traits listed in the following section were calculated with the program Clados (Nixon,

1995b), which was also used to print results. The "allstates” command w'as used to check all possible optimizations at each

node of the cladograms.

Behavioral Traits

Behavioral traits pertinent to social parasitism are listed in Table 5. These traits or attributes were compared among

social parasites and their hosts in the discussions of the evolution of social parasitism by Cervo et al. (1990b) and Cervo &

Dani (1996). As the scorings in Table 6 show, all of the variables are variable within species, aside from colony cycle length

(which is known to vary intraspecifically; Yamane, 1996). The questions that I will attempt to answer by optimization are

stated for each trait below'.

Table 5. — Behavioral traits for European Polistes species, related to social parasitism. Multistate trait 4 is treated as

nonadditive. See Table 6 for Matrix.

1. Foundation: haplometrosis (0); pleometrosis (1).

2. Cycle length: long (0); short (1).

3. Usurpation: intraspecific (0); interspecific (1).

4. Inquilinism: absent (0); parasitism (1); predation (2).

5. Timing: pre-emergence (0); post-emergence (1).

6. Usurpation tactics: aggressive (0); passive (1).

Table 6. — Matrix of behavioral traits for European Polistes species, related to social parasitism. Multistate trait 4 is treated

as nonadditive. A question mark denotes an unknown state, w'hile a dash denotes an inapplicable trait. A asterisk

denotes a polymorphism showing all applicable states; a dollar sign denotes a subset polymorphism (1,2 for

athmandibularis). See Table 5 for list of traits.

Taxon

123456

exclamans

*00000

dorsalis

*0?0 —

biglumis

010000

dominulus

10*000

nimphus

10*000

gallicus

000000

sulcifer

—11*0

atrimandibularis

—1$01

semenowi

— 11**

associus

???0 —

bischoffi

???0—

Colony foundation. Whether exclusively haplometrotic or also pleometrotic. The relation ot this to origin of obligate

parasitism is of interest (Buschinger, 1986, 1990; Carpenter et al. , 1993). As noted in Cervo & Dani (1996). \vhi e

intraspecific usurpation occurs both in colonies with nest foundation by a single female (haplometrosis) and with multiple

foundresses (pleometrosis). usurpation is less successful in pleometrotic colonies. Scorings for the outgroups, which are

polymorphic, are drawn from the following references: for dorsalis, Spieth (1948, cited asfuscatus hunter , i), and Strassmann

( pers. com.); for exclamans , Strassmann (1981). Note that even biglumis exhibits pleometrosis occasionally (Lorenzi &

146

J. M. CARPENTER : EVOLUTION OF SOCIAL PARASITISM IN POLISTES

Turii.lazzi, 1986), although that is not scored here. The question is: did inquiline behavior originate in haplometrotic or

pleometrotic ancestors?

Colony cycle length. Whether long or short. Factors influencing the extensive variation in this trait were reviewed by

Yamane (1996). Is a short colony cycle derived, the minimal requirement for interpretation as an adaptation?

Usurpation. Whether it is intraspecific or interspecific. See Cervo & Dani (1996: table 5.1), for a list of Polistes

species in which intraspecific usurpation has been reported. They also reported (Cervo & Dani, 1996: 104) observing two

cases ot interspecific usurpation in dominulus , and Cervo (pers. com.) has recently observed the phenomenon in nimphus.

These two species are therefore scored as polymorphic. Is interspecific usurpation derived from intraspecific usurpation?

Inquilinism. Whether it is absent or present, and whether it is accompanied by predation. Unlike the other behavioral

features discussed here, inquiline behavior as such does not show intraspecific variation. It is constant, and so may be treated

as a character. West-Eberhard (1996) nevertheless argued that it may have arisen in all three socially parasitic species

independently, whether they form a monophyletic group or not. That is ad hoc, as pointed out above. But whether or not the

predatory behavior of athmandibularis is primitive or derived is a question of interest, and that behavior is found within one

species, which also exhibits parasitic behavior like the other two inquilines. The feature is therefore treated as a trait,

polymorphic lor both parasitism and predation in atrimandibularis. What is the association between origin of inquilinism and

transitions in usurpation?

Liming of invasion. Whether pre-emergence or post-emergence. Is the early timing of invasion by atrimandibularis

derived, the minimal requirement for interpretation as an adaptation?

Usurpation tactics. Whether aggressive or initially passive. The scoring includes polymorphism within semenowi ,

which in one case has been observed to show passive tactics (Demolin & Martin, 1980). Are the initially submissive tactics

of atrimandibularis derived, the minimal requirement for interpretation as an adaptation?

RESULTS

Morphology

Analysis of the data in Tables 3-4 with Nona (using “ms 8”) resulted in two cladograms;

with Hennig86, 12 cladograms were reported. The length is 28, the consistency index is 0.85 and

retention index is 0.84 (see Farris, 1989, for definition of the indices). The consensus tree for

either set of cladograms is shown in Fig. 3; this tree shows the groups in common to all of the

cladograms (such consensus trees are also referred to as “Nelson” or “strict”). Implied

weighting, using the default weighting function of Piwe, resulted in the same two cladograms as

reported by Nona. Successive weighting on the 12 cladograms reported by Hennig86 resulted in

a report of six cladograms; their consensus is also Fig. 3.

The morphological characters do not completely resolve the interrelationships among the

European species, as is the case with the two published molecular data sets. However, the

morphological data do resolve interrelationships among the three socially parasitic species, unlike

the molecular data sets. The morphological data set also allowed inclusion of all the European

species, again unlike the molecular data sets, which could not include associus and hischoffi.

This demonstrates that ga/licus and biglumis are in fact not closely related. These two species

were resolved as sister-groups by the mtDNA data and the independent allele coding of the

allozyme data. The morphological characters show that associus and hischoffi are more closely

related to ga/licus.

Simultaneous analyses

None of the three available data sets completely resolves the interrelationships of the

European species, but the combination of the three matrices does so. Simultaneous analysis of

combined data, which has been called “total evidence” (KLUGE, 1989) is currently controversial

in cladistics, with some authors arguing against combining data sets ( e.g . BULL el ai, 1993; DF.

Queiroz, 1993; Miyamoto & Fitch, 1995). All such arguments are without force, as discussed

in Nixon & CARPENTER (1996a). And a decisive argument justifies combining data sets

Source: MNHN, Paris

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

147

—exclamans

16 17 18

H—I—I— dorsalis

i>o i>o i>o

13 4 6

I I I 1 I «

l»l <»l <»l 0>l 0> I 0>

—E —biglumis

0>l

H—0 —dominulus

-nimphus

1*0 0>l 0>1 0>

HI —gallic us

H —associus

S ID II

I I I

o»i o>l n>i

0—0 —bischoffi

l >0 0*1

—C —atrimandibularis

II 18

H—I—I —sulcifer

- semen ow/

Fig. 3. — Consensus tree for cladograms reported after exact analysis of the character matrix in Table 4, by either Nona or

Hennig86. This is also the consensus for the six cladograms resulting from successive weighting by Hennig86.

Characters have been optimized by the default, “slow” transformation as implemented in Clados. Character numbers

are above the hashmarks; state changes are shown below, with the respective primitive and derived conditions

separated by a “sK Filled hashmarks denote unique origins, grayscaled hashmarks indicate convergent changes, and

open hashmarks are reversals.

and determining the most parsimonious solution for all the data seeks the cladogram that is best

supported and maximally explanatory for all the data. This approach maximizes information

content and corroboration of the resulting hypothesis.

The morphological data from Tables 3-4 were combined with the allozyme data from

Carpenter et at. (1993) and the mtDNA data from CHOUDHARY el al (1994). Three separate

analyses of the combined morphological and molecular data were undertaken, corresponding to

the three different coding schemes for the allozymes presented by CARPENTER el al. (1993. tables

2-4). The same cladogram resulted from analysis with Nona regardless of the allozyme coding

scheme employed; it is shown in Fig. 4. This cladogram also resulted from implied weighting

with Piwe. Hennig86 reported three cladograms regardless of which allozyme coding scheme

was employed; these cladograms were stable to successive weighting. The consensus of the three

cladograms is also Fig. 4. The three cladograms differed only in resolving relationships among

gallicus, associus and bischoffi , based entirely on the possible optimizations for the numerous

missing values found in the latter two species, hence three cladograms are not actually supported

by the data.

148

J. M. CARPENTER : EVOLUTION OF SOCIAL PARASITISM IN POLISTES

—exclamans

biglumis

- gal/icus

- associus

- bischoffi

- do min ulus

- nimphus

- a trimandibularis

- sulcifer

—semenowi

Fig. 4. — Cladogram resulting from simultaneous analysis of morphological and molecular data.

dorsal/s

For the independent alleles coding from CARPENTER et al. (1993: table 2), analysis of 220

characters resulted in Fig. 4 with a length of 271, consistency index 0.83 and retention index

0.72. For the multistate locus coding from CARPENTER et al. (1993: table 3), analysis of 138

characters resulted in Fig. 4 with a length of 222, consistency index 0.90 and retention index

0.81. For the minimum turnover coding from CARPENTER et al. (1993: table 4), analysis of 148

characters resulted in Fig. 4 with a length of 229, consistency index 0.87 and retention index

0.77.

I he results from incongruence length difference testing are as follows. For the independent

alleles coding, the incongruence length difference is 3, and the percentage of 100 iterations

reported by Dada as equaling or exceeding that value is 37. For the multistate locus coding, the

incongruence length difference is 1, and the percentage of 100 iterations reported by Dada as

equaling or exceeding that value is 83. For the minimum turnover coding, the incongruence

length difference is 2, and the percentage of 100 iterations reported by Dada as equaling or

exceeding that value is 75. The null hypothesis of congruence accordingly fails rejection by quite

large margins for any combination of morphology, mtDNA and allozyme coding.

Optimizations

Optimization of the behavioral traits is shown in Figs 5-14. Changes are shown by

hashmarks on the branches of the cladograms. All of the traits are mapped in Figs 5-6, which

show two different, equally parsimonious optimizations. In Fig. 5, the traits are mapped

Source . MNHN, Paris

PHYLOGENE TIC TESTS OF EVOLUTIONARY SCENARIOS

149

■exclamans

-dorsalis

H- biglumis

0>1

-gallicus

-associus

-bischoffi

-dominulus

4 - 1 —

0>1 0>1

nimphus

-1- atrimandibularis

0> 1

- sulcifer

-semenow/

5. — Cladogram showing optimization of behavioral traits related to social parasitism. Hie default, slow optimization, is

shown. Plotting conventions as in Fig. 3.

- exclamans

-dorsalis

I- biglumis

0>1

—gallicus

—associus

-bischoffi

- dominulus

-nimphus

0>1

-a trimandibularis

-sulcifer

-semenow/

Fig. 6. — Cladogram showing alternative, equally parsimonious “fast" optimization. Plotting conventions as in Fig. 3.

Source

150

J. M. CARPENTER : EVOLUTION OF SOCIAL P.4RASITISM IN POUSTES

according to the default optimization in Clados, “slow” transformation, which places changes

toward the tips of the cladogram. This procedure is similar to delayed transformation (or

deltran , e.g. SWOFFORD & MADDISON, 1987). In Fig. 6, the traits are mapped according to the

alternative, “fast transformation of Clados, which places changes toward the root of the

cladogram. This procedure is similar to accelerated transformation (or “acctran”, Swofford &

Maddison, 1987).

Optimization of the first trait, whether colony foundation is haplometrotic or pleometrotic,

is ambiguous, and its placement is one difference among the two figures. The reason for this

ambiguity is shown in Figs. 7-8, which show two possible placements for this trait. Because the

trait is polymorphic in both of the outgroups, either state may be assigned to the common

ancestor of the ingroup. Moreover, because the trait is inapplicable to the social parasites (which

do not have colony foundation behavior), the optimization procedures, which treat inapplicable

values as missing data, consider either state possible for them, and so the step in this trait could

even be assigned to the common ancestor of the social parasites and their sister-group,

domimlus + nimphus. The “squeeze missing data” optimization of Clados, which places changes

so that the fewest number of taxa with missing values are included above the step, may be used

to filter out such possibilities.

One other trait shows a similar difference in placement according to optimization:

usurpation, whether it is intraspecific or interspecific. Figs 10-11 show the alternative slow and

fast optimizations. Because the trait is polymorphic in dominulus and nimphus , either state can

be assigned to their common ancestor, and thus to the common ancestor of the social parasites

and their sister-group.

Mapping of the other four traits is the same regardless of the optimization procedure.

Optimizations of the individual traits are shown in Figs 9 and 12-14. Fig. 13 shows no changes in

timing of invasion. This trait is polymorphic in sulcifer and semenowi, therefore the only changes

are parsimoniously placed within terminal lineages. Such changes are not mapped by Clados.

DISCUSSION

The social parasites in Polistes form a monophyletic group. They are thus not most closely

related to any of their hosts, and Emery's Rule is rejected. Both the morphological characters

analyzed in this paper and mtDNA data (Choudhary et a!., 1994) establish monophyly

unequivocally, and combination of these data with allozyme data (CARPENTER et a /., 1993) lead

to the same result. Emery's Rule having been dispensed with, arguments that sympatric

speciation was involved in the origin of the inquilines from their hosts are rendered moot in paper

wasps.

This conclusion raises the issue of whether the inquiline behavior arose once, or several

times. The parsimonious optimization of this behavior (Fig. 12) indicates a single origin. WEST-

Eberhard (1996) argued for the possibility of multiple origins despite monophyly of the

inquilines. There is no evidence for this, but WEST-EBERHARD (1996: 315) stated: “The law of

parsimony requires attributing the common features of a monophyletic group to their common

ancestry only in the absence of biological evidence to the contrary. The evolutionary lability of

facultative traits, and their propensity to reversals within a lineage as well as to rapid and parallel

Source: MNHN. Paris

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

151

exc/amans= 0

dorsalis = 0

big/umis= 0

■ga//icus= 0

•associus = 0 <?

bischoffi- 0 <?

- do min ulus = 1

-nimphus = 1

atrimandibularis= 0 <?

■ sulcifer= 0 <?

semenowi = 0 <?

Colony foundation: haplometrotic or pleometrotic

7 — Cladogram showing slow optimization of colony foundation. Plotting conventions as in Fig. 3. States of each taxon

are shown next to the taxon name, separated by an “=” sign. For taxa with unknown or inapplicable values, the state

possible according to the optimization procedure is shown, with “< ?” written next to the state to indicate that the

value is actually missing.

- exc/amans = 1

- dorsalis = /

big/umis= 0

■ga//icus= 0

■associus= 0 <?

■bischoffi= 0 <?

■dominu/us= 1

- nimphus = /

- atrimandibularis= 1 <?

- sulcifer= 1 <?

- semenowi = / <?

Colony foundation: haplometrotic or pleometrotic

p IG 8 _ Cladogram showing fast optimization of colony loundation.

Source

152

J M. CARPENTER : EVOLUTION OF SOCIAL P.4RASITISM IN POLISTES

fixation in related species give reason at least to consider the possibility of multiple fixations of

obligate parasitism in Po/istes. Evolutionary lability of conditionally expressed traits means that it

may sometimes be impossible confidently to track character “fixation” points using cladistics

methods, because the character can come and go (change polarity) and rapidly become fixed

1994)” k 30 °^ t '° na * ^ e,ween the branching points of a cladogram (see also FRUMHOFF & Reeve

Several points may be made to counter this argument. West-Eberhard considered

mquiline behavior to be evolutionarily labile. It is not: the social parasites are fixed for this

feature; it does not vary in its expression within the species, nor is it found in other species. This

observation also indicates the weakness in the argument of Frumhoff & Reeve (1994) cited by

Wi si-Eberhard. Frumhoff & Reeve concocted a probabilistic model to show that inference

of ancestral character states by optimization is highly error-prone. Their model may be rejected

immediately as unrealistic (see general argument in Farris, 1983), but even if their approach is

accepted, Frumhoff & REEVE failed to realize that observation of fixation for a character in a

clade provides information on the evolutionary rate of change (SCHULTZ el a/., 1996), and

specifically against the conclusion that a character has undergone a large amount of change.

Frumhoff and Reeve's argument is thus generally irrelevant to accuracy of ancestral conditions

as inferred by optimization (SCHULTZe/ a/., 1996).

Because inquilinism is not evolutionarily labile, there is no reason to entertain the ad hoc

notion that it has arisen in parallel within a monophyletic group. Social parasitism indeed

evidently arose from intraspecific usurpation (Figs 5-6, and see below), which may be considered

a “phenotypic alternative” to independent nesting (West-Eberhard, 1996). Even so, inquiline

behavior became fixed at some point, and there is no necessity to postulate that event occurring

more than once. Inquilinism is in this view really a character, providing evidence that the species

showing the feature form a monophyletic group. This conclusion also applies to the

morphological characters of the social parasites. The depressed clypeal apex, quadrate malar

space and grooved mandible shared by the parasites are interpreted as synapomorphies in Figs. 3-

4 These characters might be dismissed as evidence of phylogenetic relationship because they are

considered to be adaptations to parasitism, involved in domination of the host during usurpation.

West-Eberhard (1996: 316) referred to these characters as “morphological accoutrements of

parasitism and suggests that in the inquilines these characters: “should not, of course, be taken

as evidence that obligatory parasitism occurred prior to their speciation since these

characteristics can be convergent (or parallel) developments”.

Whether these features arose as adaptations or not, they became fixed, constant in

distribution, restricted to the inquilines and occurring in no other species. These characters show

no geographic variation whatsoever, contrary to the prediction of WEST-EBERHARD (1996: 313).

There is no necessity for supposing this fixation to have occurred more than once because the

inquilines are a monophyletic group, as established by both morphology and molecular data (Fig

4) Moreover, two of the characters show transformation series. The depression of the clypeal

apex evidently evolved from slightly to broadly flattened (character 5 on Fig. 3), and the

mandibular groove evidently changed from shallow to having pronounced ridges, to being deep

Source: MNHN. Paris

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

153

- exc/amans = 0

- dorsalis = 0

- 1 - big/umis = 1

0>l

- - ga/licus = 0

- associus = 0 < ?

- bischoffi= 0 <?

- dominu/us= 0

- nimphus = 0

- atrimandibularis- 0 <?

- sulcifer= 0 <?

- semenowi = 0 <?

Colony cycle length: long or short

Fig. 9. — Cladogram showing optimization of colony cycle length.

(character 11 on Fig. 3). These transformations occurred as the inquilines speciated, and indicate

that the common ancestor had the morphological accoutrements of parasitism. Therefore,

presumably, it also had inquiline behavior.

The optimizations in Figs. 5-6 accord with the central idea underlying Taylor's (1939)

scenario, but do not support the scenario as a whole. Interspecific usurpation evidently evolved

from intraspecific usurpation (Figs 10-11). Intraspecific usurpation in Polistes is facultative and

temporary (stage 1 in TAYLOR's scenario), and preceded the obligate and permanent usurpation

of the inquilines (stage 4 in the scenario). But is unclear whether facultative and temporary

interspecific usurpation preceded inquiline behavior. Temporary interspecific usurpation has been

reported as a facultative behavior extremely rarely, but does occur in the sister-group to the

social parasites (dominulus + nimphus). The optimization of this behavior is therefore

ambiguous: inquiline behavior could have evolved directly from intraspecific usurpation (Fig. )

or via an intervening stage of temporary interspecific usurpation (Fig. 11), which corresponds to

stage 2 in the scenario.

In either case, the other stage in Taylor's scenario, which is obligate and temporal^

interspecific usurpation, does not correspond to the behavioral changes shown in Figs -6

Interspecific usurpation is either facultative and temporary, or obligate and permanent. Indeed,

temporary interspecific usurpation has not been observed as obligate behavior. West-Ebhriiard

(1996- 313) suggested “In Polistes temporary obligate social parasitism, in which the usurper

produces some worker offspring of her own, is expected to be rare or absent if [...] obligate

(interspecific) parasitism originates in extreme climates with short nesting seasons, and invasion

154

J. M. CARPENTER : EVOLUTION OF SOCIAL PARASITISM IN POLISTES

Usurpation: intraspecific or interspecific

Fig. 10. — Cladogram showing slow optimization of usurpation.

- exc/amans = 0

- dorsalis = 0 <?

- biglumis= 0

- - ga/licus = 0

- associus= 0 <?

- bischoffi= 0 <?

- dominulus = 1

- nimphus = 1

- 1 -

- atrimandibularis= 1

- sulci fer= 7

- semenowi = 1

Usurpation: intraspecific or interspecific

Fig. 11. — Cladogram showing fast optimization of usurpation.

Source: MNHN, Paris

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

155

occurs at about the time of first worker emergence [...] At that time temperate-zone Polistes

females are already beginning to lay reproductive-producing eggs [...] Usurpers in such a species

would soon produce reproductive offspring, not workers, and “temporary” parasitism may

seldom occur”. West-Eberhard (1996: 314) concluded: “Temporary parasitism is not a

necessary step in the transition from facultative to obligatory parasitism. Nor is facultative

interspecific parasitism expected to be common [...] it may occur only when usurpers are running

out of conspecific host colonies in a population where usurpation is the most frequently

productive option - a transient situation expected to change rapidly toward obligate parasitism in

the presence of suitable hosts”.

The third stage of Taylor's scenario is thus unnecessary (as is also in fact the second).

What answers to the other questions posed about behavioral traits may be provided by the

optimizations? Taking the traits in turn, whether the inquiline behavior originated in a

haplometrotic or pleometrotic ancestor cannot be answered: the optimization is ambiguous (Figs

7-8). Given the intraspecific variation in this trait, the question may indeed be unanswerable.

A short colony cycle is evidently derived in biglumis (Fig. 9), and so is a candidate for

being an adaptation. But whether this has anything to do with the evolution of inquiline behavior

is not at all clear. As plausible as may be the notion that inquilines arose from an ancestor with a

shortened cycle (Lore;nzi & TURILLAZZI, 1986; CERVO & Dani, 1996; WEST-EBERHARD,

1996), it is not evident whether that was indeed the condition of the primitive host. If host

species were treated as a trait and optimized on the cladogram, domimilus may be inferred to

have been the ancestral host for semenowi and sulcifer , but the ancestral host for inquilines as a

exc/amans = 0

dorsalis = 0

- biglumis = 0

- ga//icus= 0

- associus= 0

- bischoffi= 0

- dominu/us= 0

- nimphus = 0

- atrimandibu/aris =

t - sulcifer = 1

- semeno wi = 7

Inqui/inism: absent or parasitism, or with predation

Fig. 12 . — Cladogram showing optimization of inquilinism.

156

J. M. CARPENTER : EVOLUTION OF SOCIAL PARASITISM IN POLISTES

■exc/amans= 0

dorsalis = 0 <?

big/umis= 0

- ga//icus= 0

■assoc/us = 0 <?

■bischoffi = 0 <?

- dominu/us= 0

-nimphus = 0

-atrimandibularis= 0

- sulci fer= 0

-semenowi = 0

Timing of invasion: pre-emergence or post-emergence

Fig. 13. — Cladogram showing invariance of timing of invasion.

- exc/amans = 0

- dorsalis = 0 <?

- big/umis= 0

- - ga//icus= 0

- associus= 0 <?

_ _ bischoffi = 0 <?

- dominu/us= 0

- nimphus = 0

-1- atrimandibu/aris = /

0> I

- su/cifer= 0

- semenowi = 0

Usurpation tactics: aggressive or passive

Fig. 14. — Cladogram showing optimization of usurpation tactics.

Source: MNHN, Paris

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

157

whole could be dominulus , gallicus or biglumis. At least the possibility that the ancestral

inquiline had a host like biglumis is not excluded.

The predatory behavior shown by atrimandibularis is evidently derived from parasitism

(Fig. 12), occurring only within that species. It thus does not represent a different pathway to

obligate parasitism; the behavior is a secondary development. This does not answer the question

as to whether the behavior originated as an adaptation to the shortened colony cycle of its host

species biglumis (CERVO & DANI, 1996), but leaves the possibility open. However, if predatory

behavior is a specific adaptation to the host biglumis , that would not seem to accord very well

with the notion that biglumis represents the primitive host for the inquilines (CERVO & DANI,

1996), or that parasitism arose in such a species (WEST-EBERHARD, 1996). The adaptation is not

primitive in inquilines, it is derived within atrimandibularis.

The post-emergence timing of invasion shown by semenowi and sulcifer is evidently

derived from pre-emergence invasion, arising separately within each of those species (Fig. 13).

The pre-emergence timing of invasion shown by atrimandibularis is thus still a candidate for

being an adaptation to the shortened cycle of its host biglumis (CERVO et a/., 1990c) - but it is a

marginal candidate, being viable only if biglumis was the original host of the inquilines.

Finally, regarding the question of usurpation tactics, the passive tactics shown by

atrimandibularis are evidently derived (Fig. 14), from primitively aggressive tactics. Initially

passive behavior is thus specialized (CERVO & DANI, 1996). It seems a better candidate for an

advanced form of parasitism than a prerequisite for parasitism - but, again, the conclusion of

derived behavior does not fit very well with the notion that biglumis or something like it as the

original host of the inquiline lineage.

In summary, the cladistic approach to the evolution of social parasitism in paper wasps

provides decisive tests of the generalization known as Emery's Rule, and Taylor's scenario for

the origin of inquiline behavior. It provides answers to some of the questions posed on the

evolution of various features of parasitic behavior, and is ambiguous on others. In terms ot the

framework for the use of phylogenetic information in evolutionary study developed by

GRANDCOLAS et at. (1994), the present application illustrates all four of the phylogenetic

patterns corresponding to tests of evolutionary processes. Adaptation is a possible explanation

for features polarized as derived, such as the predatory behavior of atrimandibularis - although

comparative functional studies remain to be done. Convergence is an unnecessary explanation for

features optimized as derived once, like the origin of inquiline behavior. A causal connection is

corroborated by association between particular traits, for example interspecific usurpation that is

both permanent and obligate, showing no time lag in relative appearance. Various reasons may

be advanced for such a connection (see WEST-EBERHARD, 1996), although tests may be difficult

to formulate. And adaptive radiation, shown by differential cladogenesis, is a possible

consequence of the origin of inquiline behavior. The inquiline clade, with three species, is not

large, but is more diverse than its sister clade, dominulus + nimphus. Yet whether that difference

is construed as impressive or not, the taxonomic context is incomplete. The European species of

Polistes are not the only members of the subgenus Polistes sensu stricto (sensu CARPENTER,

1996a, 1996b). It is possible therefore that some of the African and Asian species of the

subgenus are closely related to the dominulus + nimphus clade, similar to the situation of close

relationship of associus and bischoffi to gallicus, which remained uninvestigated by the previous

cladistic analyses based on molecular data. Further study of the phylogenetic relationships among

158

J. M. CARPENTER : EVOLUTION OF SOCIAL PARASITISM IN POLISTES

the species of the subgenus is required to address this question. And this should be accompanied

by more extensive study of the behavioral ecology of these species. As GRANDCOLAS et at.

(1994: 671) concluded: “Finally, we submit the plea that more phylogenies are needed for

comparative studies. Taxonomies should not be used for want of something better. Fruitful

collaborative or integrated works should be carried out to achieve comparative studies”.

ACKNOWLEDGEMENTS

The work of the behavioral ecologists centered at the University of Florence is saluted. I especially thank Rita Cervo

tor discussion ot the behavior of the social parasites. I am grateful to Stefano Turillazzi for providing specimens of social

parasites, Hikmet Ozbek for specimens of Turkish Polities , and Fredrik Ronquist, Bert Gustafsson and Thomas G. T.

Jaenson for Swedish specimens. Stephanie B. Mindlin helped with the study of morphological characters. Joan F..

Strassmann provided an electronic version of the mtDNA matrix. Rita Cervo, Pierre Deleporte, Philippe Grandcolas and

Mary Jane West-Eberhard read the manuscript and made various suggestions for improvement. John Wenzel and Philippe

Grandcolas assisted with French translation. Finally, I thank Philippe Grandcolas for organizing the symposium

“Phylogenetic tests of evolutionary scenarios”, thereby providing the impetus to complete this work.

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Evolution of Feeding and Mating Behaviors

in the Empidoidea (Diptera : Eremoneura)

Christophe Daugeron

E.P. 90 CNRS. Laboratoire d'Entomologie. Museum national d'Histoire naturclle.

45. me BufTon. 75005 Paris. France

ABSTRACT

The phylogeny of the Empidoidea is discussed in relation to the works of Ulrich (1971), Chv ala (1983), Wiegmann et al.

(1993), Gumming et al. (1995) and Sinclair (1995). The clade [Dolichopodidae + Microphondae] + [Tricopezinae +

Brachystomatinae + Ceratomerinae] is the sister group of [Atelestidae + Hybotidae + Empididae]. The family Empididae is

assumed to be a monophyletic group on the basis of the presence of an endoskeletal pocket in line with the laterotergite

(Ulrich, 1971, 1994), however this character is independently derived in the Tricopezinae and Ceratomerinae. The phylogeny

is used to interpret the evolution of two ethological characters, feeding and swarming habits. Optimization of these attributes

on the cladogram corroborated the hypothesis that predation is ancestral in Empidoidea. Mating swarms are found to be a

specialized behavior for the subfamily Empidinae and non-homologous of swarms of some other empidoids. Ihese

optimizations and evolutionary pathways refute the traditional evolutionary models of swarming in the Empidoidea. Finally,

the hypothesis that swarming is an adaptation for the meeting of sexes is corroborated for the Empidinae.

RESUME

Evolution du regime alimentaire et du comportement reproducteur chez les Empidoidea (Diptera: Eremoneura)

La phylogenie des Empidoidea est discutee en relation avec les travaux d'ULRicH (1971), Chvala (1983), Wiegmann et al.

(1993) et Sinclair (1995). Le clade des [Dolichopodidae + Microphoridae] + [Tricopezinae + Brachystomatinae +

Ceratomerinae) est le groupe frere des [Atelestidae + Hybotidae + Empididae). Les Empididae sont supposes former un

groupe monophyletiquc sur la base de la presence dune poche endosquelettique se situant dans le prolongement du

laterotergite (Ulrich, 1971, 1994), cependant ce caractere est appani par convergence chez les Tricopezinae et les

Ceratomerinae. La phylogenie est utilisee pour interpreter 1'evolution de deux caracteres ethologiques, les comportements

reproducteurs et alimentaires. L'optimisation de ces attributs sur le cladogranune corrobore lTiypothese dune origine

ancestrale pour la predation chez les Empidoidea. La formation d'essaims de reproduction est un comportement specialise des

Empidinae qui n'est pas homologue avec les essaims formes par d'autres empidoides. Ces resultats relutent les modeles

traditionnels devolution des essaims chez les Empidoidea. Par conlre, l'hypoth£se d’une adaptation a la rencontre des sexes

pour la formation d'essaims est corroboree pour les Empidinae.

INTRODUCTION

Species of Empidoidea present a large range of feeding, swarming and reproductive

behaviors. Many studies of these ethological characters have been carried out and several

Daugeron, C., 1997. — Evolution of feeding and mating behaviors in the Empidoidea (Diptera Eremoneura). In:

Grandcoi.as, P. (ed ), The Origin of Biodiversity in bisects: Phylogenetic Tests of Evolutionary Scenarios. Mem. Mus. natn.

Hist. nat. 173 : 163-182. Pans ISBN : 2-85653-508-9.

164

C. DAUGERON : EVOLUTIONOEBEHAVIOR IN THEEMPIDOIDEA

evolutionary hypotheses have been proposed (Hamm, 1908, 1909, 1933; ELTRINGHAM, 1927;

Kessel, 1955; Downes, 1970; TREHEN, 1971; Cuvala, 1976) but never on a strict

phylogenetic basis. Nuptial gifts have been discussed by some recent authors (THORNHILL &

ALCOCK, 1983) but herein I propose to study two other attributes: feeding and swarming habits.

Predatory habits and mating swarms have always been hypothesized as primitive habits in

the Empidoidea (CHVALA, 1983), although mating swarms have only been observed in the

subfamily Empidinae. Other empidoids form swarms but mating behavior always takes place

outside them. This point of view is traditional and deep-rooted.

Recent progress in the phylogeny of the Empidoidea allows me to test traditional

hypotheses of this kind with respect to phylogenetic evidence. Evolutionary patterns of attributes

- feeding and swarming habits - are inferred by mapping them on the phylogeny. These inferred

patterns are compared afterwards to former evolutionary hypotheses.

MATERIALS AND METHODS

A character analysis (for thirteen taxa and fifteen characters) was performed on the families and subfamilies of

Empidoidea using the program Hennig86 (Farris, 1988), results were analyzed with dados, version 1.1 (Nixon, 1992). This

paper does not focus on the phylogenetic tree itself, characters are thus presented in the appendix 1. Using ‘4.6."’ (implicit

enumeration) algorithm, a tree was obtained with the length of 21 steps, the consistency index Cl = 0.80 and the retention

index RI = 0.90 (Fig 2).

The evolution ot attributes was inferred by optimization on phylogenetic trees, using Fitch parsimony (Fitch, 1971).

Suites ol attributes are coded and entered in the matrix and their optimization is viewed and analyzed by Hennig86 as non¬

additive, under the “xx function, without outgroup and using “ccode ]"' function. Polymorphism between species or genera or

within species in a terminal taxon is coded “?” Tree drawings were performed using Treeview (Page, 1996).

PHYLOGENETIC SYSTEMATICS

Historical

Among the Empidoidea (Fig. 1), five families were recognized by Chvala (1983);

Empididae, Hybotidae and Microphoridae (resulting of the division of the traditional family

Empididae), Atelestidae (including some genera originally classified in the Platypezidae and

Hybotinae) and Dolichopodidae. In the phylogeny which he proposed, the Empidoidea and

Cyclorrhapha form a monophyletic group but the Atelestidae are the sister group of the

Cyclorrhapha, thus the Empidoidea are paraphyletic. At the present time, the Empidoidea

(including the family Atelestidae) are recognized as a monophyletic taxon supported by four

synapomorphies (ClJMMlNG et a/., 1995) and sister group of the Cyclorrhapha, forming together

the clade Eremoneura supported by ten synapomorphies (MeAi .PINE, 1989; Sinclair, 1992;

CUMMING et al ., 1995).

WlEGMANN et al. (1993) proposed some phylogenetic hypotheses and focused on the

theories (epandrial and periandrial) of male genitalia evolution. Unfortunately, as SINCLAIR

(1995: 719) noted, WlEGMANN's hypotheses are poorly supported, several characters being

highly polymorphic and the others incorrectly scored.

Sinclair (1995) reduced the family Empididae (sensu Chvala) to four subfamilies,

Empidinae, Hemerodromiinae, Clinocerinae and Oreogetoninae. The Brachystomatinae,

Ceratomerinae and Tricopezinae (The subfamily Tricopezinae was newly defined by SINCLAIR,

1995, its monophyly is supported by the presence of a median apodeme in the female

Source: MNHN. Paris

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

165

Pig. 1. — Hemerodromia sp. (from French Guiana), female, habitus. Scale bar - 1 mm.

postabdomen) are hypothesized to be a monophyletic taxon, sister group ot [Dolichopodidae +

Microphoridae] on the basis of several characters of female postabdomen largely detailed by

Sinclair (1995: 718-719, characters 1, 2, 3 and 4; see also appendix 1, characters 11-14).

Characters

The works of ULRICH (1971), Chvala (1983), WlEGMANN et ai. (1993), CUMMING et a/.

(1995) and SINCLAIR (1995) have been re-analyzed to propose a matrix of 15 morphological

characters (Appendix 1). The principal subject ot this paper is not the phylogeny ot the

Empidoidea but the evolution of ethological characters, I refer readers to the original references

for more details about the morphological characters. Nevertheless, at this point it is pertinent to

comment of two of the characters.

Prokatepisternum fused with the hasisternite (Character 3). Primitively, the basisternite

(= prosternum), a sclerite located between the front coxae, is small and isolated, but in numerous

taxa of Diptera it is developed laterally and fused with the anterior ventral episternum

166

C. DAUGERON : EVOLUTION OFBEHA VIOR IN THE EMPIDOIDEA

Atclcstidac

Oreogetoninae (*)

Clinocerinae

Empidinae

Hcmerodromiinae

Ocydromiinae (*)

Hybotinae

Tachvdromiinae

Brachvstomatinac

Ceratomcrinac

Tricopezinae

Microphoridae

Dolichopodidae

Hg. 2. — Cladogram of the families and subfamilies of Empidoidea, according to data presented in appendix 1 and treated as

described in materials and methods. *: paraphvletic taxon.

(prokatepisternum) to form a precoxal bridge (Speight, 1969). This has been observed in the

Empidinae, Hemerodromiinae, Clinocerinae, Brachystomatinae, Ceratomerinae, some

Tricopezinae (at least Heterophlebus, Hyperperacera and He/eodromia), some Dolichopodidae

and some Tachydromiinae.

Presence of an endoskeletal ridge in mesanepimeron (Character 4). ULRICH (1971)

showed the existence of an endoskeletal ridge in mesanepimeron in some empidoids, forming a

characteristic complete or incomplete pocket in line with the laterotergite. It is curious that this

character has never been used or commented by other workers since 1971. A complete pocket

has been observed in the Oreogetoninae (ULRICH, 1994), Clinocerinae ( Wiedemannia ,

Dolichocephala, Ulrich, 1971), Hemerodromiinae (Chelipoda, ULRICH, 1971), Tricopezinae

( Tricopeza , Ruhistella, Ulrich, 1971, 1994) and Ceratomerinae (ULRICH, 1994), whereas an

incomplete pocket seems present in all species of the subfamily Empidinae, and some

Source: MNHN. Paris

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

167

Tricopezinae (at least Heterophlebus). Consequently this character has been used in the matrix

(Appendix 1) under 3 states and treated as non-additive.

Phytogeny: Empididae as a monophyletic group (Fig. 2)

The monophyly of the Empididae is supported by the presence of an endoskeletal ridge in

the mesanepimeron forming a complete pocket in line with the laterotergite even if this pocket is

secondarily reduced dorsally (Empidinae) or entirely lost in the more specialized

Hemerodromiinae like Chelifera where the lengthening of thorax has led to the loss of pleural

sutures. It is hypothesized that the presence of the pocket is a synapomorphy for the clade

[Oreogetoninae + Clinocerinae + Hemerodromiinae + Empidinae], A pocket of the same

structure and position existing in Tricopezinae and Ceratomerinae, it is provisionally supposed

that these two taxa are sister groups.

Within the clade [Atelestidae + Hybotidae + Empididae], supposed monophyletic on the

basis of the absence of acanthophorites in the female (SINCLAIR, 1995), only the Clinocerinae,

Hemerodromiinae and Empidinae (and also a few species of Tachydromiinae) possess a precoxal

bridge. Consequently, these three subfamilies form a monophyletic group within the Empididae.

A precoxal bridge has appeared independently once or several times in the clade [Dolichopodidae

+ Microphoridae + Ceratomerinae + Brachystomatinae + Tricopezinae],

THE ATTRIBUTES

Feeding habits

Most Empidoidea are predators, however some are also flower visitors (pollen or nectar

feeders). Table 1 shows the different feeding habits observed in the superfamily. Two subfamilies

Table 1. — Feeding habits in the Empidoidea. A question mark indicates an unknown state.

Taxa

Predators

Nectar or

pollen feeders

Atelestidae

Oreogetoninae

in flight

Clinocerinae

in flight

Empidinae

in flight

Hemerodromiinae

on solid substratum

Ocvdromiinae

in flight

Hybotinae

in flight

Tachvdromiinae

on solid substratum

Brachystomatinae

Ceratomerinae

Tricopezinae

Microphoridae

in flight

Dolichopodidae

in flight

168

C. DAUGERON : EVOLUTIONOFBEHA VIOR IN THE EMPIDOIDEA

of the Empididae (Clinocerinae and Hemerodromiinae) as well as two subfamilies of the

Hybotidae (Hybotinae and Tachydromiinae) may be considered as entirely predatory, the

remaining families and subfamilies are both predators and pollen or nectar feeders. The

Dolichopodidae are entirely predators apart from the genus Hercostomus of which species are

nectar feeders (Laurence, 1953). The Microphoridae (genus Microphorus) are generally

predators but also often found on flowers (Chvala, 1983) but we do not know if they are pollen

or nectar feeders. The Hybotidae genera Anthalia, Allanthalia and Euthyneura are pollen or

nectar feeders but one species (at least), Anthalia bulhosa, is known to feed on pollen (DOWNES

& SMITH, 1969), the remaining Hybotidae are entirely predators (CHVALA, 1983). The

Oreogetoninae genera Ileaphila and Anthepiscopus are pollen or nectar feeders whereas

Hormopeza species are predators (CHANDLER, 1972). The Empidinae are nectar feeders but

during the mating period males hunt other insects which are offered to females as a nuptial gift.

Three remarks are necessary, (1) males never feed preys which they have caught, (2) in the genus

Hi/ara, the gift can be a simple vegetal fragment not edible to the female (Trehen, 1965), (3)

species of this genus have rarely been observed outside the habitat (generally places with

presence of water: river, lake or simple puddle) where individuals hunt and mate, consequently

evidence of their feeding habits is lacking. The feeding habits of Tricopezinae, Ceratomerinae,

Brachystomatinae and Atelestidae are almost entirely unknown on account of the scarcity of their

species in the nature. CHVALA (1983) supposed that the Ceratomerinae are flower visitors

because their proboscis is elongated, but the presence of a morphological character is not

unequivocal evidence of the existence of a behavior.

Among the Empidoidea, it is possible to distinguish four chief classes, species entirely

predators (Hybotinae, Tachydromiinae, Clinocerinae and Hemerodromiinae), species entirely

flower visitors ( Hercostomus , Anthalia , Allanthalia and Euthyneura ), species both predators and

flower visitors {Microphorus) and the flower visiting species in which predation is only

performed by males and during the mating period (Empidinae). Among the predators, the hunting

can take place in flight (Dolichopodidae, Microphoridae, Hybotinae, Ocydromiinae,

Oreogetoninae, Clinocerinae and Empidinae) or on the ground (Tachydromiinae and

Hemerodromiinae).

Swarming habits

Swarming is a well known habit in many groups of Diptera (GRUHL, 1955; Me ALPINE &

Munroe, 1968; Downes, 1969; Chvala, 1990) especially in the Empidoidea. Indeed, 5 families

or subfamilies of empidoids display this behavior; the Microphoridae, Atelestidae, Ocydromiinae,

Oreogetoninae and Empidinae. The remaining Empidoidea have never been observed to form

swarms (Dolichopodidae, Hybotinae, Tachydromiinae, Clinocerinae and Hemerodromiinae) or

are insufficiently known (Brachystomatinae, Ceratomerinae and Tricopezinae).

GRUHL (1955) distinguished synhesmic swarming from synorchesic swarming. The first is

characterized by an unorganized mass of a large number of individuals resulting from mass

emergence, the second forms coherent units characterized by an ordered flight (often species-

specific) of several individuals termed true synorchesia. Gruhl also distinguished several

evolutionary steps leading to this true synorchesia, chiefly the prosynorchesium (a pursuit flight

of males from their perching places), the monorchesium (the hovering and dancing of isolated

individuals) and the polyorchesium (the rhythmic alternation of dancing-perching-dancing of a

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

169

few individuals). Among the Empidoidea, it seems that the Empidinae form the polyorchesium

swarms, whereas the other groups, especially Ocydromiinae, have generally observed in

monorchesium swarming (Chvala, 1983).

Swarming in the Empidoidea has always been linked to the meeting of sexes and thus to

the mating. In fact, as Chvala (1980) noted, it seems that this is characteristic of the Empidinae

only. Indeed, in this group, males are seen in swarms with prey that are offered to females just

before mating. Mating begins in the swarm and ends on a solid substratum. In the other

Empidoidea forming swarms, hunting or mating have never been observed in swarms.

It seems therefore that, both structurally and functionally, swarms formed by the Empidinae

are distinguishable from these of the Atelestidae, Microphoridae, Oreogetoninae and

Ocydromiinae. That is why in table 2 we consider 3 cases among the superfamily, groups of

which species never form swarms (no swarming activity), these for which swarming represents a

monorchesium and in which hunting or mating has not been observed (swarms without mating),

and these for which swarming represents a polyorchesium or true synorchesia and which are

linked with both a predatory and mating activities (mating swarms).

Nevertheless, we will also consider the case where two attributes under two states are

successively treated, presence and absence of swarms and beginning of mating in or outside

swarms.

Table 2. — Swarming and mating habits in the Empidoidea. A question mark indicates an unknown state.

Taxa

No swarming

activity

swarms without

mating

Mating

swarms

Atelestidae

Oreogetoninae

Clinocerinae

Empidinae

Hemerodromiinae

Ocydromiinae

Hybotinae

Tachvdromiinae

Brachystomatinae

Ceratomerinae

Tricopezinae

Microphoridae

Dolichopodidae

FORMER EVOLUTIONARY HYPOTHESES

Feeding habits

Predatory activity has always been considered ancestral for the Empidoidea (Chvala,

1983) for at least three reasons, (1) it is a very widespread habit in the superfamily, the flower

visitor species being only found in a few genera and one subfamily, (2) predation is considered

the basal feeding habit of the Asiloidea and Empidoidea, (3) oldest known fossil of Empidoidea is

170

C. DAUGERON : EVOLUTION OF BEHAVIOR IN THE EMPIDOIDEA

FIRST STAGE

> Presence of swarms.

> Beginning of mating in swarms,

ending on a solid substratum.

> Significance of swarms: adaptation

for the meeting of sexes.

SECOND STAGE

> Presence of swarms.

> The whole process of mating on a

solid substratum.

> Significance of swarms: unknown

or relict swarms.

THIRD STAGE

> No swarming activity.

> The whole process of mating on a

solid substratum.

PRIMITIVE TAX A

SPECIALIZED TAX A

Fig. 3. — Model of the evolution of swarming in Diptera (after Me Alpine & Munroe, 1968; Downes, 1969; Chvala, 1983).

dated from 160 millions years (middle Jurassic) (USACHEV, 1968) before the rise of the

angiosperms.

The fact that predation is very widespread in the superfamily is not evidence of its

supposed ancestral origin. Such hypothesis can be compared to the ingroup distribution criteria

used in phylogeny to establish the polarity of characters. Now we know that this criteria is not

valuable. On the other hand, in the Asiloidea, only the Asilidae are predatory, and the habits of

the Asiloidea could be informative in this context if the Empidoidea and Asiloidea are sister

groups, but the sister-group of the Empidoidea is the Cyclorrhapha (CUMMING et a /., 1995).

For these reasons, it seems justified to test the hypothesis of plesiomorphy of predation for

the Empidoidea. We will also test the hypothesis that predation in flight is ancestral to predation

on the ground.

Source: MNHN, Paris

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

171

Swarming habits

The significance and evolution of swarms in the Diptera have been studied in several

papers, GRUHL (1955), Me ALPINE & MUNROE (1968), DOWNES (1969) and Chvala (1976,

1980, 1990). From these works, we can present consensus which may be summarized in two

points, (1) swarming is ancestral for the Diptera in general and each taxon of Diptera which

presents this behavior in particular, (2) the original function of swarming is the meeting of sexes,

whereas the mating or hunting on a solid substratum is a specialized activity. This consensus is

the result of two observations which have been detailed by Me ALPINE & MUNROE, (1) swarming

exists in the main lineages of Diptera, nevertheless being more widespread in the Nematocera

(reputed primitive) than in the Brachycera (reputed specialized), (2) for Diptera in particular and

insects in general which present a swarming activity, the meeting of sexes and the beginning of

mating often take place in the swarms. To summarize these hypotheses (MCALPINE &

MlJNROE,1968: 1167) “The remarkable correlation between swarming and mating habits [...] in

the phyletically distant Diptera, is a clear indication that swarming and coupling in flight are basic

to a dipterous condition”.

Nevertheless, there exists a large number of Diptera forming swarms of which the function

remains unknown. As presented earlier, no swarming Empidoidea has been observed to mate in

the swarms except species of the subfamily Empidinae. Several unconvincing hypotheses have

been proposed to explain the significance of these swarms (for example see PAJUNEN, 1980).

Chvala (1983) proposed that these swarms are relicts of an ancestral behavior in which mating

is correlated with swarming, mating activity of these groups would have been transferred on a

solid substratum and swarms would be without particular significance.

These hypotheses can be summarized in an evolutionary model (Fig. 3) that is applies to

the whole order Diptera. Among the Empidoidea, families and subfamilies can be affiliated to one

stage of model: (first stage) Empidinae: meeting of sexes and beginning of mating in the swarm,

swarms are an adaptation for the meeting of sexes; (second stage) Atelestidae, Oreogetoninae,

Ocydromiinae and Microphoridae: meeting of sexes and mating transferred on a solid

substratum, swarms as relict of ancestral behavior; (third stage) Dolichopodidae, Hybotinae,

Tachydromiinae, Clinocerinae and Hemerodromiinae: meeting of sexes and mating on a solid

substratum, loss of the ability to form swarms.

THE TESTS OF EVOLUTIONARY HYPOTHESES

The reconstruction of phytogenies is independent from most process theories (Eldredge

& CRACRAFT, 1980), that is why the optimization method, as described by BROOKS &

McLennan (1991) among others, allows evolutionary models to be tested objectively. The

optimization consists of mapping the previously defined attributes on the phylogeny and follow

their evolution on the cladogram with respect of the parsimony principle.

Feeding habits

Predator Flower visitor. Feeding habits were scored in two states, predator or flower

visitor. After optimization, the cladogram (Fig. 4) shows that predation is plesiomorphic for all

the Empidoidea but also for the clades [Dolichopodidae + Microphoridae], Hybotidae and

Empididae. The flower visiting habit is apomorphic for the Empidinae, predation having only

been conserved during the mating period. The flower visiting habit has appeared independently in

172

C. DAUGF.RON : EVOLUTION OF BEHAVIOR IN THE EMPIDOIDEA

several other lineages of Empidoidea, but two cases must be distinguished. The first is

represented by the Dolichopodidae, Ocydromiinae and Oreogetoninae, for which some genera

became flower visitors (see the chapter “attributes”), and the second is represented by species of

the genus Microphorus (Microphoridae) which are both predators and flower visitors. It is

possible to consider that the flower visiting habit has recently appeared in this family. The

traditional model is therefore corroborated by the phylogenetic test.

Predation in flight Predation on solid substratum. The attribute (predation) has been

considered under two states (in flight or on solid substratum). After optimization, the phylogeny

(Fig. 5) shows that predation in flight is ancestral for all the Empidoidea and the clades

[Dolichopodidae + Microphoridae], Hybotidae and Empididae. Even if predation in flight is

plesiomorphic, it must be noted that this is considerably diversified and specialized in present

taxa, for instance females of some microphorids of the genus Microphorus catch other insects in

the spider webs; the Clinocerinae and males of the genus Hilara (Empidinae) hunt on the surface

of water, the second of these wrap up prey in a silk balloon which is presented to the females just

before mating as a nuptial gift. To summarize, different forms of hunting in flight observed

among the Empidoidea are apomorphic for each considered taxon.

Hunting on a solid substratum (on the ground or on a leaf for example) is apomorphic for

the Tachydromiinae (Hybotidae) and Hemerodromiinae (Empididae) (Fig. 5). Thus it is a very

specialized type of predation that appeared by convergence in these two subfamilies. Species in

these two subfamilies also possess a convergently specialized morphology where the thorax is

elongated and the fore and sometimes middle legs are raptorial with elongated coxae, thick

femora, and bent tibiae (Fig. 1). These morphological characters are likely to be an adaptation for

predation on a solid substratum because Hemerodromiinae and Tachydromiinae are respectively

the only taxa in Empididae and Hybotidae to present them. Tachydromiinae and

Hemerodromiinae are therefore a remarkable example of both morphological and behavioral

convergences. Of course, this does not mean that the presence of such characters involves such

behaviors, unfortunately this “rule” is often applied in evolutionary biology and cases of

exaptation are often overlooked.

Swarming habits

Presence Absence of swarms. According to optimization, two equally parsimonious

patterns (4 steps) (Figs 6, 7) have been obtained. In both cases, swarming is plesiomorphic for all

the Empidoidea, [Dolichopodidae + Micophoridae], [Atelestidae + Hybotidae + Empididae], and

for the Hybotidae and Empididae themselves, whereas the absence of swarming is apomorphic

for the Dolichopodidae and [Hybotinae + Tachydromiinae], In the Empididae, the situation is

more complex because, although in the first and second patterns, swarming appears as ancestral

for the family, two cases must be considered for the clade [Clinocerinae + Empidinae +

Hemerodromiinae]. In the first pattern (Fig. 6), swarming is plesiomorphic for this clade but also

the [Empidinae + Hemerodromiinae], the loss of this behavior occurring twice, once in the

Clinocerinae and a second time in the Hemerodromiinae. Swarming remains therefore

plesiomorphic for the Empidinae whereas the absence of swarming is apomorphic for the

Clinocerinae and Hemerodromiinae. In the second pattern (Fig. 7), the absence of swarming is

ancestral for the [Clinocerinae + Empidinae + Hemerodromiinae] with a reversion for the

Empidinae, swarming being therefore apomorphic for this subfamily.

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

173

/ Atelestidae.

/ * Oreogetoninae.

....both predator and

nectar feeder

/ y Clinocerinae.

/ ’ p ^Empidinae.

p • Nr

' Hemerodromiinae...

/y ’S

* X,

^•Ocydromiinae.

* Hyt’Otinae.

p V

’ Tachydromiinae.

....predator

....nectar feeder except

during the mating period

.predator

.both predator and

nectar feerder

.predator

/ Brachystomatinae....

X X

X / Ceratomerinae.

P ^Tricopezinae.

* Microphoridae.

.both predator and

nectar feeder

p \

^ Dolichopodidae.

.both predator and

nectar feeder

predator (p)

_ unknown or doubtful habit (?)

Fig. 4. — Cladogram of Empidoidea showing optimization of feeding habits.

Mating in/outside swarms . Mating in swarms being specific of Empidinae, this behavior is

apomorphic for this group (Fig. 8). Conversely mating outside swarms is plesiomorphic for all

the Empidoidea and all clades of the phylogeny including the terminal taxa apart from, ot course,

the Empidinae.

Swarming in Empidinae: exaptation or adaptation to the meeting of sexes? The cladistic

tests of adaptation hypotheses have been reviewed by CODDINGTON (1988) and GRANDCOLAS et

Source

174

C. DAUGERON : EVOLUTION OF BEH A VIOR IN THE EMPIDOIDEA

P f

Atelestidae.

Oreogetoninae.

....?

....in flight

Clinocerinae.

Empidinae.

Hcmerodromiinae...

.on solid:

Ocydromiinae.

Hybotinac.

Tachydromiinae.

.on solid .

Brachystomatinae.

Ceratomcrinae.

....?

Tricopczinae.

Microphoridae.

....in flight

Dolichopodidae.

.in flight

predation in flight (pf)

predation on solid substratum (ps)

unknown or doubtful habits (?)

Fig. 5. — Cladogram of Empidoidea showing optimization of type of predation.

al. (1994). To summarize, a character is an adaptation for a given taxon if it has appeared in this

taxon with the additional assumption of its selective value.

If we combine the previous result (mating in swarms as apomorphic for the Empidinae)

with both equally parsimonious patterns for the first attribute (presence or absence of swarms)

then two cases are possible for the Empidinae, (1) swarming is plesiomorphic and has been

inherited from the ancestor of the Empidoidea (and swarms formed by different Empidoidea are

homologous) for which the phylogeny shows mating did not take place in the swarms (Fig. 6).

Source: MNHN. Paris

PHYLOGENE TIC TESTS OF EVOLUTIONARY SCENARIOS

175

They therefore had a different function that was not to allow the meeting of sexes. Consequently,

swarming in the Empidinae is an exaptation (GOULD & VRBA, 1982) to the meeting of sexes. (2)

Swarming is apomorphic for the Empidinae (Fig. 7) and it appeared with the subfamily (swarms

formed by the Empidinae are therefore not homologous with these formed by some other

Empidoidea). The mating in swarms arising in the Empidinae, the adaptive hypothesis that

swarming evolved for the meeting of sexes is corroborated by the phylogeny.

To summarize (Table 3): according to both patterns, the traditional model is refuted in two

points, (1) the ancestral state is not the formation of mating swarms but the formation of swarms

of which the function is unknown, the mating taking place on a solid substratum (or may be in

flight but not in swarm), (2) mating in swarms is an apomorphic behavior that appeared with the

Empidinae.

In addition, the pattern 1 refutes the adaptation hypothesis of swarming for the meeting of

sexes in Empidinae whereas the pattern 2 corroborates it. Finally, the absence of swarms as

apomorphic character is corroborated for Dolichopodidae and [Hybotinae + Tachydromiinae] by

both patterns and Hemerodromiinae and Clinocerinae by the first pattern but refuted by the

second because in this case the loss of the ability to form swarms took place for the ancestor of

the clade [Clinocerinae + Empidinae + Hemerodromiinae],

Is it possible to choose between exaptation and adaptation for the formation of swarms in

the Empidinae? In fact we can only consider one attribute (swarming) under three states (absence

- swarming without mating mating swarms) rather than two attributes (swarming mating)

Table 3. — Former evolutionary hypotheses and their tests by two phylogenetic patterns (optimizations on the cladogram).

*: in the empidids, the corroboration is only true for the clade [Clinocerinae + Empidinae + Hemerodromiinae] with a

reversion for the Empidinae.

Former evolutionary hypotheses

According to pattern 1

According to pattern 2

Mating swarms : plesiomorphic

Refuted

Swarms without mating,

relict from mating swarms

Refuted

Mating swarms: adaptation to the

meeting of sexes (in Empidinae)

Refuted

Corroborated

No swarming activity:

apomorphic

Corroborated

Corroborated *

under two states (respectively absence - presence and in or outside swarms) for the reasons

explained in the chapter “Attributes”.

Absence of swarms swarming without mating - mating swarms. After optimization, a

pattern (Fig 9) as parsimonious (4 steps) as the previous ones has been found. Swarming

176

C. DAUGERON : EVOLUTION OF BEHAVIOR IN THE EMPIDOIDEA

Ateleslidae.swarming activity

Oreogetoninae.swarming activity

f Clinocerinac.no swarming activity

/ ,

s hmpiainae.swarming activity

^ Hemerodromiinae.no swarming activity

Ocydromiinae.swarming activity

s , * Hybolinae.no swarming activity

ns X

Tachydromiinae.no swarming activity

' Brachystomatinae.?

' Ceratomerinae.?

v Tricopezinae.?

Microphoridac...swarming activity

Dolichopodidae.no swarming activity

swarming activity (s)

no swarming activity (ns)

unknown or doubtful habits (?)

Fig. 6. — Cladogram of Empidoidea showing optimization of sw-arming habits. First pattern.

without mating is plesiomorphic for the Empidoidea, [Dolichopodidae + Microphoridae],

Atelestidae, Hybotidae and Empididae, the absence of swarms is apomorphic for the

Dolichopodidae, [Hybotinae + Tachydromiinae] and [Clinocerinae + Empidinae +

Hemerodromiinae], On the other hand, the Empidinae are the only Empidoidea which form

mating swarms. This behavior is therefore apomorphic for this subfamily and as in the pattern 2,

the adaptation hypothesis for swarming to the meeting of sexes is corroborated.

Source: MNHN, Pahs

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

177

Atelestidae.swarming activity

Oreogetoninae.swarming activity

/ V

jr y

Clinocerinae.no swarming activity

. Empidinae.swarming activity

Hemerodromiinae.no swarming activity

y Ocydromiinae.swarming activity

s S Hybotinae.no swarming activity

V ns

rachydromiinac.no swarming activity

' Brachystomatinae.?

' Ceratomerinae.?

s ^Tricopezinae.?

Microphoridae.swarming activity

^ Dolichopodidae.no swarming activity

swarming activity (s)

no swarming activity (ns)

_ unknown or doubtful habits (?)

Fig. 7. — Cladogram of Empidoidea showing optimization of swarming habits. Second pattern.

DISCUSSION

Swarms formed by the Empidinae are structurally (according to the Gruhl classification,

1955) different from those formed by some other Empidoidea. Within these swarms, the

Empidinae show a succession of behaviors (hunting, meeting of sexes, nuptial gift, beginning of

mating) never observed in any other Empidoidea. In the Empidinae, swarming and mating seem

therefore correlated, this pleads in favor of the consideration of one attribute under three states

(no swarming activity, swarming without mating and mating swarms). Nevertheless the

Source

178

C. DAUGERON: EVOLUTION OF BEHAVIOR IN THE EMPIDOIDEA

IH'

Atelestidae.mating oustside swarms

Oreogetoninae.mating outside swarms

. ■ Clinocerinae.mating outside swarms

Empidinae.mating in swarms

mo %

Hemerodromiinae.mating outside swarms

p Ocydromiinae.mating outside swarms

Hybotinae.mating outside swarms

mo'

Tachydromiinae.mating outside swarms

Brachystomatinae.?

Ceratomerinac.?

Tricopezinae.?

Microphoridae.mating outside swarms

Dolichopodidae.mating outside swarms

mating in swarms

mating outside swarms (mo)

_ unknown or doubtful habits (?)

Fig. 8. — Cladogram of Empidoidea showing optimization of type of mating.

consideration of two attributes allows two patterns of which one gives results analogous with

those obtained with one attribute. Consequently it seems that the following conclusions force

themselves:

1) Swarming and mating outside swarms are plesiomorphic for the Empidoidea.

2) The absence of swarms in some Empidoidea is apomorphic for three clades,

Dolichopodidae, [Hybotinae + Tachydomiinae] and [Clinocerinae + Empidinae +

Hemerodromiinae].

Source: MNHN. Paris

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

179

Atelestidae.swarms without mating

Oreogetoninae.swarms without mating

Clinocerinae.no swarming activity

Empidinae.mating swarms

Hemerodromiinae.no swarming activity

Ocydromiinac.swarms without mating

Hybotinae.no swarming activity

Tachydromiinae.no swarming activity

Brachystomatinae.?

Ceratomerinae.?

Tricopezinae.?

Microphoridae.swarms without mating

Dolichopodidae.no swarming activity

mating swarms

swarms without mating (swm)

no swarming activity (ns)

_ unknown or doubtful habits (?)

Fig. 9. — Cladogram of Empidoidea showing optimization of both swarming and mating.

3) Mating swarms are apomorphic for the Empidinae but not homologous with swarms

formed by other Empidoidea. Thus they cannot be integrated to a global evolutionary model and

thus do not form the basis of this model as it has always been presented. On the other hand, in

the Empidoidea, swarming without mating cannot be considered a relict from mating swarms.

4) The adaptation hypothesis of swarming to the meeting of sexes is corroborated for the

Empidinae without, of course, prejudging of the selective value of this behavior.

180

C. DAUGERON : EVOLUTION OF BEHAVIOR IN THE EMPIDOIDEA

CONCLUSION

The optimization of characters on the phylogeny leads to refutable results and is the only

objective test of evolutionary models because of its independence from these models. Thus

systematics must not be only considered as the science of inventories, descriptions and

classifications of taxa in predictive systems, but also as the science of explanatory framework for

character evolution.

This method is therefore employed herein for the first time for the Empidoidea, but

important advances remain to be achieved in both phylogeny and ethology of the Empidoidea

before to offer more stable evolutionary hypotheses.

Finally, focusing on the phylogenetic patterns in the subfamily Empidinae is probably the

most interesting perspective. ClJMMING (1994) proposed an evolutionary model for this group

with reference to sexual selection. Using phylogeny, it will be therefore possible to test this

model and other hypotheses relating the origin and evolution of both nuptial gift and female

ornementations.

ACKNOWLEDGEMENTS

I thank P. Grandcolas, L. Matile and two anonymous referees for their remarks and suggestions for improvement of

this paper, and G. Hodebert for the habitus drawing. This work is part of a doctorate thesis. Soci&e entomologique de France

has provided partial funding.

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182

C. DAUGERON : EVOLUTION OF BEHAVIOR IN THE EMPIDOIDEA

Appendix 1. — List of characters and Matrix. In brackets, bold-faced and italic types indicate respectively the number of the

page and the number of the character in the original work.

1. Maxillary lacinia absent: 1, present: 0 (Chvala, 1983: 61, 72, Wiegmann et al., 1993: 66, 9).

2. Palpi connected to palpifer: 1, attached to stipites: 0 (Chvala, 1983: 61; 13; Wiegmann et al., 1993: 66, 8).

3. Prokatepistemum fused with the basistemite: 1, isolated: 0 (Chvala, 1983: 61,70; Wiegmann et al., 1993: 66, 72).

4. Mesoanepimeral suture present and forming a '/ - half of circle: 1, present and forming a / of circle, absent: 0 (Ulrich,

1971, Figs 3, 4, 5, 44, 45', 1994: 230).

5. Two discal veins: 1, three discal veins: 0 (Chvala, 1983: 61; 8\ Wiegmann et al., 1993: 68, 27).

6. Front tibiae with tubular gland: 1, tubular gland absent: 0 (Chvala, 1983: 61; 77; Wiegmann£/ al., 1993: 70, 28).

I. male cerci sclerotized. 1, not sclerotized: 0 (Ulrich, 1975; Cummin Getal., 1995: 133, 72).

8. Rotation of male hypopygium between 45°and 90°: 1, Hypopygium without rotation: 0 (Chvala, 1983: 61, 3; Cummings

al., 1995: 133, 14).

9. Rotation of both male hypopygium and segments 7 and 8: 1, Hypopygium and segments 7 and 8 without rotation: 0

(Cumming et al. , 1995: 133, 15).

10. Bacilliform sclerite and hypandrium fused: 1, no fused: 0 (Cummings al., 1995: 134, 16).

II. Stemite 8 of female articulated or fused with tergite 8: 1, well separated: 0 (Sinclair, 1995: 718, 7).

12. female cerci sclerotized: 1, not sclerotized: 0 (Sinclair, 1995: 718, 2).

13. Tergite 7 of female with a fringe of bristles on the posterior margin: 1, without fringe of bristles: 0 (Sinclair, 1995: 719,

■*)•

14. female cerci upright: 1, horizontal: 0 (Sinclair, 1995: 719, 4).

15. Acanthophorites absent: 1, present: 0 (Sinclair, 1995: 668).

Atclestidae

Oreogetoninae

Clinocerinae

0/1

Empidinae

Hemcrodromiinae

0/1

Ocvdromiinae

Hvbotinae

Tachvdromiinae

0/1

Brachystomatinae

Ceratomerinac

Tricopezinae

0/1

Microphoridae

Dolichopodidae

0/1

Source MNHN . Paris

Acoustic Communication in Crickets (Orthoptera:

Grylloidea): A Model of Regressive Evolution

Revisited Using Phylogeny

Laure Desutter-Grandcolas

E.P. 90 CNRS. Laboratoire d'Entomologie. Museum national d'Histoirc naturelle.

45. rue Buffon. 75005 Paris, France

ABSTRACT

Acoustic communication is essential in cricket biology, being related to mating behavior. Current hypotheses on the

evolution of acoustic communication in crickets consider that singing is ancestral in crickets, and that it has been lost several

times in different cricket lineages. According to studies of cricket populations, it has also been hypothesized that the loss of

acoustic communication could have occurred following a progressive transformation series. Similarly, it has been assumed

that several factors could have influenced that evolution, such as predation pressure, low efficiency of acoustic communication

due to poor environmental conditions, an evolutionary shift toward another mode of communication, population structure or

habitat of the taxa. I present a phylogenetic test of this model. Song characteristics were optimized onto the phylogenetic trees

for two clades of cricket (Grylloidea, Phalangopsidae) and the resultant phylogenetic patterns compared with the theoretical

patterns implied by the pre-existing hypotheses. My study produced four main results: (1) multiple and convergent absences of

songs occurred; (2) no linear and progressive transformation series toward complete song loss was found; (3) the polarization

of the presence/absence of songs was not always in the sequence predicted by the model; (4) reversals from song lack to song

presence were documented. Such reversals have never been hypothesized before, and the acoustic evolution of crickets

appeared highly homoplastic. Phylogenetic analyses showed that factors such as predation pressure, population structure, etc.,

cannot be characterized on the basis of their definite evolutionary effect on acoustic communication: consequently previous

hypotheses on their possible influence on cricket evolution cannot be tested. Although many papers have been written on

acoustic communication in crickets, no clear and general hypothesis yet exists for its origin and evolution Integrated studies

of both phylogeny and population biology are badly needed to generalize the results presented in this paper, and to support

new hypotheses on the subject.

RESUME

La communication acoustique chez les Grillons : un modele devolution regressive teste a I'aide de la phylogenie

La communication acoustique occupe unc place importante dans la biologic des grillons, principalement dans lc contexte de

la reproduction. Les hypotheses classiques sur V evolution acoustique des grillons considerent que ce mode de communication

leur est ancestral, et qu'il a ete perdu au cours de revolution a de multiples reprises et de maniere independante. A parlir

d'etudes de populations, un modele devolution a ainsi ete propose, selon lequel la communication acoustique aurait ete

perdue a plusieurs reprises de maniere progressive, suivant des etapes bien dehnies. Pareillement, des hypotheses out ete

emises sur les facteurs susceptibles d'influencer revolution acoustique chez les grillons (predation, efficacite de ce mode de

communication dans le milieu ambiant, habitat, structure des populations, evolution vers un autre mode de communication).

Desutter-Grandcolas, L., 1997. — Acoustic communication in crickets (Orthoptera: Grylloidea): A model of

regressive evolution revisited using phylogeny. In: Grandcolas, P. (ed.), The Origin of Biodiversity in Insects: Phylogenetic

Tests of Evolutionary Scenarios. Mem. Mus. natn. I list, nat., 173 : 183-202. Paris ISBN 2-85653-508-9.

184

L. DESUTTER-GRANDCOLAS : ACOUSTIC COMMUNICATION IN CRICKETS

Un test phylogenetique de ces hypotheses est presente, a partir des analyses phylogenetiques de deux clades de grillons

(Grylloidea, Phalangopsidae). Les patterns phylogenetiques obtenus par optimisation des chants sur la phylogenie de ces deux

clades sont compares aux patterns theoriques derives des hypotheses testees. L'hypothese de convergences pour Eabsence de

chants est confirmee par Eanalyse phylogenetique ; la progressivite des pertes n’est cependant pas corroboree, et la

polarisation des absences ou presences des chants n'est pas forcement celle predite par le modele. Des reversions sont par

contre documentees, ce qui n’avait jamais etc envisage auparavant. 1/evolution acoustique apparait finalement fortement

homoplasique chez les grillons. Les analyses phylogenetiques montrent egalement que les facteurs tels que predation,

structure de populations, ne peuvent pas etre caracterises les uns par rapport aux autres par leur effet suppose sur la

communication acoustique : les hypotheses evolutives proposees a leur sujet ne sont pas exclusives, et ne peuvent dans leur

forme actuelle se preter a une procedure de test. Bien que la communication acoustique des grillons ait fait Eobjet de

nombreuses etudes, aucune hypothese claire n’existe actuellement sur son origine et ses modalites devolution. Des etudes

conjointes en phylogenie et en biologie des populations seront ainsi necessaires d’une part pour gendraliser les resultats deja

obtenus sur les Phalangopsidae, et d’autre part pour proposer de nouvelles hypotheses sur la question.

INTRODUCTION

Acoustic communication plays a leading role in cricket biology. In most species it is

associated with mating. Songs are emitted by males only (Fig. 1), either to attract distant females

(calling songs), to attract and keep the females at close range (courting songs) or to chase male

intruders (aggressive songs) (CHOPARD, 1938; HUBER et a/., 1989). Singing is achieved by

means of a special forewing apparatus called the stridulum (Figs 2-8). This apparatus is complex,

both regarding its structure and its operative mode (MlCHELSEN & NOCKE, 1974; SlSMONDO,

1979; Koch et a/., 1988; Bennet-Clark, 1989; DESUTTER-GRANDCOLAS, 1995a), and it is

widely and exclusively distributed in crickets. It is thus currently considered ancestral in this

clade (Alexander, 1962, 1967; Otte, 1977, 1992; Walker & Masaki, 1989).

The question of how acoustic behavior has evolved in crickets has long been debated.

Alexander (1962, 1967, 1987) postulated that originally cricket songs were similar to courting

songs, emitted at close range. The subsequent evolution of acoustic communication in crickets

would have been achieved by the diversification of the emitted signals, which would have been

driven by two factors: the growing number of potentially interacting acoustically signaling

species (each species being characterized by at least its calling song), and an increase in the

number of functions for the signals. ALEXANDER (op. cil.) thus assumed that the calling song

derived from the courting song, and the aggressive song from the calling song (see also Bailey,

1991) : “The only soft, close-proximity signals among modern crickets are courtship sounds, and

it is likely that this reproductive context was the one in which the first cricket chirp was

produced. All the other signals are probably outgrowths of this fundamental situation”

(Alexander, 1987: 84).

The acknowledgment that not all crickets are able to sing (Figs 3, 6, 8) has led other

authors to consider that singing may have been lost many times in crickets. This evolution

toward muteness has been hypothesized to follow several steps based upon the life habits of

extant species (OTTE, 1977, 1990, 1992; WALKER & Masaki, 1989; Bailey, 1991). These

steps, outlined in figure 9, include: 1) Ancestrally, species sang and had three song types. 2) In

some circumstances, the calling song may have become facultative, singing and non-singing

(satellite) males living in close proximity. 3) The calling song was definitively lost, but courting

and aggressive songs still existed. 4) Species became mute, even though they still retained the

stridulum. 5) The stridulum was finally lost. This loss may or may not have been followed by the

loss of auditory organs (Otte, 1990).

Source: MNHN. Paris

PHYLOGENETIC TESTS OF EVOLU TIONARY SCENARIOS

185

CALLING SONG

COURTING SONG

AGGRESSIVE SONG

Fig. 1. — The three main songs emitted during mating by crickets (modified from Loher & Dambach, 1989). Sonagrams of

the songs in frames.

Current hypotheses on the acoustic evolution in crickets thus assume that 1) songs have

evolved progressively from the courtship song, 2) the ancestral stridulum and songs have been

lost several times in different cricket lineages, and 3) both the loss of the stridulum and that of

the songs have been achieved according to a definite and linear transformation series. No reversal

of this gradual song loss has ever been hypothesized. In order to analyze the evolution of

Source

186

L. DESUTTER-GRANDCOLAS : ACOUSTIC COMMUNICATION IN CRICKETS

acoustic communication in crickets, it is necessary to consider separately the evolution of the

stridulum and that of the acoustic repertoire. Although these traits are obviously connected (in

crickets, song s.str. is only emitted by the stridulum), there exists no obligatory correspondence

between definite states of the stridulum and the extent of acoustic repertoires (OTTE, 1977,

1992).

Hypotheses of stridulum loss have been tested in a phylogenetic context (DESUTTF.R-

GRANDCOLAS, 1997). Phylogenetic patterns support the hypothesis of a convergent loss of the

stridulum. They did not support, however, the progressive disappearance of the stridulum: a

functional stridulum could be lost in only one evolutionary step, without intermediary conditions.

A high level of homoplasy was also documented for diverse stridulum types, and phylogenetic

patterns indicate that reversal could occur. Finally the stridulum appeared evolutionarily labile.

I will consider here the hypotheses about the evolution of the cricket songs. I will not

however analyze whether courting is the ancestral song type in crickets, as this would have to be

tested at a higher phylogenetic level. Supposing that the ancestral acoustic repertoire of true

crickets comprises a calling, a courting and an aggressive songs, current assumptions on their

acoustic evolution could be described by a definite sequence of song combinations (Fig. 9). This

sequence implies that the loss of the songs is ordered, the calling song disappearing first,

followed by the courting and the aggressive songs. Given this only three of the eight possible

combinations of the three songs should exist (Fig. 10). Again no reversal is hypothesized. Here I

will perform phylogenetic tests of these theoretical patterns and ask if song loss is the only

possible evolutionary change in the acoustic evolution of crickets.

Dealing with the patterns of acoustic evolution in crickets, one cannot help asking which

factors may have influenced it. Four factors have been hypothesized to have played a role in the

evolutionary reduction of cricket acoustic repertoire (HUBER el at ., 1989; OTTE, 1992). Is it

possible first to characterize the potential influence of each factor, and second to test it using

phylogeny? The first, and most strongly advocated factor is predation. Both parasites and

predators are supposed to be attracted by calling individuals, thereby influencing long range

signals (Cade, 1975; Burk, 1982; Thornhill & Alcock, 1983; Bailey, 1991). For crickets,

this means that the calling song could be affected, but not the courting or the aggressive songs,

which are emitted at short range. The second factor is the environment, in particular the

environment’s effect on the efficiency of acoustic signal transmission (ROMER, 1993).

Communication occurs between a sender(s) and a receiver(s). Efficient communication allows

the receiver(s) to know who calls, what for and from where. Physical problems in sound

propagation in the natural environment may alter the information conveyed by acoustic signals,

especially for pure-tone signals such as cricket calls (MlCHELSEN & NOCKE, 1974; ROMER &

Lewai.d, 1992 in ROMER, 1993). Acoustic signals emitted simultaneously can also mask each

other (ROMER, 1993). Finally some environments have been supposed unfavorable for acoustic

communication because of their physical properties or because of their noisiness (for example

caves or shores, respectively: OTTE, 1992). Environmental constraints are thus more likely to

interfere with long range signals (ROMER, op. cit.) than with short range signaling. Population

structure and habitat have been hypothesized to influence song loss via sedentariness (Walker,

1974) or confinement (Boake, 1984a, b), respectively (see also Alexander, 1962). The idea is

that individuals that stay together can find each other by chance without any special attractant

Source: MNHN. Paris

-' ■

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

187

Figs 2-8. — Diversity of tegminal structures in phalangopsid crickets. 2: Noctivox sanchezi (Amphiacustae), with a normally

developed, non corneous stridulum. 3: Phaeophilacris sp., with legmina modified for communication through air pulls

(Dambach& Lichtenstein, 1978). 4: Luzarida guyarta (Luzarida group), with a normally developed stridulum, but a

corneous right legmen. 5: Paragryllodes sp., with a reduced, though functional stridulum. 6: Cantrallia huasteca

(Amphiacustae), with non overlapping tegmina and no functional stridulum. 7: Luzaridella clara (Luzarida group),

with an incomplete stridulum and a corneous right tegmen. 8: Eidmanacris multispinosa , with deeply moditied

tegmina probably showing glandular structures (Desutter-Grandcolas, 1994b). Stridulum: F, file; II, harp; M,

mirror. Scales: 2 mm.

188

L. DESUTTER-GRANDCOLAS : ACOUSTIC COMMUNICATION IN CRICKETS

CURRENT MODEL FOR ACOUSTIC EVOLUTION IN CRICKETS

1/ Ancestral condition: 3 song types (calling, courting, aggressive song)

2/ Multiple, independent losses

3/ Several definite steps toward muteness

\ Calling song facultative (satellite males) (call.* court, aggr.)

\ Calling song lost (- court, aggr.)

\ Other songs lost (—)

« Stridulum (+/-auditory organs) lost

4/ No reversal hypothesized

Fig. 9. — Current model on the evolution of acoustic communication in crickets (references in the text).

SONG COMBINATIONS PREDICTED BY THE TESTED MODEL

1/ Call. Court. Aggr.

2/ - Court. Aggr.

SONG COMBINATIONS NOT PREDICTED BY THE TESTED MODEL

Call.

Court.

Call.

Aggr.

Call.

Court.

Aggr.

Fig. 10. — List ot song combinations that could exist in crickets. Names of songs: Call.: calling song; Court.: courting song;

Aggr.: aggressive song (references in the text).

signal. Here again the long-range signal would be lost. The fourth factor that has been

hypothesized to influence song evolution is the evolutionary shift toward another communication

mode. Chemical (OTTE, 1977, 1992) and visual (Toms, 1986; BAILEY, 1991) shifts have been

proposed as replacement communication systems. Vibrational communication has also been

recorded in crickets (LoHER & Dambach, 1989), however there is currently no suggestion that

it replaced acoustics. Chemical and visual signals are efficient at both long and short range, visual

Source:

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

189

FACTORS CURRENTLY HYPOTHESIZED TO BE RESPONSIBLE FOR ACOUSTIC

EVOLUTION OF CRICKETS, AND THE SONG REPERTOIRE THEY IMPLY

1/ Predation: (Call. Court Aggr.) » (- Court. Aggr.)

21 Inefficiency of acoustic communication: (Call. Court. Aggr.) » (- Court. Aggr)

3/ Population structure / Habitat: (Call. Court. Aggr.) » (- Court. Aggr.)

4/ Shift toward another communication mode

A/ At long range only : (Call Court. Aggr.) » (- Court. Aggr.)

B/ At long range, and at short range between M/F and M/M: (Call. Court. Aggr.) » (- - -)

Cl At long range, and at short range between M/M: (Call. Court. Aggr.) » (- Court. -)

D/ At long range, and at short range between M/F: (Call. Court. Aggr.) » (- - Aggr)

E/At short range between M/F: (Call. Court. Aggr.) » (Call. - Aggr.)

FI At short range between M/M: (Call. Court. Aggr) » (Call. Court. -)

G/ At short range between M/F and M/M: (Call. Court. Aggr.) » (Call. - -)

Fig. II. — Current hypotheses on the factors that could have influenced the acoustic evolution of crickets (references in the

text).

cues being efficient only in daylight. At long range, these signals would replace the calling song.

At short range, they could play a role in interactions between male and female and replace the

courting song, or between males only and replace the aggressive song, or in both kinds of

interactions, replacing both the courting and aggressive songs. Operating over both long and

short ranges, these signals could potentially replace all types of songs.

Figure 11 shows the different song combinations that would result from the influence of

each factor on the evolution of acoustic communication in crickets. It is clear that these factors

are not mutually exclusive, and that a given sequence of songs is predicted by more than one

factor. For example, the loss of the calling song is expected from the influence of predation,

inefficiency of acoustic communication, population structure, habitat type or a shift toward

another long range communication mode. This overlap precludes a test of the influence of these

factors. Some song combinations, however, appear specific of one factor.

I present here a phylogenetic test of current hypotheses on the modalities of the acoustic

evolution in crickets, and on the factors that could have influenced it. For this I will confront the

theoretical patterns these hypotheses imply with the results of my phylogenetic analyses on two

monophyletic cricket clades, the Amphiacustae and the Luzarida group (Grylloidea,

Phalangopsidae). In each clade the optimization of song types onto the phylogeny allows me to

derive evolutionary scenarios on the acoustic evolution of the clade. These scenarios may or may

not fit the theoretical patterns and may or may not corroborate the hypotheses under study

(Coddington, 1990; Carpenter, 1989; Brooks & McLennan, 1991; McLennan, 1991;

Grandcolasc/ a/., 1994). For practical reasons, the hypotheses on the factors will be analyzed

using the Amphiacustae clade only.

190

L. DESUTTER-GRANDCOLAS : ACOUSTIC COA4MUNICATION IN CRICKETS

MATERIAL AND METHODS

Two monophyletic groups of phalangopsid crickets (Grylloidea, Phalangopsidae) were used in this study: the

Amphiacustae (Desutter-Grandcolas, 1993a, 1994a) and the Luzarida group (Desutter-Grandcolas, 1993b). Their

phylogeny has been previously analyzed with cladisties, using Wagner parsimony and the option implicit enumeration of the

Hennig86 program (Farris, 1988). Data matrices were built with unweighted morphological and anatomical characters; multi¬

state characters were coded as non additive. No song characters were then included in the matrices because of the lack of

evident primary homologies (de Pinna, 1991; Grandcolas et al. , 1994).

For the present paper, song data were collected from the literature and from my own personal observations in the field.

They were treated as attributes (Mickevich & Weller, 1989) and optimized on the cladograms using Wagner parsimony.

Each song was treated as one attribute, with two possible states (present/absent). Three attributes were considered: calling

song (Call.), courting song (Court.) and aggressive song (Aggr.).

The Amphiacustae (Figs 12, 14) comprise nine genera distributed in Central America and the West Indies. Cladistic

analyses of morpho-anatomical characters resulted in one phylogenetic tree (Cl = 0.92, RI = 0.95, 28 steps) (Desutter-

Grandcolas, 1993a, 1994a). Two monophyletic species groups exist in the genus Mayagryllus : one group {Mayagryllus 1)

presents no tegmina, that is no acoustic apparatus; the other {Mayagryllus 2) includes two apterous species (no stridulum) and

one species with reduced, not corneous tegmina and a functional stridulum. Songs have been described by Alexander &

Otte(1967) for Amphiacusta and Boake (1983, 1984a, b) for Nemoricantor. I have observed Noctivox and Cantrallia in their

natural habitat. Arachnopsita , Leptopedetes and Mayagryllus p.p. have tegminal conditions that do not allow them to sing

(Desutter-Grandcolas, 1993a, 1996). No data exist on Longunpes , Prolonguripes and Mayagryllus p.p.

The Luzarida group (Figs 13-15) comprises nine genera distributed in the northern half of South America, east of the

Andes. Cladistic analyses of morpho-anatomical characters resulted in one, incompletely resolved tree (Cl = 0.80, RI = 0.86;

20 steps) (Desutter-Grandcolas, 1993b). All available data on the singing behavior of the Luzarida group taxa (except

Palpigera, the song of w hich is unknown) result from my own personal observations in the field.

RESULTS

The Amphiacustae

Song evolution. The states of the attributes are at least partly documented in 7 of the 9

genera of the Amphiacustae, and a complete series of attributes states is available for 5 of them

(plus Mayagryllus p.p.). Acoustic communication has been completely described for 2 taxa

(. Amphiacusta , Nemoricantor ); it is absent in 3 others ( Cantrallia, Leptopedetes , Arachnopsita),

plus Mayagryllus p.p. Mapping song attributes onto the cladogram (Fig. 14) shows that the three

song types are not obligatorily present in any singing taxa (although they could be in Noctivox).

Amphiacusta has no aggressive song, while it has a calling and a courting song. Nemoricantor on

the contrary has only a courting and an aggressive song, but no calling song. The combinations

of attributes states found in the Amphiacustae are (Call Court. -), (Call. Court. Aggr.), (Call.

Court. ?) and (-). All these combinations are predicted by the model depicted in Figure 9,

except for (Call. Court. -). Also their distribution on the phylogeny of the Amphiacustae does not

support the hypothesis of a linear transformation toward the loss of acoustic communication.

The scenarios derived for each attribute are as follows:

Calling song (Fig. 16). Three equally parsimonious scenarios exist, with two steps each.

A) Calling song is ancestral; it is lost twice independently in Cantrallia and in the clade

[Leptopedetes - Mayagryllus ].

B) Absence of calling song is ancestral; a calling song appears once in [Amphiacusta (Noctivox -

Cantrallia)], and one subsequent reversal to ancestral condition occurs in Cantrallia.

C) Absence of calling song is ancestral; two independent appearances of a calling song occur in

Amphiacusta and Noctivox.

Courting song (Fig. 17). Four equally parsimonious scenarios exist, with 3 steps each.

A) Courting song is ancestral; three independent losses of courting song occur in Cantrallia,

Leptopedetes and in the subgroup [Arachnopsita - Mayagryllus ].

Source:

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

191

Figs 12-13. — 12: Noctivox sanchezi Desutter-Grandcolas, 1993a (Amphiacustae), scale: 5 mm. Note the well-developed

stridulum. 13: Ochraperites ottei Desutter-Grandcolas, 1993b (Luzarida group), scale: 1 mm. Males in dorsal view,

modified from Desutter-Grandcolas, 1993a, 1993b. Note the consistency of teginina and the type of stridulum

(right tegmen with a stridulatory file only).

B) Courting song is ancestral; the courting song is lost twice independently in Cantral/ia and in

the clade [I.eptopedeles - Mayagryllus ], and one subsequent reversal occurs in Nemoricantor.

C) Absence of courting song is ancestral; a courting song appears twice independently in

192

L. DESUTTER-GRANDCOLAS : ACOUSTIC COMMUNICATION IN CRICKETS

Amphiacusta .

Call.

Court.

Aggr.

Noctivox .

Cantrallia .

...

Leptopedetes ..

Nemoricantor ..

Arachnopsita ...

Longuripes .

Prolonguripes .

Mayagryllus 1 ...

...

■ Mayagryllus 2 ...

... -/?

-/?

Pig. 14. — Phylogeny and song attributes in the Amphiacustae (Grylloidea, Phalangopsidae). Symbols for attributes:

+: presence, absence; ?: state unknown.

Call.

Luzarida . +

Luzaridella .

Acantoluzarida ..

Leptopsis . -

Palpigera . ?

Melanotes . +

Allochrates .

Tetragonia .

Ochraperites .

Court. Aggr.

? ?

+ ?

Fig. 15. — Phylogeny and song attributes in the Luzarida group (Grylloidea, Phalangopsidae). Symbols for attributes:

+: presence, -: absence; ?: state unknown.

Source: MNHN. Paris

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

193

Nemoricantor and in the clade [Amphiacusia (Noctivox - Cantrallia)\, and one subsequent

reversal to ancestral state occurs in Cantrallia.

D) Absence of courting song is ancestral; three independent appearances of a courting song

occur in Amphiacusia , Noctivox and Nemoricantor.

Aggressive song (Fig. 18). Only one most parsimonious scenario has been found (1 step).

It implies an ancestral absence of the aggressive song and its subsequent appearance in

Nemoricantor.

A combined analysis of all three attributes shows that 12 equally parsimonious scenarios (6

steps) could explain the present distribution of song types in the Amphiacustae (Fig. 19). The

ancestral repertoire is ambiguous: it may comprise a courting or a calling song, both songs or

neither; the aggressive song is ancestrally absent in all 12 cases.

All the scenarios show convergent modifications of the calling song, the courting song or

both: the songs appear or disappear, according to the ancestral condition, in two or more taxa.

For example, when the calling song is ancestrally absent, the scenarios always imply subsequent

appearances of the calling song (Figs 19C - F, I - L); a similar situation occurs for the courting

song (Figs 19G - L). Conversely, when the calling song (or the courting song) is ancestral in

Amphiacustae, several convergent losses occur.

Factors of song evolution. Comparison with the theoretical song combinations (Figs 10-

11) shows that only three of them exist in the Amphiacustae: (- Court. Aggr.) in Nemoricantor ,

(-) in Cantrallia , Leptopedetes, Arachnopsita and Mayagryllus p.p. , and (Call. Court. -) in

Amphiacusta. These could support a potential effect of the following factors: predation,

inefficient acoustic communication, population structure, habitat, evolution toward a pheromonal

communication between males and females both at long and close range, and evolution toward a

pheromonal communication between males at close range. One should remark however that

these factors have always been supposed to have interfered with an ancestral song combination

comprising all three song (Call. Court. Aggr ). Such an ancestral song combination is however

not attested for the Amphiacustae, as the Amphiacustae ancestrally lack an aggressive song. This

means that none of the evolutionary sequence hypothesized to test the influence of currently

invoked factors is found in this group, and that no current hypothesis can account for present

data on this clade.

The Luzarida group

Song attributes are not as well known in the Luzarida group as in the Amphiacustae,

especially for the courting and the aggressive songs (Fig. 15): these attributes are known in four

and two taxa respectively, two of them being deprived of a stridulum. A complete description of

the attributes is thus available only for those non acoustic taxa (combination - - -). Other

incomplete combinations are (Call. Court. ?), (- Court. ?), (Call. ? ?) and (- ? ?). These

combinations are not incompatible with the tested model of the evolution of acoustic

communication in crickets. According to available data, scenarios could be derived only for the

calling and the courting songs.

Calling song (Fig. 20). Only one most parsimonious scenario (2 steps) exists. It implies an

ancestral absence of the calling song, and two subsequent, independent appearances in Luzarida

and in Melanotes.

194

L. DESUTTER-GRANDCOLAS : ACOUSTIC COMMUNICATION IN CRICKETS

Fig. 16. — Equally parsimonious scenarios for Ihe evolution of the calling song in the Amphiacustae. Symbols: black circle:

presence; empty circle: absence; thick line: evolutionary change. Names of taxa: Am: Amphiacusta , Ar: Arachnopsita ,

Ca: Cantrallia , Le: Leptopedetes, Lo: Longuripes , Ma 1, 2: Mayagryllus (1, 2), Ne: Nemoricantor , No: Noctivox , Pr:

Prolonguripes.

Fig. 17. — Equally parsimonious scenarios for the evolution of the courting song in the Amphiacustae. Symbols: black square:

presence; empty square: absence; thick line: evolutionary change. Names of taxa as in figure 12.

Courting song (Fig. 21). Three equally parsimonious scenarios (2 steps) are possible.

A) Courting song is ancestral; it disappears twice independently in Leptopsis and in

Acantoluzarida.

B) Courting song is ancestral; it is lost in the clade [Luzarida - Leptopsis], A subsequent reversal

occurs in Luzarida.

C) Absence of courting song is ancestral; a courting song appears twice independently in

Luzaridel/a and in Melanotes.

The combined analysis of the calling and courting songs (Fig. 22) shows that 3 equally

parsimonious scenarios exist for the acoustic evolution of the Luzarida group. They all have 4

Source. MNHN. Paris

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

195

Fig. 18. — Parsimonious scenario for the evolution of the aggressive song in tire Amphiacustae. Symbols: black triangle:

presence; empty triangle: absence; thick line: evolutionary change. Names of taxa as in figure 16.

steps and imply convergent changes of the calling song and, for two of them, of the courting

song too. The ancestral condition is absence of calling song, and presence or absence of courting

song. It should be noted that in all these scenarios the ancestrally absent calling song reappeared

twice independently, which does not corroborate the tested model.

DISCUSSION

What is the pattern of the evolution of acoustic communication in crickets?

Even if acoustic behavior is still incompletely known in the Amphiacustae and in the

Luzarida group, the phylogenetic analyses of the available songs partly invalidate current

proposals on the acoustic evolution of crickets. As already indicated above, the only hypothesis

which cannot be tested with these data is whether the courting song is the ancestral song for

crickets (Alexander, 1967; Bailey, 1991). However a courting song exists in all the taxa

which emit acoustic signals, while calling and aggressive songs may be absent.

I will consider the following questions in turn: are song losses documented? Are the

observed song combinations similar to those predicted by the model? Is the hypothesis of a linear

(regressive) transformation of acoustic repertoire attested by the phylogenetic patterns?

Songs are lacking in several taxa in the studied clades. This lack may concern the whole

three songs (mute taxa) or only one of them. The missing song is then either the calling song

(Nemoricantor in the Amphiacustae, Luzaridella in the Luzarida group) or the aggressive song

(Amphiacusta in the Amphiacustae). Both the absence of the calling song and the taxa muteness

could support the model of a regressive evolution of cricket acoustic repertoire (Fig. 9). The

absence of the aggressive song is however not consistent with it. Also the polarization of song

absence according to phylogenetic patterns suggests that a song absence in a taxon does not

necessarily mean that the song has been lost in that taxon. Song lack may be ancestral to a whole

clade. This means that song lack can be apomorphic or plesiomorphic, and this also is not

consistent with the model.

196

L. DESUTTER-GRANDCOLAS : ACOUSTIC COMMUNICATION IN CRICKETS

Fig. 19. — Equally parsimonious scenarios for the evolution of singing ability' in the Amphiacustae. Symbols as in figures 16-

18; ancestral states of attributes indicated in a frame. Names of taxa as in figure 16.

The song combinations assumed by the model shown in Figure 10 include (Call.

Court.Aggr.) as the ancestral condition, with (- Court. Aggr.) and (-) as derived conditions.

The last two combinations have been documented here. As mentioned above, however, the

combination (Call. Court. Aggr.) does not represent the ancestral condition in the studied

groups: the Amphiacustae ancestrally lack an aggressive song, while the Luzarida group is

Source: MNHN . Paris

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

197

Fig. 20. — Parsimonious scenario for the evolution of the calling song in the Luzarida group. Symbols: black circle: presence;

empty circle: absence; thick line: evolutionary change. Names of the taxa: Ac: Acantoluzarida , Al: Allochmtes , Le:

Leptopsis , Ld: Luzarida , LI: Luzaridella , Me: Melanotes , Oc: Ochraperites, Pa: Palpigera , Te: Tetragonia.

Fig. 21. — Equally parsimonious scenarios for the evolution of the courting song in the Luzarida group. Symbols: black

square: presence; empty square: absence; thick line: evolutionary change. Names of taxa as in figure 20.

Fig. 22. — Equally parsimonious scenarios for the evolution of the singing ability in the Luzarida group. Symbols as in

figures 20-21; ancestral states of attributes indicated in a frame. Names of taxa as in figure 20.

198

L. DESUTTER-GRANDCOLAS : ACOUSTIC COMMUNICATION IN CRICKETS

ancestrally deprived of a calling song. If the combination (Call. Court. Aggr.) was to occur in

these clades, owing to additional data for presently unstudied taxa, it would consequently

constitute a derived condition. Moreover, the combination (Call. Court. -), which characterizes

Amphiacusta, is not predicted by the model. Again the current model on the acoustic evolution

of crickets is only partly supported and is unable to explain the observed situation. Similarly,

none of the phylogenetic patterns presented here is congruent with the theoretical patterns of

figure 9, which means that the hypothesis of a linear loss of the songs is not supported by either

the Amphiacustae or the Luzarida group case studies.

The fact that current hypotheses on the acoustic evolution of crickets are not supported by

the phylogenetic analyses of the presence/absence of the songs, means that this evolution cannot

be summarized as mere multiple, progressive losses of songs. The phylogenetic analyses show

that neither the song combinations nor the polarization of character changes are only those

predicted by the model: other possibilities are documented, while some of those predicted by the

model are not supported. Phylogenetic patterns also suggest additional aspects of song evolution

in crickets that have never been expected before. First, reversals may occur. For example a song

which was ancestrally lacking in a cricket clade could reappear in a subclade. Such is the case for

the calling song in Luzarida and MelanOfes in the Luzarida group. Also convergent changes are

common in cricket clades, and there is no obligatory series between the possible song

combinations. Similar conclusions were drawn from phylogenetic analyses of stridulum evolution

(DESUTTER-GRANDCOLAS, 1996).

The complexity of the phylogenetic patterns that described the evolution of song and

stridulum in the studied cricket clades is not a unique phenomenon. Many authors have re¬

examined evolutionary hypotheses in a phylogenetic framework and documented complex

phylogenetic patterns, among which reversals are far from being unusual (ANDERSEN, 1979,

1994; CODDINGTON, 1988, CARPENTER, 1989; WANNTORP et ai , 1990; BROOKS & MCLENNAN,

1991; PACKER, 1991; Siddall et a!., 1993; Desutter-Grandcolas, 1993a, 1994a; ANDERSEN

& Weir, 1994; Grandcolas, 1996; many contributors, this volume). One consequence of these

results however is that the evolution of acoustic communication in crickets may have been much

more complicated than previously thought, at least in some cricket clades. The previous model

constructed to explain the evolution of acoustic communication in crickets s.l. hypothesized quite

simple transformation series. These series were in turn documented in relatively homogeneous

groups (mostly gryllid taxa), which populations could be easily studied. When a wide diversity of

tegminal structures and communication signals is involved, as in Phalangopsidae for example

(Figs 2-8), this model becomes inefficient GRANDCOLAS et al. (1997, this volume) denounced

the sampling bias that can be generated in phylogenetic reconstructions by the properties of the

clades under study: a clade that presents a wide diversity of features has experienced a larger

number of evolutionary events than a clade which is relatively homogeneous for the same

features. The study of a diverse clade may consequently lead to overestimate the frequency of

evolutionary changes and events. On the reverse, studies of poorly diverse clades may conclude

to low frequencies of evolutionary transformations. These biases do not invalidate the results

obtain in each case. On the contrary a general theory on the acoustic evolution of crickets will

have to explain the complicated cases documented in the Phalangopsidae, as well as the more

simple ones that could be found in other cricket groups.

Source:

PHYLOGENETIC ’IESTS OF EVOLUTIONARY SCENARIOS

199

Which factors may have influenced the acoustic evolution of crickets?

Answers to this question have always been based on the assumption that acoustic signals

only evolve by song and stridulum loss in crickets (ALEXANDER, 1962, 1967; OTTE, 1977, 1992;

WALKER & Masaki, 1989; Bailey, 1991). A similar approach was adopted by studies of

population biology dealing with song abilities and mating success (THORNHILL & ALCOCK, 1983;

HUBER el a/., 1989; BAILEY, 1991). The phylogenetic analyses presented here clearly

demonstrate that such is not the case: on the contrary, the acoustic evolution of crickets involves

a high level of homoplasy. The hypotheses formulated up to now to explain the acoustic

evolution of crickets have thus always been biased from the start, because an unwarranted

hypothesis (a supposed evolutionary tendency to acoustic loss) was considered attested. As such,

these hypotheses are unable to test whether loss actually occurred, or whether other evolutionary

changes may have existed. One consequence is that no sound hypothesis exists now on the

factors that could have influenced the acoustic evolution of crickets. Another problem, as already

mentioned previously, is that the hypotheses that have been proposed up to now are not mutually

exclusive. Thus the combination (- Court. Aggr.) could be used as evidence for the influence of

predation, inefficiency of acoustic communication, population structure and habitat. Ultimately

this means that the hypotheses that have been proposed up to now on the subject could be

conclusively tested in a population perspective but not in a historical perspective, although they

are supposed to concern evolutionary processes sensu lato.

What arguments have been used to support these hypotheses of acoustic evolution of

crickets? And have they already been analyzed in a phylogenetic framework? Although cricket

predation s.str. by many vertebrates and invertebrates has been recorded (WALKER & Masaki,

1989), its actual pressure has never been measured. Predation by bats in particular has been

assumed to be heavy. Some cricket species do show a high acoustic sensibility to ultrasound

stimuli, which has been demonstrated to induce negative phonotaxis in flight patterns (SALES &

PYE, 1974; HUBER et a/., 1989; HOY, 1991). Many mute taxa live however in habitats that are

not accessible to bats, such as leaf litter, tree hollows, burrows, etc., and still more acoustic or

non-acoustic species do not fly. The effect of parasites on the other hand, especially that of

tachinid flies, has been documented in populations of a few cricket species. In these infested

populations, some silent males, called satellites, stay near calling males and try to intercept the

females attracted by the songs of the calling males (Cade, 1975). It has been suggested that this

behavior could be an adaptation to avoid parasitoid infestation and constitute an alternative

strategy for mating (THORNHILL & ALCOCK, 1983; BAILEY, 1991). ADAMO et al. (1995) show

however in Gryllus integer , G. himaculatus and G. rubens that infestation enhances the tendency

of male crickets to mate, at least until tissue damage by the parasite is too high. Also Zuk et al

(1995) demonstrate that in a polymorphic population of Teleogryllus oceanicus silent males were

either parasitized, or able to switch to calling behavior depending on population density. The

effect of parasites on calling behavior is thus manifold in cricket populations and depends on the

conditions in which the populations live. Its effect on the evolutionary change of acoustic

behavior is then hard to predict for the moment until changes may have been actually fixed in

taxa (Schultz et al., 1996). A phylogenetic test of predation pressure could be achieved by

optimizing escape and acoustic behaviors displayed by the taxa; additional field work is then

necessary to characterize such behaviors.

200

L. DESUTTER-GRANDCOLAS : ACOUSTIC COMMUNICATION IN CRICKETS

The role of the habitat in the acoustic evolution of crickets has been tested using phylogeny

in the Amphiacustae (DESUTTER-GRANDCOLAS, 1995b). In this study, the phylogenetic patterns

suggested that the habitat alone cannot have been a sufficient factor to drive the acoustic

evolution of crickets. For example taxa living in caves either are wingless, or have a complete,

functional stridulum. Similarly in one given habitat, several acoustic behaviors can be found

(DESUTTER-GRANDCOLAS, op. c/7.). Population structure could be a more promising factor in

this matter, but unfortunately field data are extremely sparse. Only one taxon, Nemoricantor

mciya (Amphiacustae), has been studied in natural and laboratory conditions: it is gregarious,

living in hollow trees, and has no calling song (Boake, 1984a, 1984b). Lack of comparative data

impedes attempts to determine the role of habitat and population structure on song evolution.

Here again combined analysis of phylogeny on one hand, and habitat and population structure on

the other should permit a test of the gregariousness hypothesis.

Finally, male crickets may have glands in many parts of their body. Metanotal glands are

better known, but others exist on the hindtibiae, the wings, the tergites, the base of some sclerites

in male genitalia, etc. (OTTE, 1992; DESUTTER-GRANDCOLAS, 1995b). The only phylogenetic

analyses to date of glandular evolution in male crickets (Amphiacustae: DESUTTER-

Grandcolas, 1995b) uncovered no shift from acoustic to chemical communication systems,

except for the absence of metanotal gland in wingless taxa (probably for lack of protective

structure for the glands).

Up to now, most studies on the acoustic evolution of crickets have combined assumptions

on the patterns and assumptions on the processes, deriving the one from the other. Phylogenetic

analyses confront a phylogenetic pattern, built with as few hypotheses as possible, with

independently constructed hypotheses on the evolutionary processes (GRANDCOLAS et a!.,

1994). They actually test the hypothesized processes with the phylogenetic patterns, the

independence of the two sets of assumptions giving this method its power (GRANDCOLAS et a /.,

1997, this volume). Phylogenetic analyses have been applied here for the first time to the acoustic

evolution of crickets. These analyses have demonstrated that current hypotheses on the matter

are largely insufficient and biased. Instead they suggest far less simple scenarios for this evolution

with high homoplasy. They also clearly demonstrate that no sound hypothesis exists now on the

factors that could have influenced cricket acoustic evolution. In fact more phylogenies and more

population studies are needed to build new hypotheses.

ACKNOWLEDGEMENTS

Hie subject of this paper has been presented during the symposium “Phylogenetic tests of evolutionary scenarios”

organized by P. Grandcolas (E.P. 90 CNRS, Musdum National d’Histoire naturelle, Paris) in Paris (3-4 June 1996), with the

financial support of the Reseau National de Biosystematique (ACC-SV7). I thank three referees for their very useful

comments on the manuscript, and J. Boudinot, M. Franey, G. Hodebert for their help concerning the figures.

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Source: MNHN. Paris

Defense Strategies in Scale Insects: Phylogenetic Inference

and Evolutionary Scenarios (Hemiptera, Coccoidea)

Imre Foldi

E.P. 90 CNRS. Laboratoire d'Entomologie, Museum national d'Histoire naturelle,

45. Rue Buffon, 75005 Paris. France.

ABSTRACT

The sedentary plant-parasitic habit of scale insects increases their vulnerability to natural enemies and to adverse

environmental factors. They have evolved a range of defense strategies which improve their chances of survival and

reproductive success. These strategies are reviewed here. They include: 1. construction of protective structures from secretions

and/or excretions produced by the scale insects; 2. behavioral adaptations to exploit host-plant afforded protection; 3

modifications of their life-cycle in response to environmental factors; and 4. modifications of the female body to provide

protection for their progeny. ITe structure and formation of these protective structures were examined using SEM and by

experimentation. A cladistic phylogenetic analysis of scale insects using 54 morphological characters and 25 genera resulted

in two most parsimonious trees. This phytogeny was then used as a reference to provide hypotheses regarding the ancestral

state and the subsequent evolution of habitat choice and the type of protective structure, especially in the nymphal stages

Phylogenetic analysis suggests that the ancestral habitat attribute (feeding site) is equivocal and currently we can not choose

between the aerial (bark) or underground (roots) habitats. Hie subsequent adaptation led to colonization of branches, leaves

and grasses. Most successful groups are adapted to the aerial part of woody host plants, particularly on the branches, which

are the most exploited feeding sites by scale insect populations today. The ancestral type of protection is inferred to have been

amorphous secretions. Subsequently, different clades probably independently developed protective tests with different

combinations of secretions and anal fluid components, with a trend to find a compromise between energy costs and efficiency.

RESUME

Strategies de defense des Cochenilles : Inference phylogenetique ct scenarios evolutifs (Hem ip teres : Coccoidea)

La vie sedentaire des Cochenilles accroit leur vulnerability face a lews ennemis naturcls et aux conditions de

renvironnement. Elies out developpe au cours de leur evolution diverses strategies de defense, qui augmentent leurs chances

de survie et leurs succes reproducteurs. Ces strategies sont analvsees, en distinguant parmi elles 1. l'elaboration de structures

de protection a partir de leurs secretions et/ou de leurs excretions ; 2. l’exploitation de reflet protecteur offcrt par leurs

plantes-hotes , 3. la modification de leur cycle evolutif en reponse aux facteurs environnementaux ; 4 la modification

profonde du corps des femelles pour la protection de leur descendance. L'utilisation du microscope electronique a balayage,

ainsi que diverses experimentations, ont permis d'expliquer la formation de ces structures. Une analyse cladistique portant sur

25 genres a partir de 54 caracteres morphologiques a donne deux arbres equiparcimonieux. Cette phvlogenie sert de reference

pour etablir l'etat ancestral et les changements subsequents, a la lois pour le choix de lTiabitat et pour le type de structure de

protection. L'analyse phylogenetique suggere que l'etat ancestral est equivoque et actuellement nous ne pouvons pas choisir

entre un habitat aerien (tronc) et un habitat souterrain (racines). II est plus parcimonieux de considerer la protection par des

secretions amorphes comme l'etat ancestral Les changements subsequents de l'habitat ont conduit a la conquete des branches,

Foldi, I., 1997. — Defense strategies in scale insects: phylogenetic inference and evolutionary scenarios (Hemiptera.

Coccoidea). In: Grandcolas, P. (ed ), The Origin of Biodiversity in Insects: Phylogenetic Tests of Evolutionary Scenarios.

Mem. Mus. natn. Hist, nat., 173 203-230. Paris ISBN : 2-85653-508-9.

204

I FOLDI: DEFENSE STR.4TEGIES IN SCALE INSECTS

des feuillage des arbres et arbustes et des tiges de graminees. La branche est la partie la plus exploitee des plantes-hotes. La

protection a etd tout d'abord assuree par des secretions non organisees recouvrant le corps, puis par la constmction de

structures de plus en plus complexes, avec une tendance a trouver un compromis entre les depenses energetiques et

l'efficacite.

INTRODUCTION

The adult females of contemporary scale insects are neotenic and apterous and are adapted

to a sedentary parasitic habit, sucking sap from their host plant's vascular tissue. Not only have

the Coccoidea colonized many plant families but they have also exploited all parts, with species

living on the leaf sheaths, hypocotyl and roots of grasses and on the trunks, branches, leaves and

fruits of shrubs and trees. Scale insects are often an important component of phytophagous

ecosystems, especially in tropical and subtropical areas and many species are injurious to

cultivated plants, such as vines, palms, citrus, forest or ornamental trees and also to indoor

plants. They occur in all zoogeographical regions of the world and in a wide range of

ecosystems, from dry desert to cold tundra, humid forest or high up mountains.

These sedentary insects have evolved a series of original and effective protective structures

ensuring their survival in these diverse environments, providing not only a favorable

microenvironment with regard to temperature and humidity, but also some degree of protection

against such natural enemies as predators (mainly Coleoptera) and parasitoids (primarily

chalcidoid wasps) and also against chemicals and air pollutants.

The scale insects are undoubtedly a natural group and their evolution is particularly

interesting because the Coccoidea display a remarkable diversity of often unusual structural and

biological features. However, the relationships of several family-group taxa, as well as the

monophyly of some families remain controversial and not well established. Several authors have

attempted to estimate phylogenetic relationships within the Coccoidea but until now such

estimates have been largely intuitive. In these cases, the proposed phylogenies are not refutable

and cannot be submitted to the test of adding new taxa and new characters. A comprehensive

and interesting phylogenetic analysis of Coccoidea has been carried out by DANZIG (1980). The

following works: Danzig (1984, 1990), Cox & Williams (1986), Cox (1984), Foldi (1984),

Koteja (1974), BORATYNSK1 & Daves (1971) and Borchsenius (1956) used analytical

methods other than cladistics and are, therefore, less easily supported MILLER & KOSZTARAB

(1979) and Kosztarab (1996) presented phylograms of the intuitively modified cladograms of

Boratynskj & Daves (1971) and Danzig (1980), respectively. The use of cladistic analysis

has recently been developed among coccidologists to estimate sister-group relationships within

the Coccoidea (Miller, 1984; Miller & Miller, 1993a, 1993b; Foldi, 1995; Miller &

Williams, 1995; Qin& Gullan, 1995; Hodgson & Henderson, 1996).

In the present work, the adaptive defense strategies in scale insects were studied, and in

order to test various scenarios for the evolution of the main habitats and protective structures for

some of the main taxa of the Coccoidea, an independently reconstructed phylogeny was used as

reference (Coddinoton, 1988; Carpenter, 1989; Deleporte, 1993; Grandcolas et a/.,

1994, DESUTTER-GRANDCOLAS, 1994; MELER & WENZEL, 1995; ANDERSEN, 1995; SCHULTZ et

a/., 1996). These biological attributes (habitat and type of protective cover) have been mapped

on a cladogram and polarized by optimization with principle of parsimony and it is hoped that

this may provide a reasonable hypothesis of the ancestral state and its subsequent direction of

historical transition.

Source:

PHYLOGENETIC TESTS OF EVOLU TIONARY SCENARIOS

205

MATERIALS AND METHODS

Porphyrophora chrithmi was reared in a greenhouse on Crithmum maritimum (Umbelliferae), whereas Eurhizococcus

brasiliensis , Margarodes cadeti, M. vilis were reared on Solatium tuberosum and Cucurbita maxima and F.riococcus buxi on

Buxus sempervirens. Cladistic analysis was implemented with the Paup 3.1.1. (Swofford, 1991) and MacClade 3.05

(Maddison & Maddison, 1992) computer software packages. Character change analysis was performed by MacClade and the

parsimony analysis of the character matrix with the “Heuristic search” algorithm of Paup with the “acctran” optimization.

Multistate characters were treated as unordered and characters were unweighted. Unknown characters were coded as missing

data. The size and structure of data matrix prevented the use of the exhaustive or branch and bound methods. The data matrix

included 25 genera, representing each of the currently recognized scale insect families, with 54 characters from adult females,

adult males and first-instar nymphs. Data were gathered either from published information (Green, 1922; Jakubski, 1965;

Richard, 1986; Takagi, 1987, 1992; Gill, 1988, 1993; Kosztarab & Kozar, 1988; Williams & Watson, 1990; Morales]

1991; Miller, 1991; Marotta et al., 1995) or from direct examination of specimens as follows; Matsucoccus feytaudi

Ducasse (Margarodidae); Margarodes formicamm Guilding (Margarodidae); Stigmacoecus asper Hempel (Margarodidae);

Carayonema orousseti Richard (Caravonemidae); Orthezia urticae (Linnaeus) (Ortheziidae); Phenacoleachia zealendica

(Masked) (Phenacoleachiidae); Conchaspis vayssierei Mamet (Conchaspididae); Planococcus citri (Risso) (Pseudococcidae);

Eriococcus buxi (Fonscolombe) (Eriococcidae); Kermes vermilio Planchon (Kermesidae); Dactvlopius coccus Costa

(Dactylopiidae); Coccus hesperidum Linnaeus (Coccidae); Cerococcus quercus Comstock (Cerococcidae); Asterodiaspis

variolosa (Ratzeburg) (Asterolecaniidae); Lecanodiaspis sardoa Targioni-Tozzetti (Lecanodiaspididae); Aclerda berlesii

Buffa (Aclerdidae); Tachardia albizziae Green (Tachardiidae); Micrococcus silvestri Leonardi (Micrococcidae); Stictococcus

intermedius (Stictococcidae); Phoenicococcus marlatti Cockerell (Phoenicococcidae); Hahmococcus thebaicae Hall

(Halimococcidae); Beesonia napiformis Kuwana (Beesoniidae); Chionaspis salicis (Linneaus) (Diaspididae). The aphids

(Aphidoidea), traditionally considered as forming the sister-group of the Coccoidca and recently confirmed by cladistic

analysis of molecular data (Sorensen et al., 1995; von Dohlen & Moran, 1995), were used as outgroup to determine

polarities of characters ( Eriosoma spp. (Pemphigidae) and Myzus persicae (Aphididae).

To test hypotheses regarding the evolution of particular biological attributes, this independently obtained cladogram

was used as a reference system. The biological attributes (habitats, i.e. feeding sites on host plants, and protective structures)

were then mapped on this cladogram The scenario for their evolutionary' changes was derived by optimization using the

principle of Wagner parsimony and unordered states with MacClade 3.05 computer software.

TYPES OF DEFENSIVE STRATEGIES OF SCALE INSECTS

The strategies which have evolved to defend the bodies of scale insects and their progeny

(eggs and newly hatched first-instar nymphs) can be divided into four major groups:

1. production of structures which are made from secretions and/or excretions which either

adhere to the body or form amorphous waxy secretions, cysts or separate tests; this type of

protection, from simple to complex, is the most widespread and the most characteristic of

Coccoidea;

2. specific choice of settling site to exploit host-plant afforded protection ( e.g. those which

live beneath bark, under leaf-sheaths or on the nodes of grass stems, or which are gall formers);

3. modifications of the life-cycle in response to environmental factors, as found in the cyst-

forming Margarodinae;

4. modification of the body of the female to provide a protective cover, such as by the

formation of a marsupium, as in the Margarodids, or the heavy sclerotization of the dorsum of

soft scales, in Kermesids or Stictococcines.

All Coccoidea are protected by one of the mechanisms described above. In some unrelated

groups or in groups in which the protective mechanism has evolved convergently, it is probably

dictated by habitat-required defense strategies. However, JASCHENKO (1993) observed that some

Margarodids living in desert may utilize complementary protection and show particular

ecological adaptations, e.g. the scale insects may form a buffer layer around their body or leave

206

I. FOLDI. DEFENSE STRATEGIES IN SCALE INSECTS

the soil surface for a deeper ground layers. Mutualistic relationships with ants may appear in

some group as an alternative strategy for their protection. These four categories will now be

discussed in more detail.

STRUCTURES CONSTRUCTED FROM SECRETIONS / EXCRETIONS

PRODUCED BY SCALE INSECTS

Most scale insects secrete a series of external protective covers during each stage of their

development. These covers or tests regulate the temperature and control water loss, thus

maintaining an equable microclimate beneath the test, so that, when the test is removed, the

Coccoids die through desiccation. The diverse methods which have evolved to protect the eggs

have been illustrated recently by KOTEJA (1990).

The material used in the construction of these covers is secreted (i) by the well-developed

wax gland systems typical of Coccoidea and also (ii) from other substances eliminated through

the anus - i.e. the final products of metabolism. The range of integumentary glands which secrete

the former are diverse and their secretions are transported to the body surface through

specialized cuticular structures: pores, ducts, ductules and secretory setae (FOLDI, 1991). The

shape taken by these secretions is dictated by both their chemical composition and by the shape

of these cuticular structures, which act as moulding devices. These secretions are always

mixtures, the two most common components being waxes and resins. The relative amounts of

these components determine the characteristics of each secretion which, in turn, determine the

color and hardness of the protective covers. These secretions also play an important role in the

protection of the respiratory pathway and in assisting in honeydew elimination (FOLDI & PEARCE,

1985).

Protective covers constructed from ana! fluids

Based on the materials used in the construction of the test or cover, it is possible to

distinguish five types of protective cover, namely those constructed from: anal fluids, mixtures of

filamentous wax secretions and anal fluids, mixtures of filamentous and amorphous wax

secretions, exclusively from amorphous wax secretions, and exclusively from filamentous wax

secretions.

Cyst formation. Both sexes of species belonging to the subfamily Margarodinae have an

unusual postembryonic development that includes an atypical second-stage nymph, commonly

referred to as the cyst stage (Figs 8, 10, 12). The nymph of this cyst stage is legless and is

completely enclosed in a shell constructed from anal fluids by the insect. The enclosed nymph has

Figs 1-7. — 1:. Adult female Kermes robotis Fourcroy (Kermesidae). 2: Two adult female tests of Unaspis yanonensis

(Kuwana) (Diaspididae). 3: Group of adult female Lecanodiaspis sardoa Targioni-Tozzetti (Lecanodiaspididae).

4: Adult female Beesonia dipterocarpi Green (Beesoniidae) located under the bark of its host plant. 5: Apiomorpha

conica (Frogatt) (Eriococcidae) showed the adult female in its gall. 6: A colony of adult female Gascardia

madagascariensis Targioni-Tozzetti (Coccidae). The scale insects are engulfed in a thick yellow test composed of

secretions + excretions. 7: Detail of Fig. 6 showing a fragment of test with the included females.

Source.

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

207

Source. MNHN, Pahs

208

I FOLDI: DEFENSE STRATEGIES IN SCALE INSECTS

well-developed, functional mouthparts and, in most cases, the body is large and globular

(although it may sometimes be elongate) but it always contains a large quantity of fat body.

When the host plant lives in good environmental conditions (rain and sun assured), this cyst stage

can last from several months to about a year, depending on the species. However, under

unfavorable ecological conditions ( e.g . prolonged dry period causing the death of the host plant),

the cyst stage may be extended to several years. The second moult occurs within the cyst, giving

rise to the adult female, which again possesses legs and antennae. Emergence of the adult female

from the cyst is by first using the anterior legs to make a small opening in the shell wall and then

squeezing through to exterior. This is possible due to the great flexibility of the body. In bisexual

species, the adults then migrate to the soil surface to mate, and after this the females move back

down into the soil and oviposit on or near the roots (FOLDI, 1990a).

The function of these cysts or shells has long remained unclear, mainly because the

anatomy of the nymphs has not been well studied and because the structure and the processes of

cyst formation have not been understood. The structure and formation of the cysts of

Margarodes formicarum, M vitis, Eurhizococcus brasiliensis and Porphyrophora crithmi were

therefore studied, both experimentally and by the use of the scanning electron microscope (Figs

8-13). In most cases, the young first-instar nymphs settle on the host plant with their head down

and their anus up. After settling and feeding, the secretion starts from the spiracular wax glands,

while droplets appear from the anus and these slowly flow around the posterior end of the body

and solidify (FOLDI, 1981). Sometimes several droplets are expelled in rapid succession. Even

where the nymph settles in an oblique or horizontal position, the anal liquid flows over the body

in the same way. The continuous feeding produces a rounded body and the anal liquid, which is

regularly extruded, forms more and more overlapping layers on the body surface. If the anus is

cauterized at this stage, the production of the anal liquid ceases and the construction of the shell

stops. Alternatively, if the outer shell is removed experimentally, droplets continue to appear

from the anus and shell formation commences once again, with the body gradually becoming

covered with fine layers of secretion, the cyst finally becoming entirely enclosed. Electron

microscope studies have confirmed the existence of 5 to 30 or more overlapping layers, each

layer composed of an amorphous substance of equal or varying thickness, ranging from 5 to 100

pm thick (Figs 9, 11, 13). Thus, it appears that the structure of the cyst or shell is made

exclusively from anal liquids eliminated by the nymph. The hardness, colour, size, shape and

external surface morphology of these cysts varies considerably from one species to another. The

hardness and colour are determined by the final metabolic products, and these are linked to the

chemistry' of the sap of the host plant and perhaps also to the secretions of some currently

unknown glands located in the digestive system. In addition, the external surface of the cyst may

include many extraneous particles, such as sand, earth or pieces of vegetation and these particles

may completely mask the protective tests.

Figs 8-13. 8-9: Cyst stage o( Margarodes fomiicantm Guilding (Margarodidae). The cyst wall is formed by numerous

overlapping layers of anal fluid. 10-11: Cyst stage of Margarodes vitis (Philippi) (Margarodidae) with the detail of its

wall structure. 12-13: Cyst stage of Porphyrophora polonica Linnaeus (Margarodidae) and the detail of its wall

showing the layered structure.

Source:

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

209

Source: MNHN. Paris

210

I. FOLDI: DEFENSE STRATEGIES IN SCALE INSECTS

These cysts are generally located on the roots or collar of their host plants and are also

referred to as “ground pearls”. This name comes from their external appearance and their habitat.

They are found in the sand or soil and are hard, round and pearl-like, often shiny and colorful,

even sometimes slightly iridescent. There are ethnozoological reports of ground pearls being

used for human utility. Like true pearls, ground pearls are strung on a filament and sold as

necklaces in Bermuda and neighboring islands, in the Mediterranean area and wherever probably

Margarodes pearls are found.

Protective tunnel formation. Anal fluids are also used by Limacoccus spp. (Beesoniidae)

for the construction of their protective tunnel. In this genus, after the first moult, the second-

instar females are located inside the exuviae. The produced anal fluid is pushed forward by the

body's contraction and it is extruded through the exuvial split to the exterior. By the movement

of the anterior part of the body, the nymph forms a semicircular tunnel in the anal substance

which solidifies quickly. The nymph advances progressively in this tunnel and settles outside for

the second moult. The wall of the tunnel is composed of numerous hard layers (FOLDI, 1995a).

Structure and formation of separate tests using filamentous wax secretions and anal

fluids. The scale covers of the Diaspididae represent the most elaborate type of protective

structure whose physical properties provide an effective barrier. They are formed from a

combination of waxy filaments, mostly secreted by pygidial glands, which are cemented together

by the successively extruded anal fluid, and formed either in a circular or an elongated shape by

the movements of the body. The exuviae of previous instars are also incorporated into these

covers (Fig. 2). Cover formation and how such factors as cauterization of the anus, delayed

mating or insufficient food interfere with its construction are described in detail by FOLDI (1982,

1990b, 1990c). The cover formed by the Conchaspididae is constructed in a similar manner,

except that it does not incorporate the exuviae and the anal secretions are not distributed actively

over the dorsum (FOLDI, 1983).

Structure and formation of separate tests using filamentous wax secretions and

amorphous secretions. Such species as Cryptokermes brasiliensis Hempel (Margarodidae),

Stigmacoccus asper Hempel (Margarodidae) and Ultracoelostoma assimile (Masked)

(Margarodidae) form a protective test in which all stages of development are enclosed. The

structure and the process of formation of the protective test was studied in Cryptokermes

brasiliensis using SEM (Figs 14-21). The first-instar nymphs settled in crevices in the bark of

i'itis sp. and started feeding. Waxy secretions were produced by multilocular wax glands which

covered all the body; these were either short, curved secretions or long filaments (Fig. 14).

Figs 14-21. — 14-15: First-instar nymph of Cryptokermes brasiliensis Hempel (Margarodidae). The filamentous secretions

covering the body is completed by a series of soft ball shaped secretions. 16: Dorsal cicatrix of Cryptokermes

brasiliensis Hempel (Margarodidae). 17: Large spine-like structures with their amorphous secretions on the dorsum of

Cryptokermes brasiliensis Hempel (Margarodidae). 18-19: Detail of the coalesced ball shaped amorphous secretions

among the filamentous secretion of C. brasiliensis Hempel (Margarodidae). 20-21: Section of the cyst stage of

Cryptokermes brasiliensis Hempel (Margarodidae) showing its wall structure.

Source:

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

211

Source: MNHN, Paris

212

I. FOLDI: DEFENSE STRATEGIES IN SCALE INSECTS

Simultaneously, the perianal and anal wax glands started to produce a waxy anal tube which

served to eliminate the honeydew. This tube reached twice the length of the 1 st-instar body after

only about 24h. Amongst this tangled, loose network of secretions some small, soft, ball-shaped

amorphous secretions appeared which originated (i) from numerous cicatrices scattered on the

dorsum and (ii) from large spine-like structures scattered between the cicatrices (Figs 15,

19).These amorphous secretions were scattered over the body and hardened slowly. They

gradually increased in size and number so that they finally coalesced together. The shape of test

covering the 1 st-instar nymphs was fusiform, corresponding to the shape of the nymph's body,

although the dimensions of the internal cavity was larger than the size of the body. After the first

moult, the test (which was not completely finished yet) became more and more globular. The

2nd- and 3rd-instar nymphs continued to add new secreted material to the wall of the test,

increasing its thickeness. By the time the insect was adult, the test was 5-6 mm in diameter and

had a very rough external surface which was covered with bumps. In transverse section, the test

wall was 0.5-0.6 mm thick and appeared to have an external layer formed from the ball-shaped

amorphous secretions and an inner layer which was an amorphous mass (Figs 20-21). The test

was very hard and the final colour was black. The adult females remained enclosed in this test

and mating occurred through a small opening left by the anal tube of the immature stages; this

aperture was also used by the newly hatched nymphs for dispersal. Lecanodiaspis sardoa

Targioni-Tozzetti (Lecanodiaspididae) (Fig. 3) constructs a protective test which is formed from

long filaments, secreted by the tubular duct wax glands, which are cemented together by

amorphous secretions produced by the cribriform plates and the 8-shaped pores (FOLDI &

Lambdin, 1995).

Structure and formation of separate tests using exclusively amorphous secretions or

mixture of amorphous secretions and ana! fluid. There are two types of amorphous secretions,

the first is produced by the spine-like setae in Ortheziidae and the second by a variety of different

wax gland systems found in the remaining scale insect taxa. In the majority of soft scales, the

dorsal integument is covered by an amorphous and layered secretion, which increases the

thickness of the dorsum and assists in its resistance to unfavorable external factors. In Inglisia

vitrea Cockerell (and other Cardiococcinae), the cover is composed of a glassy, transparent

covering composed of resin. This test is comparable to that found in the Asterolecaniidae, in

which the test enclosing the female is also amorphous, hard and transparent. In Cerococcus

quercus Comstock (Cerococcidae), the test of the adult females is an amorphous, yellow, smooth

structure, although it has long waxy filaments on the inside. When the populations of these scales

are dense, the tests fuse together to form a large mass on the twigs. The exuded mixture of

amorphous secretions and anal fluid is so abundant in Kerria lacca (Tachardididae) and

Gascardia madagascariensis (Coccidae) that it engulfs the entire colony forming the

characteristic “stick secretions” on the twigs (Figs 6-7).

S tructure and formation of separate tests using exclusively filamentous secretions. The

use of only filamentous secretions for their protection is found on the adult females of many

Margarodinae, Eriococcidae and on such soft scales as the Eriopeltinae or Filippiinae. The

filamentous secretions forming either a loose network or a more structured test but it covers

always some or all of the dorsal surface of the female.

Source

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

213

Ovisac-like structures. After mating, the females of several groups (some Eriococcines, soft

scales and Margarodids) produce filamentous secretions that enclose the female's body and also

her eggs and newly-emerged nymphs. Other species construct a specific structure, the ovisac,

which exclusively encloses the eggs and newly hatched nymphs. Thus, we can distinguish ovisac¬

like structures that enclose the female plus her eggs and nymphs from an ovisac constructed

exclusively for protecting eggs and nymphs. The ovisac-like structure is found in female

Eriococcus buxi (Fonscolombe), (Eriococcidae). This species construct a separate, felted sac-like

test which encloses the body and eggs, except for a small hole at its posterior end. When

observed by SEM, the wall of this test is made exclusively from a dense network of waxy

filaments secreted by the tubular duct wax glands. Within this test, the eggs are covered by a

loose network of short waxy filaments secreted by the ventral multilocular disc-pores. These

protective tests cover the whole of the female's body and also the eggs and are composed of a

loose network of filamentous waxy secretions. This ovisac-like structure cannot be considered as

homologous to a true ovisac. For instance, mated female Margarodinae secrete by the

multilocular wax glands distributed on the entire body a loose network of long waxy filaments,

which encloses both the adult female and eggs. Flowever, in addition, short curved filaments are

secreted by the wax glands of the same type but with inclined loculi, that are distributed around

the vulva, and these filaments cover the surface of the eggs. In some species, such as those in the

genus Gossyparia (Eriococcidae), the filamentous secretions which protect the eggs only

partially cover the adult female along the margins.

Ovisac. Many females Coccoids protect their eggs during embryonic development and then their

newly hatched crawlers by constructing a true ovisac. Several unrelated groups of Coccoidea

such as the iceryine Margarodids, Ortheziids, Pulvinarine soft scale, Kermesids - e.g. Nidularia

pulvinata (Planchon) - and many mealybugs secrete a white ovisac. These ovisacs are

characteristic structures, secreted by divers wax glands, which are clearly produced from beneath

the posterior end of the abdomen of the adult females and are often ornate and have a

characteristic shape. The presence of this type of ovisac in such a wide range of Coccoidea

suggests that they evolved convergently. In groups with tubular duct wax glands, these are

considered to secrete the external part of the ovisac, as in pulvinarine, filippiine and eriopeltine

soft scales (HODGSON, 1994); indeed the Pulvinariini generally have three or four different types

of ventral tubular ducts and also produce the most complex ovisacs within the Coccidae, in terms

of the types of wax making up their ovisac (HODGSON, personal communication). In the simplest

cases, the ovisacs are composed of two types of secretions: (i) an outer layer made of long

filamentous waxy secretions which are thoroughly cemented together and which form a solid

outer layer, and (ii) an inner layer composed of short, generally curved, waxy secretions which

form a loose network around the eggs. In other taxa, such as in some soft scales species

numerous types of wax glands may participate in its construction. An exception is found in the

Ortheziids, in which the external part of the ovisac is made of (a) amorphous waxy secretions

produced by the spine-like setae located in a large submarginal band on the abdomen and (b) by

the long, thin filaments produced by the quadrilocular pores on the inner part. The construction

of these ovisacs only starts after mating and is often finished whilst females are still laying. The

best known example is the cosmopolitan Iceryci purchasi Masked which secretes an ovisac often

214

1. FOLDI: DEFENSE STRATEGIES IN SCALE INSECTS

longer than its body, in which the hard, ornate and beautiful outer part is produced by two types

of ventral wax glands: externally on the body margin are the large open centred pores and

internal to these are the multilocular pores which form a broad submarginal band around the

abdomen. The inner, looser part of the ovisac (which encloses the eggs) is secreted through the

multilocular disc-pores around the vulva area. The red colour of the newly hatched lst-instar

nymphs, with black legs, are clearly visible within this white, cottony sac.

BEHAVIORS WHICH HAVE EVOLVED TO EXPLOIT PROTECTION

AFFORDED BY THE HOST PLANT

Many Coccoids settle in confined, protected feeding sites provided by their host plants,

such under leaf-sheaths, leaf-axils, nodes of grass, in crevices or under bark, and on roots and

root-crowns. This behavioral adaptation to protected feeding sites may be observed in most

higher taxonomic groups in the Coccoidea, however the largest diversity is found in the

Margarodidae s.i

Species which live beneath bark or in bark crevices

Species of the genera Knwania , Steingelia, Neosteingelia, Xylococcus and Xylococculus

live under the bark of such trees as Pinus, Primus and Quercus. Matsucoccus spp. live in cracks

and crevices or under the bark of Pinus spp In these taxa, the cyst stage secretes a glassy test (as

described above), while the adult females secrete white woolly waxen threads over the body.

Species which oviposit beneath bark and otherwise live on the lecn>es. Stomacoccus

platani Ferris lays its eggs beneath the bark on the trunk of the host tree. The newly-hatched lst-

instar nymphs emigrate to the undersurface of the leaves. When fully growm, the mated females

migrate back to the trunks and lay the eggs beneath the bark.

Species which live beneath leaf-sheaths or on the nodes of grass stems. Several

eriococcine, pseudococcine and coccine species live under the leaf-sheaths or on the nodes of

grass stems. Their bodies tend to be flattened dorso-ventrally and are only weakly covered by

waxy secretions, although the body of Ac/erda berlesii Buffa (which lives under the leaf-sheaths

on the stems of Arundo donax) is surrounded by a large amount of glassy secretion. However,

the body of/l. berlesii is also flattened dorso-ventrally and becomes strongly sclerotized in old

females.

Gall formation. Galls are products of host-insect interactions and are a response by the

plant to chemical stimuli from salivary glands of the gall former. The gall-forming arthropod

benefits in having an improved food supply, good environmental conditions and reasonable

security. Extensive studies have been made on the gall-forming Coccoidea by Gullan

( 1984a,b,c) and BEARDSLEY (1984) The majority of galT-forming scale insects belong to the

Eriococcidae, which are abundant in Australia, principally on Eucalyptus. Galls formed by adult

females of Apiomorpha Rubsaamen (Fig. 5) have species-specific morphology and vary greatly in

size and shape, from cylindrical to globose and sometimes with arm-like extensions (GULLAN,

1984a,b). Galls of Apiomorpha are also sexually dimorphic, with the galls of males being much

smaller than those of females. There are only two gall forming Margarodids currently known,

Matsucoccus gal/icolus Morrison and Araucaricoccus queenslandicus Brimblecombe. With M.

Source: MNHN, Paris

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

215

gallicolus , which is a pest on pitch pine, the feeding activity of the crawler causes the host-plant

tissues to collapse, forming a depression beneath its body. By the time it moults to form the cyst

stage, about six to nine weeks later, the host-plant tissue has grown to completely cover the

Margarodid, except for a small hole. Once adult, the females generally disperse through this hole

to the outside, although sometimes the hole is too small and the female is then obliged to stay

and oviposit within the gall.

ADAPTATIONS OF THE LIFE-CYCLE

TO AVOID ADVERSE ENVIRONMENTAL CONDITIONS

The cyst of some species of Margarodes is highly resistant to adverse environmental

conditions, which they are capable of surviving for a long time, only undergoing their last moult

when conditions are again favourable. Prolonged absence of rain provokes the death of the host

plant and, when again it rains, this water humidifies the soil around the cysts, which initiates their

moult. Mayet (1896) noticed that the cysts of Margarodes vilis (Philippi) emerged as adult

females once they had been immersed in water, even though they had been kept without food for

seven years, while FERRIS (1919) reported an adult M. vilis emerging after seventeen years of

storage. Like M. vilis, species which are capable of surviving such long periods have a highly

resistant shell, with a thick and very hard wall. Similar observations were made by De KLERK el

al. (1980) on Margarodes capensis when females detached from their host plants under

laboratory conditions could emerge during four successive years. My personal observations on

the cysts of several Margarodes spp. is that their long-term survival is assured only for the

nymphal stages and not for the adult females, even if the latter stay inside the cyst. The adult

female of the cyst-forming species also have the ability to move from an unsuitable habitat to a

suitable one, which is a characteristic that most scale insects have lost.

This protection afforded by the cysts is particularly important when the species are

injurious to cultivated plants. For example, the cyst-forming Margarodids (Eurhizococcus

brasiliensis and Margarodes vitis), injurious to vineyards in South America, are able to resist

most control measures, including soil-applied insecticides (FOLDI & SORIA, 1989). This ability of

the cyst-forming species to survive unfavorable conditions is almost certainly more widespread

than we currently know but our observations are mostly limited to those species which are of

economic importance.

PROTECTION PROVIDED BY MODIFICATIONS OF THE BODY OF THE FEMALE

Alternative strategies for protection have been developed by some groups of Coccoids

where the body of the adult female has become modified to provide protection, either by the

ventral surface becoming invaginated to form a marsupium, as in several Margarodids, or by the

dorsum become strongly sclerotized, as in Kermesids, many soft scales and Stictococcids.

Formation of a marsupium

Although plesiomorphic in condition, the marsupium is the most remarkable invention for

protecting the eggs and crawlers. Based on the method of formation ot the marsupium, we can

distinguish two types: (i) the internal marsupium is formed by a deep invagination ot the

integument within the body to form a large cavity, whereas (ii) the external marsupium is formed

by depression of the ventral integument and the resulting cavity is covered by a secreted

216

I. FOLDI: DEFENSE STRATEGIES IN SCALE INSECTS

operculum. An internal marsupium is found in a number of unrelated genera of Margarodids,

e.g., Callipappus, Sleatococcus and Etropera spp. After mating, a deep invagination of the

integument appears in the teneral female, either ventrally or in the posterior part of the abdomen,

forming a cavity (MORRISON, 1928). Initially, the cavity is small but it progressively deepens

during egg-laying. It is normally restricted to the abdomen but can extend even into the

cephalothorax area. In species of Sleatococcus, Etropera and Perissopneumon , the cavity is

formed by the invagination of the sterno-abdominal integument. The vulva opens dorso-

posteriorly into the marsupium and the eggs are laid directly into it. In Callipappus spp., this

invagination is at the posterior end of the body, but can extend anteriorly within the body cavity

as far as the head, as in Callipappus westwoodi Guerin-Meneville in which the long, narrow

vagina opens antero-dorsally through the vulva into the marsupium.

The external opening of the marsupium in different taxa is highly variable. In Sleatococcus

spp., the opening is circular and is placed medially near the metathoracic legs, surrounded by

numerous multilocular wax glands; in Etropera spp. (BlIATTI & GULLAN, 1990), the opening is

large, forming an arc, whose outer margins lie near the metathoracic legs but which lack wax

glands, while in Callipappus spp. the opening is also large but is elongate and located at the

posterior end of the body. In females possessing an external marsupium, a part of the ventral

abdominal region containing the vulva becomes depressed and is then isolated from the exterior

by an operculum composed of wax secreted by a large band of glands which surround the cavity.

These glands produce large quantities of waxy filaments which become cemented together by an

amorphous secretion. These opercula are solid, resistant to outside pressures and very hard to

detach from the body. The eggs are laid inside this protective cavity and, once the nymphs have

hatched, they leave through a small opening at the anterio-medial part of the operculum. There is

considerable diversity in the size of these pseudo-marsupial pouches and their opercula. In

species of Aspidoproctus and Hemaspidoproctus, the cavity is small, located in the central part of

the abdomen and the operculum is thick and resistant. In Gigautococcus maximus (Newstead),

the cavity is about 3 mm deep, incorporating most of the ventral surface of the abdomen, but

with a rather softer and thinner operculum (BIELENIN, 1971).

Using the dorsal surface of the body as the protective cover

In this group, the dorsal cuticle of the female becomes thickened and strongly sclerotized at

maturity, whereas the ventral surface remains thin and often becomes deeply invaginated,

forming a cavity under the body which becomes a brood chamber used for holding the eggs and

the crawlers. This method of protection is typical of the Kermesids, many soft scales - e.g.

species of Saissetia , Coccus, Parthenolecanium and many others (HODGSON, 1994) - and the

Stictococcids (Fig. 1). However, other soft scales secrete a thick waxy cover {e.g. Ceroplastes

spp.) but, despite this, the dorsum becomes heavily sclerotized at maturity and the venter deeply

invaginated, forming the brood chamber. The eggs and crawlers are protected also under the

body ot Auloicerya acaciae Morrison & Morrison (Margarodidae) (GULLAN, 1986). Lower

( 1957) reported an interesting example in the Pseudococcidae. Species of Epicoccus, which live

in arid conditions in Australia, develop a thickened and chemically modified dorsal integument,

which is considerably expanded in comparison to the venter, thus offering excellent protection of

the female and her progeny against the drying winds, high temperature and low relative humidity

of their environment.

Source:

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

217

Protection by ants

Facultative mutualistic relationships exist between several groups of scale insects and ants.

This relationship is of reciprocal benefit because for the ants the sugar-rich honeydew represents

a food supply, and for the Coccoids the ants provide some protection against natural enemies,

i.e. predators and parasitoids. Furthermore, ants by removing honeydew, reduce contamination

of the Coccoids and so stop fungus development, which is injurious to the host plant and the

scale insects. Further protection may provided by ants that construct protective covers over

Coccoid aggregations (FOLDI, 1984). Recently, WILLIAMS (1978) and HODGSON (1994) have

described some deep morphological modifications, e.g. spiracular and anal adaptations,

characterizing scale insects living an intimate relationships with the ants in their nests.

PHYLOGENY

Currently, cladistic phylogenetic hypotheses for the entire Coccoidea are lacking, since

only keys and classification are available to show the relationships of the higher taxa within the

Coccoidea. This cladistic analysis presents one of the first attempts to produce a preliminary

estimate of the Coccoid phytogeny. The genera used are representatives of the traditionally

recognized families, however these families may not necessarily be monophyletic.

Character and character state definitions

Adult female.

1. Locular pores: (0) absent; (1) present

2. Wings: (0) present; (1) absent

3. Dorsal tagmosis: (0) distinct; (1) indistinct

4. Cornicles: (0) present; (l) absent

5. Abdominal spiracles: (0) present; (1) absent

6. Ostioles: (0) absent; ( 1 ) present

7. Cicatrix-like structures: (0) present (1) absent

8. Legs: (0) well developed; (1) reduced or absent

9. Eight-shaped tubular ducts: (0) absent; (1) present

10. Tubular ducts: (0) absent; (1) not invaginated; (2) invaginated

11. Microtubular ducts: (0) absent: (1) present

12. Pores with thoracic spiracles: (0) absent; (1) present

13. Spiracular pore rows: (0) absent; (1) simple row; (2) double rows

14. Location of anus: (0) postero-dorsum or posterior; (1) middle dorsum or venter

15. Translucent pores on hind legs: (0) absent; (1) present

16. Dermal papillae near spiracles: (0) absent; (1) present

17. Anal plates: (0) absent; (1) simple; (2) double

18. Anal opening: (0) simple opening; (1) anal ring; (2) anal ring with setae and pores; (3) anal ring with

setae

19. Mouthparts: (0) present; (1) absent

20. Number of instars: (0) 5 instars; (1)4 instars; (2) 3 instars

21. Tarsal segments: (0) 2 segments; (1) 1 segmenl

First instar.

22. Antennal segments: (0) 6 segments; (1) 7; (2) 5-3

Source:

218

I. FOLDI: DEFENSE STRATEGIES IN SCALE INSECTS

23. Apical antennae setae: (0) few hair-like setae; (1) scate with a single spine; (2) hair-like setae with stout

setae; (3) numerous hair-like setae (4) hair-like setae with fleshy seta or setae

24. Pores with thoracic spiracles: (0) absent; (1) on meso + metathoracic; (2) only mesoth.

25. Astero-type 8-shaped pores: (0) absent; (1) present

26. Bilocular pores: (0) absent; (1) present

27. Trilocular pores: (0) absent; (1) present

28. Simple pores: (0) absent; (1) present

29. Tarsal campaniform pore: (0) present; (1) absent

30. Tarsal digitules: (0) absent; (1) present

31. Number of claws: (0) 2 claws; (1)1 claw

32. Claw digitules: (0) absent; (1) present seta-like; (2) knobbed

33. Denticle on claw r : (0) absent; (l) present

34. Tibia and tarsus length: (0) ti > ta; (1) ti = ta; (2) ta > ti

35. Enlarged setae: (0) absent; (1) present

36. Femoral setae of hind legs: (0) several ; (1) 1 seta or absent

37. Tibial setae of hind legs: (0) several; (1) 1 seta or absent

38. Tarsal setae of hind legs: (0) several; (1) 1 seta or absent

39. Setae on legs: (0) abundant on all segment; (1) frequent; (2) few

40. Long caudal setae: (0) absent; (1) present

41. 8-shaped tubular ducts on the head: (0) absent; (1) present

42. Labial segments: (0) 4 segments: (1)3 segments; (2) 1 or 2

43. Labial setae: (0) 12 or more; (1)7- 11; (2) 6 or less

44. Quadrilocular pores: (0) absent: (1) present

45. Quinquelocular pores: (0) absent; (1) present

Adult male

46. Compound eyes: (0) present; (1) absent

47. Number of simple eyes: (0) absent; (1) 16; (2) 14; (3) 10: (4) 4

48. Antennal segments: (0) < 9 segments; (1)9 segments; (2) 10 segments

49. Abdominal spiracles: (0) present; (1) absent

50. Hindwings: (0) present; (1) present as hamulohalteres; (2) absent

51. Hamulohaltere setae: (0) absent; (1) 3-4; (2) 2;

52. Lateral view of aedeagus: (0) curved; (1) straight

53. Postocular ridge: (0) dorsallv weak or absent; (1) dorsally well present

54. Dorsal pore clusters on abdomen: (0) absent; (1) one median on VI and VII; (2) one median on VIII; (3)

two separated clusters on VIII.

Analysis of the character data in Table 1 with the heuristic search algorithm of Paup

resulted in two equally parsimonious cladograms. The strict consensus tree in Figs 22-23 (Tree

length: 190, Consistency index (Cl): 0.40, Retention index (RI): 0.59) shows some unresolved

relationships among the genera. The two trees differed in the placement of Coccus, which either

was placed with the pit scales (Astero-Cero-Lecanodiaspididae) or was part of the group of

relationships among the genera. The two trees differed in the placement of Coccus, which either

Aclerda + Tachardia. The placement of Micrococcus is also problematic since it is the sister

group to the Stictococcus+. According to MILLER & WILLIAMS (1995), the Micrococcidae is

most closely related to the Aclerdidae. Stigmacoccus (Margarodidae sensu MORRISON, 1928) is

the sister group of all other scale insects and is characterized by two following autapomorphies:

anal ring (18.1) and two hamulohalteres setae (51.2). Malsucoccus + Margarodes

(Margarodidae s.l.) are characterized by the following synapomorphies of the 1st instar nymph:

Source:

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

219

Table 1. — Character matrix used for the cladistic analysis of the Coccoidea.

111111111122222222223333333333444444444455555

123456789012345678901234567890123456789012345678901234

Eriosoma 000000000000000000000000000000000000000000000000000000

A 4yzus 000000100000000000000000000000000000000000000000000000

Stigmacoccus 111100000000000001020000000000110200000002000000012003

Carayonema 111100000000000003021210000000110200000002000?????????

Matsucoccus 111100000000000000120000000010120201102102200002011012

Margarodes 111100100000000000121220000010100201002102200?????????

Orthezia 111100100000000003011010000001111110001001010001011013

Phenacoleachia 111111100000000003011130000001121110000000000112010013

Conchaspis 111110100000000000021000000011121 ?01112101100140110010

Planococcus 111111100100001003011030001011120200001101000142110003

Eriococcus 111110100211001003021030001011121210001101001141110013

Kermes 11111011020000000102^040010001121211002101001132110013

Dactylopius 11111010020000000202102000001112021000200100114212?013

Asterodiaspis 11111011010110000202?04110110111020010210210014212?010

Cerococcus 11111011020120000302?021100101121200002101001142120010

Lecanodiaspis 111 11011020110000302?01110110112120000210210114211 ?110

Stictococcus 11111010011111000202124000000112000000210200014012?113

Coccus 11111010020110002302104100111112110000210221114212?110

Micrococcus 11111010020100002301124101011112000000110200010012?0?0

Aclerda 111 11011010100001201 ?03100011112101000210210114212?000

Tachardia 11111011020100001302?03200001112100100210220114212?110

Phoenicoccus 11111011110101010202?04100000112110111211220114012?0?0

Halimococcus 11111011110000010102?01200000112000111211220014012?0?0

Beesonia 11111011110100000101 ?2310000111212011121121101401101 ?0

Chionaspis 11111011110100000002?242001001120201112112200142110110

tarsal campaniform pore (29.1); femoral setae on hind legs (36.1); setae on legs (39.1); long

caudal setae (40.1) and absence of the mouthparts in adult females (19.1). However, the family

Margarodidae appears to be paraphyletic because of the position of Stigmacoccus on the tree and

the Margarodidae should be restructured into monophyletic groups. A cladistic analysis of the

Margarodidae 5./. and related groups is currently undertaken by the author (FOLDI, unpublished).

In the remainder of the tree, the monophyletic family Carayonemidae is the sister group of the

other Coccoidea and it is characterized by one autapomorphy, apical antennae with a single spine

( 22 . 1 ).

The autapomorphies representing cladistic diagnoses of the scale insects genera are as

follows: Orthezia. setae frequent on legs (39.1); presence of quadrilocular pores (44.1); 9

antennal segments (48.1) and presence of 3-4 hamulohalter setae (51.1). Phenacoleachia.

Ostioles present (6.1); 6 antennal segments (22.0), reversal and, labial segments (42.0), reversal.

Conchaspis. femoral setal on hind legs (36.1); tibial seta on hind legs (37.1); tarsal seta on hind

220

I. FOLDI: DEFENSE STRATEGIES IN SCALE INSECTS

Strict

■ — - - ■ Eriosoma

(Pemphigidae)

Myzus

(Aphididae)

Stigmacoccus

(Margarodidae)

Matsucoccus

(Margarodidae)

Margarodes

(Margarodidae)

Carayonema

(Carayonemidae)

Orthezia

(Ortheziidae)

Phenacoleachia

(Phenacoleachiidae)

Conchaspis

(Conchaspididae)

Planococcus

(Pseudococci dae)

Eriococcus

(Eriococcidae)

Kertnes

(Kermesidae)

Dactylopius

(Dactylopiidae)

Coccus

(Coccidae)

Aclerda

(Aclerdidae)

Tachardia

(Tachardiidae)

Cerococcus

(Cerococcidae)

Asterodiaspis

(Asterolecaniidae)

Lecanodiaspis

(Lecanodiaspididae)

Micrococcus

(Micrococcida)

Stictococcus

(Stictococcidae)

Phoenicococcus

(Phoeni cococci dae)

Halimococcus

(Halimococcidae)

Beeson ia

(Beesoniidae)

Ch ion asp is

(Diaspididae)

Fig. 22. — Strict consensus tree showing the hypothetical relationships within the Coccoidea.

Source: MNHN. Paris

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

221

Eriosoma

-+- Myzus

1 2 3 4 20 31 34 42 50 54

- Stigmacoccus

< 29 36 39 40 43

Matsucoccus

18 23

7 22 23

• Carayonema

Margarodes

7 30 33 35 42

39 44 48

- Orthezia

5 23 32 46

6 12 42

- Phenacoleachia

29 39 40 49

15 27 39

Planococcus

h— i—I—I—I—i—I—►—4- Conchaspis

18 23 35 36 37 38 43 48 54

6 10 20 33 35~^T

-/Ti ttEnococcus

■H—i—i—l—l—1— Kertnes

8 18 26 29 36 47

Dactylopins

18 23 40

■ Coccus

27 34 44

l'o 18 20 35 43 53

Aclerda

Tachardia

L—p Ce

24 28

Cerococcus

10 18 32 33

^ ^ Asterodiaspis

jj ^ ^2 Lecanodiaspis

■ Micrococcus

20 26 39 47

-i —i—I—I—i- Stictococcus

11 13 14 24 54

8 9 36 37 38 47 43

16 22

14 33

34 45

Phoenicococcus

12 23 24

Halitnococcus

34 50

20 23 29 33 43 4-1

Chionaspis

• Beesonia

24 27 48

Fig. 23. — Strict consensus tree with the character numbers.

legs (38.1); labial setae (43.1). Planococcus and Eriococcus group is characterized by the

following synapomorphies. presence of translucent pores on hind legs (15.1); trilocular pores

present (27.1); setae on legs frequent (39.2). Kermes. presence of anal ring (18.1); legs (8.1);

femoral setae on hind legs (36.1) and the number of simple eyes (47.3). Dactylopius : anal ring

with setae and pores (18.2) and apical antennae setae (23.2). The Cerococcus + Asterodiaspis +

Lecanodiaspis group is supported by one apomorphy, the presence of the Astero-type 8-shaped

pores. The Coccus + Aclerda + Tachardia are characterized by two synapomorphies: anal plates

17.1 and 2) and labial setae (43.1 and 2). Micrococcus: number of instars (20.1), bilocular pores

(26.1) and setae on legs (39.1). Stictococcus. presence of microtubular ducts (11.1); presence of

spiracular pore row (13.1); location of anus on the middle dorsum or venter (14.1) and two

separated dorsal pore clusters on VIII (54.3). Phoenicococcus + Halimococcus are supported by

one synapomorphy: dermal papillae near spiracles (16.1). Beesonia + Chionaspis are

characterized by two synapomorphies: tarsus longer than tibia (34.2) and the hamulohaltere are

presents (50.1).

Some nodes are supported by a few characters, such as the node relating Planococcus +

Eriococcus to Kermes+ is supported by one character, however there is a strong apomorphy,

namely the presence of tubular ducts (10.1-2). The node relating the Coccus to Aclerda+ is also

supported by a strong apomorphy, the absence of the hamulohalteres (50.2). In contrast, some

other nodes are well supported, for example the Orthezia to Phenacoleachia + is supported by

Source

222

I. FOLDI: DEFENSE STRATEGIES IXSCALE INSECTS

five characters: absence of cicatrix-like structure (7.1); presence of tarsal digitules (30.1);

presence of denticle on claw (33.1); presence of enlarged setae (35.1) and the labium with 3

segments (42.1). The node relating Phoemcococcus to Halimococctis+ is supported by seven

characters: legs are reduced or absent (8.1); eight-shaped tubular ducts (9.1); femoral setae on

hind legs (36.1); tibial setae on hind legs (37.1); tarsal setae on hind legs (38.1); eight-shaped

tubular ducts on the head (41.1) and labial setae (43.1-2).

The cladistic analysis shows the scale insects are a natural group. The monophyly of the

Coccoidea is supported by the following four autapomorphies of adult females and nymphs: the

presence of locular pores (1.1), the absence of wings (2.1) the occurrence of indistinct dorsal

body tagmosis (3.1) and the presence of a single clow on the legs (31.1). However, the

relationships of several family-group taxa, as well as the monophyly of some families remain

controversial and not well established. Further studies will be needed, with more taxa and

particularly more anatomical or morphological characters, before the relationships are well

understood.

EVOLUTIONARY SCENARIOS

Two major attributes being studied here (habitats and protective structures) were then

mapped onto the cladogram. From this it was possible to propose an hypothesis of the ancestral

states and then their evolution during the subsequent diversification of the superfamily. Since the

scale insects are sedentary (a few groups are weakly mobile), the term habitat here refers to the

final settling and feeding site on the host plant. There are difficulties in deriving evolutionary

scenarios to explain the evolution of the habitats and protective structures for the entire family-

level taxa of Coccoidea. In large groups, such as the Margarodidae, Diaspididae, Coccidae and

Pseudococcidae, position on the plant is highly variable in many lower taxonomic groups and,

similarly, many taxa within a family have quite different types of protection. For example, the

Margarodidae s.l. constitutes a large heterogeneous group with considerable behavioral diversity,

so that we can find scale insects in galls, on roots, on or under bark, or on twigs or leaves,

depending on genus or species or even instar. For these reasons, it is suggested that future

research on the evolutionary scenarios of scale insects should concentrate on diversification

within families.

For the “habitat evolution” five attribute-states were used: 1 bark; 2. branches; 3. roots; 4.

leaves; 5. stem of grasses. In the most parsimonious optimization, the cladogram (Fig. 24) shows

that the ancestral habitat attribute (feeding site) is equivocal and currently we can not choose

between the aerial (bark) or underground (roots) habitats. However, the bark or roots appears

the most probable ancestral state since it requires only 8 changes against 9 for branches. This

scenario of other habitats being subsequent derivations implies 10 changes for leaves and stem of

grasses. Sligmacoccus lives on the bark of Inga spp. Matsucoccus , is restricted exclusively to the

bark and branches of Pirns spp. Root feeding ( Margarodes) has been adopted on a large

diversity of plants, and is particularly characteristic of the cyst-forming Margarodinae. This

unique life-style may have evolved from that of leaf litter-inhabiting species which gradually

moved underground and undoubtedly represents a secondary adaptation. Carayonema is close to

the supposed ancestral state, living on the superficial roots and having well developed legs, in

contrast to Margarodes which live on deeper underground roots and have highly modified first

Source:

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

223

I- IG. 24. Hypothetical evolution ol the feeding site (habitat) in the Coccoidea, based on the phylogenetic tree in Fig. 22

legs which are enlarged as digging organs. The leaves habitat has arisen twice independently in

Phoenicococcus + Halimococcus and Planococcus + Eriococcus + Dactylopius. An

importantchange has arisen in the clades of Micrococcus and Aclerda with a shift from woody

hosts to grass host plants. Such a shift, however, was not particularly successful as no wide

adaptive radiation can be observed in these clades. The branches habitat represents the most

exploited feeding site among the Coccoidea, especially by the most speciose groups such as the

Coccidae and Diaspididae.

For “protective staictures”, six states, according to the material used for protection, were

identified: 1. filamentous secretions, 2. amorphous secretions, 3. cyst (anal fluid), 4. test (formed

by one or two types of secretions e.g. amorphous or filamentous secretion or both). 5. composed

test (formed by filamentous secretions and anal fluid). 6. associated test (formed by filamentous

secretions + anal fluid + exuvium) (Fig. 25). The type of protection is strongly associated with

habitat and a change in the protective method is correlated with a major change in way of life.

Thus, the adaptation of Margarodinae for underground life is accompanied by the use of anal

fluid in the nymphal instars, whereas Margarodid species adapted to live under bark during the

nymphal instars secrete amorphous substances. In both cases, the adult females are mobile while

224

I. FOLDI: DEFENSE STRATEGIES IN SCALE INSECTS

Fig. 25. — Hypothetical evolution of the protective structures in the Coccoidea, based on the phylogenetic tree in Fig. 22.

searching for males, but after mating produce filamentous secretions. In cases for which the

material used for protection varies in different stages of development, then the attribute state

considered was that of the nymphal stage. The most parsimonious scenario for the protective

structures suggests that the ancestor was protected by amorphous secretions since it requires

only 8 changes against 9 for filamentous secretions. In Stigmacoccus, Matsucoccus and

Carayonema spp., these amorphous secretions are secreted by cicatrice-like structures, while in

the Ortheziidae, in which they evolved independently, they are secreted by the spine-like setae.

This scenario implies 10 changes for anal fluid and for various tests. It is interesting to note that

the use of anal fluids for constructing protective structures is found both in the basal clade

Margarodidae then Conchaspididae and in the Diaspididae. In general, for the group constituting

mainly the lecanoid and diaspidoid taxa, it appears that the filamentous secretions were the

ancestral state, with three separate lines evolving from it: a felted sac (Eriococcidae), secreted

tests (Lecanodiaspididae) and the composed test (Conchaspididae, Diaspididae). Under

phylogenetic inference, this scenario for the evolution of protection suggests that lineage

diversification was achieved with 9 changes within the superfamily. This number obviously is

related to the size of the data set. Filamentous secretions represent the material most commonly

used for protection. These secretions have evolved independently in all clades of Coccoidea and

are involved not only in protecting the body but also are vital to the fiinctions of the respiratory,

reproductive and excretory systems.

Source:

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

225

The validity of these proposed evolutionary scenarios depends on several factors: firstly,

the validity of the proposed phylogeny, which was developed using heuristic methods and,

therefore, is clearly approximate; secondly, the assumption that the families studied are

monophyletic, which should be controlled in a more detailed cladistic analysis, and thirdly, the

acceptance of the selected genera represent the characteristic of the families. GULLAN (personal

communication) would add further factors like the robustness of the data matrix, as the addition

of further characters or taxa may alter tree topology; and the subjective nature of scoring of the

character states (homologies may not be correctly recognized). Of course, the corroboration or

refutation of these results is dependent on further testing with new data.

DISCUSSION

One of the major evolutionary events in scale insect history led to adult females being

neotenic and wingless, thus causing them to take on a sessile trophic habit, exploiting various

microhabitats on the host plants while sucking sap from their host's vascular tissues. This

sedentary habit ensures that scale insects have a continuous, reliable food supply for minimal

energy expenditure but with a major disadvantage that it can only be successful if the host-plant

remains healthy. In addition, being sessile makes them vulnerable to adverse environmental

conditions and attack by natural enemies, so they have evolved a range of strategies to improve

their chances of survival and reproductive success. The manner of protection may vary as a

function of the developmental stage, as in most species living in protected habitats, or may be

constant throughout development, as in most species living in aerial habitats.

It is obvious that optimal defensive strategies are those which give the greatest reduction in

mortality and the greatest increase in reproductive success with the least energetic cost. One of

the most widespread of these defense strategies is the use of a series of wax secretions produced

by an extensively developed wax gland system, even though this involves a considerable energy

investment. Obviously, the resources directed to secretions could not be allocated to oocyte

production for the direct enhancement reproductive success. The use of anal fluids represented

progress in the energetic dispensation of resources because their use is particularly economic.

Indeed, using their own excreta, these insects would appear to invest very little energy in the

production of the protective covers (cysts, composed tests, associated tests) compared with

those which secrete wax from dermal wax glands to manufacture their protective covers.

Another ingenious method of protection for the scale insects, characterizing numerous unrelated

taxa, consisted of behavioral adaptations that allow exploitation of the protection offered by the

host plant (such as cryptic life beneath the bark, under leafsheaths or nodes of grass stem or gall

formation), which lead to the reduction of the wax gland system. The exploited host plant affords

protection requiring less energy expenditure. The cyst-forming Margarodinae found an

alternative strategy to escape adverse environmental conditions by changing their generation

time, as exemplified by the well known Margctrodes vilis which can remain dormant but alive for

up to seventeen years. Apparently, simplest protection evolved in several unrelated groups by the

modification of the female's own body ( e.g. the marsupium of some Margarodids or the strongly

sclerotized dorsum of many soft scales, Kermesids or Stictococcids) which functions in the same

way as a secreted protective cover.

What are the most successful scale insects and what is their defensive strategy 7 These are

the Diaspidids - small legless insects - which mostly live on the branches and leaves. They

226

I. FOLDI: DEFENSE STRATEGIES IN SCALE INSECTS

construct, with an energetic compromise (e.g. using a mixture of secretions and anal fluids), the

most elaborate test among the Coccoidea, which is formed throughout their life cycle, serving to

protect the insect from the time of the Ist-instar nymph through to the ovipositing adult. The

efficiency of this protective cover is reflected by the success of the group since it includes more

than 2000 species distributed worldwide. In the case of the soft scales (the Coccidae), which

have nearly 2000 species and tend towards a large body size, a series of alternative strategies has

evolved, some using various and (sometimes considerable) secreted substances, others using

plant or body protection. The mealybugs, also have nearly 2000 species, are weakly mobile, and

produce various waxy secretions (but these are much less important than those in the soft scales)

and also occasionally use plant protection. In the Margarodidae, species such as those in the

genus Matsucoccus (Margarodidae s.l.) appear to represent the earliest known scale insects

(fossils) but, at the same time, appear similar to the Matsucoccus spp. of today, it is likely they

were protected in a similar manner, e.g. by secreted amorphous and filamentous secretions.

Most successful groups are adapted to the aerial part of woody host plants, particularly on

the branches, which are the most exploited feeding sites by Coccoidea and associated with divers

system of defense. The protection in relation with this habitat (branches) shows an evolution

from simple to complex structures: branches + amorphous secretions; branches + filamentous

secretions; branches + test; branches + composed test and branches + associated test. The

filamentous secretions, principally extruded by the pores and ducts, represent the material most

utilized for protection. Each taxon has found its own solution in ensuring their evolutionary

success. It may be significant that the groups which exhibit different types of protection during

their life-cycle are characterized by a low species richness.

There appears to be an obvious coadaptation between body size, habitat selection and

defense and this has caused convergent evolution of protection strategies dictated by habitat-

required defense strategies. A trend is observed in the defense strategies of scale insects to find a

compromise between energy usage and the efficiency of the protective structures. Understanding

of the extant habitats and protection and how they could have evolved in scale insect history

necessitates observation of their early evolution. Based on paleontological data, the earliest

known scale insects belong to the Margarodid genus Matsucoccus , from the Lower Cretaceous,

living on Films spp., and the fossil Coccoids from Tertiary amber, within which all the main

lineages of current families within Coccoidea have been found, are mainly Margarodids.

According to Shcherbakov (1990), ancestors of scale insects were aphid-like four winged

Precoccids but the current evolutionary hypotheses regarding the early evolution of Coccoids

suggests that they lived in leaf litter. Wigglesworth (1972), in his book “The life of insects”

suggested that the insects may have evolved in the litter layer. Koteja (1984, 1985, 1990a,b) has

also postulated that Coccoids may have evolved in the forest litter probably during the Permian

to Jurassic, where they acquired adaptations to either an epigeic (all main lineages of Coccoidea)

or an hypogeic (Margarodinae) life behavior. This adaptive radiation of early Coccoids may have

allowed them to colonize most parts of their host plants and it is a reasonable assumption that

they displayed, at this period, most of their present morphological characteristics. This is what

we observe with the Margarodidae s.l. They exploit more feeding sites (roots (Margarodinae),

bark and branches (Matsucoccinae, Steingeliinae), under bark (Xylococcinae), leaves

(Stomacoccus platani) and galls (Araucaricoccus spp., Matsucoccus gallicus) than the

Necoccoids, which are more specialized. A probable secondary radiation started in the

Source:

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

227

Cretaceous, with the colonization of the gymnosperms and angiosperms, mainly involving the

recent Coccoids. Most of the Neococcid fossils that originate from the upper Cretaceous are

similar to contemporary forms which have evolved independently in various directions,

colonizing all parts of their host plants. KOTEJA (1985) suggested also since primary habitat was

leaf litter, the scale insects may have fed on the dead and decaying remains of plants, particularly

on fungi and bacteria that are responsible for plant decay. Although the mouthparts of scale

insects are adapted for piercing and sucking nutritious fluids from plants, it is possible to admit

that they have could used decayed material as food in their early evolution. Recently,

Carayonema orousseti (Carayonemidae), was collected in the leaf litter in South America but

actually it fed on roots located near the soil surface (J. 0ROUSSET, personal communication).

Another Coccoid, Laurencella marikana (Margarodidae) was found in a similar situation. A

colony of these Margarodids had settled on the parts of the roots located at the soil surface,

covered by the leaf litter and stones (Foi.Dl, 1995b). We can suppose that similar situation may

have occurred in the early evolution of Coccoids, where some aerial part of the roots were

available for a transit to a new feeding site or habitat.

To provide a fuller explanation for the adaptive evolution (habitat and protection) of scale

insects, we need to carry out a detailed phylogenetic analysis on the Margarodidae s.l. since

several fossils show that some of them had already reached their extant morphological

organization early in Coccoid evolution.

ACKNOWLEDGEMENTS

I am grateful to Penny Gull an and Chris Hodgson for their kind availability to discuss various aspect of this study

and for providing useful criticism and improvements in the English construction of the manuscript and to anonymous referees

for their help. I also thank Douglass Miller for providing me with a copy of the character list and data matrix from his 1984

work on the phylogeny of the Margarodidae. I am also indebted to Jon Martin, Douglass Miller, Raymond Gill and Rosa

Henderson respectively for providing specimens from the collections in The Natural History Museum in London, in the

National Collection of Insects in Washington, D.C., in the California State Department of Agriculture in Sacramento and in

the New Zealand Arthropod Collection in Auckland.

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What Did the Ancestors of the Woodroach Cryptocercus

Look Like? A Phylogenetic Study of the Origin of

Subsociality in the Subfamily Polyphaginae

(Dictyoptera, Blattaria)

Philippe Grandcolas

E.P. 90 CNRS. Laboratoire d'Entomologie. Museum national cTHistoire naturelle,

45, rue Buffon, 75005 Paris. France

ABSTRACT

Studies of relationships between Cryptocercus and termites have been biased because of the use of the misleading concept

of “primitive taxon". Using the phytogeny of the subfamily Polyphaginae (including Cryptocercus ), the traits ancestral to

Cryptocercus and its sister-genus have been inferred. Cryptocercus appeared trom an ancestor distributed in tropical forests ol

Indo-Asia, inhabiting treeholes or holes in termite nests, being gregarious and displaying an alarm behavior involving

disruptive coloration of wings and pleural gland. The pattern of change from ancestral gregariousness toward derived

subsociality in the case of Cryptocercus provides indications by analogy for a modification of the theories of social evolution

in termites.

RESUME

A quoi ressemblaient les ancetres dc la blattc xylicole Cryptocercus ? Une etude phylogenetique de Porigine de la

subsocialite dans la sous-famille des Polyphaginae (Dictyoptera, Blattaria)

Les recherches entreprises a propos des relations entre la blatte Cryptocercus et les termites ont ete longtemps biaisees a

cause de futilisation du concept errone du « taxon primitif». Avec fanalyse phylogenetique de la sous-famille des

Polyphaginae (incluant Cryptocercus ), il est possible de retracer les caracteristiques ancestrales a (ryptocercus et a son

genre-frere. Cryptocercus s'est diversifie a partir d’un ancetre vivant dans les torets tropicales d'Inde et d Asie, qui habitait

les troncs creux ou les termitieres creuses, etait gregaire et montrait un coinportement d'alanne mettant en jeu une coloration

disruptive et une glande pleurale. L'hvpothese d’un passage d’un gregarisme ancestral a la subsocialite derivee dans le cas de

Cryptocercus permet de proposer par analogic, des modifications aux theories sur revolution de la socialite chez les termites.

INTRODUCTION

An understanding of evolutionary processes requires a search for both ancestral patterns

and the way these patterns have changed in the course of evolution. This quest for ancestral

patterns used either characters or taxa. In the past, taxa which were assessed as exhibiting some

Grandcolas, P., 1997. — What did the ancestors of the woodroach Cryptocercus look like? A phylogenetic study ol

the origin of subsociality in the subfamily Polyphaginae (Dictyoptera, Blattaria). In. Grandcolas, P. (ed.), I he Origin oI

Biodiversity in Insects: Phylogenetic Tests of Evolutionary Scenarios. Mem. Mus. natn. Hist, nat., 173 : 231-252. Pans ISBN

2-85653-508-9.

Source:

232

P. GRANDCOLAS : THE ANCESTOR OF CRYPTOCERCUS

ancestral characters were misleadingly considered as representing wholly ancestral taxa and were

thus named primitive taxa, missing links, living ancestors, forerunners, lower taxa, or stem-

groups (e.g. ELDREDGE, 1987). These taxa were considered as such probably because it seemed

intuitively more realistic and more simple from a gradist perspective to use some living taxa as

ancestors than to analyze independently the evolution of many different characters. Evolution

was often simply traced between two extant taxa, from a so-called “ancestral taxon” to a so-

called “evolved taxon”, as if ancestor-descendant relationships could be inferred among present

day terminals. There are many examples of such kind of statements concerning cockroaches

which were misleadingly considered as “primitive” or “ancestral” relative to termites (e.g.

TILLYARD, 1936; RAU, 1941; WILSON, 1971, 1975).

This way of thinking is especially misleading because it implies, groundlessly, that most

characters are primitive in a taxon by correlation with the primitive state of only a few traits

under study (Dawkins, 1987). It precludes any further advances or at least leads to unclear

views, in the understanding of evolutionary processes (KUKUK, 1994). It is moreover

phylogenetically nonsensical because phylogenetic characters must be considered a priori

independent of one another and may be assessed a posteriori only relatively primitive, according

to the principle of heterobathmy (HENNIG, 1966). Ancestors can never be reconstituted in their

whole and we can only infer their plesiomorphies using optimisation on phylogenetic trees. Their

own autapomorphies have disappeared with them during their evolution. Therefore, ancestors

cannot be phylogenetically defined and they will remain paraphyletic taxa (ELDREDGE &

Cracraft, 1980; Nelson, 1970, 1989).

It is such a paraphyletic picture that I intend to reconstitute here, when dealing with the

ancestor of Cryptocercus. It should be carefully kept in mind that this picture does not represent

any real living or extinct organism but is a hypothesis as to the character states that existed in an

ancestor together with autapomorphic and forever unknown traits. The prime interest of such a

paraphyletic ancestral picture is to provide heuristic indications as to the evolutionary paths

which have led to the present day situation in extant taxa. The woodroach Cryptocercus (Fig. la)

has, since the study of Cleveland et al. (1934), been especially considered a “primitive taxon”

or a “missing link” because it shows traits hypothesized as ancestral to termites, especially

xylophagy and protozoan symbionts although the actually ancestral origin of these traits remains

controversial (THORNE, 1990, 1991; NALEPA, 1991). This opinion has been discarded by

GRANDCOLAS & Deleporte (1992, 1996) and GRANDCOLAS (1994a, 1994b, 1995a, 1996a) on

the basis of the phylogenetic position of Cryptocercus. This position has, hitherto, not been

evaluated using modern phylogenetic methodology, and both a reappraisal of and search for

characters and their cladistic treatment were obviously needed (DELEPORTE, 1988;

GRANDCOLAS, 1994a, 1996a; GADE et al., 1997). Cryptocercus cannot be a “primitive taxon”

Fig. 1. — Some Polyphaginae and their habitats, a: Cryptocercus punctulatus female with two young nymphs in the

background, in their wood chamber, b: Therea petiveriana female (bearing an ootheca). c: Ergaula ccipensis male and

female (bearing an ootheca). d: treehole (.Desbordesia glaucescens) with a termite nest sheltering E. capensis in

Gabon, e: Heterogamisca chopardi female (bearing an ootheca). f: cushion shrub of Salsola sp. beneath which H.

chopardi burrows, in Saudi Arabia.

Source:

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

233

Source: MNHN . Paris

234

P. GRANDCOLAS : THE ANCESTOR OF CRYPTOCERCUS

because “primitive taxa” cannot be identified, and, according to its phylogenetic position within

the Polyphaginae (Fig. 2), its xylophagy and its intestinal symbiosis must be assumed convergent

with those of the so-called “lower termites” (GRANDCOLAS, 1995a, 1996a; GRANDCOLAS &

DELEPORTE, 1992, 1996). Cryptocercus remains however a useful model for understanding and

predicting by analogy what could have been the first stages of sociality in termites, relatively to

xylophagy and protozoa symbiosis, if one is convinced that these latter traits are ancestral to

termites and have determined their evolution toward eusociality ( e.g . MYLES, 1988; THORNE,

1990; ROISIN, 1994). By the way, it should be kept in mind that this latter hypothesis has not

been tested by termite phylogenetic analyses.

Cryptocercus as a member of the subfamily Polyphaginae (Fig. 1) is also an interesting

model to study the origin and evolution of a complex subsocial behavior in Insects: Cryptocercus

defends a wood chamber, feeds its nymphs and transfers to them protozoan symbionts via

proctodeal trophallaxis. In this paper, I examine the ancestral states of morphological, anatomical

and behavioral traits of Cryptocercus involved in its subsocial behavior and in its potentially

related behaviors such as habitat use and anti-predator behavior. These states are inferred in

reference to the best supported phylogenetic hypotheses concerning Cryptocercus and its

relatives (Fig. 2).

MATERIAL AND METHODS

Phylogenetic reference . Ancestral states for Polyphaginae and the corresponding derived states in Cryptocercus are

inferred according to current phylogenetic reconstructions (Grandcolas & Deleporte, 1992; Grandcolas, 1994a, 1996a).

Cockroach phylogenies are reviewed by Grandcolas (1997a). Grandcolas (1994a) presented a tree of the subfamily

Polyphaginae (16 taxa, 50 characters, Cl = 0.79 , RI = 0.87) which is used here. Phylogenetic analyses based on RNA and

DNA sequences (Vawter, 1991; KambhamPATI, 1995, 1996) are not taken into account, because they used too small

sequenced portions of respectively only 2 and 25 cockroach genera (belonging to a few subfamilies) and no or few genera of

Polyphagidae except Cryptocercus Their results were internally inconsistent and moreover incongment with each other and

with both previous systematic concepts (Princis, 1960; McKittrick, 1964) and later morpho-anatomical phylogenetic

analyses (Grandcolas, 1996a). Klass (1995) presented a tree for Isoptera, Blattodea and Mantodea on the basis of the study

of 14 species; however, it was not constructed according to a genuine phylogenetic analysis (no matrix of characters, no

outgroups, polymorphic characters not coded as such, etc.) and cannot be taken into consideration. According to all these

considerations, Grandcolas’ (1994) tree is preferred to others for making evolutionary inferences because it has been

obtained according to a much more extensive range of taxa and characters, and has a much higher consistency. Moreover, it

has received support from the analysis of hypertrehalosaemic neuropeptides from corpora cardiaca (Gade et al., 1997). This

does not preclude re-examination of results discussed here in the framework of a total evidence approach (Kluge, 1989).

Attribute optimization on the tree. None of the traits considered in this study were used in tree construction, except

when mentioned. Only those supported by primary homology (De Pinna, 1992) were used to build the tree (see Grandcolas,

1994). Extrinsic (e.g. geographical distributions) or poorly defined (e.g. social systems) traits are parsimoniously optimized on

the tree (as unordered states using Wagner parsimony, Farris, 1970), and are treated such as attributes (sensti Mickevich &

Weller, 1990; Grandcolas et al., 1994). This is in agreement with the principle of total evidence (Kluge, 1989), which

should be applied only to primarily homologous traits (Grandcolas et al., 1994). The ancestral states of these different traits

are commented upon here with respect to Cryptocercus if they are synapomorphic of [Therea + Cryptocercus] (the states

immediately ancestral to the tliree described species of Cryptocercus are not mentioned as such).

Eight traits were selected. Their states are listed below and in Figures 3-5 and 7-8. The states of these traits have been

generalized lor each genus on the basis of observations made on different species (Appendix 1). Geographical distributions

were established according to taxonomic literature for all described species.

Patterns of geographical distribution (Fig. 3). The analysis of this trait was restricted to the clarification of the

ancestral state ol \Ergaula + Eucorydia + Therea + Cryptocercus] (Grandcolas, 1994b). A simple optimization of the

diflerent distribution areas has been carried out on this sub-tree, without engaging in controversial methodologies of

phylogenetic biogeographv.

Source:

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

235

Blattidae

other Polyphagidae

Heterogamodes

Nymphytna

Heterogamisca

Psammoblatta

Mononychoblatta

Leiopteroblatla

Eremoblatla

Homoeogamia

Arenrvaga

Eupolyphaga

Amsogamia

Potyphaga

Ergaula

Eucorydia

Therea

Cryptocercus

Anaplectidae

Blattellidae

Pseudophyllodromiidae

Blaberidae

Fig. 2. — A synthetic phylogenetic tree presenting the position of Cryptocercus relative to cockroach families, and nested in

the subfamily Polyphaginae, according to the analyses of Grandcolas (1994a, 1996a).

Biome occupancy (Fig. 4). Five biomes or combinations of biomes are defined. “Temperate forest + desert” are

considered as a single state and not as a polymorphism involving “temperate forest” and “desert” because the species

displaying this state are distributed in all these biomes. Tropical forests include both rain and dry forests.

Habitat use (Fig. 5). Six habitats are distinguished from ecological studies (Chopard, i 938, 1969; Cohen & Cohen,

1976; Edney et al. , 1974; Ghabbour£?/ al. y 1977; Grandcolas 1994c, 1995a, 1995b, 1996b, 1997b, H awke & Farley, 1973;

Kaplin, 1996a, 1996b; Livingstone & Ramani, 1978; Nalepa, 1984, 1988a, 1988b; Roth & Willis, 1960; Seelinger &

Seelinger, 1983; pers. obs.). “Caves or burrows” and “treeholes or termite nests” (Fig. 10 are not polymorphic characters,

because some species inhabit both habitats depending on their relative availability. These habitats are combined as the same

state because they are assumed to be similar and to indicate the choice of similar specific physical conditions, namely a cavity

underground for “caves or burrows” or a cavity in a biotic structure for "treeholes or termite nests”. Cockroaches inhabiting

“sand beneath cushion shrubs” (e.g. Fig. Id) do not burrow in “loose sand” and conversely.

Social behavior (Figs 6-7). Three different behaviors may be characterized, according to the classical definitions of

Michener (1969) revised by Eicrwort (1981): solitary, gregarious and subsocial behaviors. In gregarious species (Fig. 6),

larvae and/or adults aggregate independently of relatedness (characteristics of genera according to the same studies as for

habitat use). Subsocial species exhibit parental care for the larvae which remain close to their parents. In solitary' species,

cockroaches never aggregate, even when environmental conditions could force them to be close together. A discussion

concerning these traits and their evolution in cockroaches may be found in Grandcolas (1997c).

Anti-predator behavior (Fig. 8). This behavior was coded using three different states: burrowing and freezing (in a

loose substratum), disruptive alarm (using presumably disruptive coloration of fore wings with yellow spots and pleural

glands, both traits used as characters in Grandcolas, i994a), and tremulation and obstruction (of galleries) (Livingstone &

Ramani, 1978; Ritter, 1964; Seelinger & Seelinger, 1983; Farine & Brossut, pers. com.; pers. obs.). During disruptive

alarm behavior, adult cockroaches raise their wings and exert their pleural glands while larvae rapidly burrowed in the

substratum. Wing coloration (Fig. lb) and movements are assumed to disturb predators and to provoke contusion efrects

(perhaps not to warn them because gland products are not proved yet to be deterrent). Pleural glands are assumed to produce

alarm pheromones and/or allomones (Brossut & Sreng, 1985). However, in the laboratory', pleural glands are also exerted

Source.

236

P. GRANDCOLAS : THE ANCESTOR OF CRYPTOCERCUS

DISTRIBUTION

Eupolyphaga .East Asia

Polyphaga East Asia + North Africa

+ Middle East

Anisogamia . Asia Minor

Ergaula .Tropical Africa + South Asia

Eucorydia .South Asia

Therea .India

Cryptocercus .East Asia + North America

Eremoblatta .Subtropical North America

Arenivaga .Subtropical North America

Homoeogamia . Subtropical North America

Hemelytroblatta North Africa

Mononychoblatta .Asia Minor

Leiopteroblatta .Middle East

Heterogamisca North Africa + Middle East

Nymphytria . North Africa

Heterogamodes North Africa

Fig. 3. — Distribution of the genera of the subfamily Polyphaginae.

dunng conspecific encounters, indicating that pleural glands may also assume other roles such as social or sexual

communication (Brossut & Farine, pers. com.). The disruptive alarm behavior may vary: some Ergaula species lack

disruptive coloration on the wings but they have pleural glands and are able to exert them (E. capensis in Gabon

Grandcolas, 1997b).

°otheca laying behavior. The Polyphaginae either lay their oothecae within die substratum without gluing or coating,

or they bury them (Ghabbour et al , 1977; Grandcolas, 1994c; 1995a, 1996b, 1997b, pers. obs.; Kaplin 1996b’

McKittrick, 1964; Nalepa, 1988a). * ’

Diet and intestinal symbiosis, hi addition, these two attributes were taken into consideration but were not described in

detail here because they have been studied previously (Grandcolas, 1995a; Grandcolas & Deleporte, 1996). Both have

two states: xylophagous diet (in Cryptocercus) versus saprophagous diet and presence of flagellate intestinal symbionts (in

Cryptocercus) versus absence.

Estimates of the derivative loads (Br[nck, 1977; Andersen, 1979) were provided for each node inside the

phylogenetic tree ol the subfamily Polyphaginae to which Cryptocercus belongs. Derivative loads represent the number of

derived characters m a taxon or at a node, relative to the total number of characters in the tree; these loads may be considered

Source: MNHN. Paris

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

237

estimates of the amount of evolutionary change that has occurred at each step in the diversification of a group. These

derivative loads are estimated using the tree of Grandcolas (1994a), with addition of autapomophic characters taken from

other publications (Grandcolas, 1993; 1994c) or from observations listed in Appendix 2. These estimates are obviously very

imprecise since they are based on a relatively small sample of characters. They must not be considered as indicative of true

evolutionary rates since they are free of clock assumptions (time periods are not assumed identical between nodes in cladistic

trees).

RESULTS

Most parsimonious phylogenetic patterns

The optimization of traits on the phylogeny are shown in Figures 4-5 and 7-8. All equally

parsimonious patterns are shown in the figures; the differences between these patterns do not

influence the conclusions concerning the ancestor of Cryptocercus. According to these

optimizations, 8 characters' states are listed for the ancestor of Cryptocercus (Table 1).

Distributional patterns (Fig. 3). Using a hypothesis of modification of an ancestral area by

vicariance, [India + South Asia + East Asia] is inferred to be the ancestral area of the

monophyletic group [ Ergaula , T'herea, Eucorydia, Cryptocercus ], with secondary presumptive

dispersals into tropical Africa (in the lineage leading to Ergaula capensis), and into North

America (in the lineage leading to Cryptocercus punctulatus). Using the phylogenetic pattern, the

ancestor of Cryptocercus is hypothesized to have been distributed in Indo-Asia.

Biome occupancy (Fig. 4). Two patterns implying four steps are equally parsimonious.

They differ by changes in the group [Eupolyphaga, Polyphaga , Anisogamia] either “temperate

forest + desert” is ancestral to this group with a change to “desert” in Anisogamia , or "temperate

forest + desert” appeared convergently in Eupolyphaga and Polyphaga. The subfamily originated

in deserts and secondarily occupied tropical forests (ancestor of [Ergaula + Therea + Eucorydia

+ Cryptocercus ]) and then invaded temperate forests ( Cryptocercus ). The ancestor of

Cryptocercus was thus distributed in tropical forests.

Table 1. — Characters’state of the ancestor of Cryptocercus , determined according to the optimizations on the phylogeny ol

the subfamily Polyphaginae. Optimizations of diet and intestinal symbiosis are given according to Grandcolas

(1995a) and Grandcolas & Deleporte (1996).

Character

Ancestral state

Distribution

India + Asia

Biome

Tropical forests

Habitat

Trecholes or holes in termite nests

Social behavior

Gregariousness

Alarm behavior

Yellow spots on wings and pleural glands

Diet and intestinal symbiosis

Saprophagy and lack of intestinal Protozoa

Ootheca laying behavior

Without care

Habitat (Fig. 5). Two patterns implying eight steps are equally parsimonious. They involve

the ancestral habitat “loose sand” for the subfamily, with either a change to “caves or

238

P. GRANDCOLAS : THE ANCESTOR OF CRYPTOCERCUS

BIOME - first pattern

BIOME - second pattern

Eupolyphaga Temp. For.+Desert

Polyphaga . Temp.For.+Desert

Anisogamia . Desert

Ergaula . Tropical Forest

Eucorydia . Tropical Forest

Therea . Tropical Forest

Cryptocercus . Temperate Forest

Eremoblatta . Desert

Arenivaga . Desert

Homoeogamia . Desert

Hemelytroblatta . Desert

Mononychoblatta . Desert

Leiopteroblatta . Desert

Heterogamisca . Desert

Nymphytria . Desert

Heterogamodes . Desert

Eupolyphaga

Polyphaga

Anisogamia

Ergaula

Eucorydia

Therea

Cryptocercus

Eremoblatta

Arenivaga

Homoeogamia

Hemelytroblatta

Mononychoblatta

Leiopteroblatta

Heterogamisca

Nymphytria

Heterogamodes

Fig. 4. — Two most parsimonious patterns for the evolution of biome occupancy on the phylogenetic tree of the subfamily

Polyphaginae. 'The state changes are indicated on the branches where they take place.

burrows” in the ancestor of [Arenivaga + Homoeogamia ] with a subsequent reversal to “loose

sand” in some species of Arenivaga , or two changes toward “caves or burrows” in

Homoeogamia and some Arenivaga. In either case, there was a shift toward “treeholes or termite

nests’ in the ancestor of [Ergaula + Therea + Eucorydia + Cryptocercus], Some species of

Therea secondarily changed and inhabited “ground litter” and Cryptocercus switched to “rotten

trunk”. The ancestor of Cryptocercus inhabited cavities such as treeholes or termite nest holes.

Social behavior (Fig. 7). The ancestor of Polyphaginae was gregarious with two reversals

toward solitariness occurred in species belonging to the genera Heterogamisca and

Source: MNHN. Paris

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

239

HABITAT - first pattern

HABITAT - second pattern

Eupolyphaga .?

Polyphaga .Caves or burrows

Anisogamia .Loose sand

Ergaula .Treeholes or termite nests

Eucorydia .?

Therea .Treeholes or termite nests

/ Ground litter

Cryptocercus .Rotten trunk

Eremoblatta .Loose sand

Arenivaga .Loose sand / Caves or burrows

Homoeogamia .Caves or burrows

Leiopteroblatta .Loose sand

Mononychoblatta .Loose sand

Hemelytroblatta .Sand beneath cushion shrubs

Heterogamisca .Sand beneath cushion shrubs

/ Caves or burrows

Nymphytria .?

Heterogamodes .?

Eupolyphaga

Polyphaga

Anisogamia

Ergaula

Eucorydia

Therea

Cryptocercus

Eremoblatta

Arenivaga

Homoeogamia

Leiopteroblatta

Mononychoblatta

Hemelytroblatta

Heterogamisca

Nymphytria

Heterogamodes

Fig. 5. — Two most parsimonious patterns for the evolution of habitat use, implying the habitat “loose sand” as an ancestral

state. Question marks indicate unknown states of attributes.

Arenivaga. Subsociality (familial brood care) appeared in Cryptocercus. Its ancestor was thus

gregarious.

Anti-predator behavior (Fig. 8). According to the most parsimonious pattern, the ancestor

of Polyphaginae showed “burrowing and freezing” as an anti-predator behavior. Disruptive

alarm is ancestral to [ Ergaula + Therea + Eucorydia + Cryptocercus}. Even though this state is

partly inapplicable in the totally apterous Cryptocercus (for wing coloration), its ancestor may be

inferred to have had disruptive alarm. Pheromonal pleural glands and disruptive coloration of

wings (Fig. lb) appeared in the ancestor of [Ergaula + Therea + Eucorydia + Cryptocercus] and

disappeared in Cryptocercus which acquired a particular alarm behavior, combining tremulation

in nymphs and defense of the chamber entrance by adults (gallery obstruction with pronotum).

240

P. GRANDCOLAS : THE ANCESTOR OF CRYPTOCERCUS

Oothecal laying behavior. All observed species of Polyphaginae deposit their oothecae in

the substratum without any coating or gluing, except Cryptocercus. C. punctulatus was observed

to burrow a hole in dead wood, to deposit its ootheca inside and then to enclose it (McKittrick,

1964). The ancestor of Cryptocercus deposited its ootheca without care.

Most of the changes occurring according to these parsimonious scenarios are combined to

define an overall evolutionary scenario comprising several evolutionary paths (Fig. 10): either

gregarious ancestors in Polyphaginae have changed their biomes and remained gregarious or they

have remained in the ancestral biome and changed their social behavior. Gregarious ancestors

living in a derived biome have also evolved toward subsociality.

Derivative loads

Autapomorphies of terminal taxa are listed in Appendix 2. Together with synapomorphies,

there are 108 characters. Loads are provided for each node of the cladogram (Fig. 9). The most

important loads for present discussion are present in the monophyletic group comprising

Ergaula , Eucorydia, Therea and Cryptocercus. The genera Cryptocercus, Therea, Eucorydia

have especially high derivative loads, which are at least twice the mean value of other taxa

(respectively 31.5 %, 24.1% and 25% relative to 9.5% as the mean). The difference between

Cryptocercus and its common ancestor with Therea is also the highest value recorded at a node

(12.1%). Clearly, among the set of characters examined, the amount of evolutionary change

increases as one gets closer and closer to Cryptocercus.

DISCUSSION

The ecological and behavioral ancestral attributes of Cryptocercus

Although it was never placed as the nearest relative of termites in any taxonomic or

phylogenetic scheme ( e.g . HENNIG, 1981; THORNE & CARPENTER, 1992; see also KRISTENSF.N,

1995), Cryptocercus has been considered to have a way of life ancestral to cockroaches and

termites solely because of its xylophagy, protozoan symbionts and familial way of life

(Cleveland etal, 1934; Grasse & NoiROT, 1959; Wilson, 1971;Nalepa, 1984, 1991, 1994;

MYLES, 1988). Nonetheless, according to phylogenetic analysis (GRANDCOLAS, 1994a, 1996a)

all these traits are actually apomorphic to Cryptocercus. This does not support the hypothesis

that Cryptocercus inherited these traits from a common ancestor with termites but supports the

hypothesis of origin of these traits by convergence (xylophagy, social system) and transfer

(symbionts)( GRANDCOLAS & DELEPORTE, 1992, 1996; GRANDCOLAS, 1994b, 1995a, 1996a).

According to these statements, Cryptocercus and other subsocial cockroaches do not deserve

thus to be compared with termites in a strict phylogenetic perspective (contra CRESPI, 1996).

Xylophagy, protozoan symbionts, and familial way of life were so firmly considered as

ancestral to cockroaches and termites that their origin was never questioned. Also, the origin of

subsocial behavior was poorly investigated in insects using phylogenetic comparative biology

because of the lack of phytogenies. Using the phylogeny, it is possible to infer that the ancestor

of Cryptocercus was distributed in tropical forests of Indo-Asia, and inhabited treeholes and/or

holes in termite nests (Fig. 10). It was gregarious: larvae were clumped in the same cavity, often

together with some adults which were not necessarily their parents. These adults laid their

oothecae without care in the loose litter at the bottom of cavities. The ancestors of Cryptocercus

Source .

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

241

Solitary

Gregarious

Subsocial

(Brood care)

Fig. 6. — A simplified representation of cockroach social systems involving adults (large and light grey circles) and larvae

(small and dark grey circles), their interactions cohesive (arrows directed inward), or dispersive (arrows directed

outward), and brood care (double arrows).

displayed a disruptive alarm behavior (raising fore wings with yellow spots and exerting

pheromonal pleural glands). There were many important evolutionary changes from these

ancestors since most of these character states were modified to account for the very different

present aspect and behavior of Cryptocercus. Derivative loads are especially high in the part of

the cladogram close to Cryptocercus and increase sequentially at the dichotomies leading to

[Ergaula + Eucorydia + Therea + Cryptocercus ], [Eucorydia + Therea + Cryptocercus] and

[Therea + Cryptocercus ]. Indeed, most of the characters sampled for phylogenetic studies

change close to Cryptocercus , including its divergence from the common ancestor with its sister-

group Therea. From a gregarious ancestor, inhabiting cavities ( e.g . Fig. Id) and showing a

disruptive coloration, evolution produced a descendant which was subsocial, digging into the

wood, lacking wings and strongly armored. Unfortunately, most changes concerning biome,

habitat, social system and alarm behavior occurred at the same node of the cladogram and it is

thus impossible to assess the relative sequence of these different events using my phylogenetic

hypothesis (Figs 4, 5, 7, 8). By analogy with the diversification of the subfamily Zetoborinae in

South America, it is possible that the xylophagy of Cryptocercus appeared before it dispersed

242

P. GRANDCOLAS : THE ANCESTOR OF CRYPTOCERCUS

SOCIAL SYSTEM

Eupolyphaga .

Polyphaga .

.Gregarious

Anisogamia .

Ergaula .

Eucorydia .

Therea .

Cryptocercus .

.Subsocial

Eremoblatta .

Arenivaga .

Homoeogamia .

. Gregarious

Hemelytroblatta .

Gregarious

Mononychoblatta .

...

Leiopteroblatta .

Heterogamisca .

Gregarious / Solitary

Nymphytria .

Heterogamodes .

Fig. 7 — Most parsimonious pattern for the evolution of social system.

to temperate forests because a wood diet and its life history correlates could facilitate adaptation

to a seasonal temperate climate (see GRANDCOLAS, 1995a for an evolutionary scenario linking

wood diet and adaptation to climate). It is necessary however to get additional data ( e.g. still

unknown tropical Cryptocercus species or relatives) to substantiate this hypothesis in the present

case of the subfamily Polyphaginae.

The alarm behavior changed together with social system, but the different alarm behaviors

displayed by gregarious and subsocial taxa require a high degree of behavioral coordination

among conspecifics (so-called “cooperation” according to WILSON, 1975). This coordination

could be related to behavior of cooperative groups (Mii.rNSKl, 1979). They seem thus to be

identical in this respect. Alarm behavior appeared each time to cope with communication

constraints imposed by each kind of habitat. Species living in large cavities (Fig. Id)

Source MNHN. Paris

PHYLOGENETIC TES TS OF EVOLUTIONARY SCENARIOS

243

ANTI-PREDATOR BEHAVIOR

Eupolyphaga .?

Polyphaga . Burrowing and Freezing

Anisogamia .?

Ergaula . Alarm behavior

Eucorydia . Alarm behavior

Therea . Alarm behavior

Cryptocercus Tremulation and Obstruction

Eremoblatta .?

Arenivaga . Burrowing and Freezing

Homoeogamia . Burrowing and Freezing

Hemelytroblatta . Burrowing and Freezing

Mononychoblatta .?

Leiopteroblatta .?

Heterogamisca Burrowing and Freezing

Nymphytria .?

Heterogamodes .?

Fig. 8. — Most parsimonious pattern for the evolution of anti-predator behavior.

or in ground litter (the ancestor of Cryptocercus and Therea and Ergaula species) displayed a

disruptive coloration (Fig. lb), an alarm or repugnatory gland and a burrowing ability. This could

protect them against large predators using visual perception (presumably vertebrates). Species

living in small obscure chambers in rotten trunks displayed tremulation and gallery obstruction.

This could protect them against small predators detecting their prey with help of vibrations and

odors (such as millipedes, spiders, etc., see MATSUMOTO, 1992 for depicting such predation

events in similar cockroaches belonging to the subfamily Panesthiinae). Tremulation in an

obscure cavity provides other members of the family with alarm: larvae clump beneath the female

who may close the gallery with her body (Seelinger & SEELINGER, 1983).

Source:

244

P. GRANDCOLAS : THE ANCESTOR OF CRYPTOCERCUS

From gregariousness to subsociality: an overlooked path

Most recent evolutionary theories regarded subsociality as a step toward eusociality.

Parental care (central to the concept of subsociality) is a standard principle of a kinship-based

understanding of social evolution ( e.g. NALEPA, 1994; TALLAMY, 1986). Gregariousness and

parasociality are often considered as more or less blind alleys, resulting from similar natural

selection pressures to those exerted during the evolution of subsociality ( via anti-predation,

foraging, etc.) but failing in this case to lead to more complex or integrated forms of sociality

because of the lack of kinship between the members of the gregarious groups (WILSON, 1971,

1975).

In the subfamily Polyphaginae, a presocial behavior - gregariousness - clearly preceded the

appearance of subsocial behavior in Cryptocercus (Fig. 10). What could be the significance of

such a pattern? Could presociality be exaptive (i.e preadaptive) for subsociality? This kind of

prospect is a process-oriented question and deals with models of selection whereas phylogenies

depict evolutionary pattern. In this way, it could be hypothesized that both tolerance to

conspecifics and behavioral coordination may be selected in a context of gregariousness and may

be highly exaptive in a subsocial context. Tolerance to crowding and interattraction are the first

(pre-)requisites of social relationships (ALLEE et a/., 1949; GRASSE, 1952), as revisited recently

by CRESPI (1994). Both tolerance and interattraction could be first acquired during the evolution

of gregarious life. In gregarious species, individuals cluster together because they are

interattracted together. Living in aggregations, they must tolerate spatial proximity with their

conspecifics and do not spend time or waste energy in aggressive or dispersive behaviors. Both

tolerance and interattraction could be inherited in subsocial descendants where they could have

an exaptive value because subsocial mother and larvae are closely associated and have mutual

interactions which necessitate both behaviors. The only difference between gregarious and

subsocial species could be the propensity of individuals to show tolerance and attraction toward

different kind of conspecifics, respectively in the context of non-kin individuals or in the context

of a family. In the same way, the alarm behavior of gregarious ancestors could be mediated by

the reactivity to movements of non-kin conspecifics via specialized mechanical receptors. This

reactivity as well as these receptors could have been inherited by their subsocial descendants and

have a high selective value when displayed with kin conspecifics during their own alarm

behavior. An efficient alarm behavior has, by itself, a high selective value because it allows

individuals to escape death or injury by predators or parasites. All the alarm behaviors described

in the Polyphaginae were displayed through communication within some groups of individuals. In

the same way as for social system, the sensory and neurological basis for this communication

may be selected first in one context (between non-kin) and then used secondarily in a somewhat

different context (between kin). According to this possible exaptive value of gregariousness

toward subsociality, a possible path for the appearance and change of social system could be

traced from gregariousness to subsociality, and possibly to eusociality by analogy to termites.

This hypothesis of exaptive value of gregariousness toward subsociality is quite different from

the statements that parental care seems to be more frequent in ovoviparous taxa or in oviparous

taxa carrying oothecae a long time than in most oviparous. GRANDCOLAS (1996) and NALEPA &

BELL (1997) independently reported this trend respectively in reference to a phylogenetic

hypothesis and to a traditional classification, respectively. Ovoviviparity or long-carrying of

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

245

• - Eupolyphaga

1- Polyphaga

I- Anisogamia

I - Ergaula

I - Eucorydia

I- Therea

- Crypiocercus

I - Eremoblatta

I - Arenivaga

I - Homoeogamia

I- Hemelytroblatta

1 - Mononychoblatta

• - Leiopteroblatta

I - Heterogamisca

I - Nymphytria

• - Heterogamodes

Fig. 9. — Derivative loads (ratios of apomorphies relative to the subfamily groundplan sampled with 108 characters)

indicated on the phylogenetic tree of the subfamily Polyphaginae.

oothecae are supposed by both papers - at least among several factors - to increase and promote

the relationships between the female and the larvae which are necessarily close following the

brood birth. These statements did not imply necessarily that gregariousness is ancestral and

exaptive to parental care but merely that particular reproductive mode or more generally life

history may promote parental care.

Insights by analogy concerning the evolution of termites

Evolutionary inferences concerning the appearance of sociality in termites have always

considered the prominent role of subsociality (parental care) in xylophagous ancestors. Ancestors

were hypothesized to be xylophagous and to harbor intestinal symbionts (CLEVELAND et a/.,

1934; GRASSE & Noirot, 1959). This symbiosis would have determined a subsequent evolution

toward parental care which is needed for transferring symbionts (via proctodeal trophallaxis

between mother and larvae). This care for young nymphs could have shifted from adults to older

nymphs and this could have been responsible for the emergence of a worker caste (NALEPA,

Source:

246

P. GRANDCOLAS : THE ANCESTOR OF CRYPTOCERCUS

DESERT

Caves or burrows

j Freezing + Burrowing

( ^Gregarious )

e g. Polyphaga aegyptiaca

DESERT

Sand beneath cushion shrubs

Freezing + Burrowing

RAIN + DRY FOREST

( Solitary J

e g. Heterogamisca dispersa

Treeholes or termite nests

( Disruptive alarmj

( Gregarious)

e.g. Therea nuptialis

TEMPERATE FOREST

Rotten trunk

Tremulation + Obstruction )

Subsocial

e g. Cryptocercus punctulatus

Fig. 10. — Several possible evolutionary paths according to the most parsimonious scenarios concerning biome, habitat and

social behavior depicted in the Figures 3, 4 and 6.

1988b, 1994). This scheme is, however, dependent on the assumptions that xylophagy and

symbiosis were both ancestral to termites. Cryptocercus is unfortunately not useful for testing

these assumptions directly by homology because it is not closely related to termites

(GRANDCOLAS & DELEPORTE, 1992, 1996). However, by analogy , the patterns in the clade to

which Cryptocercus belongs suggest that an ancestor of termites could have exhibited a

particular alarm or anti-predator behavior. This behavior could have promoted an evolution

toward subsociality as well as symbiosis and parental care. This kind of evolutionary relationship

between anti-predator behavior and sociality has already been postulated concerning insects (e.g.

Starr, 1985; CRESPI, 1994; but see Kukuk et al., 1989). Unfortunately, chemical or other

defenses of alates in termites are very poorly known (DELIGNE et al., 1981; Grass£, 1986). The

studies of Moore (1968, 1969) interestingly suggested that many termites (including alates of

Mastotermitidae and Termitidae) have mandibular glands with a defensive role (quinone-

secreting): a so widely distributed gland could be an indication of an ancestral pattern of

Source: MNHN. Paris

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

247

defensive behavior similar to that shown in cockroaches. However, there is also few phylogenetic

analyses of termites, except a limited molecular attempt (Kambhampati et al , 1996): additional

work is thus needed to understand whether a particular defensive behavior operated in the

ancestor of termites.

In conclusion, searching for patterns ancestral to the subsociality of Cryptocercus provides

useful insights concerning the evolution of sociality. First of all, the previous assumptions of

relictual ancestral subsociality associated with xylophagy and intestinal symbiosis as shared

ancestrally by Cryptocercus and termites are discarded. The ancestors of Cryptocercus clearly

lacked these traits. Second, gregariousness, subsociality and anti-predator behavior are

associated in the same phylogenetic pattern. This pattern may be used to implement current

models of social evolution which are too narrowly based on the relationship between parental

care and resource use.

ACKNOWLEDGEMENTS

I thank P. Deleporte, L. Desutter-Grandcolas, L. Packer, B. Thorne and J. Van Baaren lor the constructive

criticisms they made concerning this paper. I am grateful also to C. A. Nalepa to kindly provide me with her and W. J. Bell's

paper in press. I am grateful to all persons and institutions w'ho have made possible this work, including both the ecological

field studies and the systematic studies.

REFERENCES

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Appendix i. — Species which are used for the generalizations at the generic level of the ecological and behavioral traits under

study (information pertaining to each species may be found in the references cited in the material and methods

section).

Arenivaga apacha (Saussure, 1893)

A. bolliana (Saussure, 1893)

A. etratica (Rehn, 1903)

A. floridensis CAUDELL, 1918

A. mvestigaia Friauf& Edney, 1969

A. tonkawa Hebard, 1920

A. sp.

Cryptocercus punctulatus SCUDDER, 1862

C. relictus Bey-Bienko, 1935

Ergaula capensis (Saussure, 1893)

E. carunculigera (Gerstaecker, 1861)

E. sp.

Eremoblatta subdiaphana (Scudder, 1902)

Eucory>dia dasytoides (Saussure, 1864)

E. omata (Saussure, 1864)

E. westM’oodi (Gerstaecker, 1861)

Llemelytroblatta ( =Psammoblatta) afncana (Linnaeus, 1758)

Heterogamisca chopardi (Uvarov, 1936)

H. dispersa Grandcolas, 1994

77. marmorata (Uvarov, 1936)

Homoeogamia mexicana Burmeister, 1838

Leiopteroblatta monodi Chopard, 1969

Mononychoblatta semenovi Chopard, 1929

Polyphaga aegyptiaca (Linnaeus, 1758)

P. indica Walker, 1868

P. pellucida (Redtenbacher, 1889)

P. saussurei (Dohrn, 1888)

Therea petiveriana (Linnaeus, 1758)

T. nuptialis (Gerstaecker, 1861)

Source. MNHN , Paris

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

251

Appendix 2. — Autapomorphies of dilTercnt genera of the subfamily Polyphaginae, in addition to those listed in previous

publications (Grandcolas, 1993, 1994a, 1994c).

Genus

Autapomorphy

Atiisogamia

pronotum impressed on the middle

large mesonotum and metanotum (homoplastic with Leiopteroblatta)

tarsal claws short

Arenivaga

antero-ventral margin of female fore femora with a long row of short and strong

spines closely inserted

supra-anal plate moderatley lengthened and emarginate

Cryptocercus

pronotal sculpture

eyes reduced

loss of setae on external sclerites

abdominal segment VH expanded

intestinal pouch (for flagellates)

lack of clypeo-frontal suture

wings totally lacking

lack of cereal spheroid sensilla (homoplastic with Eucorydia)

lack of pleural glands

hook L3d of male genitalia not at all protruding

ventral phallomere in male genitalia

leg spines strong

inter-tergal glands (Farine et al , 1989)

Eremoblatta

middle and hind femora without apical spine

male subgenital plate very asymmetrical with two lateral projections

Ergaula

third frontal hollow-

females brachypterous while males macropterous (homoplastic with

Homeogamia)

fronto-clypeal suture invaginated where it joins the median suture

Eucorydia

metallic coloration of pronotum

yellow' spots on wings reaching the fore margin

postclypeus flat

hook L3d of male genitalia short

lack of cereal spheroid sensilla (homoplastic with Cryptocercus)

hind tubercle of R2 with a finger-like apophysis

neoformation with a projected hind lobe

fore tubercle of R2 projected

Eupolyphaga

setae with reddish coloration

L3d and L3v enveloping and rounded

outer outline of female eyes not rounded dorsallv and ventrally

Hemelytroblatta

female subgenital plate with a median constriction

Heterogamisca

hind tibiae curved

front flat alongside fronto-clypeal suture

anal field of fore wings broad

252

P. GRANDCOLAS : THE ANCESTOR OF CRYPTOCERCUS

Appendix 2. — continued.

Heterogamodes

small tarsal claws (homoplastic with Anisogamia)

female pronotum with strongly and regularly convex fore border

large tergal glands just below the metanotal hind margin

Homoeogamia

female winged (homoplastic with Ergaula , Eucorydia , Therea)

male fore wings with wide and horizontally subcostal field)

male pronotum wider on the fore border

female subgenital plate with two flaps

Leiopteroblatta

wings short with veins not visible

male eyes small

one tarsal claw' (homoplastic with Mononychoblatta)

hind femora spatulate and wide

antero-ventral carena on middle and hind femora without spines but with long and

strong setae

small ocelli in males

Mononychoblatta

tarsae with only one claw (homoplastic with Leiopteroblatta)

large metanotum and mesonotum (homoplastic with Anisogamia)

Nymphytria

small pronotum

mesonotum laterally large

hind femora spatulate only in the apical half

lack of tarsal claws in females

Polyphaga

pronotum with w'hite fore margin contrasting with dark coloration (homoplastic

partly with Hemelytroblatta)

Therea

at least four yellow spots distinctly colored on fore wings

fore wings black between yellow spots

L2v diameter not increasing

L3v posteriorly protruding

Neoformation flattened

Source:

Early Evolution of the Lepidoptera + Trichoptera Lineage:

Phylogeny and the Ecological Scenario

Niels P. Kristensen

Zoological Museum, Universitetsparken 15, 2100 Copenhagen, Denmark

ABSTRACT

New insights in the basal phylogeny of the Lepidoptera shed light on some topical issues in the debate over ecological

aspects of the early evolution of this insect “order" and its sister group, the caddisflies. The currently best supported

phylogeny of the basal lepidopteran clades is Micropterigidae + (Agathiphagidae + (Heterobathmiidae + (Eriocraniidae +

(Acanthopteroctetidae + (Lophocoronidae + (Neopseustidae + (Exoporia + Heteroneura))))))), i.e., it is a richly branched

“Hennigian comb". The larvae of Micropterigidae are “soil animals" which feed on foliose liverworts, fungus hyphae and

decaying angiosperm material; they live in very moist habitats which probably differed little from those of ancestral

Amphiesmenoptera. Exoporian larvae may similarly be broadly classified as “soil animals", and their ancestral life-style was

probably very similar to that of micropterigid larvae, except that they lived in silken webbings/galleries. While the exoporian

life-style might a priori be considered a retained plesiotvpic trait, this interpretation is rejected because splitting events “basad

from" the Exoporia + Heteroneura clade repeatedly led to canopy-living clades. It is most parsimonious to consider the ground

dwelling of exoporian larvae to represent a secondary habitat shift. The crochet-bearing larval prolegs ascribed to the ground

plan of Exoporia + Heteroneura apparently developed in response to a selective pressure for enhancing grips on a silken

webbing, rather than for enhancing movement on a smooth plant surface (although the latter role may be the principal one in

the bulk of the Lepidoptera). The preferred cladogram necessitates the assumption that an eclosion mode non-dependent on

movable pupal mandibles evolved twice in the Lepidoptera: in the Lophocoronidae and in the Exoporia + Heteroneura clade.

Larval invasion of genuine aquatic habitats is the key innovation of the trichopteran clade. Problems of recognizing an adult

caddisfly as such are briefly discussed; they are particularly serious in the case of fossils. Contrary to the claim of one school

of thought on ancestral caddisfly ecology, out-group evidence from the Lepidoptera lends no support to a theory of ancestral

caddisflies living in silken tubes. 'Hie basalmost lepidopteran clade whose larvae live in silken galleries (the Exoporia) did not

arise until the eighth splitting event recognizable among extant forms.

RESUME

Les premiers stades de ('evolution dans la lignee des Lepidopteres + Trichopteres: phylogenie et scenario evolutif

Une recente mise au point de la phylogenie basale des Lepidopteres permet d'inferer une nouvelle reconstitution des

premiers stades de revolution de l'ecologie des Lepidopteres et de leur groupe-frere, les Trichopteres. La phylogenie des

clades basaux de Lepidopteres la mieux corroboree actuellement est en fait un arbre hennigien « en peigne », arbre

abondamment pourvu en rameaux : Micropterigidae + (Agathiphagidae + (Heterobathmiidae + (Eriocraniidae +

(Acanthopteroctetidae + (Lophocoronidae + (Neopseustidae + (Exoporia + Heteroneura))))))). Les larves de Micropterigidae

sont des « animaux du sol » qui se nourrissent dliepatiques, d'hyphes de champignons, et de fragments d'Angiospermes en

decomposition ; elles vivent dans des habitats tres hmnides qui different probablement tres peu de ceux des

Amphiesmenoptera ancestraux. Les larves dExoporiens peuvent etre elles aussi considers grosso modo comme des

N. P. Kristensen, 1997. — Early evolution of the Lepidoptera + Trichoptera lineage: phylogeny and the ecological

scenario. In. Grandcolas, P. (ed.). The Origin of Biodiversity in Insects: Phylogenetic Tests ot Evolutionary Scenarios. Mem.

Mus. natn. Hist, nat., 173 : 253-271. Paris ISBN : 2-85653-508-9.

254

N.P. KRISTENSEN : EARLY EVOLUTION OF THE LEPIDOPTERA + TRICHOPTERA

« animaux du sol » et leur mode de vie ancestral etait probablement tres semblable a celui des larves de Micropterigides, a

l'exception du fait qu'elles vivaient dans des toiles/galeries de soie. Le mode de vie exoporien pourTait etre considere a priori

comme la conservation d'un trait plesiotvpique, mais cette interpretation est rejetee parce que la cladogenese des Exoporia +

Heteroneura a conduit de maniere repetee a Emergence de groupes vivant dans la canopee. II est done plus parcimonieux de

considerer la vie au niveau du sol des larves d'exoporiens comme une acquisition secondaire. Les fausse-pattes larvaires

mimies de crochets, une caracteristique du plan de base des Exoporia + Heteroneura, se sont apparemment developpees en

reponse a une pression de selection avec comme fonction l'agrippement sur une toile de soie, plutot que le deplacement sur les

surfaces lisses des vegetaux (bien que cette demiere fonction puisse etre la plus courante chez les Lepidopteres). Le

cladogramme retenu implique qu'un mode d'emergence independant de mandibules nymphales mobiles est apparu deux fois

chez les Lepidopteres : chez les Lophocoronidae et chez le clade des Exoporia + Heteroneura. La conquete par les larves de

veritables habitats aquatiques est l'innovation-cle du clade des Trichopteres. Les problemes que souleve la caracterisation des

1 richopteres adultes sont brievement discutes ; ils sont particulierement importants dans le cas des fossiles. Au contraire de ce

qui etait affirme par une ecole de pensee au sujet de l'ecologie des ancetres de Trichopteres, la reference aux Lepidopteres en

termes d'extra-groupe n'amene pas d'arguments en faveur de la vie dans des tubes de soie pour les ancetres des Trichopteres.

Chez les Lepidopteres, le plus basal des clades ayant des larves vivant dans des tubes en soie (les Exoporiens) n'est pas

appani avant le huitieme evenement de cladogenese identifiable au sein des formes actuelles.

INTRODUCTION

While many (indeed most, KRISTENSEN, 1995) current hypotheses about interrelationships

of the higher insect taxa conventionally ranked as “orders” remain inadequately supported, there

is very firm support for the monophyly of the entity Amphiesmenoptera, comprising the

Trichoptera (caddisflies) and the Lepidoptera. Numerous likely amphiesmenopteran groundplan

autapomorphies have been identified in structural traits, and the entity consistently comes out as

a monophylum in the molecular analyses I have seen (P ASHLEY et a/., 1993; WlEGMANN, 1994;

Regier et a/., 1995; WHEELER, unpublished).

The Amphiesmenoptera as a whole are one of the most species-rich lineages within the

endopterygote insects, hence within the living world, and the Lepidoptera include the largest

lineage of primarily herbivorous animals (POWELL et a/., in press). Considerable attention has

been paid to the patterns of early phylogenetic diversification within the Amphiesmenoptera, and

as far as the lepidopteran lineage is concerned a large basal section of the phylogenetic tree now

appears fully resolved.

In recent years the application of “tree thinking” to life-history traits has increasingly been

taking evolutionary “scenarios” beyond the narrative stage; MILLER & WENZEL (1995), and

leterences cited therein, provide a timely introduction to (entomological aspects of) this exciting

field. The present contribution briefly addresses some major questions concerning the ecological

scenario of early lepidopteran evolution in the light of recently gained phylogenetic insights. It

also addresses some topical issues in the debate over early caddisfly evolution.

THE ANCESTRAL AMPHIESMENOPTERAN

The numerous structural autapomorphies identified in the groundplan of the

Amphiesmenoptera are reviewed elsewhere (KRISTENSEN, 1984b; KRISTENSEN & SKALSKI, in

press, have a corrected/updated account).

The said apomorphies notwithstanding, the ancestral amphiesmenopteran must be

characterized as an overall quite generalized endopterygote insect. Thus it is notable that this

ancestor, in the adult stage, must have retained very primitive traits in the mouth apparatus

including, e.g., a movable labrum with extrinsic (frontal) retractors, mandibles with tentorial

adductors, and a labium with distinct paraglossal lobes. These plesiomorphies are still present in

Source:

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

255

the basalmost extant Lepidoptera, and nowhere else among panorpoid endopterygotes. The adult

ancestral amphiesmenopteran may well have been a spore-/pollen-feeder like two of these basal

lepidopteran families (Micropterigidae and Heterobathmiidae). In any case the moths in question

(which do not together constitute a monophylum!) have in their preoral cavity some structural

specializations (epipharyngeal brushes, spinose infrabuccal pouch) related to their feeding habits,

and these specializations show remarkable similarities with those present in some of the (similarly

pollen-feeding!) basalmost Hymenoptera (VlLHELMSEN, 1996), which presumably are the closest

amphiesmenopteran outgroups that take solid food as adults. The suggestion seems

straightforward that (as already suggested by MALYSHEV, 1968) adult spore/pollen-feeding was

ancestral in a large monophylum comprising the Hymenoptera plus the panorpoid orders

(KRISTENSEN, 1984b).

The larvae in the basal lineages of the other panorpoid insects (Mecoptera, Siphonaptera,

Diptera) may be broadly characterized as “soil animals” (Fig. 1). It is true that nannochoristid

scorpionflies (presumably the sister group of all other Mecoptera, and overall generalized

panorpoid insects) have aquatic larvae, but I am firmly of the opinion that this trait is a

specialization sui generis in the family, rather than a retained plesiotypic condition: the last-instar

larva has open spiracles and the last (non-feeding) phase of this instar is spent in the soil outside

the stream (PILGRIM, 1972). Similarly, I believe that those dipteran larvae which are aquatic are

all secondarily so. The outgroup criterion thus lends support to the notion that also the larvae of

ancestral Amphiesmenoptera were soil dwelling, i.e., that this life-style in extant Lepidoptera-

Micropterigidae is genuinely plesiotypic.

THE LEPIDOPTERAN LINEAGE

The groundplan autapomorphies of the Lepidoptera are reviewed in the references cited

above for the Amphiesmenoptera. Since lepidopteran larvae initially remained in what is believed

to have been the environment of their amphiesmenopteran ancestors, it is unsurprising that their

(few) groundplan autapomorphies include none one would immediately consider to be potential

environmental adaptations. Note, however, that contrary to a widespread belief the ancestral

lepidopteran larva probably had a prognathous head, the structure of which may be somehow

related to the life in narrow crevices in the soil/periphyton. Prognathism itself is probably

plesiomorphic at the basal amphiesmenopteran level (larvae of annulipalpian and “spicipalpian

caddisflies are prognathous, and so are those of Mecoptera-Nannochoristidae), hence at most an

exaptation sensu GOULD & VRBA(1982). However, the elongation of the pleurostome (which is

a specialization characteristic of derived prognathan heads) is a lepidopteran groundplan

autapomorphy (KRISTENSEN, 1984a); the presence of this state in the otherwise typically

hypognathous head of higher lepidopteran larvae is a morphological anomaly (DENIS & BlTSCH,

1973), which apparently is best explicable in terms of phylogenetic constraints.

An outline of basal lepidopteran clades

Principal recent references on the evolution ot the basal lepidopteran lineages are.

KRISTENSEN (1984b, in press a, b), KRISTENSEN & Skalski (in press), Davis (1986, 1987),

256

N.P. KRISTENSEN : EARLY EVOLUTION OF THE LEPIDOPTERA - TR1CH0PTERA

Fig. 1. — Cladogram of basal amphiesmenopteran lineages superimposed on major habitat types; secondary habitat shifts may

occur within terminal taxa. ACN, Acanthopteroctetidae; AGA, Agathiphagidae; AMP, Amphiesmenoptera; ANN,

Annulipalpia; ANT, Antliophora ( = Mecoptera + Siphonaptera + Diptera); DIT, Ditrysia; ERI, Eriocraniidae; EXO,

Exoporia; GLO, Glossata; GLS, Glossosomatidae; HYB, Hydrobiosidae; HYD, Hydroptilidae-Hydroptilinae; ITrB,

Heterobathmiidae; INC, Incurvarioidea; INT, Integripalpia; LEP, Lepidoptera; LOP, Lophocoronidae; NEL,

Neolepidoptera; NES, Neopseustidae; NEP, Nepticuloidea; PAL, Palaephatidae; PTI, Hydroptilidae-Ptilocolepinae;

RHY, Rhyacophilidae; TRJ, Trichoptera; TIS, Tischeriidae.

Nielsen (1989), Nielsen & Kristensen (1996) and Powell et al. (in press). Problems of

formal classification are discussed by KRISTENSEN (in CARTER & KRISTENSEN, in press); it is

here advocated that recognition of sub- and infraorders in the Lepidoptera should be

discontinued.

Four primary lepidopteran clades are currently recognized: the families Micropterigidae,

Agathiphagidae and Heterobathmiidae, and the high-rank taxon Glossata comprising all other

Lepidoptera, i.e., 99.9% of the described species. SHIELDS (1993) and IVANOV (1994)

considered the first splitting event traceable in extant Lepidoptera to have been between the

Agathiphagidae and all other clades, but for reasons discussed elsewhere (KRISTENSEN, 1984b, in

press a; Kristensen & Skalski, in press), 1 believe the interrelationships should be represented

as Micropterigidae + (Agathiphagidae + (Heterobathmiidae + Glossata))(Fig. 1); the latter

phylogeny has also received support from analyses of 18S rDNA (WlEGMANN, 1994).

Source: MNHN, Paris

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

257

The Glossata comprise six basal clades: the families Eriocraniidae, Acanthopteroctetidae,

Lophocoronidae, Neopseustidae, and the high-rank taxa Exoporia (Mnesarchaeoidea +

Hepialoidea) and Heteroneura (all remaining Glossata). A recent analysis of the interrelationships

of these clades, based on 47 characters in skeletal and “soft” anatomy, has yielded a single most

parsimonious solution (Figs 1-2), viz., Eriocraniidae + (Acanthopteroctetidae + (Lophocoronidae

+ (Neopseustidae + (Exoporia + Heteroneura)))). A suprafamilial taxon “Dacnonypha”

comprising the Eriocraniidae, Acanthopteroctetidae and Lophocoronidae is therefore non-

monophyletic and must be discarded. A detailed presentation of the analysis, including evidence

for the monophyly of each of the six clades, is given by Nielsen & KRISTENSEN (1996). Names

have been given to a selection of the high-rank clades that are recognized: the Exoporia +

Heteroneura have long been known as the Neolepidoptera, the Neopseustidae + Neolepidoptera

are called Myoglossata, and the name Coelolepida has now been applied (NIELSEN &

KRISTENSEN, 1996) to the entity comprising all non-eriocraniid Glossata.

As is well known, the vast majority (>98%) of the extant Lepidoptera pertain to the

heteroneuran clade Ditrysia; four other heteroneuran basal clades are recognized, viz. , the

Nepticuloidea (Nepticulidae + Opostegidae), Incurvarioidea (six families), Palaephatoidea

(Palaephatidae only) and Tischerioidea (Tischeriidae only). The interrelationships within the

Heteroneura remain unsettled, but the phylogeny represented as Nepticuloidea + (Incurvarioidea

+ (Palaephatoidea + Tischerioidea + Ditrysia)) may be best supported at present (KRISTENSEN &

SKALSKI, in press).

The oldest known fossil moth is Archeo/epis manae Whalley, 1985 from the Lower

Jurassic; its systematic position within the Lepidoptera is unclarified. The fossil record has so far

contributed little to the dating of early splitting events within the “order” ( cf. below), but

apparently reliably identified leaf mines of Ditrysia-Gracillariidae (Labandeira et a/., 1994)

from the Middle Cretaceous (97 myr B.P.) are evidence that all major homoneurous and

monotrysian lineages existed by that time.

Life history patterns of non-ditrysian moths

It is unknown whether agathiphagid moths feed at all, but because of the absence of

incisivus teeth on their mandibles it is unlikely that they utilize solid foods. In contrast, the adult

insects belonging to the two other pre-glossatan families feed on pollen or (in the case of some

micropterigids from New Caledonia and [D. LEES, personal communication] Madagascar) fern

spores. The stem lineage ( sensu Ax, 1987) of glossatan moths was characterized by the loss of

mandibular function in the post-pharate adult, and the development of the coilable proboscis

from the maxillary galeae. Hereby adults of all higher Lepidoptera were rendered dependent on

fluid nutrients exclusively.

Larval biologies in the non-glossatan grade are diverse. As noted above, micropterigid

larvae are soil dwelling; they feed on foliose liverworts, plant debris and/or fungus hyphae, and

they are restricted to quite moist habitats. Agathiphagid larvae are miners in kauri pine

(Araucariaceae) seeds; oviposition is believed to take place while the seed is still in the cone, but

the larval development and pupation is completed in the seed after it has fallen to the ground.

Larval heterobathmiids are leaf miners in Nothofagus (Fagaceae), apparently restricted to the

deciduous taxa; the fully grown larva vacates the mine, falls to the ground and pupates in a

cocoon in the earth.

258

N.P. KRISTENSEN : EARLY EVOLUTION OF THE LEPID0PTERA+TR1CH0PTERA

ERIOCRANIIDAE

ACANTHOPTFROCTETIDAE

LOPHOCORONIDAF

NEOPSEUSTIDAE

EXOPORIA

NFPT1CUL01DFA

INCURVARIOIDEA

Higher HETERONEURA

Fig. 2. — Cladogram of basal lineages within Lepidoptera-Glossata, with some key evolutionary events indicated.

Among the basal Glossata the Eriocraniidae have a larval biology which is remarkably

similar to that of the Heterobathmiidae in the pre-glossatan grade; they are leaf miners, almost

exclusively restricted to trees in the Fagales (with a few occurrences on the Rosales), and they

pupate in a cocoon in the earth. However, whereas in the Heterobathmiidae the egg is deposited

on the host leaf surface (and covered by a secretion) eriocraniid eggs are inserted in pockets in

the leaf, cut by the female’s piercing oviscapt (Fig. 3). The sole acanthopteroctetid for which the

life-history is known is a leaf miner in Ceanothus (Rhamnaceae), and it pupates in a cocoon in

debris under the host (Davis & Frack, 1987). Immature Lophocoronidae and Neopseustidae

are unknown, but since females of the former have a piercing “Eriocrania -type oviscapt” (as

have the Acanthopteroctetidae), it is believed that their larvae are similarly endophagous,

probably leafminers. Neopseustid females also have what appears to be a kind of piercing

Source: MNHN, Paris

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

259

postabdomen (clearly distinct from the “Eriocrania-type", though perhaps derivable from it),

hence immatures in this family may also be endophagous.

Figs 3-4. — Eriocraniid structures (SEM), illustrating putative groundplan features of Lepidoptera-Glossata. 3: Dyseriocmnia

subpurpurella (Haworth, 1828), female abdominal apex (ventral view): “Eriocrania- type" piercing oviscapt with

lateral “saws”; arrow indicates cloacal opening. 4: Same, larval mouthparts (ventral view), showing articulated

spinneret (arrow).

It is in the Exoporia that one first encounters the “typical lepidopteran caterpillar” with its

complement of five pairs of musculated, crochet-bearing prolegs (Figs 6, 7), borne on abdominal

segments III-VI and X Mnesarchaeoid larvae are “soil animals” which live in silken tunnels

among bryophytes etc, often together with micropterigid larvae, and they are “completely

unspecialized phytophages” (Gibbs, 1979). The biology of the “smaller hepialoid families” is

poorly known, but larvae of Ogygioses (Palaeosetidae) occur in habitats similar to those of

mnesarchaeids (Davis el a /., 1995; HEPPNER et al , 1995). Hepialid larvae (see Grehan, 1989)

have diverse habits. Many make tunnels in the soil or construct silken galleries among litter,

feeding on roots or leaves of a variety of plants including pteridophytes, gymnosperms and

angiosperms; some are root/stem/branch borers. Fungivory is probably widespread, and a

transition from fungivory to phytophagy during larval ontogeny has been recorded in a number of

cases.

Most of the known representatives of the smaller heteroneuran lineages feed on living

angiosperms, and so did in all probability their last common ancestor. Nepticuloid females

deposit their eggs on the surface of the host plant, but all larvae are endophagous: nepticulids

mostly leaf-miners, but a few are stem-miners; the few opostegids with known biologies are

leafrpetiole- or branch/stem/trunk (cambium)-miners (Davis, 1989). The hostplant spectrum of

this superfamily, and that of the Incurvaroidea, comprise a large array of (mostly dicot) families.

Incurvarioid females have piercing oviscapts somewhat reminiscent of the “Eriocrania- type”. In

the apparently ancestral life-history in the superfamily early larval instars are leaf-mining, while

the older instars live on the ground, bearing a portable case constructed from the excised walls of

the mine and feeding on living or dead plant material. In some Adelidae even the first-instar

larvae are free-living soil-animals, but it is remarkable that these moths also have retained the

endophytic oviposition mode. The permanently endophagous (flower/fruit/stem-boring, gall-

260

N.P. KR1STFNSEN : EARLY EVOLUTION OF THE LEPIDOPTERA * TR1CHOPTEM

making etc) larvae of the cecidosid/prodoxid clade surely exemplify a pattern which is derived

within the superfamily. The few known larvae of Palaephatoidea are initially leaf-miners, later

living between two leaves (joined by silk along the margins) and feeding on their the inner

epidermis and parenchyme cells. (E.S. NIELSEN, pers. com.); the Tischerioidea are consistently

leaf miners. In neither of these taxa are the females equipped for endophytic oviposition.

The major quest ion: derivation of angiosperm feeding in basal moth lineages

Accepting the above conclusion that the soil-dwelling, detritophagous larvae of extant

Micropterigidae are overall similar to those of ancestral Amphiesmenoptera, it is pertinent to ask

how long this larval life style persisted in the sister lineage of the micropterigids. Do such

exoporians as mnesarchaeids or palaeosetids spend their larval stage in the same environment as

micropterigids because all their lepidopteran ancestors did so? In this case all other homoneurous

moth lineages (with known life histories) would have made independent transitions from the soil

to arboreal habitats. Or was this transition made in the stem-lineage of Agathiphagidae +

(Heterobathmiidae + Glossata), with the soil-dwelling exoporians representing an evolutionary

reversal? By the way, Agathiphagid larvae are classified as “arboreal” in acceptance of the

aforementioned inference that the eggs are laid while the seed is still in the cone (and perhaps the

initial part of the larval life is spent here before the seed falls to the ground). Also, the Exoporia are

here regarded as primarily soil-dwelling, and habitat shifts within this clade are disregarded in the

present context.

With the availability now of a largely resolved phylogeny for the basal moth clades,

parsimony speaks clearly in favor of the latter solution (Fig. 1). While it requires only two steps,

the former requires at least five transitions from the soil to arboreal habitats, viz. , in the stem

lineages of Agathiphagidae, Heterobathmiidae, Eriocraniidae, Acanthopteroctetidae and

Heteroneura. It almost certainly requires at least a sixth transition also, since although immature

Lophocoronidae are unknown, the presence in lophocoronid females of a piercing “ Eriocrania-

type” oviscapt is strong evidence that these insects have endophytic larvae. Even the female

postabdomen of the Neopseustidae has a structure which presumably reflects a boring/rasping

oviposition mode that would be unexpected if the larvae lived in soil/periphyton interstices.

Judging from the cladogram of extant moths, angiosperm-feeding was first adopted in the

stem-lineage of the Heterobathmiidae + Glossata. And if the Agathiphagidae are indeed the

sister-group of all other non-micropterigid Lepidoptera, then parsimony would favour the notion

that the last common ancestor of these two lineages had canopy-living and -ovipositing moths.

The inference is straightforward that the shift has come about through the utilization of arboreal

pollen sources by adults of early moths with soil-dwelling larvae; the same kind of ontogenetic

habitat shifts are illustrated by some extant micropterigids.

How does the fossil record comply with the notion of angiosperm feeding in extant pre-

glossatan moths (viz. , heterobathmiids) being primary? A reliable fossil record of eudicot

angiosperms (which include the hosts of extant Heterobathmiidae and Eriocraniidae) dates back

no futher than the Early Cretaceous (CRANE et a/., 1995). ROZEFELDS (1988) interpreted gallery

mines in Jurassic pteridophyte leaves from Australia as being due to Heteroneura-Nepticulidae,

but the evidence is inadequate (no frass was detectable in the mines) and the identification was

discarded by KRISTENSEN & SKALSKI (in press). However, the assignment of one pre-Cretaceous

Source: MNHN. Paris

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

261

moth, viz ., the Upper Jurassic Protolepis cupredlata KOZLOV, 1989 (Fig. 5) to the Glossata is

still being upheld by KOZLOV (see KRISTENSEN & SKALSKI, in press, POWELL et a /., in press).

Fig. 5. — Protolepis cuprealata Kozlov, 1989. drawning accompanying original descriplion; tire arrow indicates the

problematical mouth appendage: proboscis or maxillary palp?

Two reservations are in order. Firstly there is, of course, a theoretical possibility that the fossil

history of eudicots may be considerably older than documented by fossils, though the counter¬

evidence presented by Crane et at. is seemingly strong (absence of characteristic eudicot pollen

in numerous rich pre-Cretaceous palynofloras from both hemispheres). Secondly, I remain

unconvinced about the glossatan nature of Protolepis. In particular I consider it likely that the

curved mouth appendages are the maxillary palps rather than haustellate galeae; conditions in

extant primitive glossatans would lead one to expect the former to be much more prominent

formations than the latter. It therefore remains a real possibility that the larva of the last common

ancestor of Heterobathmiidae and the Glossata was a leaf miner in a fagacean host, though the

possibility of later host switches in the Heterobathmiidae and/or the Eriocraniidae cannot be

ruled out. In any case structural modifications linked to the leaf-mining habit has progressed to

different stages in these early angiosperm-feeders; for example, eriocraniid larvae have lost the

thoracic legs, while these are still retained in heterobathmiids and acanthopteroctetids.

Larval spuming and larval prolegs

Silken threads play a major role in the behavioral diversification of larvae in both

amphiesmenopteran “orders”. In the first differentiated, “pre-exoporian”, lineages of the

Lepidoptera, however, the only use made of the larval silk is for the spinning of the cocoon

262

N.P. KRISTENSEN : EARLY EVOLUTION OF THE LEPIDOPTERA + TRICH0PTER4

Figs 6-7. — Mnesarchaea sp. (Exoporia-Mnesarchaeidae), crochet-bearing larval prolegs (SEM), illustrating probable

neolepidopteran groundplan configuration. 6: Side view. 7: ventral view.

before pupation; such silken cocoons occur in all the known families of this grade (remember that

Iophocoronid and neopseustid larvae are unknown), Agathiphagidae excepted. Indeed,

Agathiphagid pupae remain in the mined seed and have no need for other coverings. However, the

labial glands of the larvae are exceedingly large and their secretion presumably plays a major role in

the formation of the hard inner lining of the pupal cell. It is perhaps surprising that the development

of the “spinneret" (the slender, passively movable process with the spinning gland aperture on the

apex. Fig. 4), which is such a prominent groundplan autapomorphy of the Glossata, was not - as

tar as presently known - initially associated with any marked change in spinning behavior.

The use of silk for construction of galleries or other kinds of webbings in which larvae live

is first encountered in the Neolepidoptera. Remarkably, as noted above, it is in the same clade

that one first encounters the crochet-bearing proleg (Figs 6, 7) of the “typical caterpillar”. It is

commonplace to think of these prolegs as an adaptation to clinging to plant surfaces (e.g.

STRONG el a /., 1984). It must be emphasized, however, that the substrates on which exophagous

exoporian larvae move are silk webbings, rather than plant surfaces. Larvae of ancestral

Exoporia probably lived in spinnings among periphyton as described above for mnesarchaeids,

and as noted by Grehan (1989) leaf-feeding hepialid caterpillars usually forage in the immediate

vicinity of their tunnel/gallery entrances. Prolegs and crochets are absent (secondarily lost,

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

263

according to the most widespread view which I endorse) in the endophagous larvae of the

Heteroneura-Nepticuloidea. Prolegs are also poorly developed in the Incurvarioidea and

Tischerioidea, but more or less distinct crochets are generally retained in both superfamilies; in

case-bearing late-instar incurvarioid larvae the crochets engage in a silken lining of the case

(SCHELLAUF, 1994), and tischerioids line their blotch mines with silk.

Since silken webs and crochet-bearing prolegs evolved on the same internode on the

lepidopteran cladogram (as constructible on the basis of known, extant taxa), this cladogram

cannot in itself provide unambiguous evidence that the prolegs evolved as an adaptation to

moving on a silken web; however, functional anatomy corroborates this assumption (SCHELLAUF,

1994). The fact that the convex curvature of a caterpillar crochet faces the substrate, and the tip

therefore is directed away from the latter in the resting position ( i.e ., with the plantar muscle

uncontracted) is most readily explicable, if the crochet evolved in response to a selective pressure

for enhancing grips on a silken webbing. If the initial selective regime had been for enhancing

movement on a smooth plant surface, one would rather have expected crochet curvature to have

been reversed. The crochet-bearing prolegs are, therefore, apparently an exaptation to clinging

onto plant surfaces, which surely is their principal function in the bulk of the Lepidoptera. In

many cases the proleg grip is preceded by the larva fastening silken threads on the substrate,

and/or the distal proleg configuration is profoundly modified, as in the “Macrolepidoptera-type”

proleg.

Eclosion mode

The stem lineage of the Neolepidoptera is characterized by another notable behavioral

innovation: the exarate, decticous pupal type is replaced by the adecticous obtect type.

Functionally the loss of mobility of the pupal appendages is compensated for by the development,

in the neolepidopteran ground plan, of a spinose pupal abdomen which permits the pharate adult

to wriggle out of the pupal enclosure prior to pupation.

Though lophocoronid and neopseustid pupae are unknown, examination of the adult

structure permits important inferences. Adult neopseustids have well-developed mandibular

muscles, and it has therefore been concluded that their pupae are decticous; moreover, it is

inferred that they also are exarate, because all known decticous pupal types are so. Adult

lophocoronids, on the other hand, have the mandibular musculature completely reduced, and

their pupae are thus necessarily adecticous. However, no inference can be made as to whether

they are obtect as in the Neolepidoptera, since adecticous exarate pupae are known elsewhere

among endopterygotes.

The preferred phylogeny of the Glossata (NIELSEN & Kristensen, 1996) necessitates the

postulate that the adecticous pupae in Lophocoronidae and Neolepidoptera are independently

evolved. In the analysis the “cost” of making the origin of the adecticous pupa a unique event

through switching the Lophocoronidae to the position as sister-group of the Neolepidoptera is

three extra steps. Evidently a future discovery of lophocoronid immatures will be significant in

this context. If lophocoronid pupae prove to be obtect and spinose like those of

neolepidopterans, the support for the second phylogeny would be at least somewhat

strengthened.

It should be emphasized, however, that transitions from the decticous to the adecticous

pupal type have occurred repeatedly among endopterygote insects, and homoplasy of this trait

264

N.P KRISTENSEN : EARLY EVOLUTION OF THE LEPIDOPTERA + TRIC.HOPTERA

within the Lepidoptera is not unexpected. Functionally the transition appears easily explicable: it

frees the insect from retaining, up to the adult stage, the investment of precious proteins in the

bulky mandibular musculature, which is used only during a very brief phase of the adult insect's

life. Thus, the breakdown of the mandibular musculature which has been observed in post-

pharate eriocraniids (as in caddisflies), can begin during pupal life, whereby an earlier re-use of

components for e.g. oocyte growth or genital-duct secretions is made possible.

THE TRICHOPTERAN LINEAGE

The shift of larval habitat from the soil into the genuinely aquatic environment was

arguably the key innovation in the early evolution of the caddisfly lineage. The initial step has

probably not been a major one in an ecological sense, inasmuch as some “soil” habitats may well

be characterized as at least semi-aquatic. However, as far as known, all extant trichopteran larvae

share one significant apomorphy which one would immediately interpret as an adaptation to the

aquatic life-style: the apneustic tracheal system. Other trichopteran larval groundplan

autapomorphies are regressive traits with less obvious functional significance: greatly shortened

antennae without any extrinsic musculature, single maxillary endite lobe and very delicate

tentorium (the two Iastmentioned states are parallelled in all non-micropterigid Lepidoptera).

More or less pronouncedly terrestrial larvae occur in a number of caddisfly lineages (the

Palaearctic limnephilid genus Enoicyla is perhaps the best known example), but it has not been

questioned that these larvae are all secondarily non-aquatic. Importantly, as noted by Hinton

( 1958), the Enoicyla larva is indeed apneustic.

WIGGINS (1984) drew attention to the life-style of micro-caddisflies of the Ptilocolepus

group as being particularly close to that which might be inferred for the amphiesmenopteran

ancestor of the trichopteran lineage. Their larvae are associated with wet liverworts, as are most

micropterigid moths in the Sabatinca -group of genera, and they “crawl over dripping tiers of

these plants, as often out of water as in it”. This caddisfly taxon (comprising the W. Palaearctic

Ptilocolepus and the Amphipacific-Holarctic Palaeagapetus) is currently ranked as a subfamily in

the Hydroptilidae (Marshall, 1979). It remains debatable, however, whether the diagnostic

traits it shares with the Hydroptilinae are actually apomorphies. They are: (1) free-living lst-4th

larval instars, with tergal sclerites on thorax and I-VIII; (2) “hypermetamorphic” last (5th) instar

larva with swollen abdominal segments and tergal sclerites on all thoracic segments, living in a

two-valve case made from leaf fragments. In the light of the uncertainty about the affinities of the

Ptilocolepus-group it does seem pertinent to ask again whether they could indeed be the sister-

group of all other caddisflies, and their larvae therefore primarily semiaquatic. However, even

these larvae are apneustic (I have examined serial sections of the thorax and first abdominal

segments of larval Palaeagapetus without finding any trace of functional spiracles), and thereby

conform with the inferred trichopteran groundplan. On this basis the conclusion seems

inescapable that ptilocolepine caddises are derived from ancestors with fully aquatic immatures,

as hitherto presumed.

How does one recognize an adult caddisfly?

The trichopteran groundplan autapomorphies mentioned above are all in the larval stage.

Indeed, and in striking contrast to the Lepidoptera, adult Trichoptera are actually quite difficult

Source: MNHN, Paris

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

265

to diagnose as such. This impression is amply supported by an examination of Schmid's (1989)

somewhat detailed reconstruction of the integumental structure of the ancestral caddisfly.

Alleged autapomorphies hitherto identified in the groundplan of adult Trichoptera

(KRISTENSEN, 1991/1994) include: (1) prelabio-hypopharyngeal lobe forming large “haustellum”

(protrusible/eversible by blood pressure) with intricate system of canals (formed by modified

microtrichia) enabling uptake of fluid nutrients; (2) clypeolabral articulation and extrinsic labral

muscles absent (parallelism with Mecoptera); (3) true mandibular articulation absent (parallelism

with Lepidoptera-Glossata). Not all of these can be upheld, however. The haustellum itself

remains a good autapomorphy of adult caddis flies, indeed it is the only at all “strong” one, but

the complement of surface canals cannot. These canals were identified in the Integripalpia by

CRICHTON (1957), but while this author found all examined non-Integripalpia (Annulipalpia-

Polycentropodidae excepted, most likely due to secondary modification) to have a “granulose”

surface texture devoid of canals, Kl.F.MM (1966) construed the microtrichia on the Rhyacophila

haustellum to be aligned in a manner to form canals somewhat comparable to those of the

Integripalpia. It is on this basis that I had attributed a canal system to the trichopteran ground

plan. However, by subsequent SEM investigation I have discovered that at least the

Hydroptilidae (Ptilocolepinae included) and Glossosomatidae have no kind of longitudinal/radial

alignment of haustellum microtrichia, hence no canal system. Instead, in these taxa the haustellar

microtrichia (which are simple) are arranged along transverse crests (Figs 8-9). Since this

arrangement is reminiscent of the spine armature in the infrabuccal pouches on the

hypopharyngeal surface in the non-glossatan moths, it most probably represents the ground plan

state in the Amphiesmenoptera and hence in the Trichoptera.

It is similarly necessary to discard the obliteration of the “clypeolabral articulation” as a

trichopteran autapomorphy: I have now found that a well-developed clypeolabral membrane is

actually retained in several members of the Annulipalpia. But all the caddisflies I have sectioned

(including representatives of all primary clades, cp. below) are devoid of extrinsic labral muscles;

hence the loss of these muscles may well have been a unique event in the trichopteran stem

lineage, i.e., it can upheld as an autapomorphy of the group. So can the loss of genuine cranio-

mandibular articulations, associated with the absence of mandibular function in post-pharate

adult caddisflies.

It is important to emphasize again that none of the autapomorphies hitherto identified in

adult caddisflies are easily observable, and in particular that they are unlikely to be of use in the

case of fossils. However, attention shall here be drawn to a venational character which deserves

scrutiny as a potential aid in diagnosing Trichoptera: the distal course of the forewing CuP. In

most Lepidoptera, including all homoneurous lineages, this vein (often quite weak) is almost

straight or at most smoothly curved (Figs 10-11). On the other hand, in all extant basal clades

within the Trichoptera it is commonplace that the apical part of this vein is abruptly bent towards

the wing margin (Figs 13-15); it therefore reaches the margin only a short distance beyond the

anal vein (i.e., the apical “stem” of the “double-Y” formed by the fusion of 1A + 2A + 3 A), and

it frequently even fuses with the latter (Fig. 14). A modification of this pattern is characteristic of

the Hydrobiosidae (SCHMID, 1989). In this family (Fig. 15) the portion of CuP beyond the bend

again becomes more or less parallel with CuA2, conferring upon CuP an undulated

configuration; in some cases (Ausiralochorema Schmid and Apsilochorema Ulmer are

pronounced examples) the apicalmost part of CuP is again sharply bent, so a double

Source MNHN , Paris

266

N.p. KRISTENSEN : EARLY EVOLUTION OF THE LEPIDOPTERA+TRICHOPTERA

Figs 8-9. — Ptilocolepus granulatus (Pictet, 1834), (Trichoptera: Hydroptilidae-Ptilocolepinae), adult mouthparts (SEM,

frontal view). 8: Haustellum with aligned nucrotrichia; haustellar base largely covered by maxillary lobes (interpreted

as galeae), apex of labrum visible on top. 9: Microtrichia lines at higher magnification.

undulation” of the vein arises. Most extant and extinct Mecoptera have a straight/smoothly

curved CuP, and so do many fossils classified as stem-lineage panorpoids (see WiLLMANN,

1989), hence, this state is presumably the plesiomorphic one. But the character is obviously

homoplasious (which is unsurprising, given its simplicity). For example, some extant Mecoptera-

Bittacidae do have a marked bend, and so do the Permian Amphiesmenoptera-Microptysmatidae,

which have a six-branched Rs and therefore presumably can at most belong to the

amphiesmenopteran stem-lineage. By the way, WiLLMANN (1989) would not exclude that the six-

branched Rs could be a microptysmatid autapomorphy. It is also easy enough to find examples of

extant caddisflies in which the apical curvature of CuP is little pronounced or even non-existent

(Fig. 12), presumably character reversals. The CuP configuration can thus only be taken as an

indication of whether a given amphiesmenopteran (extinct or extant) belongs to the trichopteran

lineage, not an absolute proof.

Source: MNHN , Paris

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

267

Figs 10-15. — Forewings of various Ainphiesmenoptcra (not drawn to scale), illustrating diversity in apical CuP-configuration

(arrows). 10: Agathiphaga vitiensis Dumbleton, 1952 (Lepidoptera-Agathiphagidae); note: the pattern of vein

branching/anastomosing in the pre-cubital wing area is surprisingly variable from one individual to the next in this

taxon. 11: Sabatinca calliarcha Meyrick, 1912 (Lepidoptera-Micropterigidae), exemplifying a primitive moth with

unusually strongly bent CuP. 12: Psychomyia nomada Ross, 1938 (Trichoptera-Psychomyidae), a caddisfly with

(?secondarily) straight CuP. 13-15: Caddisllies with CuP strongly bent apically, an auxiliary ordinal groundplan

autapomorphy: 13: Rhyacophila torrentium Pictet, 1834 (Rhyacophilidae). 14: Stenopsychodes tillyardi Banks, 1939

(Stenopsychidae), showing subapical fusion of bent CuP and fused A veins. 15: Australochorema rectispinum Schmid,

1955 (Hydrobiosidae), showing “double undulation” of CuP. [10-11 original, 12-15 from Schmid (12: Memoires de la

Societe Entomologique du Canada 125, 1983; 13: Memoires de la Societe Enlomologique du Canada 66. 1970; 14 :

The Canadian Entomologist 101: 187-224, 1969; 15: Bulletin de I'lnstitut Royale des Sciences Naturelles de Belgique ,

59, Supplement, 1989)]

While Novokshonov & Sijkatcheva (1993) opened a recent review by saying that

“Caddisflies are common as fossils from the Permian onwards”, the earliest concrete evidence for

the existence of the trichopteran lineage is actually from the Lower Jurassic, and it is indirect: the

existence of the sister-lineage (namely the lepidopteran Archaeo/epis). I do consider it very likely

that the split between the lepidopteran and trichopteran lineages took place at least in the

Triassic, but reliable evidence will be difficult to obtain. The assignments of the Protomeropidae,

Microptysmatidae, Cladochoristidae, Liassophilidae, Prorhyacophilidae, and Dysoneuridae to the

Trichoptera (CARPENTER, 1992; Novokshonov & SUKATCHEVA, 1993) have all been

unfounded within the framework of phylogenetic systematics. Whereas the many costo-subcostal

crossveins and/or high number (>4) of Rs branches in the four firstmentioned taxa would seem to

268

N.P. KRISTENSEN : EARLY EVOLUTION OF THE LEPIDOPTERA + TR1CH0PTERA

preclude that these can even belong in the amphiesmenopteran “crown-group”

(Amphiesmenoptera sensu HENNIG), the two lastmentioned may indeed comprise members of the

trichopteran lineage; they may, however, equally well include stem-lineage Amphiesmenoptera

and stem-lineage Lepidoptera. The same is true of the Necrotauliidae, some Jurassic members of

which have the forewing CuP strongly bent apically; these taxa, therefore, can with some

justification be talked of as caddisflies. The Upper Jurassic/Lower Cretaceous Necrotaulius tener

Sukatcheva, 1990 reportedly has a short, annulated apical segment of the maxillary palp; hence it

has been assigned to the stem-lineage of the Annulipalpia s. str., and if this palp character is

correctly interpreted this assignment is justifiable. It would not be surprising if the extant basal

caddisfly clades were indeed differentiated by the Jurassic/Cretaceous boundary.

Basal trichopteran clades and the problems of their interrelationships

Six basal clades are currently recognized within the Trichoptera. The largest are the

Integripalpia s.str. whose larvae are tube-case makers, and the somewhat less species-rich

Annulipalpia s.str. (= Curvipalpia) whose larvae are net-spinners/retreat makers. The remaining

caddisflies are overall generalized taxa, now grouped into four families: the Rhyacophilidae and

Hydrobiosidae (larvae free-living, carnivorous), the Hydroptilidae (larvae free-living, except last

instar which make “purse-cases”) and the Glossosomatidae (larvae “saddle-case” makers). These

four families are believed by some to constitute a monophylum “Spicipalpia” which is the sister

group of the Annulipalpia (WEAVER, 1984; WEAVER & MORSE, 1986); alternatively the

“spicipalpian” families have been seen as an assemblage which is paraphyletic in terms of the

Annulipalpia (SCHMID, 1989), the Integripalpia (ROSS, 1967), or both (cladograms obtained by

Frania & WIGGINS; Wiggins, pers. com.). In spite of major recent efforts (Frania & WIGGINS,

in press) no single convincing phytogeny of the caddisfly clades has so far been obtained.

Considerations of ancestral larval habits/habitats and pupation modes have played a major

role in the current debate over these unresolved interrelationships (for an entry into the pertinent

literature see WEAVER, 1992a, 1992b; WIGGINS, 1992). In one scenario (WIGGINS & WlCHARD,

1989) ancestral caddisfly larvae are believed to have been free-living (at least in earlier instars)

and inhabiting cool lotic waters; in another (Weaver & Morse, 1986) they are believed to have

lived in silken tubes in humus/detrital mats in the lentic or “lotic-depositional” zone.

Both scenarios may well contain elements of the truth. Given the assumption that ancestral

Amphiesmenoptera (and indeed panorpoid endopterygots) were soil-dwelling, it is difficult to see

how the transition into lotic waters could have taken place via any other habitat than that

envisaged in the WEAVER/MORSE theory, though the last common ancestor of the trichopteran

crown group apparently, as noted above, has had a more fully aquatic larva than those of extant

amphibious spicipalpians like the Hydoptilidae-Ptilocolepinae. On the other hand it must be

strongly emphasized, that contrary to Weaver's claims (1992b), evidence from Lepidoptera

lends no support to the notion that trichopteran larvae in silken tubes represent an ancestral

amphiesmenopteran life-style. WEAVER referred to the tube-dwelling Exoporia, but since this

lineage did not arise until the eighth splitting event traceable among extant Lepidoptera, they

have little relevance for the question of ground plan conditions in the group, let alone the

Amphiesmenoptera. As noted earlier, none of the more basal lepidopteran lineages have larvae

that are known to live in silken galleries: out-group evidence therefore supports that the free-

living caddisfly larvae represent the ancestral life-style.

Source: MNHN, Paris

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

269

Given the long-standing interest in the behavioural diversity of caddisfly larvae, it is much

to be hoped that fortcoming renewed efforts will soon result in a trustworthy trichopteran

phylogeny upon which this diversity can be mapped and interpreted.

ACKNOWLEDGEMENTS

This paper is dedicated to Professor T. Yasuda, University of Osaka, on the occasion of his retirement. A largely similar

version of this article appears in Japanese in T. Y.asuda (ed.) Biology ofMicrolepidoptera. I am grateful to Professor G. B. Wiggins

and Dr. H. Maucky for useful information and for material of Ilydroptilidae-Ptilocolepinae. Dr. E. S. Nielsen provided

useful information about palaephatid immatures. Skilled assistance with the illustrations was provided by Mr. G. Brovad

( printing) and Ms. B. Rubaek (line drawings).

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Phylogeny and Evolution of the Larval Diet

in the Sciaroidea (Diptera, Bibionomorpha)

since the Mesozoic

Lo'ic MATILE

E.P. 90 CNRS. Laboratoirc d'Entomologie. Museum national d'Histoirc naturelle.

45. rue Buffon. 75005 Paris. France

ABSTRACT

The larvae of the Keroplatidae exhibit diverse trophic specializations, being either ferocious predators, killing their prey by

way of toxic diffuse nets, or fungi'vorous insects, spinning sheet-like webs to gather the spores of polyporous fungi. Previous

studies of trophic specializations of larvae in Sciaroidea have been based up to now on inference from morphology or on

empirical demonstration. These have led to the general notion that fungivory is ancestral for the Sciaroidea and predation

ancestral for the Keroplatidae. New phylogenies for Sciaroidea and Keroplatidae are proposed here; the Cecidomyiidae seem

to be the sister-group of all other families. Seven attributes are mapped on the cladograms - endobiosis/epibiosis,

fungivorv/other diets, presence or absence of silk secretion, predation/sporophagy, labial secretion pH - 3, net-like/sheet-like

web, optobiosis/cryptobiosis. It is concluded that fungivory and silk secretion are ancestral for Sciaroidea and predation

ancestral for the Keroplatidae while sporophagy is a specialization derived from predation. Epibiosis, with its cryptobiotic

specialization, the net-like web and the highly acid pH, are also apomorphic for Keroplatidae. Sporophagy, optobiosis, sheet¬

like web and less acid pH are correlated apomorphic traits for the tribe Keroplatini. The fossil and biogeographical data allow

dating most of these specializations back to at least the Lower Cretaceous.

RESUME

Phylogenie et evolution du regime alimentaire des lanes de Sciaroidea (Diptera, Bibionomorpha)

Les larves de Keroplatidae presentent tin regime alimentaire tres contrasts, puisque les lines sont de redoutables predateurs

qui tuent leurs proies au moyen d'une salive toxique repandue dans une toile de chasse, tandis que les autres sont infeodees

aux Polypores, dont ils recueillent les spores dans une toile de recolte. La question des specialisations trophiques chez les

larves de Sciaroidea a jusqu'ici ete abordee par des voies empiriques ou morpho-anatomiques, qui on conduit a penser

notamment que la mycophagie etait ancestrale pour les Sciaroidea et la predation ancestrale pour les Keroplatidae. De

nouvelles phylogenies des Sciaroidea, puis des Keroplatidae, sont proposees dans ce travail , les Cecidomyiidae apparaissent

comme le groupe-frere de l'ensemble des autres families de Sciaroidea. Sept attributs sont superposes aux cladogrammes -

endobiose/epibiose, mycetophagie s ././autres regimes, secretion de soie ou non, predation/sporophagie, secretion labiale a

pH+3, toile en reseau/nappe, optobiose/crvptobiose. On est amene a conclure que la mycetophagie et la secretion de soie sont

ancestrales pour les Sciaroidea et la predation ancestrale pour les Keroplatidae, tandis que la sporophagie de ces demiers est

une specialisation developpee a partir de la predation. L'epibiosc avec sa specialisation en cryptobiose, la toile en reseau et le

pH hautement acide, sont egalement plesiomorphes pour les Keroplatidae. Sporophagie, optobiose, toile en nappe et pH moins

acide sont des apomorphies correlees de la tribu des Keroplatini. La datation de l'ensemble des cladogrammes par les fossiles

Matile, L., 1997. — Phylogeny and evolution of the larval diet in the Sciaroidea (Diptera, Bibionomorpha) since the

Mesozoic. In: Grandcolas, P. (ed.), The Origin of Biodiversity in Insects: Phylogenetic Tests of Evolutionary Scenarios.

Mint. Mus. natn. Hist, nat., 173 : 273-303. Paris ISBN : 2-85653-508-9.

274

L. MATILE ; PHYLOGENY AND EVOLUTION IN THE SCIAROIDEA

et Ies donndes biogeographiques permet en outre d'attribuer a la plupart de ces specialisations un age au moins Cretace

inferieur.

INTRODUCTION

The larvae of the Keroplatidae, a family of Sciaroidea, have highly diverse food

preferences. Some are formidable predators, killing their prey by means of a toxic highly acidic

saliva dispersed on a trapping net-like web, while others are live under bracket-fungi

(Polyporaceae), where they gather spores in a sheet-like, less acidic web. Some lead a cryptic

life, deeply hidden at maximum darkness and humidity (a way of life for which the term

cryptobiosis is proposed), while others, while they do not shun obscurity, are able to live more or

less in the open ( optobiosis ) if necessary.

Trophic specialization of the larvae of Sciaroidea has up to now been addressed

empirically (Krivosheina, 1969; LASTOVKA, 1972; Jackson, 1974), or through morpho-

anatomy (ZAITSEV, 1983, 1984a, b; Matile, 1986). These works led to the conclusion that

fungivory was ancestral for Sciaroidea, and predation ancestral for the Keroplatidae. Lastovka

(1972), who noted that fungivory is most common, and therefore plesiomorphic, also assumed

that predation probably evolved from sporophagy.

1 propose in this paper to test these previous hypotheses in the light of phylogeny, to study

attributes (in the sense of Brooks & McLennan, 1991) linked to food preference in the

Sciaroidea, especially the Keroplatidae. The following questions will be addressed: What was the

ancestral food of the Keroplatidae larvae? What was the ancestral condition of their web? Was

their common ancestor a cryptobiont or an optobiont? Moreover, it has been demonstrated by

historical biogeography and by fossil data, that Keroplatidae already existed at least in the Upper

Jurassic (Matile, 1990; Grimaldi, 1990; Evenhuis, 1994). I shall try to date the appearance of

these attributes by means of fossil and palaeogeographic data.

According to some authors who have recently addressed the problem of the classification

of the Sciaroidea (or Mycetophiloidea), the superfamily consists of three families only -

Mycetophilidae, Sciaridae and Cecidomyiidae (Wood & BORKENT, 1989; COLLESS &

Me Alpine, 1991) - the last two being sister-group to the first (WOOD & Borkent, 1989). In a

recent paper (OOSTERBROEK & COURTNEY, 1995), the superfamily is suppressed as such and

included in the Bibionoidea, while the Mycetophilidae, Sciaridae and Cecidomyiidae show the

same relationships proposed in WOOD & BORKENT's paper. Nevertheless, in all three of these

papers (Fig. 1), the paraphyly of the adopted concept of “Mycetophilidae” is explicitly

recognized.

On the other hand, authors who have treated fossil as well as recent taxa recognize more

readily a group of “Mycetophilidae” families, sister-group to the Sciaridae, and then sister-group

to the Cecidomyiidae, this last family treated by some as the superfamily Cecidomyioidea

(Rohdendorf, 1964, 1974; Kovalev, 1987a; Shcherbakov eta/., 1995). Many authors have

treated the subfamilies of Edwards (1925) - Ditomyiinae, Diadocidiinae, Keroplatinae,

Bolitophilinae, Mycetophilinae, Lygistorrhininae and Sciarinae - as of family rank like the

Cecidomyiidae, but phylogenetically oriented papers are scarce (HENNIG, 1954, 1968, 1973;

Matile, 1986, 1990; Amorim, 1992; Fig. 1). I have pointed out elsewhere (Matile, 1993) that

it might not be phylogenetically sound to use only three families “in keeping with North

American tradition” (WOOD & BORKENT, 1989); neither do I feel dogmatic in thinking “that a

Source MNHN , Paris

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

275

Anisopodiformia

Scat opsoide a

Pachyneuriformia

Cecidomyioidea

Mycetophiloidea

BIBIONOMORPHA

HENNIG, 1954, 1968, 1973

Pachyneuridae

Bibionidae

Mycetophilidae

Sciaridae

Cecidomyiidae

WOOD & BORKENT, 1989

BIBIONOMORPHA

Ditomyiidae

Diadocidiidae

Keroplatidae

BOLITOPHI LI DAE

Mycetophilidae:

Lygistorrhinidae

Sciaridae

Cecidomyioidea

MYCETOPHILOIDEA

MATILE, 1990

AXYMYIIDAE

Bibionidae

PaCHYNEURIDAE

Mycetophilidae

Sciaridae

Cecidomyiidae

BIBIONOIDEA

Oqsterbroeck & Courtney, 1995

Fig. 1. — Hypotheses on the phylogeny of the Bibionomorpha, or the Mycetophiloidea + Cecidomyioidea, according to

Hennig (synthesis of 1954,1968,1973); Wood& Borkent, 1989; Matile, 1990; Oqsterbroeck & Courtney, 1995.

paraphyletic taxon cannot be a perfectly good one” (COLLESS & Me ALPINE, 1991), especially for

the kind of analyses presented here or in historical biogeography.

A hypothesis of relationships of the families of Sciaroidea (Cecidomyiidae excluded) has

been given by Matile (1986,1990) (for a review of earlier hypotheses see Matile, 1986: 376-

410), where the Sciaridae are considered the sister-group of the Mycetophilidae +

Lygistorrhinidae (Fig. 1). In this paper, a new hypothesis founded on a greater number ot

characters is proposed for the Sciaroidea.

Source

276

L. MATILE : PHYLOGENY AND EVOLUTION IN THE SCIAROIDEA

Most larvae of Sciaroidea are more or less narrowly linked to the carpophores of the higher

fungi, either spinning a web under or close to the hymenium (all Diadocidiidae, certain

Keroplatidae and Mycetophilidae), or living in the carpophore itself (some Ditomyiidae, all

Bolitophilidae, most Mycetophilidae, some Sciaridae). They feed on spores only (sporophagy,

fungivory sensu lato), on spores and hyphae, and perhaps in some cases on hyphae only. Some

species live in rotten wood, where they feed on mycelia (some Ditomyiidae and Sciaridae). On

the other hand, most Sciaridae live in the soil litter, were they are thought to be saprophagous.

Some very few species of Sciaridae and Mycetophilidae are phytophagous, while many

Keroplatidae and some Mycetophilidae are predaceous. Most Cecidomyiidae larvae are

phytophagous, but there are predatory or fungivorous species.

A number of traits are more or less narrowly associated with larval feeding habits:

secretion of silky threads to spin webs and/or pupal cocoons, endobiosis or epibiosis and, in

epibiosis structure and composition of the web. PLACHTER (1979b) assumed that the three-

dimensional web of certain Keroplatidae species was derived from a primitive, less complex web

with a wide central band. ZAITSEV (1984) thought that the first step towards fungivory in

Sciaroidea had been epibiont “grazers” feeding on mycelia covering wood, leaves, and other

substrata. In a previous work, the larval morpho-ecology of the Sciaroidea was studied. The

ancestral stock of the superfamily was presumed to be a eurybiont detritophilous larva in the

sense of Mamaf.v (1968, 1975), e.g. a fungivorous larva of soil, litter and rotting wood, without

silk secretion and bearing well-developed antennae and body macrochaetae (Matile, 1986). The

groundpian of the Diadocidiidae-Keroplatidae clade and its sister-group has been inferred as

having an endobiont larva, to be fungivorous and silk-producing, and to have a smooth and long

body, with vestigial antennae, eyes and macrochaetae, however these provisional conclusions

were not published in my 1990 monograph.

materials and methods

Hie imaginal morphological data used in the phylogenetic hypotheses discussed here was provided mainly by material

trom the Collections of the Museum National d'Histoire naturelle, Paris. The remainder came from specimens loaned by many

colleagues and institutions worldwide (cf. Matile, 1990: 24-25, 637). I have thus been able to examine adults of

representative species (most often at least the tvpe-species) of practically every known genus of Sciaroidea, with the notable

exception ol the Sciaridae, where only the largest genera have been checked. Data on the Cecidomyiidae were mostly obtained

from the literature.

Concerning the name of Sciaroidea versus Mvcetophiloidea, the superfamily name Sciaroidea is founded on

Sciaraedes Billberg, 1820, while Mycetophiloidea is based on Mycetophilites Newman, 1834 (Sabrosky, pers. com ).

Although names ol the family-group using the prefix Mycetophil- are many times more numerous than those founded on

Scar-, art. 36a (Principle of coordination for the family-group names) of the International Code of Zoological Nomenclature

imposes the use ol Sciaroidea, unfortunately resurrected from a long oblivion by McAi.pine el al. (1981).

As regards larvae, this paper is based on published works, especially those by Madwar (1937), Brauns (1954a) and

m/ 1979a > l979b ’ l979c ) for illustrations and observations, and by Lastovka (1972), Zaitsev (1984) and Matile

(1986, 990) lor interpretation and homology. Personal observations, published or not, have been added - these have been

accumulated over thirty years, in the field and in the laboratory, in tropical and temperate areas.

Concerning lire polarization of characters, the analysis by Matile (1990) has generally been followed; it bears mainly

on Keroplatidae, but can easily be extended to the Sciaroidea. The matrices of characters have been treated by the Hennig86

program (Farris 1988), with implicit enumeration (“ie” command), characters non-ordered (“cc-” command), and the

evolution of the characters has been followed with the Clados program (Nlxon, 1991). After phylogenetic hypotheses for the

groups involved were obtained, it was possible to proceed to an optimization (Farris, 1970) of the different attributes on the

cladograms Hie seven attributes studied are identified and numbered in the text; the first three bear on die Bibionomorpha

and Sciaroidea. the last four on Keroplatidae only.

Source: MNHN . Paris

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

277

PHYLOGENY

The few phylogenetic hypotheses expressed up to now on Sciaroidea have been manually

obtained, except in OOSTERBROECK & COURTNEY'S analysis, which bears on all families of

“Nematocera”, and was done using the programs Paup and Hennig86. All hypotheses -

autapomorphic family traits excluded - have taken few characters into consideration: 4 IN Wood

& BORKENT's, 8 in OOSTERBROECK & Courtney's, 9 in Matile's. I have been able to gather a

greater number of characters (30), either new or already available in the literature, which allows

the reconstruction of a new cladogram (although yet provisional) of the Sciaroidea.

Appendix I refers to these characters and their matrix, and gives the references to their

polarization when already published. The outgroups chosen are the Bibionidae (genus Bibio

Geoffroy) and the Pachyneuridae (genus Cramptonomyia Alexander), both basal to the

Bibionomorpha in Wood & BORKENT's and OOSTERBROEK & Courtney's cladograms.

Cramptonomyia (here Pachyneuridae) and Hesperinus Walker (Bibionidae), Plecia Meigen and

allied genera (Bibionidae) are sometimes considered as of family rank. The position of the

Pachyneuridae is debatable. For example the family has been placed with Axymiidae and others in

an infraorder Axymyiomorpha (WOOD & BORKENT, 1989) or a superfamily Pachyneuroidea

(KRZEMINSKA et a/., 1993). For other authors Axymyiidae stand by themselves in Axymyioidea

(Shcherbakov et ai, 1995), or the group Cramptonomyiformia is proposed (Amorim, 1992),

etc. (see review in Amorim, 1992). The reader is therefore reminded that I do not purport to

give here a new hypothesis on the phylogeny of the Bibionomorpha - the introduction in the

cladogram of a genus each of Bibionidae and Pachyneuridae derives from the necessity of

choosing at least two outgroups. The Cecidomyiidae have been taken into account because of

their presumed sister-group relationship with the Sciaridae rather than the rest of the Sciaroidea.

Autapomorphies of the families have been excluded from the analysis, as well as those of

the Bibionomorpha. We have not used OOSTERBROECK & Courtney's character 90 (absence of

sperm pump), because it is present at least in some Keroplatidae (MATILE, 1990). Their character

72 (anterior veins concentrated along costal margin) has also been eliminated because this

costalization is common in Keroplatidae and Mycetophilidae.

Phylogenetic analysis in Hennig86 gave only one most parsimonious tree, length 44,

Cl 0.70 and RI = 0.76 (Fig. 2). This tree shows the Cecidomyiidae as the sister-group of the

Ditomyiidae+ group (terminology of AMORIM, 1982) as advocated, although with some doubts,

by HF.NNIG (1954, 1970, 1973). The structure of the Ditomyiidae+ group agrees with the

cladogram of the “Mycetophiloidea” given by MATILE (1990), and there seems no necessity to

retain the Cecidomyiidae as a superfamily by themselves. The cladogram agrees also with the

phylochronogram given by SHCHERBAKOV et ai (1995) as regards the recent families, and

especially the sister-group relationship of Cecidomyiidae and Sciaroidea.

It is to be noted that several characters are yet unknown in some terminal taxa, especially

number 14 (loss of dorsal transverse connective in larval tracheal system), 29 (chromosomic

elimination) and 30 (loss of central sperm microtubule). The cladogram implies that character 14

has appeared by homoplasy in Sciaridae and Cecidomyiidae, and that characters 29 and 30 are

basal for the Bibionomorpha, with a reversal in the clade Mycetophilidae-[Lygistorrhinidae],

The Keroplatidae have been divided into three subfamilies, Arachnocampinae,

Macrocerinae and Keroplatinae (MATILE, 1981a). In addition, two tribes have been recognized in

278

L. MATILE : PHYLOGENY AND EVOLUTION IN THE SCIAROIDEA

■ Bibionidae

-Pachyneuridae

“ Cecidomyiidae

_ Ditomyiidae

Keroplatidae

Diadocidiidae

Bolitophilidae

- Sciaridae

Mycetophilidae

- Lygistorrhinidae

Fig. 2 — Phylogenetic relationships of the Sciaroidea. Hennig86, 30 characters, unordered, "ie” command Length- 44

Cl = 0.70, RI = 0.76. ' ’

the last two subfamilies: Macrocerini and Robsonomyini in Macrocerinae, and in Keroplatinae

Keroplatini and Orfeliini (MATILE, 1990). A phylogenetic analysis of these three families has been

given in MATILE ,1990, on the basis of 40 larval, pupal and imaginal characters. This analysis was

hand-treated, and I present here a quantitative analysis bearing on 45 characters (without the two

tribes of Macrocerinae, the larvae of only Macrocera being known). The outgroup chosen is the

family Ditomyiidae. The characters, polarized after MATILE, 1990, and their matrix are given in

Appendix II. The treatment of the matrix by Hennig86 gave only one tree, length 45, with high

^ ~ CI = °- 97 ’ RI = 0 93 ( F ‘g- 3 ) The tr ee has the same structure than that published in

Arachnocampinae are monogeneric and only the laivae o f Macrocera Meigen are known in

Macrocerinae. We possess larval data for only 15 out of the 73 present genera of Keroplatinae

(in fact 17, but for two genera, Platyroptilon Westwood and Neoceroplatus Edwards, the data

are incomplete). This lack of knowledge is not surprising since one of the attributes of many

Keroplatidae is precisely cryptobiosis... To leave out unnecessary noise (and pending a generic

revision of the Orfeliini, an enterprise which should take several years), the analysis has been

pursued only on the following 15 genera: 5 genera of Keroplatini ( Cerotelion Fabricius

He/eroptenia Skuse, Keroplatus Bose, Mallochinus Edwards, Tergostylus Matile) and 10 genera

of Orfelum [Neoditomyia Lane & Sturm, “Neoplatyiira” fultoni (Shaw), which should probably

be given a genus by itself Orfelm Costa, Plcinarivora Hickman, Platyceridion Toilet Platyura

MaltoTh] PrOCer ° pIatUS Edwards ' Truplqya Edwards, Urytalpa Edwards, Xenoplatyura

Appendix III lists the 14 characters (generic autapomorphies excluded) used in the analysis

ot the Keroplatini with known larvae and their matrix. Arachnocampa is used as the outgroup’

I he matrix treated by Hennig86 gave only one tree, length 19, CI = 84, RI = 86. The tree

1§ ! s not d,fferent fr° m the one which can be deduced from the general cladogram of the

Keroplatini proposed in Matile (1990).

Source: MNHN , Paris

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

279

ARACHNOCAMPINAE

MACROCERINAE

Orfeliini

Keroplatini

KHROPLATINAE

Fig. 3 — Phylogenetic relationships among subfamilies and tribes of Keroplatidae. Hennig 86 , "ie" command, 45 characters.

Length: 45, Cl = 0.97, RI = 0.93.

- Cerotelion

-- Mallochinus

- Keroplatus

- Tergostylus

.--- Heteropterna

Fig. 4. — Phylogenetic relationships among five genera of Keroplatini. Hennig 86 , 14 characters, “ie” command, unordered.

Length: 19, Cl = 0.84, RI = 0.86.

---—-- P/atyura

- Trup/aya

-- Xenoplatyura

- - Urylalpa

- -- Planar ivora

_ Orfe/ia

-« N ». fultoni

- --— Proceroplatus

-- Neoditomyia

-- Platyceridion

Fig. 5. — Phylogenetic relationships among ten genera of Orfeliini. Hennig 86 , 23 characters, ie command, unordered.

Length 42, Cl = 0.57, RI = 0.66.

Twenty-seven characters (generic autapomorphies excluded) have been used in the

phylogenetic analysis of the 10 Orfeliini genera with known larvae; they are listed in Appendix

IV, with the corresponding matrix. Arachnocampa has been chosen as the outgroup. Hennig86

gave only one tree, length 42, Cl - 0.57, RI = 0.66 (Fig. 5).

Source

280

L. MATILE : PHYLOGENYAND EVOLUTION IN THE SCIAROIDEA

The studied Orfeliini fall readily in two sister-clades, Orfelia+ and “ N.”/u/toni +, with

Platyura being their sister-group.

ATTRIBUTES

Four attributes of the larvae of Keroplatidae will be studied. In order to study the evolution

of the food-linked traits of this family, it is first necessary to consider them at the superfamily

level, as well as in the outgroups chosen.

A study of the Bibionomorpha as a whole leads to the consideration of three attributes,

which will be useful in the following analyses:

Endobiosis vs epibiosis. Endobiont larvae live inside their source of food, epibiont larvae

live outside their source of food.

Fungivory sensu lato vs various other preferences. Fungivorous larvae feed on hyphae

and/or spores inside the fruiting bodies of higher fungi, or on mycelium in rotten wood or litter,

or feed exclusively on spores falling from the hymenium of Polyporaceae. These three categories

belong to fungivory s.i

Silk secretion. Many larvae secrete silk for various purposes, and at least for the building of

the last instar cocoon, in which the larva will pupate. Others have no silk secretion and naked

pupae.

The attributes of the Keroplatidae to be studied are as following:

Predation vs sporophagy. These terms are self-explanatory, taking into account that the

"fungivory” of Keroplatidae is restricted to spores escaping from the hymenium of bracket-fungi

Net-like web vs sheet-like web. Some keroplatid larvae spin a diffuse, three-dimensional

web bearing fishing lines (Figs 6, 8, 10). Others secrete a wide, mostly two-dimensional web

(Fig. 7).

pH of web. The webs spun by the larvae bear drops of an acid labial fluid; according to

species, the pH stands between 1 and 2.7 or, in other cases, is higher than 3.

( ryptobiosis vs optobiosis. These new terms are coined for epibiont larvae living in hidden,

obscure and water saturated cavities, such as under stones or rotting trunks, in phytotelma, etc!

(cryptobionts). In contrast, other epibiont larvae live more in the open, on the walls of caves,

under bracket-fungi, under overhanging cliffs or stream banks, under leaves, etc. (optobionts).

Bibiomd larvae are mostly scavengers or plant-feeding, living in the soil on roots, grasses

and decaying plant material (Hardy, 1981, and references therein). Larvae of Pachyneuridae are

associated with rotten wood (VOCKEROTH, 1974; Krivosheina & Mamaev, 1988); whether

t ley are true xylophagous insects or feed on mycelia inside the wood has not been ascertained

Most Cecidomyiidae larvae are plant-feeding and gall-forming, but the more basal are

flmg.vorous (Mamaev, 1975; Gagne, 1986). There are also some endoparasites and some

predatory species on insects and mites, a habit that evolved separately several times according to

Gagne (this author has also noted the anatomo-morphological exaptations to plant-feeding

shown by the‘ancestral” fungus-feeding species - sucking mouthparts, extra-intestinal digestion

and spatula). Cecidomyiidae larvae are epibionts or endobionts and most secrete silk at least for

the cocoon in which they will pupate.

Source: MNHN , Paris

PHYLOGENE TIC TESTS OF EVOLUTIONARY SCENARIOS

281

In the Ditomyiidae, larvae of Ditomyia Winnertz feed on hard bracket-fungi such as

Coriolus versicolor and others, and those of Asioditomyia japonica (Sasakawa) have been found

in Lenzites betulina. Symmerus Walker and Australosymmerus Freeman are said to be

xylophagous (Madwar, 1937; MUNROE, 1974); however CHANDLER (1993) cites Symmerus

annulatus (Meigen) reared from a hard ascomycete fungus, Hypoxylon rubiginosum. The term

“frass” referred to by MUNROE for the substance left in their galleries by larvae of S. coqulus

Garrett is ambiguous, since it can apply to either larval excrement or saw dust left by

xylophagous animals. It is very possible that all Ditomyiidae larvae found in rotten wood feed on

the mycelia that it contains. There is no pupal cocoon, the pupation takes place in the

substratum.

Feeding habits of the larvae of Diadocidiidae have been uncertain for a long time (Brauns,

1954a). I have often observed them under rotten wood invaded either by mycelia or by

encrusting Polyporaceae. In specimens killed in fixative fluid, spores desegregating progressively

towards the rear of body were observed, and the discovery of Diadocidia ferruginosa (Meigen)

on Peniophora sp. (CHANDLER, 1993) confirms the fiingivory of the family. Diadocidiid larvae

are epibionts and spin a silky tube and a pupal cocoon.

Bolitophilidae have strictly endobiont fungicolous larvae and breed mostly in

Strophariaceae, Cortinariaceae, Polyporaceae and Boletaceae (HUTSON et al., 1980). They spin

neither web nor pupal cocoon

Keroplatidae comprise either predators or sporophagous larvae, rarely species showing a

mixed diet (cf. MATILE, 1986, 1990). Cerotelion , a normally sporophagous species, has been

recorded once as feeding on a recently dead larva, and once as cannibalistic (a pupa of its own

species) (Mansbridge, 1933). However, these observations on Cerotelion have been made in

breeding jars where spores can get scarce, or disappear. On the other hand, first instar larvae of

Macrocera nobilis Johnson are scavengers, and the following instars are predators (PECK &

RUSSEL, 1976). All larvae of Keroplatidae spin webs and are epibionts, except those of the genus

Planarivora Hickman, or at least of their Tasmanian representative, Planarivora insignis

Hickman, which is an endoparasitoid of land planarians, but nonetheless spins a pupal cocoon

after emerging from its dead host (Hickman, 1965).

The food preferences of mycetophilid larvae are very diverse, ranging from predation, with

epibiont web-spinning species, to phytophagy (but exclusively linked with liverworts - in two

clades: Mycomyinae and Gnoristinae.), through true fungivory, the most common diet. Most

known larvae live in a hygroscopic web, except in subfamily Mycetophilinae. Almost without

exception there is a pupal cocoon ( Speolepta Edwards, no cocoon; some Mycetophilini genera, a

pupal case).

Sciaridae comprise some true fungivorous, phytophagous, coprophagous and xylophagous

species, but mostly they are litter forms, where they probably feed on mycelia (STEFFAN, 1981).

They spin webs and pupal cocoons.

The feeding habits of the studied families of Bibionomorpha are summarized in Table I.

The term “xylophagous” has been put between brackets because it is not known with certainty if

larvae of Pachyneuridae, some Ditomyiidae and some Sciaridae are really wood-eating, or rather

feed on mycelia in rotten wood.

282

L. MATILE ; PHYLOGENY AND EVOLUTION IN THE SCIAROIDEA

Table 1. — Food preferences of the larvae of Bibionomorpha. Legends: end/epi = endo- or epibionts; silk = silk secretion;

[xylo] = xylophagous; pred. = predators; fungic. = fungicolous; creo-fung. = creo-tungicolous; phytoph. =

phytophagous; saproph. = saprophagous; parasit. = parasitoids. livervv. = liverworts.

Families

end/epi

silk

[xylo.]

pred.

fungic.

Food

creo-f.

phytoph

saproph

parasit.

Bibionidae

end

Pachyneuridae

end

Ditomyiidae

end

Diadocidiidae

epi

Keroplatidae

epi

Bolitophilidae

end

Mycetophilidae

end/epi

liverw.

Sciaridae

end/epi

Cecidomviidae

end/epi

Larvae of Keroplatidae have very diverse feeding habits. Members of the Arachnocampinae

(monogeneric), and Macrocera in Macrocerinae (first instars of all other genera are unknown)

are predators of insects and other small invertebrates, first instar larvae of at least one species of

Macrocera being scavengers. In the Keroplatinae, known Orfeliini are predators ( Neoditomyia ,

Neoplatyurd' fultoni, Orfelia, Platyceridion, Platyura, Proceroplatus, Truplaya,

Xenoplatyura ), except Planarivora , a parasitoid, and Urytalpa , feeding habit unknown (but see

below). Three genera have been discovered recently, that even attack ants: Truplaya (Kovac &

MATILE, in press), Proceroplatus (AIELLO & JOUVET, in press; MATILE, in press) and

/ latyceridion (CHANDLER & MATILE, in prep ). All known Keroplatini are spore-feeders

(( erotelion, Heteropterna, Keroplatus, Mallochinus, Tergostylus), with Cerotelion , as already

noted, occasionally able to eat dead or immobile prey, at least in captivity. Two other species of

Keroplatini, belonging to genera Ptatyroptilon and Neocerop/atus , have been found in

connection with rotten wood invaded by mycelia or with bracket-fungi (DURET, 1974; MATILE,

1982), and are very probably spore-feeders.

Larvae of Arachnocampa and Neoditomyia are found in natural and artificial caves and

tunnels, but also in more open conditions such as under leaves (PUGSLEY, 1984; MATILE, 1990,

1994, StOrm, 1973; Jackson, 1974), while Keroplatinae Keroplatini live mostly under bracket-

fungi, either on standing trees or fallen trunks and branches (MATILE, 1990, and references

therein). All of these are therefore optobionts. Macrocera larvae are cryptobionts except in

cavermcolous conditions (MATILE, 1990, 1994, and references therein). All known Orfeliini

except Neoditomyia (tropical caves and forests) are also cryptobionts, living in deeply burrowed

cavities under stones or fallen trunks, in bamboo internodes or domatia of ant-plants (PLACHTER,

1979a, 1979b; MATILE, 1990, and references therein; JOLIVF.T, 1996, KOVAC & MATILE, in

press; AIELLO & Jolivet, in press; MATILE, in press; CHANDLER & MATILE, in prep.).

The webs of keroplatid larvae have three more or less distinct parts: a central tube in which

the larva moves when active - a shelter web, usually hidden in some secondary cavity of the

substratum - and a feeding web. For predators, the feeding web comprises a more or less dense

Source: MNHN. Paris

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

283

Table 2. — Food preference and other attributes of larvae of Keroplatidae (pH data from Plachter, 1979a).

Genera

food

pH of web

net shape

cryptobiosis

Arachnocampa

predator

“very acid"

net

Macrocera

predator

2,4 - 2.7

net

Platvura

predator

1,3 - 1,6

net

Truplaya

predator

net

Xenoplatyura

predator

1-2

net

Urytalpa

3,6 - 4.0

net/sheet

Planarivora

parasitoid

pupa only

Or fell a

predator

1,3- 1,6

net

“NCfultoni

predator

net

Proceroplatus

predator

net

Neoditomyia

predator

net

Platycericlion

predator

net

Cerotelion

creo-sporo.

1.3 - 1,6

net/sheet

Mallochinus

Keroplatus

sporoph.

3,0 - 3,4

sheet

Tergostylus

sporoph.

not toxic

sheet

Heteropterna

sporoph.

not toxic

sheet

system of crossed lines, from which drop “fishing lines”, short or long according to the space

available. Shelter and feeding webs bear numerous droplets of saliva containing oxalic acid,

sometimes in very high concentration (BUSTON in MANSBRIDGE, 1933; PLACHTER, 1979a). All

are individual webs, but can be re-used by later generations in some species of cave-dwelling

Macrocera (Peck & RUSSEL, 1976). These predator systems will be called “net-webs”. All have

a pH of 2.7 or less. In the webs of spore eaters, the fishing net is replaced by a wide mucous film

which covers the hymenium, and is often collective, sheltering larvae of several instars - these

will be called sheet-webs. The saliva of at least some of these sporophagous species also contains

oxalic acid. Keroplatus has a pH of 3 or more, but Cerotelion is highly acid, and has a web (Fig.

9) intermediate between the net type and the sheet type (crossed lines, but no fishing lines). Small

invertebrates introduced in webs of Tergostylus and Heleropterna have shown no particular

reactions (as with Keroplatus ), and it may be inferred that their acidity is also weak. The sheet-

webs of Keroplatus tipuloides Bose can be re-used by later generations (Matile, pers. obs ). All

these data are summarized in Table 2.

In summary, examination of the table shows that when known, the pH is always correlated

with the type of the web: 2.7 or less for net-webs (predators), 3 or more for sheet-webs (spore-

feeders). Cerotelion , which has an intermediate web and, although spore-feeding, can show

predatory behavior, at least in laboratory conditions, is an exception. It is easy to deduce from

this that Urytalpa must be a spore-feeder. The only species whose larva is known, U. ochracea

(Meigen), was observed “practically swimming” in its sheet-like web (PLACHTER, 1979a), a

behavior which does not imply an ambushing predator. 1 he web of U. ochracea is not exactly a

sheet: the central thread is not wide and ribbon-like, but instead there are triangular

284

L. MATILE : PHYLOGENY AND EVOLUTION IN THE SClAMOIDEA

accumulations of fluid secretion at its emplacement, where most of the fluid secretion

concentrates (Pl.ACHTER, 1979a). Regarding predation, one can add that one species each of

Platyceridion, Proceroplatus and Truplaya are ant-eating.

MAPPING THE ATTRIBUTES ON THE CLADOGRAMS

With the phylogenetic hypotheses for the groups involved, it is now possible to proceed to

feeding habit optimization, first at the suprafamilial level, then for the Keroplatidae. At the

suprafamilial level, we shall study three attributes, fungivory in its broad sense (as opposed to

various other diets), endobiosis or epibiosis, and silk secretion. For the Keroplatidae, the four

attributes studied are those indicated in Table 2, e.g. predation vs sporophagy ( (Jrytalpa being

considered a spore-feeder), highly acid pH vs less acid pH, net-web vs sheet-web, and optobiosis

vs cryptobiosis.

Fungivory. The optimized cladogram (Fig. 11) suggests that the Ditomyiidae are truly

primarily fungivorous (two lines have been drawn, since fungivory of several genera is not

ascertained) and that fungivory sensu Icito is most probably ancestral to the Sciaroidea +

Cecidomyiidae lineage.

Epibiosis. All terminal taxa of the cladogram are endobionts except in the clade

Keroplatidae-Diadocidiidae, where epibiosis may be assumed ancestral (Fig. 11). This way of life

appeared independently in certain Mycetophilidae and Cecidomyiidae.

Silk secretion. For silk secretion, the optimized cladogram (Fig. 12) shows that its

acquisition is ancestral for the Sciaroidea. A loss in the Ditomyiidae and one in Bolitophilidae, is

more parsimonious (two steps) than an independent appearance in Keroplatidae-Diadocidiidae, in

the Sciaridae+ clade and in the Cecidomyiidae (three steps).

Food preferences. The optimized cladogram on food preference (Fig. 13) shows that the

ancestral condition of the Keroplatidae is predation, as hypothesized by ZAITSEV (1983) and

Matile (1986). Sporophagy has appeared twice, once in Urytalpa and once in the Keroplatini

clade, but is not yet stabilized in Cerotelion , and perhaps Mallochinus (the only indication we

have on the larval biology of this genus is that its habits correspond to that of Keroplatus as

described by Dufour in 1839). Sporophagy is therefore a new specialization from predation.

Lastovka'S hypothesis (1972), according to which predation probably evolved from

sporophagy, is thus refuted.

Net-like web vs sheet-like web, and pH of web. Table 2 shows that these characters are

correlated with the food preference of the larvae. Thus net-webs with a high acidity are ancestral

Figs 6-10. Larvae of Keroplatidae in their webs. 6: Arachnocampa luminosa (Skuse) (New Zealand) in a crevice of a cave

wall with suspending lines, central tube and long fishing-lines. 7: Heteroptema chazeaui Matile (New Caledonia) on

the underside of a bracket-fungus; the larva hangs in a translucent sheet, only the central tube and attaching lines are

visible. 8: Macrocera fasciola Mcigen (Europe) hanging from the ceiling of a quarry, with central thread and net-web

with short fishing lines. 9: Cerotelion lineatum (Fabricius) (Europe) on underside of a bracket-fungus; there are two

central tubes, dense lines and no fishing lines. 10: Neoditomyia aerospicator (Jackson) (Central America) under a leaf

in tropical rain-forest, with suspending threads, central tube and fishing lines. Length of mature larvae: A. luminosa.

3-4 cm, M. fasciola. N. aerospicator. C. lineatum, 2,5-3 cm; H. chazeaui, 2-2,5 cm. Fig. from Matile, 1990, except

10, a combination of a photograph of N. aerospicator by Jackson (1974), and a sketch of attitude of larva of N. andina

Lane in Storm (1973).

Source: MNHN, Paris

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

285

Source: MNHN , Pahs

286

L. MATILE : PHYLOGENY AND EVOLUTION IN THE SCIAROIDEA

BIBIONIDAE

PACHYNEURIDAE

DITOMYIIDAE

KEROPLATIDAE

DIADOCIDIIDAE

BOLITOPHILIDAE

SC1ARIDAE

MYCETOPHIL1DAE

LYGISTORRHINIDAE

CECIDOMYIIDAE

Fig. 11.— Evolution of fungivory s.i (thin grey lines) and appearance of epibiosis (thick grey lines) in the Bibionomorpha.

BIBIONIDAE

PACHYNEURIDAE

DITOMYIIDAE

KEROPLATTDAE

DIADOCIDIIDAE

BOLITOPHILIDAE

SCIARIDAE

MYCETOPHILIDAE

LYGISTORRHINIDAE

CECIDOMYIIDAE

Fig. 12. — Absence (thin grey lines) or presence (thick grey lines) of silk secretion in the Bibionomorpha.

Source: MNHN. Pahs

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

287

Arachnocampa

Macrocera

Platyura

Truplaya

Xenoplatyura

Urytalpa

Planarivora

Orfelia

"N". fulloni

Proceroplatus

Neoditomyia

P/atyceridion

Cerotelion

Mallochinus

Keroplatus

Tergostylus

Heteropterna

predator

parasitoid

ereo-sporophagous

sporophagous

Fig. 13. — Food preferences of the known larvae of Keroplatidae.

for the Keroplatidae, while sheet-webs with low acidity are derived. These last features are

characteristic of the Keroplatini clade and of the genus Urytalpa , and have appeared at least

twice. PLACHTER's (1979c) hypothesis of plesiomorphy of the sheet-web is therefore refuted.

Cryptobiosis and optobiosis. As regards cryptobiosis and optobiosis, the superposition of

these attributes on the cladogram (Fig. 14) gives two equally parsimonious scenarios (3 steps). It

cryptobiosis is ancestral, tolerance to light must have appeared at least three times: in

Arachnocampa, Neoditomyia and the Keroplatini. On the other hand, if optobiosis is ancestral,

then cryptobiosis must have appeared independently once in Macrocera and once in the Orfeliini

clade, with a reversal in Neoditomyia.

Source . MNHN . Paris

288

L. MATILE ■ PHYLOGENYAND EVOLUTION IN THE SCIAROIDEA

However, endobiosis is the ancestral condition of the Bibionomorpha, as shown on Fig. 11

Bibionid, pachyneurid and ditomyiid larvae live in closed, obscure and humid galleries, and we

may therefore infer that cryptobiosis is the ancestral condition of keroplatids.

THE TEMPORAL DIMENSION

The study of the evolution of the attributes of the Bibionomorpha, and especially of the

Keroplatidae, can be refined by taking into account the temporal dimension. The oldest Diptera

are known from the Trias of Australia, North America and Europe (EVENHUIS, 1994;

SHCHERBAKOV et a/., 1996, and references in both works). As regards the recent families of

Bibionomorpha, the earliest fossils are known from the Upper Triassic for the Bibionidae, the

lower Jurassic for the Mycetophilidae, the Upper Jurassic for the Pachyneuridae, the Upper

Jurassic/Lower Cretaceous for the Cecidomyiidae, the Lower Cretaceous for the Keroplatidae

and the Sciaridae, the Eocene for the Ditomyiidae, and the Eocene/Oligocene for the

Diadocidiidae and the Lygistorrhinidae (EVENHUIS, 1994).

The fossil data, mapped on the cladogram, and the principle of equal age of sister groups

(Fig. 15), indicate that all the present families had appeared as such at least by the beginning of

the Cretaceous, and more probably by the Upper Jurassic.

The optimization of silk secretion and predation on the cladogram is given in Fig. 16. Silk

secretion must have appeared in the Sciaroidea clade at least by the Upper Jurassic. Its

disappearance in Ditomyiidae must be at least pre-Eocene, from which the extant genus

Auslralosymmerus Freeman is known. For Bolitophilidae, Bolitophila Meigen is known from

Eocene-Oligocene, and the mesozoic fossils belong to the extinct genus Mangas Kovalev

(perhaps not a Bolitophilidae at all), the larval biology of which is of course unknown; the loss of

silk secretion cannot therefore be dated other than pre-Oligocene.

Regarding predation (Fig. 16), no data can be obtained from the optimized cladogram

unless a further phylogenetic analysis is conducted for the three families in which it appeared

independently.

Fungivory and epibiosis are mapped on figure 17. Fungivory, ancestral to the Sciaroidea,

must have appeared at least by the Upper Jurassic. Epibiosis in the clade Diadocidiidae-

Keroplatidae should be dated from the Lower Cretaceous, but its acquisition in Mycetophilidae

and Cecidomyiidae cannot be dated without a further phylogenetic analysis of these families.

Fig. 18 combines the palaeontological and biogeographical data on the cladogram of the

Keroplatidae. The two fossils appended to the Macrocera lineage represent two genera

belonging to Macrocerinae, but of uncertain position inside the subfamily. These are

Schlueterimyia cenomanica Matile, from the Upper Cretaceous, and an undescribed genus from

the Lower Cretaceous (Grimaldi, 1990). The biogeographical datings can be found in Matile

(1990), except for Planarivora. This genus has a southern transatlantic distribution - New-

Zealand and South America - and thus can be dated at the latest from the Upper Cretaceous

(Matile, 198 lb).

The optimized chronocladogram (Fig. 19) shows that the various food and web

specializations of the family must have appeared at least by the end of the Lower Cretaceous,

with the exception of the parasitoid habit, which dates from the Upper Cretaceous (assuming that

the life-story of the neotropical species of Planarivora is the same as that of the Tasmanian

Source: MNHN. Paris

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

289

Arachnocampa

Macrocera

Platyura

Truplaya

Xenoplatyura

Urytalpa

Planarivora

Orfelia

Proceroplatus

« N ». fultoni

Neoditomyia

Platyceridion

Cerotelion

Mallochinus

Keroplatus

Tergostylus

Heteropterna

cryptobiosis

optobiosis

Fig. 14. — Distribution of cryptobiosis and optobiosis in the Keroplatidae.

species), and the independently acquired sporophagy of its sister-group Urytalpa , which may be

presumed to be of the same age.

In the same way, the cladogram of the figure 20 demonstrates the origin of cryptobiosis in

the Lower Cretaceous, and of optobiosis in Keroplatini at least at the end of the same period.

CONCLUSION

The optimization and dating of the cladograms allow inference of the ancestral larval state

of the Bibionomorpha as an endobiont, as is the case for Sciaroidea, even if they contain

numerous epibionts, which thus should have appeared more recently. Fungivory is another

Source

290

L. MATILE : PHYLOGENY AND EVOLUTION IN THE SCIAROIDEA

Fig. 15. — Pre-Miocene fossil data (black square) available on the taxa studied in this paper. BIB = Bibionidae; PAC =

Pachyneuridae; DPI = Ditomyiidae; DIA = Diadocidiidae; KER = Keroplatidae; BOL = Bolitophilidae; MYC =

Mycetophilidae; LYG = Lygistorrhinidae; SCI = Sciaridae; CEC = Cecidomyiidae. Geologic time scale after Evenhuis

(1994). For graphical reasons, no distinction has been made for Lower and Upper Jurassic.

ancestral trait of Sciaroidea, as supposed by most authors. ZAITSEV 's (1984) hypothesis of an

epibiont ancestral larva for the fungicolous clades is thus refUted. The endobiosis and fungivory

of the ancestral Sciaroidea is corroborated by their larval morphology. The larvae of this

superfamily are indeed deprived of the anatomical tools necessary for predation: their antennae

are most often reduced to a cupule with a few sensillae, their organs of vision are rudimentary,

and they have no well-developed sensorial macrochaetae. This kind of morphology is not that of

a predator, but of an animal living in the middle of an important amount of food, as noted by

Source: MNHN. Paris

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

291

Fig. 16. — Temporal evolution of silk secretion (thick light grey lines) and predation (thick dark grey lines) in the

Bibionomorpha. Black squares: pre-Miocene fossil data.

Source: MNHN. Paris

292

L. MATTE K PHYLOGENY AND EVOLUTION IN THE SCIAROIDEA

Fig. 17. — Temporal evolution of fungivory (light grey lines) and epibiosis (dark grey lines) in the Bibionomorpha. Black

squares: pre-Miocene fossil data.

Mamaev (1968, 1975) for the Cecidomyiidae. The Keroplatidae and Diadocidiidae are epibionts

but nevertheless possess this endobiont morphology.

Source: MNHN . Paris

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

293

j/j* J

* ✓✓ ✓

///////.*'

Fig. 18. — Pre-Miocene fossil data (black square) and biogeographical data (black disk) available on the taxa studied in this

paper. Ara - Arachnocampa; Mac = Macrocera; Pla Platyura; Tru Truplaya; Xen = Xenoplatynra; Ury

Urytalpa; Plan Planarivora; Otf OrJ'elia; Neo = Neoplatyura; Pro Proceroplatus; Neod : Neoditomyia; Plat

= Platyceridion; Cer = Cerotelion; \lal Mallochinus; Ker Keroplatus; Ter = Tergostylus; Het = Heteroptema.

Geologic time scale after Evenhuis (1994).

Silk secretion is apomorphic for Sciaroidea; it appeared during the Jurassic and was

subsequently lost in Ditomyiidae and Bolitophilidae. Epibiosis occurred at least three times, once

in the clade Keroplatidae-Diadocidiidae, once in Mycetophilidae and once in Cecidomyiidae.

Cryptobiosis is apomorphic for the Keroplatidae, and appeared in the Lower Cretaceous,

while optobiosis arose independently three times, once in the Keroplatini during the Lower

Cretaceous, once in Arachnocampa at least by the Upper Cretaceous, and once again in

Neoditomyia , probably at a much later time, during the Miocene.

Predation arose once in the Keroplatidae at some time during the Lower Cretaceous, and

at least twice, at an undetermined period, in Mycetophilidae and Cecidomyiidae The net-like

web of the predator forms is not derived from the sheet-like web, as assumed by PLATCHER

(1979c), but the opposite.

294

L. MATILE : PHYLOGENYAND EVOLUTION IN THE SCIAROIDEA

Z/////A/////////

Eocene/

Oligocene

1‘uleocene

Upper

Cretaceous

Lower:

('retaceous

Upper

Jurassic

predator. pM<3, net web

parasitoid

creo-sporophagous, pi I, intermediate web

sporophagous, pH>3, sheet web

1- ig. 19. I emporal evolution of food preference in the Keroplatidae. See fig. 18 for abbreviations.

Sporophagy in Keroplatidae arose twice, once in the Lower Cretaceous (clade

eroplatim), and once probably in the Upper Cretaceous (genus Urytalpa). In these groups

sporophagy seems correlated with a sheet-like web and a labial fluid with a pH of 3 or more The

sporophagy of these Keroplatidae is derived from a predator diet, and not the opposite as

assumed by Lastovka (1972). It is not therefore homologous to the “ordinary” ftingivory found

in other Sciaroidea. J

Source: MNHN . Paris

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

295

cryptobiosis

+ optobiosis

Fig. 20. — Temporal evolution of cryptobiosis and optobiosis in the Keroplatidae. See fig. 18 for abbreviations.

We may consider the ancestral larval stock of the Sciaroidea as an endobiont fungicolous

insect, without silk secretion, perhaps living as far back as the Upper Jurassic - fossil Sciaroidea

have been described as early as the Lower Jurassic (see KALUGINA & Kovalev, 1985;

KOVALEV, 1987b), and of these at least the Pleciofungivoridae certainly are correctly placed in

the superfamily. The keroplatidian clade, the larvae of which have an endobiont morphology

(antennae, eyes and other sensorial organs reduced, scraper mouthparts), became epibionts

during the Lower Cretaceous and were then able to exploit at the best their silk- and oxalic-

secreting capacity and adopt a predatory diet - making up for the lack of predatory organs by an

extension of the body: the hunting net-web. The extension of the net-web to a sheet-web, an

Source

296

L. MATILE ; PHYWGENY AND EVOLUTION'IN THE SCIAROIDEA

intermediary state of which still can observed in Cerotelion, and a variant in Uryla/pa, allowed

them to switch to a new food source: the collecting of bracket fungi spores.

The most important problem posed by the hypothesis of Cretaceous sporophagy in

Keroplatini is that the oldest and certain fossil Polyporaceae are only known from the Miocene.

Some “bracket-fungi” have been described from earlier periods, back to the Carboniferous, but

that they really belong to Polyporaceae is apparently still disputed. Nonetheless, the genus

Fomites, described from the Lower Miocene of Lybia, is closely allied with the present genus

homes (Locquin & KOEN1GER, 1981), and the ancestral stock of the Polyporaceae should

therefore be much older. If the present hypothesis is founded, this family of fungi should have

appeared at least by the Lower Cretaceous.

Although we know many fossils of Bibionomorpha from the Lower and Middle Jurassic,

none is close to the Keroplatidae. One may therefore think that the acquisition of all these

attributes occurred during a very short period of time, no more than a few tens of MY, between

the end of the Jurassic and the beginning of the Lower Cretaceous. It was followed by a stasis

more than 100 MY long, marked only by the divergence of the clade Urytalpa-Planarivora

towards sporophagy for the first, parasitism for the second, probably during the Upper

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..I.

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a cHUcal _n of the wn g

Z *TZZ2£r

y&ggz&s*" w 8 —- -*

h.'mansbbjdoe, ■“* c ™ P ,a "« * O.

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n. .. McAlpine Manual of Nearctic Diptera Volume /. Biosystematics Research Centre, Research Branch

Agriculture Canada. Monograph No. 28. Ottawa: 1-7.

Nixon, A 1991. — Clados Version 1.1. Documentation. Cornell University. Ithaca, NY, L.H. Bailey Hortorunv 1-38

0os T^■L?^ZS ! p G lS7-7l^ y ' 08 “ ,, of a ” ne "'“ erous ““ ofDip,era

Pi.AfimtR H., 1979a. - Zur Kenntnis der Praimaginalstadien der Pilzmitcken (Diptera, Mycetophilidae). Teil I: Gespinstbau

Zoologische Jarbucher. Abteilungfur Anatonue, 101 168-266 P

Rachter R 1979b. - Zur Kenntnis der Praimaginalstadien der Pilzmiicken (Diptera, Mycetophilidae). Teil D: Eidonomie

aerLanen. Zoologische Jarbucher, Abteilungftlr Anatomie, 101: 271-392.

Plachter, H. 1979c. — Zur Kenntnis der Praimaginalstadien der PilzmUcken (Diptera, Mycetophilidae). Teil HI Die

1 uppen. Zoologische Jarbucher, Abteilungfur Anatomie, 101: 427-455.

Pucsley, C VV- 1984. — Ecology of the New Zealand Glowworm, Arachnocampa luminosa (Diptera: Keroplatidae) in the

Glowworm Cave, Waitomo. Journal of the Royal Society of New Zealand , 14 (4): 387-407.

V La [toTiSr* 1 d ' Vd0P ”“ , ° f W0 -™8' d ^ faleontol^ce^o

Rohdendorf, B. B., 1974. — The Historical development of Diptera. Edmonton, University of Alberta Press: 1-360

SnotERBAKov D. E Lukashevich, E. D. & Blagoderov, V. A., 1995. - Triassic Diptera and initial radiation of the order.

International Journal of Dipterological Research, 6: 75-115.

SrE "centm Research iTr-' ^1 n !■ R ^ C ^ PINE " Manual of Nearctic Diptera. Volume 1. Biosystematics Research

Centre, Research Branch. Agriculture Canada. Monograph No. 28. Ottawa: 247-255.

ST ^vr;tolhH 3 H^ F 7 an8 f eSPin , Ste , lmd Verhalle " d6r LarVCn VOn Ne °di<omy,a andina und Columbiana Lane (Diptera

Mycetophilidae). Zoologischer Anzeiger, 191 (1/2): 61-86. V 1

n " :SKE n;,!L J n 981 r M 0 n>ho!ogy ? nd terminol °gy • Larvae J - F McAlmne, Manual of Nearctic Diptera. Volume 1

tta \a, Biosystematics Research Centre, Research Branch. Agriculture Canada. Monograph No. 28: 65-88.

° C T,T'!7Vn’ ' 974 ~ Nott ! s ° n the biology of Cramptonomyia spenceri Alexander (Diptera: Cramptonomviidae)

Journal of the entomological Society of British Columbia, 71: 38-42.

W °°^J 99 k ~ Ho,,lolo 8>; a,ld Phylogenetic implications of male genitalia in Diptera. The ground plan. In: L

Proceedings of,he “ In,en,ational Con * ress 7 ^ Hag.;

W00D vLhc 'T n Phylo r y and clasSlficallon of the Nematocera. /„: J. F. McAlpine, Manual of

kSSpSTS: S™70: Centre, Research Branch. Agnculture Cn.d,

Source MNHN. Paris

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

299

Zaitsev, A. L, 1983 — [The anatomy of the larval intestine of mycetophiloid Hies (Diptera, Mycetophiloidea) in connexion

with their trophic specialization], Biologicheskii Nauki , 1983 (4): 38-43 [in Russian, English summary].

Zaitsev, A. I., 1984a — [The directions of morphological specialization of digestive system of larvae of higher mycetophiloid

flies (Diptera, Mycetophiloidea)]. Biologicheskii Nauki, 1984 (1): 3844 [in Russian, English summary].

Zaitsev, A. I., 1984b — [The main stages of specialization of mycetophiloid flies larval mouthpieces (Diptera,

Mycetophiloidea)]. Biologicheskii Nauki , 1984 (10): 3846 [in Russian, English summary'].

Appendix 1. — List of the characters used in the study of the Sciaroidea (plesiomorphic state: 0; apomorphic states: 1, 2)

(WB = Wood & Borkent, 1989; LM = Matile, 1990; OC = Oosterbroeck & Courtney, 1995) and character

matrix.

Larva (unknown for Lygistorrhinidae)

1. Antennae: with several segments: 0. Antennae one-segmented, cylindrical or disc-like: 1 (LM: 386, char. 9, for

Bolitophilidae; OC: 295, char. 15).

2. Frontoclypeal apotome: short, not extended to posterior margin: 0. Frontoclypeal apotome long, extending to posterior

margin of head capsule: 1 (LM: 385, char. 2).

3. Posterior tentorium as a rod independent from the head capsule from the metatentorina on: 0. Posterior tentorium laterally

fused with the head capsule, forming a transverse bridge, unsclerotinized at least at middle: 1. The “posterior bridge"

of the Sciaroidea is here interpreted as homologous to the posterior tentorium, as demonstrated by its muscles

insertion and the discovery of the metatentorina (Matile, 1967, 1990; see also discussion in OC: 308, char. 101). The

condition is variable in Cecidomyiidae (cf Mamaev & Krivosheina, 1965, 1993).

4. Anterior tentorial arms: strong: 0. Anterior arms thread-like: 1 (see discussion in OC: 308, char. 02). The condition is

variable in Cecidomyiidae.

5. Maxillae: pyramidal: 0.Maxillae flattened and strongly sclerotinized: 1. Teskey (1981) has pointed out that the maxillae of

Nematocera are mostly membranous and passive, and that “a notable exception" was found in the larvae of Sciaroidea.

In fact, maxillae of Ditomviidae resemble closely those of Bibionidae (see also discussion in WB: 1353).

6. Maxillae: cardo free: 0. Cardo fused or closely apressed to anterior margin of head capsule: 1 (WB: 1351, char. 27; OC

296, char. 25).

7. Maxillary' palpus jutting out: 0. Palpus reduced, flush with the maxilla: 1 (WB: 1356, char. 45, in analysis of

Psychodomorpha; LM: 385, char. 3; OC: 296, char. 26).

8. Mandible of the ordinary, pyramidal sort: 0. Mandible as a half-circle, toothed at margin, one or more rows of spinules: 1.

Character not formally included in LM analysis, but dicussed p. 386.

9. Body cylindrical, more or less flattened: 0. Body strongly constricted: 1. In Bibionomorpha, the state 1 of this character

exists only in Pachyneuridae and Ditomviidae, and I think it is an adaptation to life in wood or ligneous bracket-fungi,

therefore apomorphic.

10. Subanal region without appendices or macrochaetae: 0. Subanal region with one or the other: 1. Same than character 9.

11. Metathoracic spiracle present: 0. Metathoracic spiracle absent: 1 (WB: 1351, char. 30).

12. Abdominal spiracle VIII present: 0. Spiracle WI absent: 1 (Steffan, 1981; LM: 385, char. 4).

13. Other abdominal spiracles: present and open: 0. Abdominal spiracle absent or closed (1). (LM: 385, char. 6).

14. Tracheal system: at least 5 dorsal transverse connectives: 0. At most one connective: 1 (OC: 302, char. 53). State of

character unknown in Pachyneuridae and Bibionidae.

Pupa (unknown for Lygisiotrhinidae)

15. Prothoracic horns large: 0. Prothoracic horns small: 1. Character not formally included in LM analysis, but discussed p.

385. Thoracic horns are well developed in Bibionidae, Ditomyiidae and Cecidomyiidae, as well as in most other

Nematocera (see f. ex. Brauns, 1954b).

Imago

16. Ocular bridge: absent: 0. Ocular bridge present: 1 (WB: 1352, char. 33). The condition is variable in Ditomyiidae and

Mycetophilidae, where a few genera have an ocular bridge; see also discussion in OC: 309, char. 104 Some Sciaridae

and Cecidomyiidae have no eye-bridge, but this is obviously a loss, and the character has been coded 1 in these two

families.

300

L. MATILE : PHYLOGENY AND EVOLUTION IN THE SC1LROIDEA

17. No tibial spurs 11-111: 0. Tibial spurs present: 1. Spurs II-m are absent in some genera of Mycetophilidae, Keroplatidae and

Sciaridae; this is again obviously a loss, and the charcater has been coded 1 in these three families. See discussion in

LM: 418, A.3.3.

18. Vein R4 long: 0. R4 short or absent: 1 (LM: 385, char. 1; also: 434, A.4.5.8.).

19. Two basal cells: 0. One basal cell: 1. This polarisation is obvious from the dipterous wing groundplan; see for example

McAlpine, 1981:31 &ff.

20. Transverse tb subvertical: 0. tb longitudinal: 1 (LM: 386, char. 5; also: 426, A.4.5.).

21. Transverse ta subvertical: 0. la longitudinal: 1 (LM: 386, char. 8; also.: 426, A.4.5.). The condition of this transverse,

when recognizable, is variable in Cecidomyiidae.

22. Transverse mcu present: 0. mcu absent: 1 (LM: 386, char. 7).

23. Costa continuous around wing: 0. Costa abbreviated at apex of wing: 1 (OC: 304).

24. Insertion of abdomen on thorax wide: 0. Insertion narrow” 1. Insertion very narrow: 2 (LM: 386, char. 12; also p. 379-383).

25. Mediotergite partly included in abdominal segment I: 0. Mediotergite free: 1. Character not formally included in LM

analysis, but dicussed p. 379-383.

26. Laterotergite narrow: 0. Laterotergite wide: 1 (LM: 386, char. 11).

27. Coxae short: 0. Coxae long: 1. See discusssion in LM: 413, A.3.1.

28. Sclerotized part of aedeagus tubular: 0. Aedeagus flattened: 1 (Wood, 1991; OC: 307, char. 92).

29. Somatic and germ cells with same number of chromosoms: 0. Some chromosomes eliminated in somatic cells: 1 (WB:

1352, char. 32; OC: 307, char. 98). State of character known only in some species of Sciaridae and Cecidomyiidae, and

one species of Mycetophilidae.

30. Central microtubule of sperm tail present: 0. Central microtubule absent: 1. (OC: 307 , char. 95 - polarity inversed in text,

but not in character matrix). Keroplatidae polymorphic (coded ?). State of character unknown in Bibionidae,

Pachvneuridae, Ditomyiidae and Lygistorrhinidae.

Bibionidae

Pachvneuridae

Ditomyiidae

Diadocidiidae

Keroplatidae

Bolitophilidae

Mycetophilidae

Lygistorrhinidae

Sciaridae

Cecidomyiidae

123456789111111111122222222223

012345678901234567890

00000000000007001000000000007?

00000000111007001000000000007?

00110110111000071010001110117?

11111110001110101110001111117?

11111110001110101110001211117?

11111111001100101111001111017?

111111110011001711111112111100

777 ????????? 7 ? 701111111211117 ?

111111100011011111111110010111

007701000010010101117100000111

Appendix 2. — List of the characters used in the study of the subfamilies of Keroplatidae and tribes of Keroplatinac

(plesiomorphic state: 0; apomorphic state: I; LM = Matilf., 1990) and character matrix.

Larva

1 Headcapsule short and round: 0. Head capsule short and rectangular: 1. Head capsule long and narrowed in middle: 2 (LM:

2 Anterior tentorial arms very thick: 0. Anterior tentorial arms reduced: 1. Anterior tentorial arm strongly reduced: 2.

3. One pair of stemmata: 0. Two pairs of stemmata: 1 (LM: 474).

4. Antennae small. 0. Antennae large, reaching almost middle of genae: 1 (LM: 475).

5. No lateral labral lobes: 0. Two labral lateral lobes. 1 (LM: 475).

Source: MNHN . Paris

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

301

6. Maxillary cardo normal: 0. Maxillary cardo strongly lenghtened: 1 (LM: 475).

7. Mandibles short, Bibionid-like: 0. Mandibles long and narrow: 1 (LM: 371).

8. Larva hemipneustic: 0. Spiracles absent or non fonctional: 1 (LM: 371).

9. Abdominal spiracles present, either opened or closed: 0. No abdominal spiracles: 1 (LM: 477).

10. Malpighian tubules normal 0. Malpigian system cryptonephridian: 1 (LM: 371).

11. Oesophagus short: 0. Oesophagus as long as middle gut: 1 (LM: 371).

12. SR sensilla present: 0. SE sensilla absent: 1 (LM: 371).

13. Abdomen smooth, without hypodermal colored bands: 0. Abdomen fmely annelated, with colored hypodermal bands: 1

(LM: 371).

14. No luminous organ, or a simple luminous organ linked to fat body or black bodies: 0. A complex luminous organ formed

by the Malpighian tubules and a tracheal reflector: 1 (LM: 477).

Pupa

15. Nototheca simple: 0. Nototheca with a sagittal crest: 1 (LM. 473).

Imago

16. Foramen magnum in dorsal position: 0. Foramen magnum in central position. 1 (LM, 1990: 387).

17. Mediocellar sclerite absent: 0. mediocellar sclerite present: 1 (LM: 389).

18. No cerebral sclerite: 0. A cerebral sclerite: 1 (LM: 388).

19. Antennae simple: 0. Antennae thickened or pectinated: 1 (LM: 395). The state of character is variable in Orfeliini

20. Postmentum present: 0. Postmentum absent: 1 (LM: 398). The condition is variable in Orfeliini.

21. Four palpomeres, if less than 4 the last one not thickened and porrect: 0. One or two palpomeres, the last one thickened

and porrect: 1 (LM: 397).

22. Prestemite present: 0. Prestemite absent: 1 (LM: 401).

23. Transverse suture complete: 0. Transverse suture incomplete: 1 (LM: 402).

24. Postpronotum lateral and distinct: 0. Postpronotum dorsal, more or less fused with praescutum: 1 (LM: 399).

25. Mesepimeron almost as wide vcntrally than dorsally: 0. Mesepimeron narrow or absent ventrally: 1 (LM: 411).

26. Metepimeron almost as wide as high: 0. Metepimeron much wider than high: 1 (LM, 1990: 412; the epimeron and

epistemite have been inadvertently inversed while lettering fig. 1080-1087).

27. Laterotergite narrow and subvertical: 0. Laterotergite wide and and oblique: 1 (LM, 1990: 406).

28. Alular incision present: 0. Alular incision absent: 1 (LM, 1990: 426; the presence of an alular incison is here considered as

the groundplan of Sciaroidea, its disappearance in Arachnocampa and Bolitophila a reversal).

29. Costal vein extending alter apex of wing: 0. Costa shorter: 1 (LM, 1990: 431).

30. R4 present or absent, R1 and R5 close to one another: 0. R4 absent, and at the same time R1-R5 widely separated: (LM:

435).

31. No radiomedian coaptation: 0. A radiomedian coaptation: 1 (LM: 436). State variable in Ditomyiidae.

32. Basal and ta transverse fused: 0. Basal transverse distinct from ta. 1 (LM: 438).

33. Coxae of about the same length: 0. Coxae I longer than the two other pairs: 1 (LM: 414).

34. Tibiae bearing macrochaetae: 0. No tibial setae: 1 (LM: 417).

35. Tibiae D-HI with apical combs: 0. No apical tibial combs: 1 (LM: 421).

36. A pair of spiracle on abdominal segment I: 0. No abdominal spiracles I (LM: 448).

37. male: segment VIE about half as long as VU: 0. Segment VIE shorter, more or less retracted under Vfl: 1 (LM: 450).

38. male: Hypoproct complete or membranous, but not notched basally: 0. Hypoproct deeply notched basally: 1 (LM: 452).

39. male: Stemite IX distinct: 0. Stemite IX fused or lost: 1 (LM: 456).

40. male: Tergite X present: 0. Tergite X absent: 1 (LM: 451). Condition ambigous in Ditomyiidae (LM: 452).

41. male: Ejaculatory apodeme developed: 0. Ejaculatory apodeme reduced to a dorsal rod: 1 (LM: 469).

42. female: Tergite VE1 entire or weakly reduced: 0. Tergite VIE strongly reduced or membranous, invaginated under VE: 1

(LM: 471)

43. female: Stemite Vfll complete basally: 0. Stemite VIE completely separated in two halves: 1 (LM: 471).

44. female: Tergite IX entire: 0. Tergite IX reduced: 1. Tergite IX entirely membranous: 2 (LM: 471).

45. female: Cerci two-segmented: 0. Cerci one-segmented: 1 (LM: 472).

302

L. MATILE ; PHYLOGENY AND EVOLUTION IN THE SCIAROIDEA

123456789111111111122222222223333333333444444

012345678901234567890123456789012345

Ditomyiidae 000000000000000000000011110000700001100700000

Arachnocampinae 201000111111111110010100000101010000001011000

Marocerinae 110111110111100001000011101010101110110100010

Keroplatini 110010110111100000101011111010100001110100111

Orfeliini 110010110111100000770011111010100001110100101

Appendix 3. — List of the characters of 5 genera of Keroplatini (plesiomorphic stale: 0; apomorphic states: 1, 2; LM =

Matile, 1990) and character matrix

Imago

1. Eyes not or slightly emarginated above antennae: 0. Eyes strongly emarginated: 1 (LM: 390).

2. Antennal scape beakless: 0. Antennal scape with a beak: 1 (LM: 394).

3. Four palpomeres: 0. Two palpomeres: 1. One palpomere: 2. (LM: 396).

4. Mouthparts long, jutting out from the lower eye margin: 0. Mouthparts short, not jutting out from eye margin: 1 (LM: 398).

5. Scutellum haired on entire disk: 0. A pair of discal setae: I. Scutellum bare on disk: 2 (LM: 404).

6. Laterotergite haired: 0. Laterotergite bare: 1 (LM: 407).

7. Tibial setuale irregular: 0. Tibial setae in regular rows: 1 (LM: 416).

:L Abdomen with an intercalar sclerite: 0. No intercalar abdominal sclerite: 1 (LM: 450).

9. male: abdomen cylindrical: 0. Abdomen flattened: 1 (LM: 445).

10. male: tergite IX as a flat plate: 0. Tergite IX expanded laterally: 1 (LM: 445).

11 male: hypoproct at least partially sclerotinized: 0. Hypoproct entirely membranous: 1 (LM: 452).

12. male: perigonostylar bridge complete: 0. Perigonostylar bridge incomplete: 1 (LM: 458).

13. male, inner margin of gonostyle not more sclerotinized than rest of appendice: 0. Inner margin of gonostyle strongly

sclerotinized and denticulated: 1 (LM: 466).

14. female: stemite VUI infolded at most on basal half: 0. Stemite VIII infolded at least at 3 / 4 of its length: 1 (LM: 471).

12345678911111

01234

A rachnocampa

Cerotelion

Mallochinus

Keroplatus

Tergostylus

Heteroptema

00002000000000

11101100000010

11101000000010

01100011101101

00210111111101

00210111110101

Appendix 4. — List of the characters used in the study of 10 genera of Orfeliini (plesiomorphic state: 0; apomorphic states: 1,

2; (LM= Matile, 1990) and character matrix

Imago

• Antennae threadlike: 0. Antennae pectinated ou serrulated: 1 (LM: 395).

2. 4 palpomeres: 0. Three palpomeres or less: (LM: 396).

3. Three ocelli: 0. Two ocelli: (LM: 389).

4. No parachrostical stripes. 0. Two wide parachrostical stripes: 1 (LM: 403).

5. Prospiracular setae present: 0. Prospiracular setae absent: 1 (LM: 410).

6. Mediotergite rounded at apex: 0. Mediotergite strongly angulous: 1 (LM: 405).

7. Laterotergite setiferous: 0. Laterotergite bare: 1 (LM: 407).

Source: MNHN . Paris

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

303

8. Mesanepistemite setiferous: 0. Mesancpistemite bare (LM: 410).

9. Metanepistemite setiferous: 0. Metanepisemite bare: 1 (LM: 412).

10. C continuing widely alter tip of R5: 0. C stopping at tip of R5, or a little farther: 1 (LM: 431).

11. M2 and M3 entire: 0. M2 et M3 interrupted before wing margin: 1 (LM: 438).

12. Basis of M present as a true vein: 0. Basis of M absent or present as a fold: 1 (LM: 438).

13. Radiomedian fusion bearing setulae: 0. Radiomedian fusion bare: 1 (LM: 438).

14. Lower veins haired dorsally: 0. Lower veins bare:l (LM: 442).

15. Anal vein long: 0. Anal vein short: 1 (LM: 441).

16. Tibial setulae irregular: 0. In regular rows: 1. Some darker rows of closely set setulae: 2 (LM: 416).

17. Outer tibial spurs 11-111 long: 0. Outer tibial spurs II-in reduced: (LM: 418).

18. male: abdomen cylindrical: 0. Abdomen petiolated and laterally compressed: 1 (LM: 445).

19. male: hypopygium capable of rotation: 0. hypopygium non rotatable: 1 (LM: 67, 451).

20. male: Tergite FX long or short, but as a dorsal plate: 0. Tergite IX long or very long, strongly expanded laterally: 1 (LM:

456)

21. male: aedeagus short: 0. Aedeagus long, extending at least to tergite VII (LM: 469).

22. male: gonostyles with one segment, either divided or not: 0. Gonostyles at least two-segmented: 1 (LM: 465).

23. male: gonocoxites approximated ventrally: 0. Gonocoxites widely separated ventrally, the aperture closed by a ventral

desclerotized process: 1 (LM.461).

12345678911111111112222

01234567890123

Arachnocampa

Platyura

Orfelia

Neoditomyia

Xenoplatyura

Jrytalpa

Truplaya

Proceroplatus

Platyceridion

Planarivora

“N." fultoni

00011001110001000000000

00011011110010000000000

00001111100101120000010

10100000100101111000000

00001111001101000111111

00011011110100000111100

00000111111101010111111

10001000100111011000000

11101000107111011000010

01010110100110000011110

10001010100111010010000

Source: MNHN , Paris

The Probabilistic Inference of Unknown Data

in Phylogenetic Analysis

Andre Nel

Laboratoire d'Entomologie. Museum national d'Histoire naturelle,

45. me Buffon. 75005 Paris. France

ABSTRACT

Unknown characters and attributes are inferred in phytogenies using a probabilistic method. The probability of the position

of fossil taxa having uncertain relationships, because of the lack of unambiguous synapomorphies, can be calculated using a

similar method. These methods allow a better definition of the limits of actualism in Paleontology and can be applied to

palaeoclimatic and palaeoenvironment studies.

RESUME

Inference probabiliste de donnees inconnues en analyse phylogenetique

II est propose une methode probabiliste d'inference phylogenetique de caracteres et attributs d'etat inconnu ainsi qu'une

methode analogue de calcul de la probability de la position de taxa fossiles, a priori incertaine par manque de

synapomorphies non ambigues. Ces methodes permettent de quantifier les hypotheses d’inference basees sur les liens de

parente des taxa fossiles et ainsi de definir les limites de Putilisation du principe de l'actualisme en paleontologie, en

particular pour la paleoclimatologie et les analyses paleoenvironnementales.

INTRODUCTION

One of the main problems in Paleontology is the reconstruction of the palaeobiotas and

palaeoclimates by comparison between fossil and recent taxa. One can use the actualist method

which extends the Recent biological and ecological data to the past. FtJRON (1964) gave an

example which represents a good summary of the use of actualism: “Les grands Foraminiferes

[...] vivaient dans des mers chaudes. [...] mais c'est evidemment la repartition des recifs

coralliens qui nous donne les renseignements les plus precis”. But incorrect use of actualism

could be misleading and several examples reveal particularly unreliable lor the study of very old

palaeoenvironments. After BRYANT & RUSSELL (1992), there are two different methods of

inference of Recent data to the past: a) after the morpho-functional inference theory, a fossil

organ identical to a Recent one had a similar function ; b) after the phylogenetic inference theory.

Nel, A., 1997. — The probabilistic inference of unknown data in phylogenetic analysis. In: Grandcolas, P. (ed.), The

Origin of Biodiversity in Insects: Phylogenetic Tests of Evolutionary' Scenarios. Mini. Mus. natn. Hist. not.. 173 305-327.

Paris ISBN : 2-85653-508-9.

306

A. NEL : PROBABILISTIC INFERENCE OF UNKNOWN DATA

a fossil taxon related to a Recent one had a similar biota, under a similar climate and

environment. Being limited to functional data, the first type of inference is often useless for

palaeoclimatic analysis. Furthermore, confusions between the two types of inference are frequent

and are leading to abusive conclusions, supported by weak evidences. Because of the lack of

clear synapomorphies with Recent groups, the phylogenetic positions of fossil taxa are frequently

very uncertain. Evenly, one would be tempted to use phenetic methods for classifying these taxa.

Either BRYANT & RUSSELL's method (/oc. c/7.) only give qualitative phylogenetic inferences. As

methods of quantification of data inferences and of phylogenetic positions of taxa are lacking, we

have attempted to define them with a probabilistic theory based on cladistic analysis. We did not

attempted to use a maximum likelihood method of analysis because the informations concerning

the various probabilities for the ancestor state, change of states along the branches, etc. (Darlu

& TASSY, 1993), are never available for the inference of complex palaeoclimates or

palaeoenvironmental informations.

DATA INFERENCES (FOSSIL / RECENT)

Using phylogenetic systematics, it is possible to extend informations from Recent data to

the fossil record on the basis of the systematic position of the fossil taxon. Informations (of

palaeoclimatic and palaeoenvironmental types between others) are then to be considered as

attributes (sensu Mickevich & Weller, 1990; Deleporte, 1993; Grandcolas, 1993;

GRANDCOLAS el a!., 1994). An attribute is a trait of extrinsic type. Its primary homology {sensu

De Pinna, 1991, before any phylogenetic analysis) is not assessed, but its similarity can be

postulated, in order to give the same name to traits of the different taxa. A character is, in

phylogenetic analysis, a trait unambiguously homologous in several taxa before any the

phylogenetic analysis. The polarization of an attribute is to be made by optimization on the

phylogenetic tree. BRYANT & Russell (1992) have established a general method of inference of

characters (or attributes), the states of which are unknown for taxa already included in a

phylogenetic analysis : if the taxon (fossil or not) is included in a group having an homogeneous

state for the considered attribute (or character), the probability for the (fossil) taxon to have an

information homologous to the data given by the Recent taxa increases. On the contrary, if the

(fossil) taxon is only the sister-group of a Recent group, the inference of information becomes

more uncertain and cannot be justified with the sole hypothesis of parsimony. Only an hypothesis

of phylogenetic proximity provides support for the hypothesis of inference. This method of

inference only tests for presence/absence of a character in one taxon while it is present in other

taxa. It does not concern the possible autapomorphies of the fossil taxon for the studied attribute.

It is impossible to infer phylogenetically an unknown autapomorphic character for a fossil taxon,

on the basis of characters of different type of the nearest Recent relatives. “Phylogenetic

inference is conservative” (Bryant & RUSSELL, 1992).

The method of BRYANT & RUSSELL is based on the outgroup “ascendant” algorithm of

Maddison el al. (1984) : the situation of a character (or an attribute) at each internal node of

the tree is parsimoniously inferred by the situations at the two immediately adjacent nodes. For a

character X with two states “a” and “b”, an internal node is labeled “a” if the two immediate

adjacent nodes are labeled “a” and “a” or “a” and “a or b”. Symmetrical situation occurs with

“b”. Nodes are labeled “a or b” if the adjacent nodes are labeled “a” and “b”, or “a or b” and "a

or b”. The external node with the missing information is then supposed to share the same state as

Source: MNHN. Paris

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

307

the immediately internal adjacent node. This method is problematic for the inference of

characters that have been used in the construction of the minimal tree, using adequate softwares

because the computer programs Hennig86 and Paup 3.1.1 trend to affect definite values to the

missing entries, even if they do this in very different ways : in Paup, “only those characters that

have non-missing values” are supposed to “affect the location of any taxon on the tree”

(SWOFFORD, 1990) because Paup assigns to the taxon affected by the missing character the

character state that would be most parsimonious given its placement in the tree. Equally

parsimonious trees are constructed for the concerned character and then discriminated on the

other non missing characters. PLATNICK et al. (1991) have tested Hennig86 and Paup and would

confirm the assumption of SWOFFORD. They add that Hennig86 trends to attribute global

peculiar states to missing data, depending of the tree topology. Paup gives a less resolved

solution than Hennig86, because it interpret the missing data in the construction of the minimal

trees. Nevertheless, if the missing data are reinterpreted and used in the construction of the

minimal tree, it is delicate to test their value on the basis of the same tree. This difficulty does not

exist if the concerned character is considered as an attribute, not included in the preliminary

construction of the tree and independently tested after this construction.

Bryant & RUSSELL could not quantify their hypothesis of congruence, but it is possible to

calculate the probability of the following event: [the missing information is homologous to the

information given by the nearest relative taxa], A preliminary hypothesis is necessary: the

inference of the unknown situations for the F-taxa will not add homoplasies or steps to the

general shape of the concerned attribute in the minimal tree. All the situations that do not imply

supplementary homoplasies or supplementary steps are then supposed to be equally probable.

Following this condition, the probability of the event [the studied taxon has a peculiar state for

the studied character] can be calculated by making the ratio of the number of favorable situations

by the total number of possible situations.

Bipolar attribute X

Theoretical procedure. X is supposed to have two states “a” and “b”. As the polarity of the

attribute and its homoplasy rate are completely unknown, we consider that it can equally be in

the states “a” or “b” in the root of the tree. Then, the minimal scenarios (with the lowest number

of steps) that explain the known distribution of the attribute (excluding the F-taxon) are

reconstructed for the two situations “state a for the root” (or “root : a”) and “root : b”.

Then, two options are possible:

option (1): either these two minimal scenarios concerning the possible situations of the root

can either be considered as equally probable, even if one can imply more steps than the other.

option (2): or the minimal scenarios that explain the known distribution of the attribute

with a “root : b” is affected of a weight (x); then the minimal scenario for the “root : a” has a

weight (1 - x). They are not considered as equally probable; 0 < (x) < 1. Option (1) is a peculiar

case of option (2), with (x) = 0.5. Nevertheless, option (1) corresponds to the minimal a priori

scenario (equal weight for the two situations of the root).

After, the F-taxon is re-included in the tree, then are only accepted the situations where the

alleged state for F can be reconstructed without adding supplementary homoplasies or steps in

the tree (“favorable cases”), in order to keep the same minimal lengths for the new trees. This

method of inference do not add other hypothesis than the two possible situations in the root of

308

A. NHL : PROBABILISTIC INFERENCE OF UNKNOWN DATA

the tree. Finally, the “favorable cases” are counted, and the probability of the event (F is in the

state “a”) labeled “p (F : a)” is simply the following ratio:

p (F : a) = (number of cases favorable to the state “a”)/(number of favorable cases)

Application. 1) If a taxon F is simply the sister-group of a known taxon A, without further

information, the probability for the event [F and A share the same state for a character X] = 0,5,

which can be written p (F : a) = 0,5 = p (F : b). A simple information of sister-group relationship

does not allow any prospective for unknown characters.

2) If a taxon F is the sister-group of a known taxon Al, [F + Al] being the sister-group of

a known taxon A2, and if Al and A2 share the state “a” of the character, unknown for F (Fig. 1):

Bryant & Russel's method infers the situation “a” for F.

Using the probabilistic method,

with option (1) for the roots, I have:

p (F : a) = 1 and p (F : b) = 0 (Fig. 1)

with option (2) for the roots, I have:

p (F : a) = [x + (1 - x)] / [x + (1 - x)] = 1

Thus the results of the two methods are congruent, in either situations.

3) If the taxon A2 has the contrary state “b”:

After BRYANT & RUSSEL'S method, the inferred situation is “a or b” for F.

Using the new probabilistic method,

with option (1) for the roots, we have:

p (F : a) = 2/3 and p (F : b) = 1/3 (Fig. 2).

with option (2) for the roots, we have, as p (F : a) depends on x:

p (F : a) (x) = [x + (I - x)] / [(x + x + (1 - x)] = 1 / (1 + x)

As 0 < x < 1, p (F : a) (0) = 1 ; p (F : a) (1) = 0.5 ; and p (F : a) (0.5) = 2/3 [as x = 0.5

corresponds to option (1)].

More generally, 0.5 < p (F : a) (x) ^ 1

With the minimal scenario for the roots, p (F : a) = 2/3

The results of the two methods are congruent but we can quantify the alternative “a or b”.

4) If we add to the schema of Figure 1 the information (Fig. 3) of an out-group (including

one or several taxa) A3 which has a state “b” :

Bryant & Russel's method infers the situation “a” for F.

With the probabilistic method,

with option (1) for the roots, I have:

p (F : a) = 1 and p (F : b) = 0

with option (2) for the roots, I have:

p (F : a) (x) = [x + (1 - x)] / [x + (1 - x)] = 1

The two results are clearly congruent. Adding supplementary taxa which would be

branched lower in the phylogenetic tree will not change the probabilities for the terminal branch

which includes F.

Source: MNHN . Paris

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

309

A2 : a F : a ? A1 a

A2 : a A1 : a

Bryant & Russel’s method

of inference

Option 2 : weight (1 - x)

A2 : a A1 :a

Option 2 : weight (x)

a F

a A2

a F

a A2:

F : a implies no

F : b implies one

supplementary step

F: a implies no

supplementary step

A2 : a

b A1

a A2

a F

b A1

a A2

a F

b Ai

F : b implies a

supplementary step

F : b implies a

supplementary step

F : b implies two

supplementary steps

Fig. 1 1 — p(F : a) = 1 ; other situations also imply supplementary steps.

5) But if the ingroup includes different taxa with different states, or polymorphic taxon(a),

the probability will decrease. In Figures 4 and 5, we give two different examples.

First example: If a third taxon A3 with the contrary state “b” is added to the situation of

Figure 2 (Fig. 4) as sister group of [(A 1 + F) + A2], the probability is p (F : a) = 1/2 for the two

310

A. NEL : PROBABILISTIC INFERENCE OF UNKNOWN DATA

A2 : b F: a or b ? A1 a A2 : b A1 : a A2 b A1 : a

a orb

Option 2 : weight

Option 2 :

(1 -x)

weight (x)

b F

a A2

b F

Al :

b F

Al :

F : a implies no

supplementary step

F : a implies no

supplementary step

F : b implies no

supplementary step

Fig. 2. — p(F : a) = 2/3 ; other situations imply supplementary' steps.

options (1) or (2), it has decreased, compared to the result of Figure 2. This result remains

congruent with the predictions of BRYANT & RUSSEL'S method (inference of "a or b”), but there

is a kind of “attraction” of the low branches. Nevertheless, if further taxa having the state “b” are

added more basally, the result will not change.

First example: If a third taxon A3 with the contrary state “b” is added (Fig. 5) as sister-

group of [(Al + A2) + F]:

Bryant & Russel's method gives the inference “b” for F.

With probabilistic method, 1 have:

with option (1) for the roots:

p (F : a) = 1/3

with option (2) for the roots:

p (F : a) (x) = (l — x) / [x + (1 - x) + (1 -x)] = (1 -x)/(2-x)

p (F : a) (0) = 0.5 ; p (F : a) (1) = 0 ; and p (F : a) (0.5) = 1/3 (minimal scenario for the

roots). More generally : 0 < p (F : a) (x) ^ 0.5, because 0 < x ^ 1 and p (F : a) is a decreasing

function of x.

Thus, in this case, the two methods are not congruent, but the probabilistic method agrees

with the intuitive assumption of more uncertainty in the inference if the sister taxon (Al + A2) of

F is polymorphic.

Source: MNHN, Pahs

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

311

A3:b A2:a A1 :a

Option 2: weight

0 ■ x)

A3 : b A2:a A1 :a

Option 2 : weight (x)

Fig. 3. —p(F :a)= 1.

6) In the case of several taxa with an unknown state for character X (Figure 6), Bryant &

Russell ( loc. cit.: 410-411, Fig. 4) concluded that no peculiar F-taxon is privileged in the

inference of the informations. My study leads to similar results.

In the situation of Figure 6, BRYANT & RUSSEL'S method implies the same inference (“state

a”) for the two taxa FI and F2.

The probabilistic method gives the same probabilities for FI and F2, for the two options

(1) or (2), clearly not depending on the position of the fossil taxa in the tree:

p (FI : a) = 1 = p (F2 : a)

Similar results can be obtained with more F-taxa in similar positions.

7) The same calculations have been made in the case of two F-taxa (Fig. 7), but with a

situation similar to that of Figure 2:

Bryant & Russel's method gives the same inference of “a or b” for FI and F2 but it does

not add information to the situation of Figure 2.

With probabilistic inference, I have

with option (1) for the roots:

p (FI : a) = 3/4 but p (F2 : a) = 1/2

312

A. NEL : PROBABILISTIC INFERENCE OF UNKNOWN DATA

A3 : b A2:b A1 :a

Option 2 : weight

(1 - x)

A3 : b A2:b A1 :a

Option 2 :

weight (x)

Fig. 4. — p(F : a)= 1/2.

with option (2) for the roots:

p (FI : a) (x) = (x + 1) / (2x + 1) and p (F2 : a) (x) = 1 / (2x + 1)

p (FI : a) (0) = 1 ; p (FI : a) (1) = 2/3 ; and p (FI : a) (0.5) = 3/4

p (F2 : a) (0) = 1 ; p (F2 : a) (1) = 1/3 ; and p (F2 : a) (0.5) = 1/2

Source: MNHN. Paris

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

313

A3 : b A2:b A1 :a

A3 : b A2:b A1 : a

Option 2 :

weight (x)

Fig. 5. — p(F : a) = 1/3.

More generally:

2/3 < p (FI . a) (x) < 1 and 1/3 < p (F2 : a) (x) < 1

because 0 < x < 1 ; p (FI : a) and p (F2 : a) are decreasing functions of x.

Thus, in this case, the probabilities are not the same, because of the “attraction” of the low

branch. Furthermore, all the probabilities decrease with the number of F-taxa between A2 and

Al. This result is congruent with the assumption that the possibilities of the displacements of the

positions of the transformations within the tree increase with the number of F-taxa between Al

and A2.

8) With n F-taxa in the same situation as in Figure 7, probabilistic method gives [option

(1)]:

p (F1 : a) = (n+1) / (n+2), p (F2 : a) = n / (n+2), ..., p (Fi : a) = (n+2-i) / (n+2), .... and

p (Fn : a) = 2 / (n+2)

If the rank “i” of a F-taxon is supposed constant, the probabilities p (Fi : a) increase with n.

For example, p (FI : a) increases with n. Nevertheless, the possibilities of having the state “b” for

some of these F-taxa increase with the number of taxa between A2 and Al, even if the “distance”

(number of steps) between Al and A2 do not increase.

314

A. NEL : PROBABILISTIC INFERENCE OF UNKNOWN DATA

The better possible schema is that with two known taxa in the state “a” and an out-group

in the state “b”.

Multistale attribute

Definition. In many cases, the attributes have more than two states (multistate attribute or

character, especially for the climatic analysis). For example, in a “temperature” analysis based on

the scale of David et al. (1983), the attribute shows five states [Icy - Cold - Temperate - Hot -

Torrid], For each state, an arbitrary value can be attributed, ranging from “a” to “e”. Several

scenarios can be envisaged.

If the various states seem to correspond to a gradual process, it is possible to envisage the

hypothesis of their polarization following a gradation without any “jump” between two

successive states, from an extreme state to an other; i.e. [- a -» b -» c -» d -> e +] or [- e -» d

—> c —> b -> a +] for a “temperature” analysis; or from an intermediate state towards the extreme

states: [+ e *- d <— c (-) —> b -» a +] for example.

It is possible to deny any gradual process a priori , but to still suppose the existence of an

evolution from a plesiomorphic state towards one or several apomorphic states, with possible

“jumps” over some states. For example, a possible polarization would be[-a->b—»c—»d->e

+]. In that case, the number of possible polarization's quickly increases. There are nine

possibilities for three states but 64 possibilities for four states of a character.

Theoretical procedure. If it is possible to define the more probable scenario for the

attribute after the analysis of the known taxa following the parsimony method the scenario that

implies the weaker quantity of homoplasies or steps. BRYANT & Russel's method can be applied

using similar processes of inference of the situations at the nodes as for bipolar characters.

Probabilistic method can also be used with the following change : the minimal scenarios (with the

lowest number of steps) that explain the known distribution of the attribute (excluding the F-

taxon) are reconstructed for all the situations of the root “root a”, “root b”, “root c”, etc.

They can be considered as equally probable, even if one can imply more steps than the

other [option (1)]. The option (2) gives different weights x a , xb, x c , etc., to the various situations

of the roots, with the £i (xi) = 1. As the various values of the xj are unknown, this option is

practically inapplicable. Next step is to re-included the F-taxon in the tree, then are only accepted

the situations where the alleged state for F can be reconstructed without adding supplementary

homoplasies or steps in the tree (“favorable cases”), in order to keep the same minimal lengths

for the new trees. This method implies that we deny any gradual process a priori ( contra first

scenario as above).

Application. For an attribute X with three states “a”, “b” and “c” within a group of taxa,

including the taxon F (Fig. 8):

Bryant & Russel's method gives the inference of “a or b or c” for F, even if the

situations for Al, A2, and A3 are permuted.

Probabilistic method [with option (1)] leads to a similar conclusion but it is more precise

because it will be affected by permutations of the situations for Al, A2 and A3, for examples :

If Al is “c”, A2 is “b” and A3 is “a” (Fig. 8), then p (F : c) = 2/6 = 1/3; p (F : b) = 3/6 =

1/2 and p (F : a) = 1/6.

Source: MNHN. Paris

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

315

a? FI

, i

a Al

A2 :

m a

Option 2 : weight

(1 -x)

_Option 2 :

weight (x)

Fig. 6. — p(Fl : a) = p(F : a) = 1 ; other situations imply supplementary steps.

If At is “b”, A2 is “c” and A3 is “a”, then p (F : b) = 2/6 = 1/3; p (F : c) = 3/6 = 1/2 and p

(F : a)= 1/6.

Both these results are congruent with the position of sister-groups between A1 and F.

Similar results can be obtained within each case of permutation between Al, A2 and A3.

In the situation of Figure 9, the results of the two methods slightly differ. BRYANT &

RllSSEL's method gives the inference “b” for F but probabilistic method [with option (1)] gives p

(F . b) = 3/4 and p (F : c) = 1/4, similarly to the situation of Figure 5.

Conclusion

It is possible to calculate a probability law for each character or attribute which is unknown

for a taxon included in a phylogeny. These calculations give the maximal estimation of the

probability for the inference, because the additions of steps due to the presence of the F-taxa are

rejected, but they could have happened. These two different methods of inference explain the

weakness of the theory of actualism concerning the ancient palaeobiotas. It is not directly the

antiquity of the fossil taxa which renders less probable the inference of the attributes to the fossil,

but if a fossil is older than another one, it has more “chance” to be only the sister-group of

Recent taxa, thus, it only provides information of low probability. The scale of measure of the

reliability of the inference is not directly temporal but phylogenetic, thus it is not directly related

with the time factor.

316

A. NEL : PROBABILISTIC INFERENCE OF UNKNOWN DATA

A2 : b F2 : a or FI : a or A1 : a

A2:b A1:a

Option 2 : weight

<1 -x)

A2 : b A1 :a

Option 2 :

weight (x)

Fig. 7. — p(Fl : a) - 3/4 ; p(F2 : a) = 1/2 ; other situations also imply supplementary steps.

Application : pa/aeoc/imatic and palaeoenvironmenial phytogeny

Procedure. All the palaeoclimatological studies based on the fossil data use the comparison

between fossil taxa and their "nearest” Recent relatives. More especially, palaeoclimatic studies

of the Quaternary are now based on the elaborate method of the “Mutual Climatic Range” or

Source: MNHN. Paris

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

317

F : a or b

A3 : a A2 : b A1 : c

A3 : a A2 : b A1 : c A3 : a A2 : b A1 : c

A3 : a A2 : b F : a A1 : c

F : a implies no

supplementary

step

A3 : a A2 : b F : b A1 : c

F : b implies no

supplementary "

step

A3 : a A2 : b F : c A1 : c

F : c implies no

supplementary

step

Fig. 8. — p(F : a) = 1/6 ; p(F : b) = 1/3 ; p(F : c) = 1/2.

Source: MNHN. Paris

318

A. NEL : PROBABILISTIC INFERENCE OF UNKNOWN DATA

A4 : a A3 : b F:b?A2:b A1 :c

A4 : a A3 : b A2 : b A1 : c A4 : a A3 : b A2 : b A1 : c A4 : a A3 : b A2 : b A1 : c

A4 : a A3 : b F : b A2 : b A1 : c

a F : b implies no

supplementary

a step

A4 : a A3 : b F b A2 : b A1 : c

b F : b implies no

supplementary

b sle P

A4 : a A3 : b F : b A2 : b A1 : c

C F : b implies no

supplementary

c stcp

A4:a A3:b F

C A2 : b A1 : c

C F : c implies no

supplementary

c step

Fig. 9. — p(F : a) = 0 ; p(F : b) = 3/4 ; p(F : c) = 1/4.

Source: MNHN. Paris

PHYLOGENETIC TES TS OF EVOLUTIONARY SCENARIOS

319

"MCR” of Atkinson et al. (1987). It establishes a theoretical palaeoclimate which corresponds

to the “mutual intersection of the tolerance range” of the various subfossil taxa present in the

studied deposit. This method implies that: the climatic tolerances of the studied species did not

vary through the time, the (sub)fossil taxa can be identified as being living species, the various

climatic tolerances of the (sub)fossil taxa have an intersection, all the informations share the same

weight, a priori. This method becomes difficult to apply for strictly fossil taxa but the method of

phylogenetic inference can help. The complex nature of a climate implies precise definitions of

the used parameters. For example, David et al. (1983) defined a (palaeo)climate after the

combination of three types of climatic factors: [glacial - cold - temperate - hot - torrid], [arid -

dry - sub humid - humid] et [stable - alternative], Axelrod (1992) proposed another climatic

scale based on the definition of the “equable climate” characterized by a mean annual

temperature of 14°C and a mean annual variation of 0°C. Whatever the scale, it is necessary to

distinguish the different (palaeo)climates using discrete scales, in order to consider the data as

characters (or attributes) which can be tested by a phylogenetic analysis.

The theoretical method is derived from BRYANT & RUSSELL (ioc. cit. : 409, Fig. 1) with the

two following steps:

As a first step, an analysis of inference, taxon after taxon, of the characters or attributes of

unknown state. Each fossil taxon is integrated, when possible, in a phylogenetic analysis based on

the present morphological characters, but not based on the attributes which shall be studied after.

For each climatic attribute (temperature, humidity, stability) and each taxon, the probability law

of the attribute is established. A study of correlation [structure - function] based on the preserved

characters of each fossil is to be made in parallel with the study of phylogenetic inference. The

conclusions of the two phylogenetic and extrapolated procedures are compared. If the results are

congruent, the law of probability of the concerned attribute is taken up for the taxon. Otherwise,

the taxon is considered as doubtful and is not used for the following step. Its phylogenetic

placement is reexamined and its law of probability is recalculated, and compared again to the

results of the study of correlation [structure - function].

As a second step, an analysis of inference of the states of the attributes for the studied

palaeoenvironment is based on all the inferences established during the first step. By putting

together all the data for all the taxa (Fj), for each attribute X, is calculated a series of coefficients

[Pj (X)]j. The “i” correspond to the states of the attribute X.

Each Pj (X) = Sj [P (X : i for Fj)]

with the Fj corresponding to all the present taxa.

A law of probability L (X) of the attribute X for the concerned palaeobiota, can be

established. On the basis of this law of probability, a mean value E (X) for the attribute can be

calculated:

E (X) = Pj (X) / Si [Pi (X)]

The results of the phylogenetic analysis are to be tested, when possible, by independent

data gathered with a direct physical analysis (analysis of the Oxygen isotopes, or of

Deuterium/Hydrogen, etc., MILLER et al., 1988). Similarly, the results of phylogenetic

biogeography are to be tested using the independent geological data (NELSON, 1985). If the

results are congruent,

320

A. NEL : PROBABILISTIC INFERENCE OF UNKNOWN DATA

A: a F: a B.b A:a Fa B b

'F related to A‘

implies no

supplementary step

'F related to B'

implies no

supplementary step

A : a

F: a

B : b

F related to A'

_[mplies no

supplementary step

A : a

F a

B : b

'F related to B'

implies one

supplementary step

Fig. 10. — p(F is related to A) = 2/3.

they are considered as probable. Otherwise, the law of probability of the attributes can be verified

for all the taxa and new data are to be found out before solving the problem.

Examples. Within this theory, for a study of palaeotemperature T (with the rate [glacial :

“a” - cold : “b” - temperate : “c” - hot: “d” - torrid : “e”].

If we consider a taxon F has the following law of probability:

p (T : “b” for F) = 3/4, p (T : “c” for F) = 1/4

and p (T : “a” for F) = 0 = p (T : “d or e” for F)]

(corresponding to the situation in Fig. 9).

Then, F has more weight for the calculation of the law of probability of the global

palaeotemperature of the palaeobiota than a taxon F' with the following law of probability for the

palaeotemperature:

p (T : “b” for F') = 2/6

and p (T : “c” for F) = 3/6, p (T : “a” for F) = 1/6, p (T : “d or e” for F') = 0

(corresponding to the situation in Fig. 8).

This method of weighting gives a greater importance to the taxa which correspond to

highly specialized climatic conditions. It allows a less empirical evaluation of the weights.

Source: MNHN, Paris

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

321

Applications concerning “ Mutual Climatic Range ” The same method of weighting can be

applied in the subfossil record as a modification of the “Mutual Climatic Range”, by giving a

more important weight to the taxa specialized to only one type of biota or of climate. A Recent

(or subfossil) taxon which is present under climates for which the temperature ranges from type

“5” to type “3” directly gives, without inference analysis, the following law of probability:

p (T < 3) = 0, p (T : 3) = p (T : 4) = p (T : 5) = 1/3

Unlikely, a living taxon present under a climate for which the temperature is of type “5”

gives the law of probability:

p (T < 5) = 0 and p (T : 5) = 1

The same method is to be applied to all the taxa. The following analysis is that of the

precedent step.

Applications concerning non inference of an attribute allochtony. If the law of probability

for an attribute of a F-taxon does not correspond to the general law of probability of the biota, its

climatic or environmental constraints could have changed relatively to the nearest relative taxa or

the concerned F-taxon is allochtonous for the concerned palaeobiota.

Problem of the living fossils or relic taxa (sensu DELMMRE-DEBOUTEMILE <£

BOTOSANEANU, 1970). Theoretical problem : the characters or attributes which are only present

in one Recent taxon A cannot be easily inferred in the fossil record, whether they are

autapomorphies of A or symplesiomorphies of the group including A. For all the possible

hypothesis of weighting of the homoplasies, the probability p (F : a) = p (F : b) = 1/2, situation of

simple information of a sister-group relationship between F and a Recent taxon A, and the

inference or the non-inference of the attribute X from A on F are equally probable. This situation

occurs specially in the cases of relic taxa, which are the only Recent representatives of fossil

groups. They are poorly informative in the inference of their own characters or attributes. The

relic species are often located in peculiar “refuges” which are very different of the palaeobiotas of

their nearest fossil relatives, as already noticed for some marine taxa which are supposed to have

“migrated” from shallow water zones towards deep water zones during the Palaeozoic or

Mesozoic (the Mollusk Neopilina galatheae Lemche, 1958 or the Crinoids for examples,

DELAMARE-DEBOUTEVILLE & BOTOSANEANU, 1970).

As a first example, I can show that the Isoptera Mastotermitidae are poor palaeoclimatic

indicators. The Recent termite Mastolermes darwiniensis (sole living representative of the family

Mastotermitidae) lives under the very peculiar climate and biota of the savanna (“bush ") of

Northern Australia (Gay & Calaby, 1965: 396), but seems to be absent in the evergreen forest

(Emerson, 1965: 27). This insect is an excellent climatic and environmental indicator for the

present days. Contrary to the hypothesis of NEL & PA1CHELER (1993), the direct inference in the

past of all these climatic and environmental data, using the presence of fossil Mastotermes spp in

Cenozoic palaeoenvironments, has a low probability of 0.5 because these fossils have (in the best

case) only relationships of sister species with the Recent taxon. Thus, it is impossible to say that

these fossils lived in palaeobiotas similar to that of M darwiniensis. The two fossil genera

Blattotermes and Spargotermes , other known Mastotermitidae, give no more palaeoclimatic and

palaeoenvironmental informations because they are, in the best case, only the sister genera of

Mastotermes. The Kalotermitidae (and other isopteran families) live under temperate, hot or

322

A. NFL : PROBABILISTIC INFERENCE OF UNKNOWN DATA

torrid climates and the Mastotermitidae live under hot or torrid climates. Either if we consider

that the Mastotermitidae are really the sister-group of the Kalotermitidae (ROONWAL, 1985), or

the sister-group of all other isopteran families (KambhampaH el al., 1996), inference analysis ol

the attribute “temperature”, with the two states “temperate” (“a”) and “hot or torrid” (“b”),

shows that the probability for the fossil Mastotermitidae to have lived under “hot or torrid”

temperatures p (F : “b”) = 2/3 and the contrary probability p (F : “a”) = 1/3 (situation of figure

5). In a different way, BRYANT & RlJSSEL'S method gives the inference of the state “b” for F and

appears less precise. This example shows that only a small part of the information can be inferred

in the fossil record.

As a second example, the Brachiopoda, Lingulidae show a case of ineffectiveness of the

inference method. These animals usually live on the light bottom of the tide zone but PAINE

(1970) indicates a species (Lingula albida) living in deep water. The phylogenetic inference of

the former biota in the fossil record, as proposed by GALL (1971: 24) for the Triassic of Vosges

(France), is difficult to establish because of the lack of phylogenetic analysis of the group which

integrates the fossil taxa. The Triassic, Devonian and Ordovician Lingulidae are attributed to the

genus Lingula s.l., and their real relationships with the Recent genera Glotlidia and Lingula

remain uncertain. The probability they had lived in deep water is equal to the probability they had

lived in shallow water. Some more precise informations concerning the substrate on which these

animals did live can be found out after the morphological and physical analysis of the fossil shells

and ancient substrate (PAINE, 1970), the phylogenetic data being useless.

INFERENCE OF THE POSITION OF A TAXON

Theoretical procedure

The available characters in the fossil record are frequently highly homoplastic (for example

some of the odonatan venational structures). Thus, it is difficult to attribute a fossil taxon to a

precise group on the sole basis of these ambiguous characters. Nevertheless, it is possible to

estimate a probability for the event : [the taxon is related to a group rather than to another one],

following a probabilistic method similar to the precedent. This method can be applied to a taxon

F clearly related to two possible groups A and B, but which does not share any clear

synapomorphy with A or B, to the exclusion of one of the two groups. The two events [F is

related to A] and [F is related to B] are opposite.

Two hypotheses of scenario can be made:

First, with the supplementary hypothesis that, for each concerned character, the

probabilities for the additions of new steps are equal to zero and that the other possible situations

of polarity are equally probable, the probability of the events [F is related to A] and [F is related

to B] can be calculated with the quotient of the number of favorable cases by the total number of

possible cases.

Second, a weight p (arbitrary, medium or maximal) can be given to the simple addition of a

new step (0 < p < 1 if p is calculated as a percentage or a rate of homoplasy). The non-addition

of a step will have a weight q = 1 - p. Furthermore, [p = 0] corresponds to the probability zero

for the addition of a new step.

X is a character that is supposed to have two states “a” and “b”. As the polarity of the

character is completely unknown, we consider that it can equally be in the states “a or b” in the

root of the tree. Then, in the simple tree made with the two taxa A and B, the minimal scenarios

Source . MNHN . Paris

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

323

(with the lowest number of steps) that explain the known distribution of the attribute (excluding

the F-taxon) are reconstructed for the two situations “root a” and “root b”, and considered as

equally probable, even if one can imply more steps than the other. After, the F-taxon is re-

included in the partial tree of the taxa A and B, then are only accepted the situations where the

alleged state for F can be reconstructed without adding supplementary homoplasies or steps in

the tree (“favorable cases”), in order to keep the same minimal lengths for the new trees.

Examples

If the state “a" is shared by F, A and B, no homoplastic situation appears whether we

consider X as an apomorphy or plesiomorphy. The character “a” is not informative.

p ([F is related to A]) = p ([F is related to B]) = 1/2

It the state “a” is present in F and A but absent in B, the polarity of which is ambiguous

(presence of several homoplastic situations concerning the character in the phylogenetic analysis)

(Fig. 10). If p = 0, there are only three “possible” situations, with two “favorable” for the

hypotheses [F is related to A], the universe of the possibilities is: {(root a ; F is related to A)

noticed (root a ; F-A) ; (root a ; F is related to B) noticed (root a ; F-B); (root b ; F is related to

A) noticed (root b ; F-A)}. F is more probably to related to A than B.

Probabilities are:

p (F is related to A) = 2/3 and p ([F is related to B]) = 1/3

If we suppose that p for the added steps is not nil, there are four “possible” situations with

different weight. The universe of the possibilities is: {(root a ; F-A) with a weight q ; (root a ; F-

B) , q ; (root b ; F-A), q ; (root b ; F-B) p}.

The probability are:

p ([F is related to A]) = (2q) / (3q + p) or

p ([F is related to A]) = (2q) / (2q + 1)

As there are two favorable cases with the weight q against four possible cases, including

three cases with a weight q and one with the weight p. If p = 0, we find again q = 1 and the

precedent probability. For all the possible values of p, the “best” possible value of the probability

is that corresponding to p = 0, because 2/3 > (2q) / (3q + p) for all values of p :

(2q) / (3q + p) = 2 (1 - p) / (3(1 - p) + p) = 2 (1 - p) / (3 - 2p) = (2 - 2p) / (3 - 2p)

and (2 - 2p) / (3 - 2p) < 2/3 if (2 - 2p) x 3 < (3 - 2p) x 2 if 6 - 6p < 6 - 4p

if 6p > 4p (with 0 < p <1)

If we add a character X2, also of uncertain polarity, independent of XI and with state “a”

shared by F and A and state “b” for B, the universe of the possible events is the product of the

universes of the possibilities corresponding to XI and to X2.

If the weight p = 0 for the homoplasies, the universe is: {(root “a” for XI, root “a” for X2

and F is related to A) [or with an abbreviated notation: (a: XI, a: X2 ; F-A)] ; (a XI, b: X2 ; F-

A); (b: XI, a: X2 , F-A); (b: XI, b: X2 ; F-A); (a: XI, a: X2 ; F-B)}. All the cases of the type

(one of the roots is in the state “b” and [F is related to B]) imply an homoplasy and are not

counted. There are five possible cases with four favorable to [F is related to A], Consequently, p

([F is related to A]) = 4/5 and p ([F is related to B]) = 1/5. The probability for (F is related to A)

increases.

324

A. NEL : PROBABILISTIC INFERENCE OF UNKNOWN DATA

If the weight p is not nil, the homoplasies are counted and the universe becomes {(a: XI, a:

X2 ; F-A), weight q 2 ; (a: XI, b: X2 ; F-A), q 2 ; (b: XI, a: X2 ; F-A), q 2 ; (b: XI, b: X2 ; F-A), q 2 ;

(a: XI, a: X2 ; F-B), q 2 ; (b: XI, a: X2 ; F-B), pq ; (a: XI, b: X2 ; F-B), pq ; (b: XI, b: X2 ; F-B),

p 2 }. There are four cases favorable to “F-A” with a weight q 2 . There are also four cases

unfavorable to “F-A”, one with a weight p 2 , two with a weight pq and one with a weight q 2 .

p ([F is related to A]) = (4 q 2 ) / (5 q 2 + 2 pq + p 2 ) = (4 q 2 ) / [4q 2 + (p + q) 2 ]

As (p + q) = 1,1 find:

p ([F is related to A]) = (4 q 2 ) / [4q 2 + 1]

If p = 0, q = 1 we find again p ([F is related to A]) = 4/5. The best possible value of p ([F is

related to A]) occurs when p = 0 (the homoplasies are impossible) because : (4 q 2 ) / [4q 2 + 1] <

4/5 is equivalent to 4q 2 < 4 or q 2 < 1. Otherwise, if p is different of 0, the probability p ([F is

related to A]) varies between 4/5 and 0.

In the case of n characters XI, X2, X3, X4, ..., Xi,..., Xn which are all in the same

situation (with an uncertain polarity, independent, with state “a” shared by F and A and state “b”

for B),

If p = 0, the universe of the possibilities is of cardinal (2 n + 1), with (2 n ) events in favor of

[F is related to A], thus:

p ([F is related to A]) = (2") / (2" + 1) and p ([F is related to B]) = 1 / (2 n + 1)

If p is not nil, the cardinal of the universe increases to the value 2 x 2 " = 2" ‘.

2" events are favorable to [F is related to A] with a weight q n , the other events correspond

to [F is related to B], with one having the same weight q n , n events have the weight pq n ', (n!) /

[2! (n - 2)!] events have the weight p 2 q "~ 2 , (n!) / [3! (n - 3)!] events have the weight p' q n ',

etc., and one event has the weight p n .

The probability p ([F is related to A]) = (2 n q n ) / [(2 n + l)q n + npq" 1 + {(n!)/[2!(n -

2)!]}p 2 q n 2 + {(n!)/[3!(n - 3)!]}p'q n 3 + ... + p"]. There is an usual remarkable identity in the

denominator thus:

p ([F is related to A]) = (2"q n ) / [(2 n q n + 1)

This formula generalizes the preceding ones. Furthermore, if p = 0 and q = 1, we find again

the formula (2 n ) / (2 n + 1). For all cases, the maximal value of p ([F is related to A]) is equal to

(2 n ) / (2 n + 1), when p varies from 0 to 1.

If there is a character X (bipolar, a or b) with the state “a” shared by A and F but not by B

and one character Y (bipolar, a or b) with the state “b” shared by B and F but not by A (situation

symmetrical of Figure 10).

In the case of a weight p = 0 for the added steps, the universe of the possibilities is : {(a :

X, a : Y ; F-A); (b : X, a : Y ; F-A) ; (a : X, b : Y ; F-B) ; (a : X, a : Y ; F-B)} ; there are four

events with two favorable to [F is related to A] and 2 are favorable to [F is related to B], p ([F is

related to B]) = p ([F is related to A] = 2/4 = 1/2.

If p is not nil for the added steps, the universe becomes : {(a : X, a : Y ; F-A), q 2 ; (b : X, a

: Y ; F-A), q 2 ; (a : X, b : Y ; F-B), q 2 ; (a : X, a : Y ; F-B), q 2 ; (a : X, b : Y ; F-A), pq ; (b : X, a

: Y ; F-A), pq ; (b : X, a : Y ; F-B), pq ; (a : X, b : Y ; F-B), pq). p ([F is related to A]) = (2q 2 +

2 pq) / (2q 2 + 2 pq + 2q 2 + 2 pq) = 1/2.

In the two hypothesis, the two informations of X and Y “neutralize” each other.

Source: MNHN, Paris

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

325

Generalization

If we have n characters of the type X with the state “a” in common to F and A and m

characters of the type Y with the state “b” in common to F and B.

In the case of a weight p = 0 for the added steps, the universe holds [(2") + (2 m )] events

which are distributed into (n+ m) -upsets of two types:

(2 n ) events of the type (a : YI, a : Y2, a : Yi, .... a : Ym, a or b : XI, a or b : X2, a

orb : Xi,..., a orb : Xn, F-A);

(2 m ) events of the type (a or b : Yl,..., a or b : Yi, a or b : Ym, a : XI, a : Xi, ..., a

: Xn, F-B).

Consequently,

p ([F is related to A]) = (2 n ) / [2 n + 2 m ]

p ([F is related to B]) = (2 m ) / [(2 n ) + (2 m )]

In the case of a weight p for added steps, then:

p ([F is related to A]) = 2 n q n [q m + mpq^ 1 + ... + p m ] / 2 n q n [q m + mpq”"' + ... + p m ] + 2 m q m [q"

+ npq" 1 + ... + p n ],

then:

p ([F is related to A]) = 2"q n [p + q] m / (2 n q n [p + q] m + 2 m q m [p + q] n )

as (p + q) = 1, then:

p ([F is related to A]) = 2 n q n / (2 n q n + 2 m q m )

This formula generalizes and replaces all the precedent ones.

p = 0 and q = 1 give again p ([F is related to A]) = (2 n ) / [2 n + 2 m ] which is the maximal

possible value when p varies from 0 to I. If m = n, p ([F is related to A]) = 1/2. The

contradictory informations “neutralize” each other.

Furthermore, p ([F is related to A]) = 1/2 (for all the values of m and n) if q = 1/2 i.e. if the

weight p of the addition of steps = 1/2. Even if there are distinctly more characters in favor of a

relation with A rather than with B (n » m), if the probability that all these characters implies

additions of new steps is too important, it is impossible to decide.

BECHLY et at. (1997) apply this method to the peculiar case of the Lower Cretaceous

English Zygoptera Cretacoenagrion (taxon of uncertain position because of the lack of

information). There is a maximal probability of 4/5 for the event [Cretacoenagrion is related to

the Lestoidea rather than to the Coenagrionoidea] but it is still impossible to state positively that

it is a Lestoidea.

If the number of shared characters between F and A but not by B increases, the probability

of the event [F and A are related] increases. This result is congruent with an intuitive approach of

the problem. This method does not prove that F is really related with A and would not replace

the cladistic method based on the principle of the fundamental importance of the synapomorphies

for the determination of the relationships between the taxa. This method gives an estimate of the

probability p ([F is related to A] ) but the calculation of the exact value of this probability depends

on the determination of the rate p of the homoplasies. The result can greatly vary with the value

of p. A probability, even very high, is not a proof.

326

A. NEL : PROBABILISTIC INFERENCE OF UNKNOWN DATA

CONCLUSION

Although these methods of probabilistic inferences could appear not very easy to use, they

have the advantage of quantifying the possibilities of transferring Recent biological and

environmental data to (sub)fossil taxa. Thus, they limit and refine possibilities of global

transferring of actualism. Quantification of inferred palaeoclimatic data allows establishments of

more precise palaeoclimatic hypotheses, susceptible of being tested by physical analysis.

Comparisons between palaeoclimatic hypotheses of different palaeobiotas shall be easier to

attempt because these hypotheses are based on the same method. The probabilistic inferences of

taxa positions cannot replace phylogenetic analyses but they are better than subjective and not

quantified hypotheses.

ACKNOWLEDGEMENTS

I thank very' much P. Grancolas (Laboratoire d'Entomologie, MNHN) for his help and advises. I also thank P. Darlu

(Laboratoire d'Anthropologie biologique, Universite de Paris-VII) for the helpful contradictory discussions on the problem of

probabilistic inference.

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Biology> of Termites, volume 2. New York, Academic Press: 1-643.

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The Origin of Hexapoda: a Developmental Genetic Scenario

Jean S. Deutsch

Laboratoire « Evolution Moleculaire », Universite P. et M. Curie (Paris 6)

Bat B, 707, case 241.9 quai St-Bemard, 75252 Paris Cedex 05, France

ABSTRACT

The similarities and differences in the body plans of Crustacea and Hexapoda are discussed and analyzed. Based on

phylogenetics and comparative developmental genetics, an evolutionary scenario is proposed on the origin of Hexapoda.

Basically, it is assumed that Hexapoda would derive from an ancestor bearing crustacean-like characters. Changes in the

pattern of expression of Hox genes would be correlated to the observed changes in body plans. Secondarily, the "master gene"

Distal less, required in limb formation, would have passed under the control of the Hox genes. This change would have

produced the reduction of leg pairs to a number of three, and would be fixed by terrestrial life. The interest of the interplay of

comparative developmental genetics and of phylogenetics is stressed, the former being able to propose realistic evolutionary

scenarios at the genetic level, the second to critically test them.

RESUME

L'origine des Hexapodes : un scenario de genctique du developpement

Le present article decrit un scenario concemant l'origine evolutive des Hexapodes. Sur la base de phytogenies recemment

proposees, a partir de donnees tant moleculaires que morphologiques, on suppose que les Hexapodes deriveraient d'un ancetre

de type Cmstace. Dans la lignec conduisant aux Hexapodes, un changement se serait produit dans le profil d'expression des

genes Hox. Ce changement rend compte des differences de plan du corps entre Crustaces et Hexapodes. Dans un second

temps, le gene Distal less, responsable de la morphogenese des appendices, serait passe sous controle des genes homeotiques.

Cela aurait provoque la reduction a trois du nombre de paires de pattes. Ce changement aurait ete fixe par l'habitat terrestre

des Hexapodes. La rencontre necessaire de la genetique du developpement et de l'analyse phylogen&ique est soulignee, la

premiere pennettant de proposer des scenarios devolution vraisemblables au niveau genique, la seconde pennettant de tester

la validite de ces scenarios particuliers.

DEVELOPMENTAL GENETICS AND EVOLUTIONARY BIOLOGY

Until the birth of the “Synthetic theory”, genetics (Mendelism) and evolutionary biology

(Darwinism) developed separately and sometimes were in conflict. Similarly, for a time, genetics

and embryology were quite separate fields. This time is now behind us, as shown by the recent

recognition of developmental genetics by the Swedish Academy, awarding the Nobel Prize to the

founders of the developmental genetics of Drosophila, E. Lewis, C. Nusslein-Voli iard and E.

WlESCllAUS (see Deutsch et a /., 1995). In parallel, developmental biologists today direct their

research to the molecular and genetic mechanisms of development. However, for epistemological

Deutsch, J. S., 1997. — The origin of Hexapoda: a developmental genetic scenario. In: Grandcolas, P. (ed.), The

Origin of Biodiversitv in bisects: Phylogenetic Tests of Evolutionary Scenarios. Mem. Mus. natn. Hist, nat., 173 : 329-340.

Paris ISBN : 2-85653-508-9.

330

J. DEUTSCH : THE ORIGIN OF HEXAPOD A

and also obvious practical reasons, up to now, both developmental biology and genetics have

focused on a small number of model organisms.

The time is now ripe for a new field: comparative molecular developmental genetics, at the

crossroads of evolutionary biology, genetics and embryology (LAWRENCE & MORATA, 1994).

The growth of this new field is indeed currently boosted by i) the discovery of the homeobox

twelve years ago and the widespread distribution of homeobox genes (Gehring, 1994) which

opened our minds to the idea of the evolutionary conservation of developmental genes across the

Metazoan kingdom, and ii) the extraordinary power of newly developed tools in molecular

biology.

Developmental genetic information can be of high phylogenetic value. It yields new

available characters, that can be integrated like other characters in phylogenetic analyses. In my

opinion, the type of data generated by this new discipline deserves more particular attention, due

to their dual quality of being both genetic and developmental. As genetic, because the genome is

the place where the whole history of life is engraved, as a consequence of the Darwinian principle

of “descent with modification”, which must be the basis of all phylogenies. As developmental,

since embryologic and larval characters may be of higher taxonomic ( i.e. phylogenetic) value

than adult ones, according to Darwin himself, (Darwin, 1859), as he experienced in his study of

the crustacean cirripedes. Without taking for granted Garstang’s sentence that “ontogeny

creates phytogeny” (for a comment see DEVILLERS & TINT ANT, 1996), it should be stressed that

evolutionary radiations in the Metazoa correlate with changes in the body plan, which is the

result of genetically controlled developmental processes.

The interface of developmental biology and phylogenetics could be the promise of a “New

synthesis” in the theory of evolution (GILBERT, 1991).

THE PURPOSE OF THE PRESENT ARTICLE

Here I emphasize the juxtaposition of developmental biology and phylogenetics by

proposing an evolutionary scenario of the origin of Hexapoda based mainly on our current, and I

must confess, still scarce, knowledge of the developmental genetics of crustaceans and insects.

So doing, I include myself in the tradition of developmental genetics. M. Akam (Akam et

a /-, 1988) synthetized the hypotheses of Lewis (1978) on Hox gene evolution and the

developmental model proposed by RAFF & Kaufman (1983), itself derived from Snodgrass,

and proposed a scenario in which insects derived from an annelid-like ancestor by progressive

steps. These included onychophoran- and myriapod-like states, correlated with an increase in the

number of Hox (homeotic) genes (see below for more details on Hox genes).

Given the improvements of our knowledge in both phylogenetics, which now rejects any

close relationship between annelids and arthropods, (EERNISSE et a/., 1992; KlM et al ., 1996) and

of comparative molecular developmental genetics, which has shown that a large gene complex

was likely already present at the origin of arthropods (see below and Fig. 1), the main features of

Akam’s 1988 scenario are presently unvalidated. Nonetheless, this model has been quite useful

in two ways: summarizing the current knowledge of different scientific fields and stimulating new

experimental research.

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PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

331

Chordata

HoxPG 1 2 3 4 5 6 7 8 9 10 11 12 13

Cephalochordata — X/WMA I:

(Amphioxus)

7 7 7

Branchiostoma floridae

Diptera

Lepidoptera

Coleoptera

Branchiopoda

Cirripedia

Xiphosura

lab pb Dfd Scr Amp Ubx abA AbdB

Drosophila melanogaster

Drosophila virilis

Tribolium castaneum

? ? □□ E1IG9 H

Artemia franciscana

mmnnmw ? n

Sacculina carcini

Limulus polyphemus

1. — The evolution of Hox genes. Right : The Hox genes of a selection of arthropod species are represented, after

available data in the literature. Each Hox gene is represented by a square of a distinct color. Gene names are given

above the squares for Drosophila melanogaster. Genes of the same color in different species are assumed to be

orthologous. A question mark means that the gene of interest has not been reported to date, which does not prove that

it is not present. The squares are lined on a bar when genetic linkage has been demonstrated by genetic and/or

molecular evidence. A split in this bar indicates a split of the Hox complex at this position. The absence of a bar in a

given species indicates that up to now there is no direct experimental evidence for the grouping of the Hox genes in a

complex in this case. For sake of clarity, non homeotic genes physically present within the gene complexes of

Drosophila are not represented. Left : A likely phylogenetic tree of the artliropod species represented is drawn. Top :

For comparison, the Hox gene complex of the Amphioxus , probably close to the ancestral chordate one, is drawn

(Garcia-Fernandez & Holland, 1994). The numerals on top of the diagram indicate the conventional chordate

paralogy group of Hox genes (Scott, 1992).

Source:

332

J. DEUTSCH : THE ORIGIN OF HEXAPODA

If the scenario I present here had only a portion of the value of Akam's in this regard, I

would be fully satisfied. But my main purpose is to describe an example of what can be done in

the field, rather than to present a completely realized scenario.

THE BODY PLAN OF CRUSTACEANS AND HEXAPODS

The body plans of Crustacea and Hexapoda show a great parallelism. Both include

unsegmented parts at each end, the acron and telson, and three groups of segments, or tagmata,

in between. The first tagma is the head. The cephalic parts of crustaceans and hexapods are very

similar to each other.

The second tagma of crustaceans is called the pereion. It includes a number of segments,

extremely variable according to the various sub-classes or orders. Each pereionic segment bears

a pair of ventral appendages. This is a strong rule: only very few and derived crustacean species

do not bear appendages on all pereionic segments. The number of pereionic segments, although

quite variable, is never three. The second tagma of Hexapoda is the thorax, always composed of

three segments. Each hexapod thoracic segment bears a pair of legs, hence the name. The

presence of the three pairs of legs is again a strong rule, loss of legs always being a derived state.

On the other hand, the structure, function and even the mere presence of wings or wing-like

appendages, are quite variable and distinctive traits among Hexapoda orders.

The third tagma of Crustacea is called the p/eon. Again, it is composed of a highly variable

number of segments, ranging from none at all in Cirripedia to more than twenty in some

Notostraca {Triops). Depending on the crustacean order, or sometimes even genus, the pleon

may or may not bear appendages. The third tagma of Hexapoda is the abdomen, composed of a

fixed number of 11 segments. Only Collembola and some Diptera have a reduced number of

abdominal segments. At the adult stage, the last two abdominal segments may be reduced. The

hexapod abdomen does not bear locomotory limbs.

In Crustacea, the male genitalia are always located on the segment that marks the border

between the pereion and the pleon (the last pereionic segment, sometimes called the genital

segment). The female genital aperture may be located in the same position, or more anteriorly,

depending on the Order. In Hexapoda the genitalia are always located in a posterior position: in

males probably primarily on the 9th or 10th abdominal segment, in females probably primarily

behind the 7th sternum.

Despite the differences just described, the gross partitioning of the segmentation pattern of

both Crustacea and Hexapoda into three parts leads to the proposal that the three tagmata of

these two classes are homologous structures, following the corresponding order along the

anterior to posterior axis. The homology between crustacean and hexapod heads leaves little

doubt, keeping in mind that the exact number of head segments is still controversial, and that

there are some characteristic differences between the cephalic appendages of Crustacea and

Hexapoda. The homology between the second and third tagmata is less obvious but up to now

has been generally agreed upon, and it is common in most classical zoology textbooks to find the

term “thorax" used as a synonym for the crustacean pereion, and “abdomen” for the pleon.

PHYLOGENETIC RELATIONSHIPS

I he monophyly of the Hexapoda is rarely contested. Among Hexapoda the relationships of

the various orders are in general agreed upon. It is also the case for the basal groups, the

Source. MNHN. Paris

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

333

relations of which are becoming better clarified thanks to recent advances in cladistic analyses

(KRISTENSEN, 1991, 1995; MINET& BOURGOIN, 1986).

The situation is just the reverse for Crustacea: some sub-classes are clearly monophyletic,

such as the Malacostraca. But the relationships between groups are still very uncertain. Thus, it

is difficult to decide which of the crustacean sub-classes or super-orders represents the sister

group of Malacostraca. These problems are probably related to the diversity of body plans

among Crustacea, and to the deep ancestry of the stem taxa of each lineage. Recent molecular

phylogenetic studies have not shed light on this question (ABELE el al., 1992).

Another major problem concerns the relationship between Hexapoda and Crustacea.

Myriapoda, Hexapoda and Crustacea together belong to a “Mandibulata” clade, distinct from the

other arthropod classes, namely the extinct Trilobita and the extant Chelicerata. The Mandibulata

are generally assumed to be monophyletic. The most “classical” view is to consider the

Myriapoda as the sister-group of Hexapoda. They could be united into a clade called

“Tracheata”, on the basis of several similarities interpreted as synapomorphies, including the

uniramous morphology of the limbs and the presence of tracheae, hence the name.

However, recent molecular phylogenetic studies have led to the hypothesis that Hexapoda

would be more closely related to Crustacea than to Myriapoda (BOORE el a /., 1995; FRIEDRICH

& TAUTZ, 1995; TURBEVILLE et a/., 1991).This would lead to the rejection of the clade

“Tracheata” comprising Hexapoda and Myriapoda. Although still controversial, this phylogenetic

hypothesis is supported by morphological arguments, mainly based on the striking similarity

between the patterns of wiring of the nervous system between Crustacea and Hexapoda, which

differs from that of Myriapoda (WHITINGTON el al., 1991; OSORIO et a!., 1995; Osorio &

Bacon, 1994). In addition, certain traits, previously taken as synapomorphies grouping

Myriapoda with Hexapoda, such as the presence and morphology of the trachea, are now

considered as convergent adaptations to terrestrial life. It has even been proposed that hexapods

might be evolved from a crustacean ancestor, thus making the class Crustacea paraphyletic

(Friedrich & Tautz, 1995; Nielsen, 1995, p. 162). (For a contradictory view on arthropod

phylogeny, see FRYER, 1996).

COMPARATIVE DEVELOPMENTAL GENETICS

The body plan of metazoans is under the control of a particular set of genes, the homeotic

or Hox genes, highly conserved in structure and function in triploblasts at least. Each Hox gene is

a “master gene” or “selector gene” which determines, in a specific domain along the anterior

posterior axis of the body, a particular morphogenesis programme during development. Hox

genes were first discovered in a hexapod, the fruit fly and favourite genetic model Drosophila

melanogaster They are now known in a variety of insects. Recent studies on the branchiopod

Anemia (AVEROF & AKAM, 1993) and on two cirripede species, (E. MouCHEL-VlELH & J. S.

Deutscii, unpublished) show that the crustacean ancestor possessed a complement of the same

eight typical Hox genes as found in Drosophila and other insects (Fig. 1). In particular,

Crustacea possess clear orthologues of both Drosophila Ubx and ahdA genes. This is not the

case in the annelid Holobdella, where the Hox genes Lox2 and Lox4 are closer to each other than

to either Ubx or abdA, indicating that the Ubx/abdA duplication postdated the divergence

between Annelida and Arthropoda (WONG el al., 1995) . Unfortunately, data from the single

chelicerate studied until now, Limulus, do not permit a determination of the precise relations of

334

J. DEUTSCH : THE ORIGIN OFHEXAPODA

orthology with the other arthropod homeotic Hox genes, because of the short length of the

fragments cloned and of the tetraploidy of the Limulus genome (CARTWRIGHT et al., 1993).

Hence, it is not yet possible to assess whether the UbxIabdA duplication is shared by all members

of the phylum Arthropoda or by Mandibulata only (Fig. 1).

The variation in body plan between Crustacea and Hexapoda cannot be attributed to a

simple change in the number and/or structure of the Hox genes. However, striking differences are

observed between the pattern of expression of homologous Hox genes between Hexapoda and

Crustacea. Each Hox gene is expressed in a specific domain along the anterior-posterior axis of

the animal during development. The specific domain of activity of each Hox gene actually results

from this spatial specificity of expression and from the combinatorial interactions between the

Hox genes' products. In Drosophila the four more “posterior” Hox genes are Antennapedia

(Amp), Ultrabithorax (Ubx), abdomina/A (abdA) and Abdomina/B (AbdB). The specific domain

of Antp is the thorax, the Ubx domain comprises the posterior half of the second thoracic

segment, the third thoracic and the anterior half of the first abdominal segment, the abdA domain

expands from the second to the fourth abdominal segments, and AbdB reigns over the most

terminal abdominal segments. Besides details, this pattern of expression and activity is highly

conserved in all Insects where it has been studied to date. The same pattern of expression,

including the same anterior limit of the domain in the thorax, has been found for the Ubx gene in

such different Insects as the dipteran Drosophila, which bears a single pair of wings, the

orthopteran Schistocerca , which bears two wing pairs (Kelsh et al., 1994), and the zygentoman

(= thysanuran sensu stricto) Thermobia , which bears no wing at all (CARROLL et al , 1995) . In

contrast, in the crustacean branchiopod Artemia the pattern of expression of these Hox genes is

quite different. Antp, Ubx and abdA are all expressed in the pereion (the so-called “thorax”)

while AbdB expression is restricted to the genital segments (in Artemia, the genitalia are located

in the last two pereionic segments) (Fig. 2). Our preliminary results on Cirripedia, where the

female genital aperture is located in the first pereionic segment, support the idea that AbdB

specificity is genital rather than far-abdominal (E. MOUCHEL-VIELH & J.S. DEUTSCH,

unpublished).

From these results, AVEROF and AKAM proposed a reconsideration of the homology

between the different tagmata of the two arthropod classes (Akam, 1995; AVEROF & Akam,

1995) In Crustacea, the segment bearing the male genitalia always marks the border between

the pereion and the pleon, while the female aperture may or may not be located more anteriorly.

The crustacean genital segment (or segments) would be homologous to the genital segments of

Hexapoda, which are always far-abdominal (see above). The crustacean pereion would not be

homologous to the hexapod thorax, but rather to the whole (thorax + abdomen) (see Fig 2).

WHAT ABOUT LEGS ?

Hexapoda are distinct from Crustacea by their terrestrial life. The terrestrial life of some

crustacean species and the aquatic life of some hexapods are clearly secondary derived states.

Moreover, they differ by the number of pairs of ventral appendages. All hexapods have three

pairs of legs, one pair on each thoracic segment. Crustaceans never have three pereionic

segments. Most have more than three, with the only exception of Ostracoda. Hence, most

Crustacea have more than three pairs of legs.

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

335

pereion G pleon

Fig. 2. — The homology between the tagmata of Crustacea and Hexapoda, according to Averof& Akam( 1995). The domains

of expression of the Hox genes Antp, Ubx, abdA and AbdB are represented on a schematic drawing of Anemia (top)

and Drosophila (bottom). For clarity sake, the Hox expression domains are represented on the body plan of an adult,

although they have been observed at embryonic and/or larval stages. G : genital segments; the genital segments

classically belong to the pereion in the Crustacea, and to the abdomen in the Insccta.

It is logical to assume that the body plans of these two arthropod classes are related to

their eco-ethological habits: the crustacean ventral appendages are mainly used for swimming,

while in a terrestrial environment it might be easier to use a small number of legs. Other

terrestrian mandibulates, such as Myriapoda and the terrestrian isopod crustaceans use quite

different strategies for walking: their pairs of legs are superabundant, but reduced in size, and

homonomous. Although probably primarily homomous, hexapod pairs of legs are not only

reduced in number, they are also different from each other, in morphology, musculature and

innervation. This differentiation might well be under homeotic control. Whether these two

properties (number reduction and differentiation) are correlated is an open question. Hence, this

magic number of three thoracic segments and three pairs of legs in Hexapoda could be of

adaptive value.

Is it possible to reconcile the absence of legs on the hexapod abdominal segments with

AVEROF and Akam's hypothesis of homology between the hexapod abdomen and a part of the

crustacean pereion?

In Drosophila the formation of thoracic legs and cephalic appendages requires the

expression of the selector gene Distal less (DU). In the thorax, the expression of Dll is repressed

by the homeotic genes Ubx and abdA in the abdomen (VACHON et a/., 1992). Lack of expression

336

J. DEUTSCH : THE ORIGIN OF HEXAPODA

of Ubx , as in the bxd mutant, yields to the formation of an additional pair of legs, a weird fly

bearing four pairs of legs (BENDER et al., 1983, and references therein).

The absence of abdominal legs in Hexapoda is not such a straight rule as it seems at the

first glance. Some insect nymphs and larvae possess abdominal appendages. .An example is given

by the so-called “prolegs” of caterpillars. In the butterfly Precis coenia , the formation of these

prolegs has recently been studied (PANGANIBAN el al., 1994) . In the embryo, the Hox gene A nip

is unexpectedly expressed in a few patches of abdominal cells, where Ubx and abdA are no

longer expressed. This unusual Antp expression is correlated with the expression of Dll, and the

formation of the prolegs (WARREN et al, 1994). Hence, the presence of abdominal legs in

lepidopteran larvae is under the same genetic control that operates in the formation of thoracic

legs. In that case, the change results from a subtle and localized variation in the pattern of Hox

expression.

Another case of abdominal appendages in Hexapoda is the presence of abdominal styli in

adults machilids (Archeognatha) and silver-fishes (Zygentoma = Thysanura s. 5.). It is generally

admitted that machilid styli represent a primitive trait. “The abdominal styli of machilids are

generally regarded as remnants of telopodites” (BlTSCH, 1994) . Fossils support the homology of

these appendages with true “legs”. The abdominal styli of several extinct species are composed

of several articles (plurisegmented), sometimes followed by a claw. This morphology is quite

similar to thoracic legs (for a review, see BlTSCH, 1994).

The role of DU has been recently examined in two crustaceans, the branchiopod Artemia

and the malacostracan Mysidopsis. DU is expressed in every branch of the developing limb,

whether it is uniramous or biramous. The mode of expression of Dll and probably its function, as

known in the uniramous insect limb, thus also applies to biramous limbs. In contrast to insects, in

the pereionic limbs of Artemia, Dll is expressed in the same cells in which the Hox genes

Ubx/abdA are simultaneously expressed (PANGANIBAN et al, 1995). The anterior limit of

expression of Ubx/abdA coincides in Artemia with the transition from maxillae to pereiopods,

while its posterior limit in Mysidopsis corresponds to the transition from presence to absence of

pleopods. In addition, the anterior limit of its expression varies in different malacostracan species

studied with regard to the number of pereiopods transformed into maxillipedes (PATEL, 1995).

Three conclusions can be derived from these comparative developmental genetics analyses: i) Dll

plays the same role in the developing limb in Crustacea as in Insecta, and probably in other

Arthropoda (PANGANIBAN et al, 1995); ii) the Hox genes play a role in Crustacea as well as in

Insecta in directing the morphological diversity of limbs; and iii) contrary to Insecta, DU is not

repressed by IJbx abdA in Crustacea, and probably not regulated by any Hox gene.

EVOLUTIONARY SCENARIO

Summarizing these data, the following evolutionary scenario can be drawn.

i) The gross pattern of expression of Hox genes in Artemia , i.e. expression of Antp, Ubx and

abdA in the pereion, AbdB in the genital segments, and no expression of Hox genes in the pleon,

is primitive.

ii) Several times, various genetic mutations have occurred during the evolution of crustaceans,

affecting the regulation of the Hox genes. These produced changes in the limits of the expression

Source: MNHN. Paris

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

337

domains of Hox genes. They account, at least in part, for the morphological diversity of extant

and fossil Crustacea.

iii) One of these changes happened to make a distinction between the first three pereionic and

following segments, thus creating a “thorax” and an “abdomen” within the pregenital region. In

addition, at the same time or subsequently, subtle differentiation between the three thoracic

segments was generated These changes were fixed during the change from aquatic to terrestrial

life.

iv) Dll, the master gene in the morphogenesis of appendages, acquired the cis-acting regulatory

sequences that are a target for the products of the Hox genes. DU thus became integrated within

the panel of genes regulated by the homeotics. As a result, the abdominal legs were repressed.

This does not imply any important change of the Hox genes themselves or of their regulation,

accounting for the striking stability of the body plan within Hexapoda (including fossils).

The above hypotheses constitute a scenario, meaning that the temporal succession of the

proposed events in the order i) to iv) is part of the hypotheses.

TESTS OF THE SCENARIO AND OPEN QUESTIONS

Obviously, the present scenario needs more data in order to be supported, from both

phylogeny and molecular developmental genetics.

The first major open phylogenetic question is the relationship between Crustacea and

Hexapoda. Morphological, developmental and molecular data have to be collected and

considered in phylogenetic analyses in order to help resolve this important question.

As stressed above, the relationships between the different sub-classes and orders of the

Crustacea need to be clarified, by collecting more developmental genetic information on more

species. Although quite powerful, and more and more facilitated by the technological advances of

molecular biology, molecular genetics is costly in time and money. It is of major importance that

the species used as models in comparative developmental genetics should be selected on the basis

of their phylogenetic position. This would not impair in any way the critical requirement of

independence needed for phylogenetic tests of an evolutionary scenario (see GRANDCOLAS et al .,

this volume). Once obtained, the developmental genetic data could be drawn on an independently

derived phylogenetic tree.

More specifically, it is necessary to address the following questions :

To what extent does the pattern of expression of Hox genes as found in Artemia apply to

other Anostraca, to other Branchiopoda, to other members of “basal” groups of Crustacea

(“basal” taken here in the sense of “a lineage emerging early in evolution from the main branch”)?

To what extent is this pattern different from what is observed in Malacostraca? Since the

published data are incomplete, the differences reported could result from a difference in the stage

at which the larvae of the two crustaceans Anemia and MysiJopsis were observed, rather than to

a specific difference.

If the difference between Anemia and Malacostraca is confirmed, it would be of extreme

importance to look for the expression of Hox genes in the pereion and in the pleon in Crustacea

representative of other “basal” groups, in order to address the question whether this difference

338

J. DEUTSCH : THE ORIGIN OFHEXAPODA

correlates to greater development of muscles and nervous system in the pleon of Malacostraca as

compared to other Crustacea.

What is the pattern of expression of the Hox genes, and in particular abdAJUbx, in

members of more “basal” hexapod groups, such as Archeognatha and Collembola, rather than the

representatives in which it has been observed, i.e. in Zygentoma and Pterygota. In other words,

is this pattern an apomorphy of the clade Insecta, or could it be a extended to the whole

Hexapoda class?

What is the pattern of expression of DU in the larval abdomen of machilids, and is it

submitted to the same Hox control as found in other hexapods?

CONCLUSION

In the present work, I have proposed an evolutionary scenario on the origin of Hexapoda,

and suggested some guidelines to test it.

Some readers may think that this type of “gross” evolutionary question is not worth dealing

with. I have used this question as an example to illustrate the approach. But the same approach

could be applied to a variety of evolutionary problems at any level of taxonomy. In the

Hexapoda, evolutionary scenarios based on comparative developmental genetics can be drawn

about such questions as the origin of the pterygote radiation (see CARROLL, 1995; CARROLL el

a/., 1995) or the origin of the holometabolous radiation (see DEUTSCH, 1996). More specific

problems can also be addressed. The number and morphology of sex combs, located on the first

leg of males, is a differential character in Drosophilid species between montium and

me/anogasler groups. Not surprisingly, this character is genetically determined: a “montium-like”

mutant of D. melanogaster has been isolated (F. DOCQUIER, P. SANTAMARIA, and J. S.

Deutsch., in prep ). This example illustrates that developmental genetics might have something

to tell even at the sub-genus level.

Enhanced interaction between phylogenetic analysis and evolutionary developmental

genetics will not only provide more data to improve the robustness and/or consistency of the

proposed phylogenetic trees, (evolutionary patterns) but in addition may give an estimation of

the validity of evolutionary scenarios (processes).

ACKNOWLEDGEMENTS

I wish lo acknowledge the colleagues and friends who helped me during the preparation of my talk at the MNHN

symposium on "Phylogenetic lests of Evolutionary Scenarios” and during the writing of the present paper Philippe

Grandcolas, for inviting me to present a communication at the meeting, for kindly sharing his own paper before publication,

and lor suggestions on the manuscipt, Thierry Bourgoin for providing me with scientific literature and for discussions, Eric

Quebec and Yves Turquier for so many discussions; in addition, I am grateful to Charles and Gretchen Lambert’ who

made the etlon to read my manuscript in order to correct my English, and do it in such a way as they significantly improved it.

i-inatly, 1 am sincerely grateful to two anonymous reviewers for useful suggestions and even more for correcting some

blunders. Any possible other mistake and disputable ideas are mine.

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Panganiban, G., Sebring, A., Nagy, L. & Carroll, S., 1995. — The development of Crustacean limbs and the evolution of

Arthropods. Science, 270: 1363-1366.

Patel, N., 1995. — The evolution of arthropod segmentation and body patterning. In: P. Bazzicalupo, U. di Porzio, A.

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Vachon, G., Copen, B., Pfeifle, C., McGuffin, M. E., Botas, J. & Coien, S. M., 1992. — Homeotic genes of the Bithorax

complex repress limb development in the abdomen of the Drosophila embryo through the target gene Distal-less. Cell ,

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Warren, R. W., Nagy, L., Selegue, J., Gates, J. & Carroll, S., 1994. — Evolution of homeotic gene regulation and

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Source . MNHN. Paris

Linking Phylogenetic Systematics to Evolutionary Biology:

toward a Research Program in Biodiversity

Philippe Grandcolas, Joel Minet, Laure Desutter-Grandcolas,

Christophe Daugeron, Loic Matile & Thierry Bourgoin

E.P. 90 CNRS. Laboraloire d'Entomologie. Museum national d'Histoire naturelle.

45. me Buffon. 75005 Paris. France

"Les recherches d'histoire naturelle, mime celles qui ne

semblent etre que de pure et de vaine curiosite, peuvent avoir

des utilites tres reelles, qui sujjiroient pour les justifier

aupres de ceux memes qui voudroient qu 'on ne cherchdt que

des choses utiles, si avant de les blamer on avoit la patience

d'attendre que le temps eut appris les usages qu'on en peut

fa ire "

(DE REAUMUR. 1719)

As a matter of epilogue for a volume dealing with comparative studies, and although we

hope that the reader is (now) convinced of the usefulness of phylogenetics, we would like to

conclude in retrospection with the situation of systematics among life sciences.

This situation may be explained in the frame of evolutionary biology, because systematics

deals with the study of organisms with regard to their natural relationships which are

evolutionary patterns. Although self-evident, this matter of fact is often neglected. This oversight

as well as some current received wisdoms concerning systematics must be exposed because they

impede the realization of major syntheses and integrated studies in biological sciences.

Life sciences seem now on turn to be revolutionized by their two extremities. On one hand,

biological processes are more and more thoroughly analyzed using molecular techniques and a

single organism now includes virtually hundreds of wide research fields. On the other hand, we

better and better understand how to compare and infer relationships between organisms using

Grandcolas, P., Minet, J., Desutter-Grandcolas, L., Daugeron, C., Matile, L. & Bourgoin, T., 1997. —

Linking phylogenetic systematics to evolutionary biology: toward a research program in biodiversity In: Grandcolas, P.

(ed.), The Origin of Biodiversity in Insects: Phylogenetic Tests of Evolutionary Scenarios. Mem . Mus. natn. Hist, nat., 173

341-350. Paris ISBN : 2-85653-508-9.

Source MNHN, Paris

342

A RESEARCH PROGRAM IN BIODIVERSITY

modern phylogenetic methodology. Advances in these two extremities are the most recent

manifestation of a long-lasting epistemological dichotomy, general biology versus comparative

biology, “Investigations can seemingly inquire about either the uniformity of life or the diversity

of life, aspects that can be referred to as general biology and comparative biology, respectively”

(Nelson & Platnick, 1981).

Advances in general biology seem quite gradual at least with the continuous addition of

new technical means and conceptual tools, and the discovery of new biological structures, from

the organism to the cell, to the chromosome and to the gene and biomolecule. The increase of

knowledge in this gradualistic perspective is indeed exponential.

Advances in comparative biology have been more punctuated with the recent and definitely

new phylogenetics elaborated according to HENNIG's (1950, 1966) methodological principles,

following former conceptions dating back at least to eighteenth century. These principles brought

a total revolution in the definition of relationships, turning down both intuitive classifications and

unproper similarity algorithms. Organisms may now be compared with a clear reference to their

phylogenetic relationships - i.e. to their evolutionary history - and not only as different items

vaguely placed in an intuitive or misleading classification.

The main challenge of the next decades will be to unify biology by the implementation of a

research program aimed at connecting general and comparative biology (Fig. 1). It would not be

sound to only analyze and understand more and more processes in a few unrelated organisms

(e.g. Drosophila , Raltus, Homo , Arabidopsis, etc.), or to only produce tens of phylogenetic trees

and classifications for little-known organisms (Kellogg & SHAFFER, 1993). This challenge will

probably suffer resistance from a priori anthropocentric and utilitarian-centered views which

C om pa rative

Biology

General

B iology

Horn o

Rattus

Drosoph ila

Arabidopsis

I ig. 1. Connecting general and comparative biology in a same research program will make necessary to take into account

that lew model organisms are studied by general biology and that they should be combined in the frame of

phylogenetic relationships to be fully interprctable in the light of comparative biology and evolution.

have always been very common in science and have tried to constrain its development in a way

detrimental to both its usefulness and the increase in knowledge (e.g. DE Reaumur, 1719).

The famous aphorism “nothing makes sense in biology, except in the light of Evolution”

(DOBZHANSKY, 1973) is highly significant in this respect. We may paraphrase: nothing makes

sense in biology, except in the light of a phylogenetic system which permit to consider all

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

343

processes in a complete historical perspective. This is true indeed for all studies in biology, even

if some researchers often do not fully realize that their conclusions totally rely on the concept of

phylogenetic relationships: for example, many hypotheses of evolutionary convergence are

commonly accepted for two structures, two states or two processes without recognizing that

these hypotheses can only be substantiated by a genuine phylogenetic reference - we mean they

cannot be said substantiated by an old and intuitive classificatory scheme.

STUDYING EVOLUTION IN POPULATIONS OR EVOLUTION IN GLADES?

From the beginning, Evolution was perceived as a theory which needed to be substantiated

not only according to the observation of patterns but also according to assumptions about

processes at work (PERRIER, 1886). The promoters of the idea of evolution imagined processes

such as spontaneous generation and inheritance of acquired characters (Lamarck, 1809) or,

later, descent with modification and natural selection (Darwin, 1859) to explain the origin of

hierarchical, inclusive and ordered patterns they observed.

The rise of genetics and ecology at the beginning of our century confirmed the existence of

descent with modification and promoted natural selection as a major process in evolution.

Evolutionary biology became a science of process and interest for tokogenesis replaced interest

for phylogenesis (Tassy, 1991). Evidence for this fate is found in the assertion of some

evolutionists who have argued that the great epoch of systematics or phylogeny, in terms of

discovery, is the past, dating back to the eighteenth century, when the binominal nomenclature

(A,C)

(B)

(D)

A B C D I

Fig. 2. — Hie first scheme above summarizes the former procedure of explanation in evolutionary biolog)' (in an hypothetical

group [A, B, C, D]): processes (e.g. selective regime, reaction norm, heritability) and traditional taxonomic levels were

used to explain away patterns. The second scheme beneath summarizes the procedure of phylogenetic tests of

evolutionary scenarios: both patterns in clades and processes in populations or organisms are actually studied, and the

results are compared in a genuinely heuristic way.

and then the idea of evolution appeared (MAYR, 1982). The concept of natural selection, now

central to present evolutionary biology, has put the patterns in the shadow (Eldredgf, &

Cracraft, 1980), although the main promoter of natural selection, Charles Darwin himself,

clearly acknowledged the important duality of pattern and process (Dupuis, 1984, 1992).

344

A RESEARCH PROGRAM IN BIODIVERSITY

In this context, evolutionists focused on processes which were either extrapolated to

explain patterns in ad hoc narrations as nicely emphasized by ELDREDGE & CRACRAFT (1980), or

were combined with patterns in a same synthetic - we mean artificial - and pleasant explanation

of evolution ( e.g. Mayr, 1963) (Fig. 2, above). From this point of view, many evolutionary

studies were carried out on organisms and populations since the beginning of the century. These

studies obviously focused on the processes existing within organisms and populations and

extrapolated them back to the past macroevolutionary events. BROOKS & McLennan (1991)

concluded from a fair retrospective that an eclipse of true historical studies occurred in ecology

and ethology because of lack of phylogenetic and comparative studies. Indeed, most historical

studies were carried out by extrapolation and failed to analyze the past. This assertion does not

concern paleontological studies which deal per se with the past and suffer from another kind of

extrapolation, the hypotheses of actualism (NEL, 1997 in this volume).

Extrapolation of our knowledge to past and unknown phenomena is certainly an heuristic

means to propose provocative hypotheses but it is not a fair way to validate these hypotheses.

Extrapolation is in itself a model comprising not only factual knowledge but also many

unwarranted hypotheses (mainly hypotheses by analogy from the present to the past). Thus, we

need to study evolution both in clades and in populations. Evolutionary biology must not be

restricted to the study of only one of these fields, on pain of either ignoring the diversity of

processes and their respective roles, or being unable to generalize the role of well-known

processes to explain the diversity of life in itself.

THE NATURE OF SYSTEMATICS AND SOME RECEIVED WISDOMS

Systematics is useful in evolutionary biology because it is central to studies of evolutionary

patterns. But today it carries certainly an odd image in life sciences. After a great period of

discovery and importance a hundred of years ago, it has been considered aflwerwards by many

people as a marginal discipline in life sciences, a kind of narrative task whose goal is seen as to

give unpronounceable latin names to as many species as possible, thus perceived by many

researchers as “not modern science, not good science”. In this perspective, the systematist would

be only bound to identify specimens provided by other scientists who need names, and some have

added nowadays to the basic requirement - latin names - , a classification or a phylogenetic tree.

Let us abandon this incomplete image. In systematics as in any other science, data must be

collected first (field sampling of organisms), they must be described and analyzed (description of

taxa and phylogenetic inference), and interpreted (evolutionary histories drawn from

phylogenetic trees). It is this whole set of activities which can be used to answer scientific

questions concerning evolution. Systematics does not only provide people with names and

classifications - which are obviously useful - but also with a reference system in evolution

(phylogenetic trees). The reference system itself is not only a system for storing and retrieving

information concerning names, but also a very powerful means to draw evolutionary histories for

traits of interest (ELDREDGE & CRACRAFT, 1980).

Systematics - which was and which still is the science of evolutionary patterns - has been

revitalized these last decades by methodological advances (Hf.NNIG, 1950, 1966). it can now

generate refutable assumptions about evolution, which can be freed from evolutionary models

derived from population studies. Modern systematics is independent from these evolutionary

models because it only uses the principle of descent with modification (the minimal concept of

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

345

Evolution) to explain patterns, i.e. “aspects of the apparent orderliness of life” (ELDREDGE &

CRACRAFT, 1980: 1). At the opposite, population or organismic studies search for processes,

“mechanisms that generate these patterns” (ELDREDGE & CRACRAFT, 1980: 1).

This is the opportunity to reconcile both approaches in the study of evolution. Patterns and

processes must be studied in their respective domains - clades and populations - and be

compared afterwards to derive better-corroborated hypotheses about the past (Fig. 2).

In this perspective, several received wisdoms may be found in the literature that obscure

the actual role of systematics in today life sciences. These received wisdoms must be denounced

to fully allow integrated studies of evolution to develop, using systematics and population

biology.

Is there still something to search for at the taxonomic-organismic level?

Many speculations have been produced during these last years about the number of extant

species. Whatever may be the number of unknown taxa, it is obvious that many remain to be

found. A better question should be answered: do unknown taxa represent uninformative replica

of already known taxa or original and “useful” new taxa?

Most research scientists know that it is impossible to simply answer such a question “yes”

or “no”, because research is not a straightforward activity and wonderful results are often

provided which differ from original conceptions or research fields.

A valuable answer to this question may be twofold. First, the frame of knowledge is not

uniform: it is necessary to understand that past studies of biodiversity have not dealt randomly

with faunas and floras for two or three centuries: some places or organisms were sampled over

and over, some others were ignored. Important gaps in knowledge remain and must now be filled

up, if one wants to have a good estimate of the contents of biosphere. Many scientific disciplines

rely on such accurate estimates of these contents. Second, a prospective attempt may be done,

using retrospectives of recent periods: many problems of biology have been solved thanks to an

increase of knowledge of faunas and floras, for example when one taxon recently discovered

gives up “the solution”. It can be a fungus responsible for a local resistance against a dangerous

illness in trees. It can be an insect species corroborating a famous hypothesis concerning the

evolutionary process of social behavior For all these reasons, it is clearly necessary to search for

new taxa in faunas and floras.

However, these taxa must be searched for through modern and integrated field and

laboratory studies by experts in a scientific discipline and in a group of organisms (recording

ethological, ecological, biochemical, etc. information), and not essentially searched for in blind

mass-collecting as practiced during the last centuries or even still recently. It is only in this way

that scientific research can take rapidly benefit from systematics, also because the information

relevant to the question the investigator wants to answer is sampled together with the specimen

(CODDINGTON eta/., 1991).

Morpho-anatomy versus molecules?

New research fields opened out during these last decades in relation to outstanding

technical advances in molecular biology Consequently, enthusiastic professions of faith appeared

which predicted revolutions in the understanding of Evolution. Newly available tools appeared

especially powerful to people who simply forget that there already exist tools positively useful to

346

A RESEARCH PROGRAM IN BIODIVERSITY

reconstruct phytogenies and that already allow most available and robust phylogenetic

hypotheses to exist (morphology, anatomy, histology, etc.), as shown by the retrospective ot

SANDERSON et al. (1993). For example, for the period 1989-1991, more than 40% of published

phylogenies in high-standard journals were based on morphology.

It is still very common to read such kind of unfounded assertions: “A second reason for the

surge of interest in comparative studies is that phylogenetic relationships among extant

organisms are being estimated with increasing precision, largely as a result of advances in

molecular biology” (Harvey et al., 1996) or “During the last decade, [...]. Together with

improved phylogenies based on, for example, molecular sequence data, DNA hybridization, and

other molecular methods [. . .], it will lead to a dramatic increase in the power of comparative

studies for clarifying selection and evolution.” (ANDERSSON, 1994). This plea is however true for

the organisms which are by themselves structurally closer to molecules than to multicellular

organisms (viruses,... ).

As emphasized by WAGELE & WETZEL (1994) or PHILIPPE (1997), molecular data cannot

be the “only” or the “best” data which can be used to infer phylogenies, because these qualifiers

do not make sense a priori in science (NELSON, 1994). Assertions of a priori explanatory

contribution of any data set are misleading. For example, STEARNS (1992) asserted “Two key

advances were Hf.nnig's (1950) introduction of phylogenetic systematics (also called cladistics)

and molecular systematics, where the non-transcribed part of the genome provides data

independent of the confusing changes that evolution can produce in phenotypes”. The dichotomy

genotype/phenotype has nothing to do with phylogenetic methodology. For inferring

phylogenies, heritable characters must be used whatever their very nature. How could we know

a priori that evolution has produced more confusing changes in phenotypes than in genotypes in

our case study? The value a priori of these characters is by definition unknown each time and

cannot be extrapolated from one case study to another one.

In this perspective, molecular data are obviously very welcome to join the pool of other

data - which needs to be as large and relevant as possible - and can help us in a number of cases

to propose corroborated phylogenetic hypotheses (WENZEL, 1997 in this volume).

However, it is especially important not to throw out the baby with the bath water, and not

to abandon morpho-anatomical studies and to shift completely toward molecular studies. Both

studies are obviously necessary and complementary because we need to understand how both

morpho-anatomy and genome evolved, because we need to combine reasonably independent sets

of data and because we need the largest sample of data possible.

Are comparative studies too much speculative?

Many evolutionary biologists describe only the processes presently at work in populations.

This may lead one to believe that only direct or experimental observations can be used to

understand how evolution occurred because other observations such as comparative hypotheses

- the phylogenetic patterns - may seem a contrario too circumstantial. In this context,

extrapolations to the past evolution seem often correctly substantiated to many people, if they

are based on such present observations.

The key-word in this point of view is “extrapolation”. The most careful studies of present-

day processes must extrapolate to the past to generalize their results: we are unaware of one

study of populational or organismic evolutionary biology which does not make assumptions to

Source: MNHN, Paris

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

347

extrapolate to past evolutionary events. This is indeed a most interesting and significant part of

these studies, but the least substantiated.

As emphasized by one of us in the preface of this volume, these extrapolations are

conjectural and may become either sound hypotheses or gratuitous speculation, depending on

their refutability. Extrapolations can be refuted only if some independent patterns exist which

allow to test them. This test is feasible using phylogenetic patterns, which do not depend on

intentional assumptions of evolutionary processes. Phylogenetic patterns are the less gratuitous

and the more refutable reconstructions of the past, because we only need for inferring them the

basic hypothesis of descent with modification. Interaction between studies of present-day

processes and studies of past patterns can provide us with well-corroborated results.

In conclusion, comparative hypotheses are not specifically speculative. Indeed, they

prevent evolutionary hypotheses from being too much speculative.

Too many model organisms in too many studies?

To the eyes of practicioners of general biology, the plethora of taxonomic groups used by

comparative biologists may be taken as an impossible scientific challenge and an unreasonable

scattering of model organisms. This point of view is obviously related to an idiosyncratic

perception of science by people who need to develop scientific studies in one model because of

substantial technical feasibility constraints (KELLOGG & SHAFFER, 1993). For example,

developmental genetics deals with very few organisms (DEUTSCH, 1997 in this volume).

Comparative biology has not to cope with these limitations. On the contrary, comparisons by

homology and by analogy are the very nature of comparative biology (NELSON, 1970; LORENZ,

1974). It is thus essential to increase the number of sampled clades used in comparative biology

to test the generality of evolutionary patterns as far as possible. But these models must be

carefully chosen to answer the questions of interest. It is not the number but the a priori quality

of these models which has to be controlled (GRANDCOLAS et al., 1997 in this volume).

Is the time scale of evolution compatible with phylogenetics and the sampling of biodiversity?

Famous studies of processes in populations (e.g. DOBZHANSKY, 1970; WHITE, 1954) have

tied down the idea that evolution is generally rapid, except for a few relict species. Thus,

sampling the biodiversity may be seen as an impossible challenge also for this reason: what is the

need for describing species less rapidly than they appear and disappear?

First, some biologists studying processes have themselves considered that species may be

relatively long-lived; for example, DOBZHANSKY et al. (1977) cited estimates ranging between

50,000 years and 1,000,000 years. Actually, many paleontological works have shown that

present-day taxa may be very ancient or that, more generally, species may be relatively long-lived

(for example, in insects, BRUNDIN, 1988, MATILE, 1990, 1997 in this volume, or in mammals,

Jaeger & FIartenbf.RGER, 1989). Specifically, paleontology and comparative biology can show

that the preconceived idea of necessarily rapid evolution is not generally true: biogeographers

and paleontologists have documented that the present faunas include both recent and ancient

stocks, the most ancient dating back to the Cenozoic or even to the Mesozoic. This is another

example of misconceptions related to the only care of studies in general biology.

Generalizations may thus be false either because they are based on too few indep indent

case studies or because they are based on a priori and totally speculative ideas. For example,

Source. MNHN. Paris

348

A RESE/IRCH PROGRAM IN BIODIVERSITY

particular models of evolution have been hypothesized under which some kinds of phylogenetic

reconstructions are flawed ( e.g. FELSENSTEIN, 1978; FRUMHOFF & REEVE, 1988), but these

models of evolution are impossible to assess a priori right or wrong in a particular case, i.e. prior

to any phylogenetic reconstruction (see for example CARPENTER, 1997, and GRANDCOLAS el al.,

1997, both in this volume). So their usefulness is nil.

Biodiversity: what's in a word?

The concept of Biodiversity has nowadays a central position among scientific and political

debates and policies. There are many different claims for its restriction to an organismic versus a

genetic or a molecular significance, or to process versus pattern viewpoint. In our mind, the

origin, maintenance and loss of biodiversity will be respectively better-known or prevented

thanks to a high “biodiversity” of research scientists and scientific approaches.

The “biodiversity” of approaches should respect the natural hierarchy of research fields.

What could be the meaning of genetic or molecular approaches without any population or

organismic approaches (Barbault, 1988) and what could be the meaning of all these

approaches without any phylogenetic framework? We could add, without any appropriate and

recently corroborated phylogenetic framework.

As argued by DUPUIS (1992), this framework is not only a database system in which taxa

and processes are stored and may be retrieved. This last view has been popularized because it

emphasizes the most immediate and technological utility of systematics: identification and

classification. No more systematists, no more identifications or classifications! This could be the

immediate prejudicial effect that disappearance of systematics could have (e.g. WILSON, 1971;

S.A. 2000, 1994).

But the phylogenetic framework is also an explanatory system which permits to test the

macroevolutionary extrapolation of present-day processes and an heuristic system which permits

to propose new research directions (Janvier, 1984; PACKER, 1997 in this volume). In this way,

phylogenetic systematics is a federating discipline and framework which connects all parts of life

sciences and generates a research program in biodiversity.

ACKNOWLEDGEMENTS

We wish to thank Pierre Deleporte, Daniel Goujet, Judith Najt, Jean-Marc Thibalid, Wanda Weiner, and John

Wenzel lor discussions and comments on the manuscript. The authors are however the only persons responsible for the ideas

presented in this paper

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Nelson, G. F., 1994. — Homology and systematics. In\ B. K. Hall, Homology: The Hierarchical Basis for Comparative

Biology. Academic Press: 101-149.

Nelson, G. & Platnick, N., 1981. — Systematics and Biogeography, Cladistics and Vicariance. New York, Columbia

University Press: 1-567.

Packer, L., 1997. — The relevance of phylogenetic systematics to biology: examples from medicine and behavioral ecology.

In: P. Grandcolas, The Origin of Biodiversity in bisects: Phylogenetic Tests of Evolutionary Scenarios. Memoires du

Museum national d'Histoire naturelle, 173: 11-29.

Perrier, E., 1886. — Im philosophie zoologique avant Darwin. Paris, Felix Alcan: 1-292.

Philippe, H., 1997. — Interet et limites des phylogenies moleculaires. Dossier Pour La Science, 14: 84-87.

Reaumur, R. A. F. de, 1719. — Histoire des guespes. Histoire de l'Academie Royale des Sciences: 1-230.

S.A. 2000, 1994. — Systematics Agenda 2000. Charting the Biosphere. Technical Report. SA 2000: 1-34.

Sanderson, M. J., Baldwin, B. G., Bharathan, G., Campbell, C. S., Von Dohlen, C., Ferguson, D., Porter, J. M,

Wojciechowski, M. F. & Donoghue, M. J. 1993. — The growth of phylogenetic information and the need for a

phylogenetic data base. Systematic Biology , 42: 562-568.

Stearns, S. C., 1992. — The Evolution of Life Histories. Oxford, Oxford University Press: 1-249.

Tassy, P., 1991. — L'arbre a remonter le temps. Paris, Christian Bourgeois: 1-352.

WAgele, J. W. & Wetzel, R., 1994. — Nucleic acid sequence data are not per se reliable for inference of phylogenies.

Journal of Natural History , 28: 749-761.

Wenzel, J. W., 1997. — When is a phylogenetic test good enough? In: P. Grandcolas, 'Hie Origin of Biodiversity in Insects:

Phylogenetic 1 ests of Evolutionary Scenarios. Memoires du Museum national d'Histoire naturelle, 173. 31-45.

White, M., 1954. — Animal Cytology and Evolution. Cambridge, Cambridge University Press: 1-454.

Wilson, E. O., 1971. — The plight of taxonomy. Ecology , 52: 741.

Source: MNHN . Paris

SUBJECT INDEX

actualism (see also extrapolation) 9, 305, 315, 326

ad hoc hypotheses 9, 10, 31, 55 sq., 110, 116, 140, 146,

152,344

adaptation (see also coadaptation, exaptation. radiation)

10, 12, 14, 32, 39 sq., 48, 54, 60 sq., 65, 68, 74, 87,

94, 104 sq., 119, 130, 138, 139, 145, 152, 155, 157,

163, 171, 173 sq., 199, 203 sq., 214 sq., 222 sq., 242,

255,262 sq., 299, 333, 335

aggressive behavior 138, 145 sq., 157, 184, 186 sq., 244

alarm behavior (see also defensive or anti-predator

behavior) 231,235 sq., 242 sq.

analogy (see also homoplasy, pattern) 10, 55, 61,231,

234, 244 sq., 344, 347

ancestor 13, 15, 26, 42, 86 sq., 91,94, 97, 104, 106, 114,

125, 130, 132, 139 sq., 146, 150, 153, 155, 174 sq.,

224, 226, 231 sq., 237 sq., 254 sq., 259 sq., 268, 274,

306, 329 sq.

anti-predator behavior (see also alarm or defensive

behavior) 234, 239, 246 sq.

ant-attendance (see also trophobiosis) 109-124

apomorphy (see also derivative load, innovation) 34 sq.,

39-41,67, 74, 98, 111, 116, 119, 139, 164 sq., 195,’

218 sq., 232 sq., 240, 245, 251,254 sq., 262 sq., 267,

273, 277, 293, 299 sq., 305 sq., 314, 321-325. 333,

338

aquatic (habitat, see also marine) 97, 100, 253, 255, 264,

268,334, 337

attribute 18, 24 sq., 62 sq., 91 sq., 100, 106, 109, 111,

113 sq., 126 sq., 140 sq., 163 sq., 169, 190 sq., 205

sq., 234 sq., 273, 280, 284, 305 sq.

behavior: see aggressive alarm, anti-predator, defensive,

feeding, mating, sessile, singing, social behavior

behavior use in phylogenetic analysis 32, 39, 64, 141

biodiversity 9, 110, 341, 345, 347 sq.

biogeography 10, 32, 118, 234, 273 sq., 288, 319, 347

biome (see also desert, forest, savanna) 125 sq., 235 sq.

bootstrapping 31, 33 sq., 85

Bremer support 34

Brownian motion 73, 77 sq., 81 sq., 87 sq.

cave habitat 92, 186, 200, 235, 280, 282

causation (see also coadaptation) 14, 109 sq.

character: see apomorphy, coding, DNA, function,

heterobathmv homoplasy, lability, missing data,

morpho-anatomy, plesiomorphy, polarity, RNA,

sampling, unknown character

circularity 31, 35, 37 sq., 40, 63, 119, 140

cladistics ( see also phylogenetic analysis) 26, 31,35, 39

sq., 43, 53,56, 59 sq., 74, 141, 146. 152, 204 sq.,

232, 237, 325

cladogenesis 66, 128, 130, 140, 157

classification (see also systematics) 26, 180, 217, 244,

256,342,344,348

clock (evolutionary', see also model) 59, 237

coadaptation 65 sq., 226

cocoon (see also silk, web) 257 sq., 280 sq.

coding (character) 11, 13, 18 sq., 33, 39, 136, 143,

146 sq.

coevolution 59, 78

communication (acoustic, see also singing behavior, or

others) 183-202, 236,242, 244

comparative biology 9-10, 11,53-71,73 sq., 94, 109,

140, 158, 200,341-349

congruence 9, 31, 35, 54, 62 sq., 141, 307

consensus (tree) 24, 31, 33 sq., 85, 111, 146 sq., 218, 221

constraint (phylogenetic, see also inertia) 74, 87, 119,

255

convergence (evolutionary, see also analogv, homoplasv)

9,35,40,65, 139, 172,240,343

coprophagy (see also dung, food choice, diet) 125, 281

corroboration (see also test) 22. 54, 56, 60-61,66-67,

147, 225

Cretaceous 16, 117, 226, 257, 260-261,268, 273. 288,

325

defensive behavior (see also alarm or anti-predator

behavior) 205, 225, 246-247

derivative load 240

development: see eclosion, ontogeny

descent with modification ( see also heritability) 9, 32, 3;),

55, 62, 330, 343-345

desert 92, 132, 204-205, 235-237

detritophagy (see also saprophagy) 260

diet (see also food choice, coprophagy, detritophagy,

fungivory, nectarivory, phytophagy, predation,

saprophagy, xvlophagy) 38, 126, 130, 132, 236-237,

242,273,281,284,294-295

dimorphism 91, 101, 105

DNA (see also molecular biology, RNA) 33, 37-38, 135

144, 146-148, 234,256, 346

dung (see also coprophagy) 125-134

eclosion (see also egg, oviposition) 253, 263

effect (phylogenetic) 73-90

egg (see also eclosion, oviposition) 92, 101, 126, 155,

205-206,213-216,259-260

Source:

352

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

Eocene 132, 288

eusociality (see also social behavior) 9, 11-29, 234, 244-

245

evolution: see adaptation, clock, coevolution, gradual - ,

lability, radiation, regression, scenario, selection,

stability, trend

exaptation 65-66, 94, 172-175, 244-245, 255, 263, 280

explanation (power of) 9, 37, 41,49, 56-59, 110, 343

extinction 94, 141

extrapolation (see also actualism) 9-10, 54, 57, 59, 319,

343-348

feasibility (research) 64, 347

feeding behavior: see diet, food choice

flightlessness: see “oogenesis-flight” syndrome, wing

food choice (see also diet, coprophagy, detritophagy,

fungivory, nectarivory, phytophagy, predation,

saprophagv, xylophagy) 99, 101, 105, 113, 1 16, 119,

125-134, 136, 138, 163-182.203,208,210,214,217,

222-227, 255, 259-260, 273-303

forest 125-134, 204, 235, 237, 240, 242, 282, 284, 321

fossil (see also paleontology) 13, 55, 59, 117, 169, 226-

227, 253, 257, 260-262, 267, 273-274, 288-296, 305-

327, 336-337

function (character) 12, 63, 65, 119, 139, 169, 171, 174-

175, 184,263-265, 305,319, 332

fungivory (see also sporophagy) 259, 273-303

gall (-making insects) 205, 214-215, 222, 226, 259. 280

general biology 55, 57, 341-343, 347

genetics (see also genotype, tokogenesis) 9, 13, 18, 32,

329-340, 343, 348

genotype (see also genetics) 346

gland (allomonal, pheromonal, wax-secreting) 182 187

200, 206, 210, 212-214, 216. 225, 231,235-237, 239

243,246,251,262

gradual (evolution) 185, 314

grass (see also savanna) 111, 125. 128, 130, 132, 203

205,214, 222-225, 280

gregariousness (see also social behavior) 109. 121 200

231-252

ground (see also litter, soil, sand) 9, 100, 109, 111-118.

168, 170, 172, 205, 210, 222, 253, 258-260

groundplan 245, 254-259, 262, 264-265, 267, 276, 301

habitat (see also aquatic - , branch, cave, grass, leaf,

litter, marine - , root, sand, wood) 87, 91-92, 94* 100-

104, 106, 109-124, 125-134, 168, 183. 186, 189 193

199-200, 203-205, 222-227, 234-246, 253, 256-257

259-260, 264, 268

heritability (see also descent with modification) 62-63,

343,346

heterobathmy 232

heuristic (power) 9, 56-57-59, 232

homology (see also pattern) 19, 39, 41,62-64, 111, 119,

127, 139-141, 163, 174-175, 179, 190,213,225,234,

246, 276, 294, 299, 306-307, 332, 334-336, 347

homoplasy (see also analogy, convergence, reversal) 9-10,

22, 31, 33, 36, 41,62, 65-66, 139, 183, 186, 199-200,

251-252, 263, 266, 277, 307, 314, 321,322-325

host (of parasite) 9, 15-16, 73, 78, 80-82, 85-86, 135-136-

139, 145, 150, 152, 155, 157,281

independence (logical) 31, 39-40, 55, 68, 73, 75, 88, 180,

200,337

independent contrasts method 73, 75, 77-88

inertia (phylogenetic, see also constraint) 59, 64, 67

ingroup 9, 13, 18, 24, 35, 53, 58, 64-68, 116, 143, 170,

309

innovation (see also apomorphv) 11, 26-27, 92, 130, 253,

263-264

inquilinism (see also parasitism) 100, 135-157

interattraction (see also social behavior) 244

Jurassic 170, 226, 257, 260, 267-268, 274, 288, 290, 293,

296

lability (evolutionary) 9, 140, 150, 152, 186

life cycle (see also reproduction) 203, 205, 215, 226

likelihood 36, 61

litter (see also ground, soil) 100, 199, 222, 226-227, 238,

240, 243,259, 276, 280-281

mating behavior (see also nuptial gift, reproduction) 9,

99, 101, 104, 163-180, 183-185, 199,210,212-213

215, 224

marine (habitat, see also aquatic) 91, 100, 105, 321

maximum likelihood analysis 31, 36, 38, 41,306

Miocene 132, 290-293, 296

missing data (see also unknown character) 59, 150 205

307

model (formulation) 9-10, 13, 36-38,47-52, 53-54, 56-

61,64, 67-68, 73, 75, 77-78, 82, 88, 110, 140J52,

163, 170-172, 175, 179-180, 183, 188, 190, 193, 195-

198, 234,244,247

model organisms 100, 121, 330, 342, 347

Source:

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

353

modeling: see model

molecular biology (see also DNA, RNA) 13, 25, 38. 49,

59, 79, 84, 111, 135-136, 144, 146-147, 152,205,

247, 254, 329-331, 333, 337, 341,345-346, 348

morpho-anatomv 274, 345-346

mutualism (see also trophobiosis) 9, 109, 111-114, 119

121

mycetophagy: see fungivory, sporophagy

nectarivory 167-168

neighbor joining 36

nest (of social insect) 21-22, 24-25, 91, 112, 121, 135-

139, 145, 152-153,217,231,235,237-238, 240

niche (ecological) 59. 87, 99, 105, 125, 128, 130

null hypothesis or model (see also test) 10, 40, 47, 49,

51,68, 73, 76, 80-81, 148

nuptial gift 164, 168, 172, 177

Oligocene 288

“oogenesis-flight" syndrome 92, 101, 105

ontogeny 93, 101,259-260, 330

outgroup (see also polarity') 140, 255, 306

oviposition (see also egg) 208, 214-215, 226, 240, 257

259-261

paleontology (see also fossil) 305, 347

parallelism (see also convergence) 265, 332

paraphyly 102, 118, 127, 142, 164, 166,219,232.268,

274-275, 333

parasitism (see also inquilinism) 40, 91, 102, 106 135-

161, 199, 203-204

parsimony 9, 31, 33-40, 53, 55, 58-60, 68, 74, 116, 121

150,204,314

pattern (see also cladogenesis, convergence, parallelism,

polarity, reversal) 9, 11, 53-71,75, 91, 94, 101, 104-

106, 110, 139, 164, 180, 183, 186, 189, 200,231,

247, 254, 338, 343-344, 346, 348

Permian 117, 226, 266-267

phenotype 9, 74, 77, 82, 346

pheromone 42, 193, 235, 239, 241

phylogenetic analysis: see apomorphy, cladi sties,

heterobathmy, ingroup, monophyly, outgroup,

paraphyly, parsimony, plesiomorphy, polarity, relict

phytophagy (see also, diet, food choice) 100, 114. 117,

204, 259, 276, 281

plant: see grass, root, wood

plasticity^ 64

plesiomorphy 61,67, 109, 119, 141, 170, 172, 176, 195,

216, 232, 254-255, 266, 274, 287, 314, 321, 323

polarity (character, see also outgroup) 9, 12-14, 18-20,

26,60, 65, 116, 139-140, 152, 157, 170, 183, 195,

198, 204,307,314,322-324

polymorphism (character) 11, 17-20, 22, 24-27, 91-107,

113, 145-146, 150, 164, 199,234, 309-310

polytomy 35, 75

population biology 9, 13, 17-18, 22, 27, 48, 57, 60-61,

68, 74,91-92,97, 101

preadaptation: see exaptation

predation (see also food choice, diet, anti-predator or

defensive behavior) 9, 103, 119, 135, 138-139, 145-

146, 157, 163, 167-169, 171-172, 174, 183, 186, 189,

193, 199, 204, 217,235, 243-244, 273-274, 281-284,

288,290-291,294-295

prediction (power of) 9, 13, 16, 33,41,49-51, 53, 56-59,

67, 92, 101-102, 104, 152, 183, 189, 190, 195, 198-

199, 234,310

probability 9, 34, 37, 43, 66, 83, 152, 305-327

“primitive" taxon 231-232, 234

process (see also adaptation, coadaptation, coevolution,

exaptation, radiation) 9, 31, 32, 36, 37,42, 48, 50,

53-71,74, 87, 105-106, 110, 116, 139, 171, 199, 200,

231-232, 244,330, 338, 341-349

radiation 66, 118, 130, 140, 157, 223, 226, 330, 338

reconstruction (of evolution) 9-10, 14.33,36,37 40 55

58, 60-61,68, 74, 94, 171,347

reference system (systematics as) 342, 344, 348

refutation (see also test) 54, 56, 57, 60-61,67, 225

regression (evolutionary) 195, 264

relic taxon (geographically) 321

relict taxon (phylogenetically) 67, 171,247, 347

reproduction (see also egg, mating behavior, nuptial gift,

oviposition) 67, 103, 155, 184,245

reproductive success 138, 203, 225

reversal (see also homoplasy) 9, 20, 22, 35, 64-65, 98,

150, 183, 185-186, 190, 193-194, 198,219,238, 260.

266,287

richness (specific) 73, 78, 80, 85-86, 88, 226

RNA (see also DNA, molecular biology) 41, 136, 234

robustness (of phylogenetic tree) 54, 59, 338

role: see function

root (plant) 111,116, 203-204, 208, 210, 214, 222, 226

227, 259, 280

sampling (taxon or character) 11, 14-15, 22, 24, 33, 39,

42, 59, 64, 75, 78, 85, 88, 198, 237, 241,245, 344-

348

sand 208,210,235,237-239

saprophagy (see also detritophagy) 236-237, 276, 282

savanna 125-134

scenario (evolutionary) 9, 13, 26, 31-32, 39, 54, 60, 87,

103-104, 106, 110, 133, 135, 137, 140,189, 204. 329-

330. 338

Source

354

PHYLOGENETIC TESTS OF EVOLUTIONARY SCENARIOS

seasonal (climate) 91-92, 101, 104, 106, 138, 153, 242, W

selection (natural) 9, 11-12, 14, 48, 74, 77, 82, 87, 94,

104-105, 119,174, 179, 244,343

selection (sexual) 74, 77, 180

selective value or pressure: see selection

sessile behavior 109, 121,225

silk (see also cocoon, web) 172, 253, 259, 260-262, 268,

273, 276, 280-281,283-284, 286, 288, 291,293, 293

singing behavior (see also communication) 183-202

size (body) 24, 73, 78, 80, 87, 128, 130, 132, 226

size (ingroup): see ingroup

social behavior (see also eusocialitv, gregariousness,

subsociality) 9, 11-29, 109, 121, 135-161,231-252

solitary way of life 11, 17-27, 235, 238

soil (see also litter, ground) 205, 208, 210, 215, 227, 253,

255,257, 259-261,264,268

speciation 276, 280

sporophagy (see also fungivorv) 273-274, 276, 280-281,

283-284, 289, 294, 296

stability (evolutionary) 9, 67, 337

stability (habitat durational) 91-107

statistics (see also type of error, bootstrapping, Bremer

support) 9, 26, 31, 34, 36-37, 40-42, 49-50, 54, 59,

61,64-68, 73-74,78,81,94, 110

subsociality' (see also social behavior) 9, 109, 119, 121.

231-252

successive approximations weighting 18, 19, 24, 31, 37

subterranean life: see cave habitat

symbiosis 232, 234, 236, 237, 240, 245-247

svstematics (see also cladistics, classification,

phylogenetic analysis, reference system) 11-12, 32,

56, 180, 267, 341-349

web (see also cocoon, silk) 11-12, 14, 172, 253, 263,

273-303

wing (see also “oogenesis-flight'’ syndrome) 21-22, 91-

107, 184, 187, 217-218, 225-226, 231,235-236, 241,

265, 267-268, 300-303, 332, 334

wood (see also xvlophagy) 25, 234, 240-241,276, 280-

282

xylophagy (see also wood) 232-246, 280-282

taxon: see primitive - , sampling

test (of hypothesis, see also null hypothesis) 9, 11-12, 14-

18, 26, 31-45, 48-49, 53-71,73, 75-76, 141,204, 343,

346

tokogenesis (see also genetics) 141, 343

total evidence (analysis) 13, 18, 23-24, 39, 62, 146, 234

trait (see also attribute, character) 62-63, 141

tree (phylogenetic): see bootstrapping, Bremer support,

polytomy

trend (evolutionary) 73, 75, 81-88, 226, 244

trophobiosis (see also ant-attendance) 109-124

type of error (I or II) in tests 40, 73, 75-76

[biblouI

\MLSF ; JM f

\PAfttS,

unknown character (see also missing data) 59, 205, 305-

327

Remerciements aux rapporteurs / Acknowledgements to referees

La Redaction tient ii remercicr lesexperts exterieurs au Museum national d’Histoire naturelle dont les noms suivent, d'avoir bien voulu

contribuer, avec les rapporteurs de 1 Etabhssement, a revaluation des manuscrits (1988-1997) :

MdmofreTdu fo "° Wing re f eree * who - wi,h Museum referees, have reviewed papers submilled in the

Adkison D.

Macon

U. S. A.

Afzelius Bjorn

Stockholm

Su£de

Akesson Beni 1

Goteborg

SuSde

Amiard Jean-Claude

Nantes

France

Andres H.

Hambourg

Allemagne

Baba K.

Kumamoto

Japon

Bachelet Guy

Arcachon

France

Bachmann G H.

Bally A. W.

Halle-Wittenberg

Houston

Allemaagne

U. S. A.

Baud C. A.

Geneve

Suisse

Bellan Gerard

Marseille

France

Ben-Eliahu Nechama

Jerusalem

Israel

Bergc.ren M

Fiskebackskil

Su&de

Bernet-Rollande M. C.

Puteaux

France

Bernot L.

Anthony

France

Bernoulli D

Zurich

Suisse

Berti Nicole

Paris

France

Bertotti G.

Amsterdam

Pays-Bas

Bessereau Genevieve

Rueil-Malmaison

France

Best M.

Leiden

Pays-Bas

Bhaud Michel

Banyuls-sur-Mer

France

Blake James A.

Woods-Hole

U. S. A.

Boss K

Harvard

U. S. A

Bourdon R.

Roscoff

France

BourliEre F.

Paris

France

Bourseau J.P.

Villeurbanne

France

Bouroullec J.

Pau

France

Bresson F.

Paris

France

Brosset A.

Paris

France

Bruce Alexander J

Helensvale

Australie

Burke Robert D.

Victoria

Canada

Butler P. M

Surrey

Grande-Bretagne

Butman Cheryl Ann

Woods-Hole

U. S. A.

Calde D.

Toronto

Canada

Garrick Frank

Brisbane

Australie

Cambefort Yves

Paris

France

Cassagneau Paul

Toulouse

France

Castelli Alberto

Modena

Italie

Chace F. A

Washington

U. S. A.

Charest P.

Quebec

Canada

Cherix Daniel

Lausanne

Suisse

Clark P

Londres

Grande-Bretagne

Cloetingh S.

Amsterdam

Pays-Bas

Coan E.

Palo Alto

U. S. A.

Combes C.

Perpignan

France

Cornelius P.

Londres

Grande-Bretagne

Cornudella Lluis

Barcelona

Espagne

CUZIN-ROUDY J.

Villefranche-sur-Mer

France

Davie P

Brisbane

Australie

De Broyer C.

Bruxelles

Belgique

Deharveng Louis

Toulouse

France

DesbruyEres Daniel

Brest

France

Dhainaut Andre

Villeneuve d’Ascq

France

Dorresteun Adriaan

Dreux P.

Mayenee

Paris

Allemagne

France

Duchene Jean-Claude

Banyuls-sur-Mer

France

Duffels J P.

Amsterdam

Pays-Bas

Dupuis Y

Chatenay Malabry

France

Eibye-Jacobsen Danny

Copenhague

Dane mark

Eldredge L. L.

Hawaii

U. S. A.

Fain A

Bruxelles

Belgique

Fauchald Kristian

Washington

U. S. A.

Fischer Albrecht

Mayence

Allemagne

Fitzhugh Kirk

Los Angeles

U. S. A

Fleury Anne

Orsay

France

Floret J. J.

Paris

France

Forey P. L.

Londres

Grande-Bretagne

Fournier Judith

Ottawa

Canada

Francois Y.

Paris

France

Fransen C.

Leiden

Hollande

Gagne R

Washington

U. S. A.

Gambi M. Cristina

Napoli

ltalie i

GEmuJ. M.

Bail leu 1

France

Gentil Frank

Roscoff

France

George David

Londres

Grande-Bretagne

Giangrande Adriana

Lecce

Italie »•

Gibbs Peter E.

Plymouth

Grande-Bretagne

Gillet Patrick

Angers

France

Glasby Chris

Canberra

Australie

GlEmarec Michel

Brest

France

Goerke Helmut

Bremerhaven

Allemagne

Gooday A. J

Surrey

Grande-Bretagne

Gorin G.

Genfcve

Suisse

Grasshoff M.

Frankfurt

Allemagne

Grassle Frederick

New Brunswick

Canada

Grassle Judith

New Brunswick

Canada

Gruet Yves

Nantes

France

Guglielmo L.

Messina

Italie

Guillaumet J. L.

Caen

France

Gunzenhauser B.

Zurich

Suisse

Hamley Timothy

Brisbane

Australie

HARDEGEJorg Detelf

Oldenburg

Allemagne

Hayward P J.

Swansea

Grande-Bretagne

Healy John

Brisbane

Australie

Hensley D. A.

Puerto Rico

U. S. A.

Hilbig Brigitte

Massachusetts

U. S. A.

Hodgson Alan

Grahamstown

Afrique du Sud

Holte Boerge

Tromsoe

Norv&ge

Holthuis L. B

Leiden

Hollande

Hooper J. N. A.

Brisbane

Australie

Horvath Frank

Budapest

Hongrie

Hove Harry Ten

Amsterdam

Pays-Bas

Hutchings Patricia

Sydney

Australie

Ingrisch S.

Frankfurt

Allemagne

Jenkins Farish

Cambridge

USA

Jouin-Toulmond Claude

Paris

France

Jordan P

Solothurn

Suisse

Kasinsky Harold E.

Vancouver

Canada

Kendall Michael

Plymouth

Grande-Bretagne

Kensley B

Washington

U. S. A.

Kielan-Jaworowska Z

Oslo

Norv&ge

KlLBURN R

Pietermaritzburg

Afrique du Sud

Knight-Jones Phyllis

Swansea

Grande-Bretagne

Knight-Jones Wyn

Swansea

Grande-Bretagne

Kohn A

Seattle

U.S. A.

Komai T.

Chiba

Japon

KrantzG. W

Corvallis

U. S. A.

Kudenov Jerry D.

Alaska

U S. A.

LagardEre J.-P.

La Rochelle

France

Lana Paulo Da Cunha

Parana

Brasil

Laubier Lucien

Paris

France

Laubscher HP

Bale

Suisse

Laverde-Castillo J. J. A

Bogota

Colombie

Le Tendre L.

Courbevoie

France

LegayJ. M.

Villeurbanne

France

Lemaitre R.

Washington

U.S.A.

Levin Lisa A

La Jolla

U. S. A.

Lovelock P E R.

La Hague

Pays-Bas

Mackie Andrew

Cardiff

Grande-Bretagne

MacLaughlin P

Anacortes

USA.

MacPherson E.

Barcelona

Espagne

Manning R

Washington

U. S. A

Marshall B

Wellington

Nouvclle-Zdande

Mascle Alain

Rueil-Malmaison

France

Mauchline J

Oban

Grande-Bretagne

Maurer Don

Long Beach

U. S. A.

Maxwell P.

Waimate

Nouvelle-Z£lande

McAlpineJ. F.

Ottawa

Canada

McKenna M.

New York

U. S. A.

McLaughlin P

Washington

U. S. A.

Meistrich Marvin L.

Houston

U. S. A

Messing Charles

Dania

U.S.A.

Mettam Chris

Cardiff

Grande-Bretagne

Muir Alexander Ian

Londres

Grande-Bretagne

Nagel P

Saarbriicken

Allemagne

Newman W. A

San Diego

U. S. A

Nc. Peter

Singapore

Malaisie

Noel R

Pau

France

Oliva Rafael

Barcelona

Espagne

Olive Peter James William

Tyne

Grande-Bretagne

Orousset Jean

Paris

France

Paterson Gordon L. J

Londres

Grande-Bretagne

Patterson C

Londres

Grande-Bretagne

Paxton Hannelore

North Ryde

Australie

Perez Farfante I

Washington

U. S. A

Perkins Thomas H

Saint Petersburg

U.S A.

Perthuisot J P.

Nantes

France

Petersen Mary E.

Copenhague

Danemark

Petti bone Marian H

Washington

U. S. A

Peyrot-Clausade M

Marseille

France

Pleuel Fredrik

Stockholm

Su£de

Poccia Dominic L.

Amherst

U.S.A.

POCKLINGTON Patricia

Halifax

Canada

PONTIER J.

Villeurbanne

France

Poor G.

Victoria

Australie

Puig H.

Paris

France

Purschke Giinter

Osnabruck

Allemagne

PUTHZ V.

Schlitz

Allemagne

Raikova Olga

Saini-P6tersbourg

Russie

Ramil F.

Vigo

Espagne

Reish Donald J.

Long Beach

U. S. A

Rentz D. C R

Canberra

Australie

Richer de Forges B

Noumea

Nouvelle-Calddonie

Rieman F

Bremerhaven

Allemagne

Roure Francois

Rueil-Malmaison

France

Rouse Greg

Washington

U. S. A.

San Martin Guillermo

Madrid

Espagne

Tudge Christopher

Brisbane

Australie

Sarda Rafael

Blanes

Espagne

Vacelet J.

Marseille

France

Savage D. E.

Berkeley

U. S. A.

Van Ameron H. W. J.

Krefeld

Allemagne

Schmid M.

Paris

France

VanSoest R. W. M

Amsterdam

Hollandc

Schmid Stefan M

Bale

Suisse

Vickery Vernon R.

Ste-Anne-de-Bellevue

Canada

Schroeder Paul

Pullmann

U. S. A

Vokes E.

New Orleans

U. S A.

Sen wander M

La Hague

Pays-Bas

Vovelle Jean

Paris

France

Scott A. C.

Surrey

Grande-Bretagne

Vul M. A.

Lvov

Ukraine

Sibuet Myriam

Brest

France

Wagele J. W.

Bielefeld

Allemagne

SlGVALDADOTTIR Elin

Stockholm

Suede

WarEn A.

Stockholm

Suede

Simon Joseph L

Tampa

U. S. A.

Warren Lynda

Cardiff

Grande-Bretagne

Spiridonov V.

Moscou

Russie

Watson J.

Essendon

Australie

Stefanescu Mihai 0.

Bucarest

Roumanie

Watson Nikki

Armidale

Australie

Stork N. E.

Eondres

Grande-Bretagne

Westheide Wilfried

Osnabriick

Allemagne

Takeda M.

Tokyo

Japon

Williams A.

Washington

U. S. A.

Tan C. G. S.

Singapore

Wilson Mike

Cardiff

Grande-Bretagne

Taylor P. D

Londres

Grande-Bretagne

Wilson Robin

Victoria

Australie

Thibaud Jean-Marc

Paris

France

Wittmann K.

Vienne

Autriche

Thurston M H

Surrey

Grande-Bretagne

Zevina G. B.

Moscou

Russie

Toulmond Andr£

Paris

France

Zibrowius Helmut

Marseille

France

Tricart J.

Strasbourg

France

Ziegler Peter A.

Bale

Suisse

ACHEYE D’lMPRIMER

EN Jl’IN 1997

SI R EES PRESSES

E IM PRIM ERIE F. PAIEEYRT

A ABBEVILLE

BRL.DUl

MOSCUM’

P^KlS

Dale de distribution : 20 juin 1997.

Depot Ugal: juin 1997.

N° d'impression : 10118.

Source: MNHN , Paris

2 7 JUIN1997

Source: MNHN . Pans

DERNIERS TITRES PARUS

RECENTLY PUBLISHED MEMOIRS

A partir de 1993 (Tome 155), les Memoires du Museum sont publies sans indication de serie.

From 1993 f Volume 155), the Memoires du Museum are published without serial titles.

Tome 172 : Alain Crosnier et Philippe Bouchet (eds), 1997. — Resultats des Campagnes Musorstom.

Volume 16. 667 pp. (ISBN : 2-85653-506-2) 600 FF.

Tome 171 : Judith Najt & Loic Matile (eds), 1997. — Zoologia Neocaledonica, Volume 4. 400 pp.

(ISBN : 2-85653-505-4) 440,80 FF.

Tome 170 : Peter A. Ziegler & Frank Horvath (eds), 1996. — Peri-Tethys Memoir 2: Structure and

Prospects of Alpine Basins and Forelands. 552 pp. + atlas. (ISBN : 2-85653-507-0) 440.80 FF.

Tome 169 : Jean-Jacques Geoffroy, Jean-Paul Mauries & Monique Nguyen Duy-Jacquemin (eds),

1996. Acta Myriapodologica. 683 pp. (ISBN : 2-85653-502-X) 538,69 FF.

Tome 168 : Alain Crosnier (ed.), 1996. — Resultats des Campagnes Musorstom. Volume 15. 539 pp.

(ISBN : 2-85653-501-1) 538,68 FF.

Tome 167 : Philippe Bouchet (ed.), 1995. — Resultats des Campagnes Musorstom. Volume 14. 654 pp.

(ISBN : 2-85653-217-9) 600 FF.

Tome 166 : Barrie Jamieson, Juan Ausio & Jean-Lou Justine, 1995. — Advances in Spermatozoal

Phylogeny and Taxonomy. 565 pp. (ISBN : 2-85653-225-X) 440,80 FF.

Tome 165 : Larry G. Marshall, Christian df. Muizon & Denise Sigogneau-Russell, 1995.

Pucadelphys andinus (Marsupialia, Mammalia) from the early Paleocene of Bolivia. 168 pp.

(ISBN : 2-85653-223-3) 176,30 FF.

Tome 164 : Jeanne Doubinger, Pierre Vetter, J. Langiaux, J. Galtier & Jean Broutin, 1995. — La

(lore fossile du bassin houiller de Saint-Etienne. 358 pp. (ISBN : 2-85653-218-7) 479,92 FF.

Tome 163 : Alain Crosnier (ed.), 1995. — Resultats des Campagnes Musorstom. Volume 13. 518 pp.

(ISBN : 2-85653-224-1) 550 FF.

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Source:

Phylogenetics systematics provides life sciences with a reference system for the study of bio¬

diversity. One of the most interesting utilities of this system is to permit the inference of evolutionary

histories concerning traits under study. These evolutionary histories - the phylogenetic patterns - are

themselves heuristic for a better understanding of evolution. They may also be used to test previous¬

ly proposed models of evolutionary processes extrapolated from population studies. In either case, the

histories of the various orders of Insects reconstructed in this volume show that pre-conceived ideas

concerning evolution are often flawed : reversals and convergences are manifold in supposedly stable

traits such as flightlessness, mutualism, communication or social systems, and supposedly convergent

traits, such as social parasitism in wasps, may be shown to be homologous. Thus, these contributions

facilitate reconsideration of diverse evolutionary models. A methodological warning is also delivered:

comparative biology is conjectural per se and there is therefore today a basic need for decreasing the

number of unwarranted hypotheses by analogy or extrapolation which are too often used to infer phy¬

logenetic reconstructions.

This volume contains 18 contributions from 20 authors, dealing with both methodological

problems and case studies on 11 different groups of Insects. These contributions will provide the rea¬

der with leading and original accounts of the diversity of insects viewed from an evolutionary pers¬

pective; they will certainly be useful to every biologist interested in evolution, phylogenetics, or ento¬

mology.

Philippe Grandcolas is research. scientist in the team E.P. 90 CNRS, Laboratoire

d’Entomologie, Museum national d’Histoire naturelle, Paris. He works on phylogenetic systematics

and behavioral ecology of cockroaches in the tropics.

EDITIONS

DU MUSEUM

57, RUE CUVIER

75005 PARIS

ISBN 2-85653-508-9

ISSN 1243-4442

490 FFTTC (France)

479,92 FF HT (Etranger)