On The Taxonomic Value Of The Morphology Of Wing Scales In Some Heliconiinae (Lepidoptera, Nymphalidae)

6 Pages·1996·2.4 MB·English

by  Ralf H Anken

ON THE TAXONOMIC VALUE OFTHE MORPHOLOGY OFWING SCALES
IN SOME HELICONHNAE (LEPIDOPTERA, NYMPHALIDAE)
RalfH.Anken ^
ABSTRACT
WingscalesofparticularBrazilian/Ze/zcon/Mierato(Lirmacus,1758)and//,besckei(Ménétnés,1857)
(Lepidoptera:Nymphalidae)formswerecomparativelyanalyzed.Scalestakenfromtheredpostdiscalforewing
recto banddidmorphologicallynotdifferbetweensexes,speciesorlocalitieswhereasredscalesfromthebind
wingversosurfacesstrikinglydifferedbetweenthetwospeciesinvestigated.Blackandgreyscalesofeachof
thetaxa/sexesthatweretakenfromthebasalareaofthehindwingversosurfacesdifferedamongsexesand
amongspecies.Thefindingsarediscussedinthecontextofthepossiblethermoregulatoryandtheaerodynamic
propertyofwingscales.
KEYWORDS.Heliconius,scales,Taxonomy,Brazil.
INTRODUCTION
One of the principal characters used in taxonomic studies on butterflies is the
morphology of the male genital apparatus. It is highly conserved within species and
therefore, its anatomical investigation normally Warrants a correct Identification of a
given specimen with regard to its specific status. Nonetheless, sibling species can
frequently only be discemed from each otherby considering long series ofeach taxon,
taking into account a variety of geographical, ecological and morphological features,
particularly concemingthemorphology andbiologyofimmature stages. Withregardto
adultandpreservedspecimens, asmostlyfoundincollections,however, nothingbutthe
genitalapparatusandtheouterappearancecanbesubjectedtocomparativeinvestigations
since geographical andecological informations uponpreserved specimens are normally
kepttotheminimumandthelarvalstagesareoftennotknown.ANKEN(1995a,b)found
out, thatthemorphologyofhomologous scales (squamulae) inthe sibling speciesPieris
rapa^(Linnaeus, 1758)andP./2ap/(Linnaeus, 1758),alltakeninsouthwestemGermany,
obviously varied according to their shape. The noted differences between the scale
morphology were therefore regarded as a species-distinctive feature, the both species
1.Ludwigstr.14,D-73249Wemau,Germany.
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ANKEN
140
being discemible from each otherby the shape ofscales ratherthan by the morphology
ofthe genital apparatus.
ANKEN & BREMEN (in press) add some information to the question, to which
extent homologous scales differ in more or less closely related nonsibling species. In
aggreementwithGRODNITSKY &KOZLOV (1991), thatstudyrevealedaremarkable
taxonomicvalueofthescale-morphologyamongmembersofPapilionidae,sincetheydo
not use scales as thermoregulatory Clements as otherbutterflies andmostmoths do. The
morphology ofPieridae and Papilionidae scales are therefore rather due to functionally
indifferent evolutionary radiations than to an adaptation to thermoregulatory pressures.
Thescale-morphologyofsometropicNymphalidae,whoalsomightnotusescales
forthermoregulation(GRODNITSKY&KOZLOV, 1991)wasinvestigated,focusingon
sibling species ofthe genus Heliconius (Kluk, 1802) in orderto find out, ifthey can be
discriminated by their scale morphology and to contribute to the question, what the
biological relevance ofscales might be.
MATERIALANDMETHODS
ThenomenclaturefollowsSMART(1977)withregardtothesubspecific rankattributedtoHeliconius
melpomenephyllis (Fabricius, 1775). It is beyond the scope ofthis investigation to prove this systematic
positioning,buttousethenamesmerelyinordertoStateasexactlyaspossibletheindividualtaxon,sothata
readermaydiscriminateandrecognizethemwithoutbeingfoggedbynomenclaturaltermsonlyintellegibleto
thespecialist.Therefore,allauthorsofagivenform,subspeciesandspeciesarestatedinthefollowing,evenif
thisisnotcarriedoutfullyaccordingtotherulesofZoologicalNomenclature.ThetaxaarecommoninBrazil.
Allspecimensusedwerecollectedbytheauthorandtheyaredepositedinhisprivatecollection.
Thefollowingforms(onlyfreshindividuaiswithoutexternaisignsofbeingwom)wereinvestigated:
BRAZIL. Mato Grosso do Sul: Navirai, 7 c^of Heliconius eratophyllis i. artifex (Stichel, 1909), 26. X.
1993.Paraná: FozdoIguaçu,5õoíH.besckei(Ménétriés,1857),26.X.1993;39 ofHeliconiuseratophyllis
f.artifex,26.X.1993;6 õofHeliconiuseratophyllisf.artifex,26.X.1993.
TheprotocoltotakescalesfollowsANKEN(1995b).Thescalestobeinvestigatedweretakenfrom(1)
theredpostdiscalforewingrectoband,(2)theredspotsofthebasaláreaofthehindwingverso,and(3)from
theblackishgreyvicinityofthescalesof(2)byamoistenedbrush.Afterhavingbeentransferredtomicroscopical
slides,theywereallowedtodryandweresubsequentlycoverslippedusingHydromatrix.Fromeachexperimen-
tal group (i.e., species/geographicalpopulation/sex), atleastthreeindividuais wereanalyzedconcemingthe
respectivemorphologyofthesquamulae.Therefore,atleastthirtyindividualscalesperindividualweredrawn
usingacameralúcidaequippedbinoculartransmissionlightmicroscopeatamagnificationof400x.Thedrawn
series-images(calledSIinthefollowing)werecoded,comparedtoeachotherandanyobservationswerenoted.
ThecodingwasemployedinordertopreventtheexperimenterofknowingthespecificnameofanSI,which
mightunwillinglyhaveledtobiasedresults.Theresultsobtainedwereattributedtotherespectiveexperimental
group.TheSIsinthefigurescompriserandomlychosenscalesofrandomlychosenindividuaisofeachanimal
group. In the course ofextensive preliminary examinations, it had been found out, that such short SIs are
satisfactorilysuitedtodemonstratethegeneralmorphologicalappearanceofthescalesofagivenexperimental
group.AdditionallytosomeSIs,composedimages(CIs)werepreparedbydrawingonescaleovertheotherby
theuseofalight-plateandtransparentpaper.ThescalesofafiguredClwerethesameasshownintherespective
SI.
RESULTS
Ali scalesanalyzedrevealanapicalfieldwithmoreorlesspronouncedprotrusions
(processi), which vary among the same individual and from species to species. Ali
postdiscalredforewingrecto scales (figs. 1-4) arequitenarrowandrevealseveralapical
processi. Veryfewscalesonlyhavetwoprocessi(fig. 1, 12th. scale; thisfeaturehasonly
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Onthetaxonomicvalueofthemoiphologyofwingscales... 141
beenobservedinfemaleH. erato) and also extremely broad scales with more than four
Processiareuncommonbutwerefoundinallanimaisinvestigated(figs. 1-4,lastscales).
Anydifferencesbetweenthe SIsofredforewingrecto scales (figs. 1-4) aremoreclearly
revealedregarding the respective CIs (figs. 9a-d). The CI ofa female H. erato (fig. 9a:
Paraná)resemblesthatofmale//, eratoindividuais(fig.9b:Paraná;fig.9c:MatoGrosso
do Sul),buttheapicalfieldlooksnotasvariableasdoestheoneinthemales. The scales
apicalfieldofamale//. besckeispecimen (fig. 9d: Paraná) appearsquitehomogeneous,
indicating a low variety among different scales.
Redscalestakenfromthebindwingversosurfaces(figs.5-8andfigs.9e-h;SIsand
CIs,respectively) donotonlymorphologicallyclearlydifferfromthose oftheforewing
recto in being considerably larger. Moreover, they vary among the biological entities
investigatedmuchmorethoroughlythanthescalesdescribedbeforedo:infemale//.erato
specimens, the scales are quite narrow and the processi are pronounced but extremely
variableconcemingtheirparticularshape(figs. 5,9e).Male//, eratobutterfliesfromthe
samelocality(Paraná)revealbroaderscalesandfang-likeapicalprotrusions(figs. 6,9f),
whereasthehomologousprocessiinmale//. eratofromMatoGrossodo Sul arethumb-
likeandvaryconsiderably (figs. 7, 9g). Moststrikingly, the scalesfrommale//, besckei
fromParanádo notreveal any protrusions at all (figs. 8, 9h).
TheVariationamongblackandgreyscalesofeachofthetaxa/sexesthatweretaken
from the basal areaofthe hindwing verso surfaces is overhelmingly considerable (figs.
10-13). Nonetheless, it can be pointed out that the male //. erato specimens, although
taken at different locations, to some extent resemble each other, whereas the male //.
besckeihas only two differentkinds ofgreyish/black scales onthebind wing versothat
donotstrikinglydifferfromtheotheronesofthistaxonandthefemale//.eratohasscales
not appearing in any otherbutterfly investigated, especially thenarrow andbroad giant
scales.
DISCUSSION
The red scales taken from the forewing recto only somewhat differ between
Heliconius erato and //. besckei. Their Variation among male //. erato from different
localities andfrommaletofemale//. eratofromthe samelocalityisnotpresumedtobe
significantaswell.Alsoacomparisonamongredscalesfromthebasalareafromthebind
wing verso does notreveal any obvious differences among the //. erato specimens, but
homologous scalesfrom//. besckeistrikinglydiffer. Regardingthescalyfumishmentof
the basal bind wing recto surface conceming other than red scales (i.e. greyish/black
ones),//. eratohasavarietyofdifferentlyshapedscales (especiallythefemale),whereas
inH. besckei only some different and simply organized types ofscales were found.
It is not yet clear, what the particular function of butterfly scales might be.
NACHTIGALL(1967)argued,thatscalesinspecializedbutterfliesmaycontributetothe
physicalbasis ofsailplaning. GRODNITSKY &KOZLOV (1991) proposed, that scales
mightprevent abutterfly from getting water sOaked or glueing to a spiders net orresin.
Most comprehensive and based on large amounts of data, however, is the theory of
GRODNITSKY & KOZLOV (1991), according to which scales may act as
thermoregulatoryunits.Itisfarbeyondthescopeofthegivenstudytodiscussthepossible
biological relevance of the scales investigated, but to clarify their possible use for
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u: ANKEN
taxonomy. Nevertheless, it is intriguingthatjusttherecto scalesdonotdifferamongthe
taxa/sexes/geographicalentitiesinvestigated:membersofthegtnusHeliconiusfrequently
exhibit sailplaning behavior (according to NACHTIGALL, 1967, this behavior is
substantiallybasedontheaerodynamicsofrectowingscales)andtheytakesunbathswith
opened wings therewith exposing the recto surfaces and the respective scales to sun
radiation (as not all butterflies do: some European satyrid Hipparchia spp., e.g,, try to
avoid sunshinedirectedtothe recto surfaces butnevertheless place themselves to direct
sunlightbycollectingitbytheversosurface; ownobservations).Withthat,thesimilarity
in wing Scale morphology regarding recto surfaces in Heliconius might be based on
similarevolutionarypressures,i.e.,similarfunctionalrequirementssuchasaerodynamics
and gathering sun radiation derived heat. Since these environmental pressures may not
affecttheversosurfacescales,theirmorphologymightbeduetofunctionallyindifferent
evolutionary radiations, consequently leading to a variety of morphological different
Figs. 1-4. Series images (SIs) ofred scales. From postdiscal forewing recto band - Heliconius eratophyllis,
Paraná: 1,9;2,d;MatoGrosso: 3,d;4,H.besckei,Paraná,õ.Bars=25|im.
Iheringia,Sér.ZooL,PortoAlegre, (81): 139-144,04out. 1996
Onthetaxonomicvalueofthemorphologyofwingscales 143
w
Figs.5-13.Seriesimages(SIs)ofredscales.Fromhindwingversosurfaces.Heliconiuseratophyllis,Paraná:
5,ç;6,&,MatoGrosso:7d; 8,H.besckei,Paraná,õ\9,ComposedimagesoftheSIsshowninfigs. 1-8. 10-
13,(SIs,sameanimaisinthesameorder).TheseSIsweretakenfromblackandgreyscalesthatwerecollected
fromthebasalareaofthehindwingversosurfaces.Bars=25|im.)
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ANKEN
144
teatures concomitantly employed during the course of the evolution of functionally
relevant features like the recto scales, the wing shape and the male genital apparatus.
Especially functional indifferent attributes may be consideredto be oftaxonomic value,
since function-related ones are liable to appear in similar fashions in taxonomically
distantly related animais as analogous structuresjust do due to physical properties. The
arguments used abovemaythereforeexplainafinding ofthepresentstudy, accordingto
which red scales taken from the hind wing verso basal area (which is estimated to be
funcionally irrelevant) clearly differbetweenH. erato andH. besckei indifferent on the
sexandthegeographicallocality.EMSLEY(1964, 1965)pointedoutthatbothsiblingand
conmimic species may be distinguished from each other by Consulting the particular
arrangement ofred spots in this wing area.
Theresultsofthepresentstudyclearlyrevealaspecies-specificmorphologyofred
scalestakenfromthisparticularwingarea.Regardingindividuaisindoubt,aninvestigation
onscalesofthisareamaythereforeaddfurtherdataofobviouslyunambiguoustaxonomic
significance. An investigation of greyish/black scales of the same wing part also may
Warrantasecure Identificationon species level sincethevarietyofthese scales seems to
be species-specific as well. Further investigations onthe verso andrecto scales ofother
conspecific and conmimic Heliconius will add some more data on the taxonomic and
functional relevance ofparticular scales.
CONCLUSIONS
Itis concluded, thattheforms ofHeliconius erato andH. besckei investigated are
discemible from each other by the shape of basal hind wing verso red scales and the
particularfumishmentofthiswing areawithblackishscalesrevealingaspecies-specific
variety, whefeas the variety among female and male H. erato is less distinct. These
findings,ascomparedtothefindingsregardingscalesfromtherectosurfaceofthewings,
where no species-specific features were seen, may be due to different functional
requirements ofverso and recto wing scales, the formerbeing oftaxonomic value.
REFERENCES
ANKEN,R. 1995a.BasalhindwingrectoblackscalesdiffermorphologicallyinPierisnapiL.andPierisrapae
L.,Ent.Gaz.,Faringdon,46:254.
.1995b.ZurgeographischenVariabilitäthomologerDeckschuppenvonPierisrapaeL.nebstvergleichenden
BemerkungenzuP.napi(Lepidoptera:Pieridae).Ent.Z.,FranLkfurt,105:326-339.
ANKEN,R.&BREMEN,D.OnthemorphologyofbasalhindwingrectoblackscalesinsomePapilionidae
(Lepidoptera:Rhopalocera).Ent.Rec.J.Var.,London,inpress.
EMSLEY, M. 1964. The geographical distributionofthecolor-pattemcomponents ofHeliconiuserato and
Heliconiusmelpomene withgeneticalevidenceforthe systematicrelationshipbetweenthetwo species.
Zoológica,NewYork,49:245-289.
. 1965. Speciation inHeliconius (Lepidoptera: Nymphalidae): Morphologyandgeographicaldistribution.
Zoológica.NewYork,50: 191-254.
GRODNITSKY, D. & KOZLOV, M. 1991. Evolution and functions ofwings and their scale covering in
butterfliesandmoths(Insecta:Papilionida=Lepidoptera).Biol.Zent.bl.,Leipzig, 110:199-206.
NACHTIGALL, W. 1967. Aerodynamische Messungen am Tragflügelsystem segelnder Schmetterlinge.Z.
vergl.Physiol,Berlin,54: 210-231.
SMART,P. 1977. Kosmos-EnzyklopädiederSchmetterlinge. Stuttgart,Franckh-Verlag. 279p.
Recebidoem22.05.1995:aceitoem08.01.1996
Iheringia,Sér.ZooL,PortoAlegre, (81): 139-144,04out. 1996