PYCHE. - downloads.hindawi.comdownloads.hindawi.com/journals/psyche/1894/045131.pdf · *Vol. 63, pp. 28-35. the earlier stages, we should attach moreimportance to the early dissimil-arity

PYCHE.

CONVERGENCE AND POECILOGONY AMONG INSECTS.

BY ALFRED GIARD, PARIS, FRANCE.

[Professor Alfred Giard in the An-nals of the Entomological Society ofFrance* presents a careful discussion ofconvergence and poecilogony amonginsects and a resum6 in the form of a

rather free translation may be of interestto some who do not have access to thispublication. HERBERT OSBORN.]

It is a well known fact to entomolo-gists that certain insects which are

very similar to each other in the adultstate have larvae which are quitedifferent. Many examples of thispeculiarity have been indicated, princi-pally among the Lepidoptera, thelarvae of which are better known thanthose of other groups. But all insectswith complete metamorphoses maypresent the same phenomena, and, ifit is more rare among the ametabola,it is because, among these, the passagefrom the larval to the adult stage is

gradual, by insensible steps, and thelarvae and imago are subject to muchthe same conditions. One of the ques-tions of much importance and at thesame time a problem of much difficultyto solve is to determine if, in the recog-nition of the agreement between similaranimals which present differences in

* Vol. 63, pp. 28-35.

the earlier stages, we should attachmore importance to the early dissimil-arity than to the similarities of theadults. The question would beanswered immediately in the affirma-tive if the principal of Fritz Mueller,the fundamental biogenetic law ofSerres and Haecke], were applicablein its exactitude. That is to say, ifthe various ontogenetic states of ananimal repeated exactly the phylogenyor the successive ancestral forms.Were this so, embryology would indi-cate the true relation of the parents.The more or less perfect resemblance

of the adults in certain cases would beinterpreted as the result of convergencedue to similar ethology of these adultforms. But, among animals withmetamorphosis, embryonic forms aresubject during a long period to themodifying action of the surroundingsand often, also, their evolution dependsin a large measure upon the ethologyof the adult. Accordingly, the prin-ciple of Fritz Mueller is applied withdifficulty and singularly though actuallythe determination of the relation of theparents becomes more arduous thebetter we know the different phases ofdevelopment. If it be true that partialknowledge happens thus to complicate

172 PSUCttt?. [December I894.

the problem, we may hope that a more

complete knowledge, that is a knowl-edge of the dynamic embryology ofa large number of species, will giveus the solution.At present we may distinguish two

principal categories of insects whichare similar in adult stages and differ inearlier stages of development.

First" certain insects pertaining tothe same genus or to distinct genera,sometimes even widely separated,which prescott in all cases larval stageswhich are quite different and in eachcase adult forms similar by conver-gence, a convergence due to the sur-

rounding conditions (protective resem-blance, mimicry direct and indirect,isotypy, etc.).Second: among other insects the

different generations of the same spe-cies considered at different points oftheir geographical distribution, at dif-ferent seasons of the year, or in differentconditions of nutrition, have larvaewhich are dissimilar while the adultsare very similar to each other andpresent very slight modifications. Itis to this form that we apply the term

Poecilogony.* In this case the larvaehave become divergent in adaptingthemselves to different ethological sur-roundings. The final result is the

*A. Giard, Sur le bourgeonnement des larvesd’Astellium spongiforme Gd. et sur la poecilogoniechez les ascidies composes (C. R. de l’Academiedes Sciences, Fevrier 89x).

A. Giard, Nouvelles remarques sur la poecilo-gonie (C. R. de l’Academie des Sciences, -7 Juinz89z).

same in all cases but from the pointof view of consanguinity and thereforeof natural classification the two cate-gories are far from having the same

signification.The related species of poecilogonic

origin have between them direct parent-age and approach each other notwith-standing their embryonic divergencies.The species which resemble each otherby convergence can on the contraryhave only phylogenic separation andmust be considered as naturally distinct.From a practical point of view it is not

always easy to decide if two similarforms are poecilogenic or convergentspecies. In certain cases, however, thedistinction is easy and no doubt is per-missable. When, for example, thespecies which by selection have becomeconvergent, belong to genera sufficientlyseparated, the profound anatomic char-acters and the embryonic characters arenot altered by convergence to the pointof" being unrecognizable. The resem-blance is only superficial and if the oldernaturalists have been deceived by asimilar aspect of the adults the error isnot possible to-day. Mimicry, so perfectin Leptalis and Ithomia, of Paibilioparactoxa and tuiblaea mictamus ;imitation of Danaides or ofthe Acraeidesby different species of Papilio or ofDiadema do not impose upon any en-

tomologist.The resemblance although less exact

in other respects of Dichonia aprilinaand 3/foma orion is, nevertheless, an

example of the same kind. Even whenconvergence of the adults takes place

December x894.] PSYCIIE. 173

among congeneric species, that whichdeprives us in great part of the advan-tage of indications of comparativeanatomy, we can in most cases stillrecognize the origin as entirely distinctfor the two species and establish theresemblance as due to the effect of thesurroundings upon the imago.

It is this which occurs, for example,in the case of isotypy. Some relatedforms such as Pieris brassicae andieris rajbae the numerous Euplaeae,etc. The fact that these species frequentthe same localities without mixing andwithout crossing indicates that thelarval differences which they present inthe midst of identical conditions aredifferences of ancestry. This is stillmore evident when it is applied toHymenopterous parasites (Isotypes) ofwhich the larvae have the same hosts orof parasites of plants of which the larvaefeed side by side upon the same plant.lZtormomyia capraeae Bremi is distin-guished with difficulty in the adult statefrom another Cecidomyian living alsovery often upon the willow (Salix ca-

The gall has been described bySchlechtendahl under No. 332. * Butthe larvae of these two Diptera remaindistinct and produce very different gallsupon the leaves ofthe same tree. Thereis here no doubt that the resemblanceof the adults is simple convergence anddoes not indicate a closely relatedancestry.

* Sehlectendahl, Die Gallbildungen (Zoocecidien)t89x, p. 4o.

When, in the place of living in thesame surroundings the larvae have adifferent habitat the question becomesmore difficult to solve.Gu6n6e in a remarkable memoir upon

some European bombyces has con-sidered as distinct species two types,Bom@x s2bartii Hb. and ttomhyxcallunae Palen, which represent onethe southern and the other the northernform of 23. quercus L.

If one examines an extensive collec-tion of 2. uercus such as that of ourcolleague M..1. Fallou he will easilysee that it is almost impossible toseparate the adults of these threespecies. Certain forms of 2. uercuspassing manifestly, as Gu6n6e andBellier de la Chavignerie already haverecognized, in part to 2. spartii, inpart to 25’. callunae.Gu6n6e had discovered that the

young caterpillar of 2. callunae differsfrom that of 23. uercus, but that the.divergence diminishes after the firstmoult and finally disappears. Onemay attempt to see in this dissimilarityof the larvae in the early state a proofof the primitive separation of the twospecies. But the habitat differs suffi-ciently to explain this divergence. Oneof the two forms, without doubt 2.callunae, represents the first ancestrallarva which is modified in 23. quercusand 2. sbartii and this species maytruly be considered as a poecilogonicform slightly modified in the adultstage.

t Annales Soc. ent. Fr. I858, 435-442.

174 PS/"C/-//. [December t894.

We have elsewhere direct proof ofthe existence of poecilogony amonginsects. In two very important memoirspublished in Russian and of which wehave a translation by our learnedcolleague C. R. von Osten Sacken, theRussian entomologist Portchinsky hasdemonstrated that the common 2Ffuscacorvina presents two distinct forms indifferent parts of its wide habitat. Inthe north of Russia this coprophagousfly generally deposits z4 eggs of mediumsize from which arise larvae that presenttwo very distinct phases of evolution.In the Crimea where coprophagousinsects are more abundant and con-

sequently the struggle for life moreintense, the same Dipteron depositsonly one large egg in which themetamorphosis is very rapid and con-densed and recalls that of the Pupipara,the larva arriving almost immediatelyat its last phase of development.Analogous cases are known amongdifferent Lepidoptera and notably inthe mulberry silk-worms (Sericariamori). In the south of Europe thisspecies furnishes an interesting racecalled Trevoltini which not only pro-duces several generations annually butis distinguished fi’om the type in thatthe caterpillars have only three moultsin place of four. Cultivated in thenorth this race regains the ordinarycharacters of the species (the sec-ond or third year) as shown by Robi-net.*As the caterpillar of Sericaria mori

varies more or less the physiologicalpeculiarity of the suppression of onemoult attracts the eye, but in othercases structural modifications are moreapparent.Th. Goossens has indicated several

very interesting examples of geographicpoecilogony. Deilethila euphorMaedoes not present in Ardache and inVat the ordinary yellow points and therosy spots are replaced by spots of a

pale yellow. The caterpillar of Jrfelio-this marglnata, light or green in theNorth is more often of an almost blackbrown in Provence. In the south ofFrance the dorsal part ofthe caterpillarof Zygaena fausta is almost alwaystawny. At Paris this part is watergreen.?When in cases of this kind the adults

of two poecilogonic varieties come todiffer but little at the two extremities ofits habitat, we do not err if we establishtwo species, saying: Without doubtthe perfect insects differ bzt little, butthe larvae present differences so greatas not to permit us to unite the twoforms. This is certainly what occursfor a large number of species calledrepresentative for the old and the newworld, Triaena psi and T. occiden-talis, for example. Comparison of themonographs of Gu6n6e and Abbot isvery instructive in this respect.

Sometimes even the variation of theadults rests exclusively upon the ana-tomical characters of the genitalapparalus of such a kind that the

* Robinet, Art d’lever les versa soie; traduction + Th. Goossens, Des variations sur les chenillesdu comte Dandolo, x825, p. 3x7. (Ann. Soe. ent. Fr., x87, p. xxS).

December x894.] PS’C//’. 175

poecilogonic forms, while preserving a

great resemblance in the adult state,cannot be crossed and this inability tocross facilitates the divergence of thetwo species even if they come incontact in some point of their habitat.It is thus, that, according to Grote andSmith, Afrotis haru@ica and A. rufi-

fera are the American representativesof the European A. au#er and A. rubi,from which they differ only in thegenital armature of the male; but thatthese modifications may be effectivethey should perhaps recede and deter-mine the poecilogony instead of beingcaused by it or produced by it. Thisquestion is hard to solve at present andstands with the numerous problemsthat Romanes has stated in his work on

physiological selection. In other cir-cumstances poecilogony seems to bedue to the varying nourishment of thelarvae. If certain caterpillars aremodified directly by the supportingplant as is known to be the case amonga great number of species, we knowalso that some are adapted definitely toa determined plant and are protectedby a permanent form, a different livery.Poulton has stated, as well as otherauthors, that many caterpillars die ofhunger rather than touch nourishment

for which their race has lost the habit.Perhaps it is to poecilogony of nourish-ment that we should attribute thedifferences found in the caterpillarsof Cuculia verDasci and C. scrofula-riae, moths, the similarity of which inthe adult state is not easily explainedby convergence. Further, certain casesof resemblance among insects, in whichthe larvae differ but live in the same

localities, sometimes upon the. same

plants, are difficult to interpret underone or the other of these alternativeswlich we have indicated (convergenceor poecilogony). We cite for exampleLithosia comjblanana and Z. luri-deola, Deilebhila euphorbiae and D.nicaea.

Finally the only purpose in this shortnote is to state a very importantproblem of general biology, touchingat once embryology, ethology andtaxonomy. Perhaps on certain sidesthe problem is capable of experimentalsolution. In any case the questionought to receive light from our spe-cialist friends, if they will study into thenumerous cases of the kind enumeratedabove, which pass daily under theireyes, and of which they; better thanany others, can state precisely theactual value.

In "The butterfly hunters in the Carri-bees" (N. Y., Scribner) Mr. E. M. Aaron,in the guise of a learned "Dr. Bartlett," takestwo boys of a friend collecting in theBahamas, Hayti and Jamaica, and bringsthem back laden with spoil and honors,culminating in their election into thePhiladelphia Academy. What with history

and other matters butterflies themselves playa minor part, but there are some observa-tions due to personal experience which lenda certain value to the book. It ought tointerest boys, for it has the odor of thecamp about it, but we could wish there hadbeen less of the mercantile spirit in it. It iswell printed.

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PYCHE. - downloads.hindawi.comdownloads.hindawi.com/journals/psyche/1894/045131.pdf · *Vol. 63, pp. 28-35. the earlier stages, we should attach moreimportance to the early dissimil-arity