Colour polymorphism of Callimorpha dominula (Linnaeus, 1758) in Italy, and the problem of polytopic subspecies (Lep. Arctiidae, Callimorphinae)

20 Pages·1996·9.1 MB·English

by  Alberto Zilli

Vlitt.Münch.Ent.Ges. 86 79-98 München,15.12.1996 ISSN0340-4943
Colour polymorphism of Callimorpha dominula (Li.waels, 1758)
in Italy, and the problem of polytopic subspecies
(Lepidoptera, Arctiidae, Callimorphinae)
Von Alberto Zill/
Abstract
RelictpopulationsofCallimorphadominula(Llsnaels,1758)fromSicilyarecharacterizedbyindividualsvirtually
indistinguishable from those occurring in the Alps and northwards. This is in profound contrast with the
phenotvpesfoundinpeninsularItalyfsubsp.personaHlbner,1790).Thenominatesubspeciesbecomes,therefore,
a fx>lytopic subspecies. A general revie\%'ofthecolour polymorphism ofthespecies in Italy isalso provided.
Following a critical discussion ofsome pathways through which reoccurrence ofcharacters between distant
fX)pulationsofasamespeciesmayoccur,particularemphasisislaid uponthepossibilitythat,inspecialcases,
thereoccurrenceisnotindependent,asclaimedsofar.Itisputforvvardthatsomecasesofpolytopismmightbe
parsimoniouslvexplained consideringtheshifttoward a differentarrayofcharactersofthepojnilationsinter-
posed bet^veen others, subject to stabilizing selection. It is suggested that archaic dominula populations in
peninsularItalvundervventmelanismandflavism,asnowobser\'edinpersona,andstartedbeinginvolv^edwith
a'southem'.Vlüllerianmimicryringbasedonyellowandblackpatterrts.Becauseofthepaucityoftheday-flying
mothsbearingthevellow/blackpatteminSicily,duetoalackofcolonizationfromthemainland,thedominula
populationsintheislandwouldnothavemettheproperecologicalcontextforundergoingasimilarshift.Abrief
discussiononthesubspeciesconceprttriestoshowhovvmisusedthesubspeciescategoryisintaxonomy,notleast
becauseofconfusionbetweeninductiveanddeductivep>rocesseswhilecircumscribingsubspeciesanddeficien-
cies in the concept itself. Events of character reoccurrence, and hence polytopic subspecies, are belie\'ed to
represent a valid reason for abandoning the use of the subspecies category as scarcely informative or even
misleading.
Contents
1 Introduction
2 TheItalianpopulations
2.1 SituationinNorthItalyandperiphery
Z2 SituationinpeninsularItaly
13 SituationinSicily
2-3.1 Literaturedata
232 Helddata
3 Polytopicsubspecies
3.1 Originofcharacterreoccurrence
3.1.1 Ecologicaldeterminismfselection)
3.1.2 En\'ironmentalinductionduringde%'elofmient
3.13 Chance(probabilistice\'ents)
3.1.4 Commongenealog)'(phylogenesis)
3.1.4.1 Geographievicariance
3.1.4.2 Dispersal
3.1-43 "Shift"ofthein-betweenpopulations
4 HowtoexplainthepresenceofnominatedominulainSicily?
4.1 .Melanismandtheshiftred-yellowinApenninicday-flyingmoths
3 Remarksonthesubspeciesconcept
5.1 Polytopicsubspedesandtheiroutshotsonthesubspedesconcept
79
1 Introduction
TheScarletTigerMoth, Callimorpha domuiula (Linnaeus, 1758), is a well-known and outstanding western
palaearcticspecieswhichhasbeertafavouritesubjectforgeneticalandpopulationalstudies. Infact,after
thepioneeristicworkbySTANDFuss(1896),muchresearchhasbeencarriedoutontheformalandecological
genetics of domimtla, among the others by eminent researchers such as Clarke, Goldschmidt, Cockayne,
Kettlewell, FisHER, FoRD, OwEN, and Sheppard.
Detailsonthebionomicsofthespeciescanbedrawnfromseveralsources(e.g.Wenzel1936,Kettlewell
1943, Fisher & Ford 1947, Cook 1959, 1961a, 1961b, 1961c, 1962a, Cook & Kettlewell 1960, Owen 1993,
1994, 1996),howeveritisofinteresttostresstwomainfeatures,namelytheday-flyinghabitsofthemoth
(whichisalsopartiallynight-active)andthetendencytoformlocal,isolatedcolonies(Kettlewell1943,Ford
1971).Inparticular,aspotteddistributionofthepopulationsiswell-pronouncedalongpeninsularItaly,the
speciestherebecomingdecisivelylinked tomountainousareasasitdoesnottoleratethexericconditions
characteristicoflowaltitudemediterranean-typeecosystems.
Thecxitstandingpatternoidomuiula(fig. 1)and thewayofbeingdisplayed,e.g.whileflyingorresting
uponflowersinthesunshine,areparticularlycharacteristicofadistasteful,aposematicorganism.Thespecies
wasinfactshowntobeprovidedwithtoxicsubstances(Rothschild1961,Kayetal. 1969,Edgaretal. 1980)
and,accordingly,isrejectedbynaturalpredatorssuchasbirds(Frazer&Rothschild1960,Rothschild1985).
According torecentrevisionarywork (Freina & Witt 1987), the EuropeanpopulationsofC. dominula
shouldbesplitintofourwelldelimitedsubspecies,namely(fo»H'H///rt(s.str.),powpalisWitsche,'[926,persona
(Hübner,1790),andbithynicaStaudincer,1871 Themaindifferencesbetweenthesesubspeciesaresumma-
.
risedintable1.Exceptforbitln/iiica,theotherthreesubspeciesmeetinNorthernItaly,originatingPolymorphie
populationsinthecontactzones(Rocci1913,Turati1919,1923,Kettlewell1943,Cook1962b,E. Bertaccini,
in Utt.) (fig. 1).
TheremarkabledistributionofthecolourpolymorphismshownbytheScarletTigerMothgivesafine
opportunityofreviewingthepuzzlingphenomenon ofthepolytopicsubspeciesand itsconsequencesin
taxonomy.
2 The Italian populations
Broadlyspeaking,nominatedominulaoccursinNorth-WestItaly,whereasmelanicpopulations(ssp.pompalis
Nitsche, 1926) are found more easterly along the Alpine ränge, in the Dolomites and surroundings.
Callimorphadominulapersona(Hübner,1790)isexclusivetopeninsularItaly,rangingfromtheTusco-Aemilian
Apennines to Calabria (fig. 1).
Thepersonaphenotypesgreatlydifferfromthoseoftheothereuropeansubspecies,beingcharacterized
byhindwingsandabdomeninwhichtheusualredcolourofthebackgroundisreplacedbyyellowandby
much more conspicuous black markings. The melanism of persona is clearly polygenic, in fact several
phenotypicclassesalongacontinuumcanberecognized,andintheextremeformstheblackmarkingsare
entirelyspreadoverthehindwingsandtheabdomen.Theforewingapexisalsostatedtobemoreacutethan
inthenominatesubspecies(Freina&Witt1987),butthistraitissounconstantthatotherauthorsmaintained
thecontrary (e.g. Treitschke 1834). Also the forewings areaffected by the melanism, as evidenced by the
reduced size of their pale spots, but only to a limited extent.
Because of the striking phenotypic differences between persona and nominate dominula some earlier
Table 1. Maindifferencesbetween the European subspeciesofCalliinorplm doiuimiln (Linnaeus) currentlyrecog-
nized. FW, forewing; HW, hindwing.
subsp. FW spots HWcolour abdominalstripe HW melanism
domiinila no
yes
yes
no
80
authors even put forward that they reprcsent two distinct species (e.g. Esper 1794, Boisduval 1834, 1840,
Tkfitschke 1834, Dui'Onchei, 1836, Herrich-Schäffer 1845). Kettlewell's (1943) credit is to have critically
weighted thetwoalternativehvpothesesabouttheconspecificityoidoiuiiuilaandpcrsojinthrougharemark-
ablyelegantreasoning froma methodological Standpoint,which isherebrieflysummarised.
Objecti\'elv,someevidencewouldagreewiththeexistenceoftwospecies,aboveallthelowfertilityand
larval \'iabilitvoithecrossesdoiniiniln (s.str.) x persona,aswell astheassortativematingsoccurringwhen
doiiiiinilii (s.str.) males are given the choice between both types offemales (Standfuss 1896, Goldschmidt
1924). Ün theotherhand, theoccurrenceoverlargeextensionsofNorth Italyofpopulationsinwhichthe
diagnosticcharactersofpersoiiti, i.e. melanismandflavism,arenomorelinked isdefinetelyunsubstantial
withtheexistenceofmorethanonespecies(Kettlewell1943).Asamatteroffact,polymorphicpopulations
with yellow unmelanic individuals are known in both the western and eastern districts of North Italy
(Piedmontand Friuli),whercasponipalifipopulations,inshort'redpersona ,occurovermostofthecentral-
eastern Alpine sector (Rocx 1913, Nitsche 1926, Dannehl 1928, Kettlewell 1943, Cook 1962b, Freina &
i
Witt1987).Lastbutnot\east,doniinulamalesareinanycaseattractedhypiersonafemales,wheneverdonü)nda
femalesshouldbeabsent,andcopulatewiththemproducingsomeviableoffspring,alsoobtainablethrough
the reverse crosses (Kettlewell 1943).
Owing to thescantydataavailable,itcannotbeascertained whethertheassortativematingsbetween
doiiiiniilaandpersona,aswellasthelowerfertilityoftheircrosses,revealtheoccurrenceoftwodifferentiated
evolutionarylineages.TheSituationmightinfactrepresentnomorethanasimpledistanceeffectindependent
ofthesubspeciesidentifiedbytaxonomists,e.g.acaseofoutbreedingdepressionComingoutfromthecross
of differently coadapted genotypes sampled from distant populations (cf. Oliver 1972, Endler 1977,
Templetonetal. 1986).ResearchonthecourtshipbehaviouroftheScarletTigerMoth,involvingacomplex
arrayofVisual,chemicalandacousticSignals(cf.Brakefield&Liebert1985:238),andcrossingexperiments
betweensamephenotypes(e.g.dontiniila xdonüntila)fromdifferentareaswouldbedecisive.Interestingly,
someexperimentsonmatechoiceinadominulapopulation from England evidenced preferentialmatings
betweendifferentgenotypes(Sheppard1951, 1952,Sheppard&Cook1962,Ford1971),beingoneofthefew
known cases of disassortative mating (Partridge 1983).
DespitetheremarkableamountofworkonthegeneticsoidoininnlainEngland,althoughcontradictory
(e.g. Cockayne 1928, Kettlewell 1943, Fisher & Ford 1947, Wright 1948, 1978, Sheppard 1951, 1952, 1953,
1956,Kettlewell1952,Cook&Kettlewell1960,Williamson1960,Sheppard&Cook1962,Ford&Sheppard
1969, Lees 1970, Ford 1971, White 1985, Jones 1989, 1993, Clarke et al. 1990, 1991, 1993, Owen & Clarke
1993, Owen & Goulson 1994), far fewer data are available on the colour polymorphism of the Italian
populations.Frommuseummaterialitisevidentthatmanyamateurshadjustcrossedspecimensnorthand
southoftheAlpstoobtainbeautifulhybridsfortheircollections.Howevermorerationalapproacheswere
followed by Standfuss (1896), Oberthur (1911), Goldschmidt (1924), Cockayne (1928) and Kettlewell
(1943). Unfortunately, most of the experimental crosses were partial or with contradictory results, so a
thoroughpictureofthegeneticsofthecolourpolymorphisminItalyisstillwanting.Itisnottheaimofthis
paper to summariseagain the old data available (cf. forreviews Cook 1962b, Ford 1971, Robinson 1971),
ne\'ertheless,attentionshouldbefocusedonthenormalredcolouroidominulawhichisseeminglyincom-
pletelvdominantovertheyellowoftheItalianforms(thetrueSituationbeingprobablyquitecomplex),while
thegeneresponsiblefortheyellowaberrationsoidoiniiiiila(s.str.),occurringthroughoutthespecies"ränge,
behavesasttHallyrecessive.Itremainstobeascertained,therefore,whetherthegeneresponsibleoftheyellow
oftheItalian formsisactuallydifferentfromthedominulayellowgene,assuggestedbyKettlewell(1943),
possiblymorethanonegenebeinginvolved,orthediscrepancymaybeduetodifferentialexpressionofthe
samegeneindifferentiatedgenecomplexessuchasthoseofdistantpopulations,asmootedbyFord(1937).
Regardingthemelanismoipersona,thetraitisfairlywelldescribedbyincompletelydominantgeneswith
additiveeffectsinatwo-lociSystem(Goi.dschmidt1924).However,Kettlewell(1943)stressedthedifference
betweenyellowdominulaandunmelanic/vrsoHrt,namelytheenlargedblackdorsalstripeoftheabdomenof
theiatter(oftenblackeningtotallytheurites),and referred tothatcharacter,exclusivetomostoftheItalian
populations, as a "primary melanistic factor". This factor is usually associated with 'secondary" ones, i.e.
thosedarkeningthehindwings,butitisinheritedindependently.
Owingtothegreatvariabilityofthespecies,affectingalsomanyothertraitssuchasforewingSpotting
(e.g.number,shape,size,colour,etc.),severalauthorstriedtodistinguishbynomenclatureanykindofform
(cf.Biok1937).Thenameswereoftenmisapplied,sometimesconferringtoanindividualaberrationtherole
ofa geographical raceor,converselv,applvingthenameofa localracetovaguelyresemblingaberrations
collectedelsewhere.Othersourcesoferr(.)rswerehonnMiymsusedtodepictdifferentforms,misidentifications
81
and iipplic.ilion Id wild spriimtMis ot iiiimcs llic iisc ol wliu li slioiiKI li.uc hfcn icstrirlcd lo l.ibor.ilory
liybrids.Theni.iincdiisciuicikristh.il i(is.idillu iill l.iskI(hI.i\' lolr\'locliuul.ilclowImlipliciiolv|>u il.isscs
Ix'lon^i'dspcvinuMisivported ini.uinislii-liU'r.iluii-vviliioiil.ulc'(.|ii.ilc'iiluslMlions. I orIhcs.ikcolclcirnossit
isliu'ivlorrsii^^i'stedavoidingusingnamesotIhctornisand lodircvllyivlatt'lotlu'irmorphologicalIvaliires.
Morc'ovt'r,niislabellingotbredsptvinicnspivscrvfd inmuscums,parliciil.ulv inthocaseofaiiilicialhybrids
(o.g.lrc>ating(/(ij/;/;;////; xjH'l^solun^sil Ihcywcrccolk-ttt-d inUu-wildorinllu'[iLufol ivsidencool tlu'bivt'dcr),
is also sonii'lhin;!, llial [HCJiK-litrs a tari'hi! appiriiaiion ol llu' atIn.il dislnbiilion ol Ihf rolour loinis.
2.1 Situation in North Italy aiui [icriphory
Asatistactorypictiireofthecok)urpolyniorphisniinNorlii It.ilywillhcprt)bablyncverattainedasihfciirrent
patti'rn ot gcographic Variation siiggusts coniplcx ilynaniics in spacc ^nd tinic. Ihe dislribiilion of thc
nu'l.niisni,inparticnlar,isclcarlymosaic-likoinaspatiallyiH'ti'rogiMU'ousaroasuchasthatotthosouthorn
Alps.Wetindpolymorphicpopulationswithspecimcnsrangingtroni mn-mMdoiiiiiiuln[opoiiipnliseastand
westofthecoreareaoftheso-calledssp.paiiipnlis(e.g. iTiiili; I.onibanlia aml Ticino). Asonemightexpect,
normaliloiuiiiiiliidoalsooccnrwithin therangi>of/'(i/;;/'/(/;s(Danni in l''?.S,('ook l%2b)and viccversa, i.e.
pi'iiipuli:. phi'holypes weil t)nlsid(' ils piilaluc iani',f (Tukaii (^ Vikii^ \'->\'1, \\. Hi kiai i ini, in liü., A. /ii ii
pers.t)bs.in Liguria).pA'eninthepopulationselearlyreterabletont)niinale(/()»/;///////honi l'iednionl,nul l'riiili
a number of the individiials show one or nioreof Kini iwii i's melanistie laelors.
Regardingthered/yellowpolymorphism,yellowspccimensha\'eollenIh'i'iireportedtromi'iedmontand
l.iguria CruKATi & Vfritv 1'^)12, Roh i 1913, Ki rriivviii \94^) anii .uf so Ireqiient in F-riuli that yellow
monomorphic populations aic llie rnle lor nian\' .neas (C'iuik I''(i2b, C . Mokandini pers. conini.).
Iti.^nalsobenoted thatallIheunniel.iniespt'iimiMissoulhol IheAlps,whencompared tosamplesnorth
ol Ihe alpnie ränge (e.g. North Swil/erland, Haxaria), show soine redn(lioii ol Ihe si/e ol lorewingspots.
C oneerning thesituatimiofcolom^polvniorphism in areas pi-ripheral to italy, mostol thepopulations
correspond to the nt)minate subspeeies. II niighl be worth noting, however, that specimens with golden
forewing spots are reported froni Wallis (Ki i ii i\\i i i l'*4.'^) and in part of Slovenjia orange hindwinged
individualsare prosent. Thespecies has also beeii re|>orled in C'orsiea (I'kiina & Wii r 1487: h3\), but this
datuni has not been confirmed by Runc;s (19HS).
lhuler llu'secircumstancesitshould berlear how niisU'.ulinr, Nie naniingot subspeeiesis fora eorri'it
iippreeialion ot thegeographic wiri.ilion ol IheSiark't liger Molli in n.ilnri',
2.2 Situation in peninsular llaly
Roughly south oftheTusco-Aemilian Apenninie watershed the Situation is i|uite simple, as only persona
phenotvpi'SarefounduptoCalabria (e.g.Cosia IS42,Stani)iuss ISSS,C'ai hi ki \ ISS7,SiAnnFk 1916,Fki:ina
i<i Wii I \'-)H7,ßikiACClNietal. 1994). Differeneestlohowt'vi'riKiurbelween po|>iil.ilions.isloIhi'Irequeney
ot the various melanistie morphs.
Despitesomeredorreddishspecimenspreser\eil in publii aiul prixaleiollections,cleare\ick'nu'ol .mv
of such individuals collected in the wild south of the very northern Apennines seemingly exists only in
StaljhI'R's (192.^) report. This was believed by Kiniii':wi1 1 (1943) to ri'(-iresi'nt a new mutation. The rare
occurrence of reddish specimens due lo norlhein alleles in peninsiiLn lLil\ is, oii Ihe contrarv, well in
agreementwithpopulationalthinking.
23 Situation in Siciiy
Iherecent rediscoveryofpopulationsol IheScaiiel 1 iger Molh inSuilvga\i'im|-ielusloi'xaluatecritically
Ihe theori'ticil problems ot Ihe pt)lvlopic subspi'ciesand ol Ihen laxonoinu licalnu'nl.
82
2.3.1 LilcTdlure data
Asbasc'd on litcrature,onlyonespccimciiofthcScarlct Ii^crMolh liad cvcrbecnCDÜected withcertainty
in Sicily (Makiam 1937). Mowuvlt, pcrsoini had becn generically rL'ported forSicily by Dui'onc iihi. (18%),
Spui.kk (1906) and Kirniwi.ii. (1941), all of whom sccmingly madc rufcrcncc to Hsi-i.k's (1794) and Ti<ii-
TSCHKi's(1834)quotations.Neverthclcss,thercisslrongcvidcnccthat,ashappened ina longlistofnominal
taxa, thcauthors wereconfusingSouth llalyand Sicilybccausctheseregionsonccjointly bclongcd tothe
SingleKingdomofthetwoSicilies,beingnonethelessknownalsoasIheKingdomofNaplcsandtheKingdom
ofSicily. TKiiiTscuKi- (1834) did notexplicitlyState thatpersona wasoccurring in Sicily, but that thedealer
G. Da(ii obtaincd somespecimensbredexlarvaeafterhisexpeditionsinSouth ItalyandSicily("inNeapel
und Sicilien"). TheexactcollectingsiteofDaiii. istherefore unknown. Asa matteroffact, nospecimen in
Tki.nstiiKi.'scollection(Natural IlistoryMuseum, Budapest)islabelled"Sicilien"asotherspeciescollected
byDaiii.inSicilyared..Ronkay,inlitt.).Hi;iiMi<(1790,quoted byOiiiimiiik,1911),whoapparentlyexamined
the same material in coli. j.C. Gikninc, (Frankfurt) like Esru< (1794) did later, was more precise in stating
thatthespecimensofpersonahad beenscntfrom thedistrictofNaplestoFrankfurtbytheKingandQueen
ofthetwoSicilies. ftisimportanttonotethatnospecimeno(personafromSicilyhasbeenfound uptonow
in theNatural History MuseumofVienna, wherethematerial byGi-kmnc. ispreserved (Hoknetal. 1990).
Makiam's (1937) record is froma beechwood ofM. Soroat m 1700a.s.l. in the Nebrodi ränge (North-
WestSicily).Thisrecord waslargelyoverlooked duetoboth thescantycirculationoftherelevantbulletin
andMakiam'smisidentifications.Thisled thesingletontobelinked tossp./^r'rso/w,sinceatthatümL-persona
wasprobablyacriticallyconsidered asthevalid nameforeverypopulation southoftheFo Valley. In fact,
Makiam(1937)firstidentifiedthespecimenasro/z/rt/zoi'/(nameofsomehybridst/()/»;;/»/rt x persona),and later
considered it to represent a variety of persona (Makiani 1939, and specimen's label). Contrary to the
expectations,thatspecimen(preservedinMuseoCivicodiStoriaNaturalediTerrasini,prov.Falermo)fully
conforms to nominaledominula, asalsoevidenced by Mariani's (1937) description and illustration.
2.3.2 Field data
Recently,severalspecimensoftheScarletTigerMothhavebeencollectedinSicilybyS.Btu.A,E. Bektaccini,
G. FiLMi, B. Giandolio, W. Hocems,and F.F. Romano, all from Nebrodi Mts, and correspond todoniinuln
(s.str.) (e.g. Bektaccini et al. 1994).
Asa matteroffact,theSicilianspecimens,beingcharacteristicofthenominatesubspecies,arenotonly
'taxonomically' unrelated topersona, still present in thesouthernmost tip ofCalabria (Sialuek 1916), but
alsototheothertwored-hindwingedsouthernsubspecies,vi'/..ponipalisandhithyuiai.Therängei)hiominula
(s.str.), hence, passes over peninsular italy and includesSicily (at least some part of the Island), For that
reason C. dominula dominula (Linnaeus 1758) becomes a polytopic subspecies.
Lastbutnotleast,theSicilianspecimensshowtraitscharacteristicofdominulanorthoftheAlps.Infact,
featureslikethewideforewingspots,theverysmallblackspotsofthehindwingand theextremelynarrow
black abdominal stripeareall unusual characteristics forany dominula population from .\'orth Italy.
3 Polytopic subspecies
In a polytypic species, a subspeciesshould bedefined as polytopic when it reoccurs in widely separated
areasamongwhich populationsbelongingtoothersubspeciesarefound.Suchareoccurrenceissaidtobe
independentaccordingtoWilson & Bwjwn (1957), Mayk (1963)and Mayk& Asm/xk(1991). In particular,
Mayk(1963)States:"...Thedistributionofthesubspecieswillbedeterminedlargelybythecorrelationbetween
thediagnosticcharactersand theenvironment;consequentlytherängeofa subspeciesmaysometimesbe
disct)ntinuous (polytopic subspecies).". Successively Mayk (1969) writes: "...it may happen that several
unrelatedand moreorlesswidelyseparated populationsacquireanidentical phenotype.Theevolutionist
knowsthat such populationsare not identical genetically, butsincethesubspeciesis notanevolutionary
concept,taxonomistssometimescombinesuchvisuallyidenticalpopulationsintoaSinglesubspccifictaxon.
Suchageographicallyheterogeneoussubspeciesiscaliedapolytopicsubspecies.Theonlyalternativetoits
recognition is not to recognizeany subspecies in sucha species.".
83
In modern evolutionary biology the subspecies concept is generally thought to have outlived its
usefulness (e.g. Wilson& Brown 1953, Minelli 1994),beingofsomeuseonlyfortaxonomicconvenience,
e.g. in the Classification of population samples (Mayr 1969), to depict cases of categorical geographic
Variation(Thorpe1987)orsubjectivelyperceived partitionsofcontinuousvariability(Cracraft1992).The
conceptual difficultiesengendered by thetraditional subspeciesconcept led Böhme (1978, 1979) to revisit
it from an ecological pointofview, aiming atestabUsliing a new role, possibly more linked to the reahty
ofbiological phenomena. Alternatively,sometaxonomistsrefused a priori thesubspeciesasa taxonomic
categorywithoutnatviralcounterpartinthewild (e.g.Poole1989).Nevertheless,thestudyofintraspecific
geographic Variation is of great evolutionary interest. Within this context, a rather neglected issue is
represented by thecharacterstates (hereafter 'characters', forthe sake ofbrevity) which are only shared
by distant populations ofa species.
3.1 Origin ofcharacterreoccurrence
It is evident that only the polytopism of the characters can be observed in nature; any reference to
subspecificentitieswould infactrepresentanabstractionsubjecttoseverecriticism(e.g.Wilson&Brown
1953). Therefore,forthesakeofnaturalness, thepresentsectionischieflydevoted tocharactersand their
States.Nevertheless,toalloweffectiveextensionofanycommenttothesubspeciesproblem,thediscussion
is restricted to characters discontinuously varying on a regional scale (e.g. Leucodonta bicoloria [Denis &
Schiffermüller],1775,acrossthePalaearcticRegion,cf.Schintlmeister1989),eventhough,possibly,through
transitionzoneswithpolymorphicpopulationsorintermediateindividuals.Infact,imderthesecircumstanc-
esthegeographicrecjuisitesnecessaryfordelimitingsubspeciesareclearlymet.Aimingatcircumventingthe
conceptualandoperationaldifficultiesforsubspeciesrecognitiondueto theexistenceoftransitionzones,
it is worth noting the arbitrary proposal of the so called 'seventy-five per cent rule', that is to say the
recognition of different subspecies in case at least 75 % of the individuals of adjacent subspecies are
determinable (Amadon 1949).
Inothercases,thedistributionofdifferentmorphscanbemosaic-likeaccordingtotheunevenpresence
ofsomealternativeecologicalfactorsonalocalscale(e.g.f.staticesandf.henseriofProcrisstaticesLinnaeus,
1758,cf.Reiche1964,Alberti1978,Tarmann1979).Suchatightcorrespondencemaybedueeithertodirect
habitat selection by the relevant genotypes, or to habitat correlation induced by external agents (e.g.
differentialpredationonalternativephenotypesaccordingtotheenvironmentalpatcheswhicharechosenfor
resting,environmentalinduction,etc.)(Weins1976,Aldridgeetal.1993,Jonesetal. 1993,Fraiersetal.1994).
Intheextremecasestheseprocessescanevenleadcontiguouspopulationstoshowsharpdiscontinuitiesas
tostrikingcharacters,butthecanonicalgeographica!requisitesfordelimitingsubspeciesareclearlymissing.
Fromatheoreticalpointofview,anywithin-speciesreoccurrenceofcharactersindistantpopulationscan
be due to: ecological determinism, environmental induction during development, chance, and common
genealogy.Suchcauseswillnowbereviewedseparately,althoughJointpresenceoroverlapsbetweenthem
might theoretically occur in nature, not least when more than two sites are involved.
3.1.1 Ecological determinism (selection)
This point corresponds to Mayr's (1963, 1969) idea. The independent evolution of identical traits due to
similarselectivepressuresisarathercommonphenomenonand mostofthetaxonomists" polytopicsub-
speciesderivefromthiskindofevents.Kudrna(1977)definesthesamebasicphenomenonas "pseudopoly-
typism", hopefully tocircumvent theconceptual problems arising when a taxonomist finds itdifficult to
make a decision.
Almostanycharacterisapossiblecandidateforpolytopism,includingphysiologicalandbiochemical
ones.However,theeffectsofecologicaldeterminismareeasilyobserved incertaincrypticmothschoosing
stones forresting which, matching with the local rockcolours, may show recurrent "adjustment toback-
ground' (cf. Ford1955) (e.g. speciesundergoingalbinism when theysettleincalcareousorchalkyareas).
Amodelfortheevolutionofphenotypicsimilarityiswellrepresentedbysomebark-camouflagingspecies
thatindependentlydevelopedmelanicpatternsinseveralindustrializeddistrictsofEurope(cf.Kettlewell
1973). Episodes of altitudinal or thermal melanism (Mani 1968, Kettlewell 1973), if not exclusively due
to environmental induction, can also produce similarity through selectionistic processes (e.g. between
separated mountain populations in contrast with lowland ones).
84
Character polytopism, determined by Community differences between areas, can occur in Batesian
mimics,vvhene\'ermatchingwithdifferentmodeis,oreiseMülleriancomimics,possiblyfollowingdifferential
selectionassociated with changesofthe abundance ofthedifferent pattern types in which thecomimics
themselvesareinvoh'ed.
Theselectionresponsibleofthecharacterreoccurrencemavacteitherondifferentgenesproducingan
equivalentphenotypiceffectoronasameunit(e.g.ararebutvvidelydistributedallele)whichistherefore
fixed in two ormore distantareas. It is noteworthy that many earlierauthors admitted that phenotypes
characteristicofparticulargeographicracesoccurredelsevvhereasaberrationsacrossthespecies"ranges.An
excellentaccountonthedilemmabetweenhomologousandanalogousgenesdeterminingcharacterreoccur-
rence within- and between species is Lattin's (1961).
3.1.2 Environmental induction during development
Totalh' different kind of environmental intluences capable of leading to phenotypic similarity between
separatedareasisex'idencedbvtraitswhichrepresentproductsorbv-productsoftheinteractionbetween
genesandexternalfactorsduringtheorganisms"de\elopmentalpathways.Themorphologicalresponseto
environmentalStimulicanfallwithinthelimitsofthenormofreactionofgivengenotypesorrepresenttrue
phenocopies,i.e.developmentalaberrationswhichoftenresemblewildmutantsorphenotypesparticularto
specialregions(Nijholt1991).Laboratoryexperiencesdemonstratedthepossibilityofobtainingimagines
resembling thoseparticulartogivenregionsbymanipulating parameterssuchaslight, temperatureand
humidity(Standflss1896,Kohler&Feldotto1935,Robinson 1971).Depositionofmelaninaswellasother
pigmentsisoftencorrelated withphotoperiodicresponseorfluctuationsofotherfactors(Vltllalme1969,
Watt1969,Hoffnlann 1973,Kettlewell1973,Shafiro1976,Douglas&Grlla1978,Br.akefield&Mazzotta
1995).Similarly,thepresenceortheabsenceofgivensubstancesinthedietcandeterminedramaticphenotypic
effects (PiCTET 1905, Wigglesworth 1972, Wilson 1985, 1986). Therefore, should therängeofspecies show
aparticularshape,thereoccurrenceofagivencharactermightbeduetodifferentialexpression(switching,
penetrance,etc.)ofgenesaccordingtoexternalfactorsvaryinggeographically,sothatsimilarepiphenotypes
are locall\" produced on a scattered basis.
3.1.3 Chance (probabilistic events)
Althoughstochasticeventsshouldalwavsbeconsideredaspossibledeterminantsofbiologicalphenomena,
the probabilityofcharacterpolytopism exclusively due to chance appears decisivelylow. An accidental
arousal ofa trait common to otherpopulations might theoretically happen in a popuIation (concordant
mutation).However,thatcharacterwillbelikelytofacedifferentselectiveregimesbecauseofthediversity
ofthe relexant ecological scenarios. Accordinglv, should that character increase in frequency and attain
fixation,morelikelvecologicalexplanationsshouldbetested,unlessitisaneutralcharacter,viz.notaffecting
theadaptivelevelsofitsbearers. Hvpotheticallv,neutralcharacterscouldpersistinsomepopulationsand
e\enattainfixationbvgeneticdriftor,followingthedifferentrouteoffounder'seffect,anewcolonycould
originate frombearers ofthemutant trait. Thereare, however, conceptualand operational difficultiesin
establishingwhetherornotonecharacterisadaptive.Inanycasegeneticanalysesshouldbecarriedoutto
ascertainthepossibilitx'oflinkagebetweentherelevantgenes(possiblvevenslightlydisadvantageous)and
othersgreatlyenhancingthefitnessofthebearers(e.g.somephvsiologicaltrait),inwhichcaseselectionists
hypotheses would again explain the phenomenon (cf. Koiima & Lewontin 1970).
Contrarytoa longheld opinion,thereissomeevidencethatgenitalicpiecesnotinvolved inlock-and-
keymechanisms(orinchoosingsubstrataforo\iposition)donothaveahighadapti\esignificance(Cesarom
etal. 1994),beingcomparativelvfreefromfunctionalrestraints.Therefore,toacertainextenttheyshould
be unaffected by strong selective pressures such as those modelling other characters, e.g. wing pattern
characteristics, which areamongst the most important ones in relating an indi\idual to its environment
(abiotic,biotic,andsexual).Therefore, thevcould theoreticallvbeselected tofeststochastichypothesesof
characterreoccurrencebetween distant populations. However, this would requiretheexistenceofsharp
discontinuityinthegenitaliabetweenadjacentpopulationsofthesamespecies,whichisinconflictwithbeing
recognizedasconspecific.Infact,duetotheclearh-polvgenicnatureofsuchmorphologicaltraits,anyabrupt
gapbetweenmorph typesprovidesindirecte\idenceofgeneticdivergenceofacertainextent.
85
3.1.4 Commongenealogy(phylogenesis)
Thepossibilityofcloserkinshipbetweensomewidelyseparatedpopvilationsratherthantheneighbouring
onesisnotnecessarilyinvalid.ItfoUowsthatthereoccurrenceofcharactersisnotindependent,asclaimed
byWilson&Brown(1953),Mayr(1963,1969)andMayr&Ashlock(1991),butderivesfromatightergenetic
and phylogeneticcontinuityatinfraspecificlevel. Atleastthreemodeiscanbeproposed.
3.1.4.1 Geographie vicariance
Sharingthesametraitswouldbetheresultofpastgeneflowwithinonegroupofpopulations,uponwhich
ordinarybiogeographiceventsactedbyfragmentingitsrängeandallowingthederivedsubgroupstocontact
otherconspecificpopulations. From theoriginal groupofpopulationsderivetwoormoreseparatedsub-
groups,scatteredinacontinuumofconspecificbutlesserrelatedpopulationshavingexperiencedpartially
differenthistories.Theclosergenealogyamongthesub-groupsisinferred,indeed,bythecharacterswhich
remain shared, at least for some time.
3.1.4.2 Dispersal
When long distance dispersal is taken into account, the possible Constitution of a polytopic complex is
evident. For example, following prevailing wind directions a given territory canbe colonized notby the
nearmostpopulations,butbyindividualsfromdistantpopulationswhichthenceintroducethecharacters
oftheirown population (founder'seffect).
3.1.4.3 'Shift' of the in-between populations
Itisunnecessaryalwaystoinvokemovingindividualsorcomplexrängedynamicstoexplainnon-independ-
entcharacterreoccurrence.Givenageographiccontinuumofhomogeneouspopulations,apseudovicariant
pattern may arise from the shift of the middle ones toward a different array of characters, with the
populationsatbothextremitiesremainingunaffected.
Thephenomenoniscomplementarywiththeoneaccounted forbyecologicaldeterminism,although
decisivelymoreprobable.Infact,insteadofbeingtwodistantgroupsofpopulationsconverginginresponse
to similar selective pressures, it is the group in-between which undergoes changes because of different
ecological conditions. Ecologystill playsa majorrole,butdoes notproduceindependentpolytopismbut
rather the diversification of some populations interposed between conservative ones, at the same time
becomingapolytopiccomplex. Underthesecircumstancesitisafruitlessdiscussiontoseparatepaleoeco-
logicalfactors(i.e.historicaltypes)fromcurrentecology,asthisdistinctionhindersthetemporalcontinuity
ofasamephenomenon.Aprogressivelychangingecologicalbackgroundallowsboththeshifttowardnew
characterstatesand theirmaintenance.
AsimilarreasoningwasfollowedbySheppardetal.(1985)whilereconstructingthehypotheticalancestral
pattern of Heliavüiis mclpoiuciic (Linnaeus, 1758) and H. craio (Linnaeus, 1758). The authors rejected
consideringthepatternsoccurringintheAmazonbasinasancestral,notleastbecauseofthesimilarityof
patternsbetweenpopulationsnorthandsouthofthatbasin.Infact,ifthissimilarityhadbeenindependent,
it would have required admitting highly improbable phenomena of convergence and assuming, if not
independent,dispersaloverthousandsofkilometresalongtheAndeanrimofthebasin.Sheppardetal.(1985)
parsimoniouslyconcludedthattheAmazonianpatternsweresecondarilyderivedandtheextra-Amazonian
onesclosetotheancestral.
4 How to explain the presence of nominate doininiiln in Sicily?
Itshould benoted thatauthoritativediscussionson thepolytopicsubspecies (e.g. Mayretal. 1953, Mayr
& Ashlock1991)did noteventakeintoaccountthepossibilityofcharacterreoccurrenceinmorethanone
character, since reoccurrence of more characters would have represented a probabilistic and biological
nbsurdity.TheclosematchingbetweentheSicilianandnorthernspecimens,whencomparedtopersona,is
thereforeparticularlysurprising,whenconsideringthenumberofthecharactersinvolvedand thedegree
ot their genetic/ontogenetic independence (hindwing background colour, width of theabdominal black
stripe, hindwing mclanism and width ofthe forewingspots). Thorpe (1987), in fact, hasproperlypointed
outthatwhilestudyinggeographicvariabihtytheactualcongruenceofdifferentcharactersisofvalueonly
if they are geneticallv/ontogenetically independent. Moreover, with characters mutually independent,
liighlevelsofcongruencebetweensamplesfronidistantareaswouldsuggestunderlyingvicariance-events
asresponsible(viz.phylogenetickinship),whereaslowcongruencewouldindicatecontrolbypresent-day
ecological factors (Thorpe 1987).
ToInterprettheoccurrenceofdoiiiiiiiila phenotypes in Sicily, what is known about thegenetics ofthe
colour forms and the presence of pcrscvuj phenotvpes in the southernmost tip of Calabria immediately
permitdiscardinganyhypothesisofenvironmentalinduction.Stochasticexplanationsarealsohazardous,
asthecharactersinvolvedaresomanv-Therefore,assuminganarchaicpresenceoipersonaontheNebrodi
Mts, to return back to nominate doniiiiula would have required too many character reversals.
Nevertheless,according tothecanonicalworkinghypothesisforthecharacterpolytopism,analogous
selectiveregimeswouldhaveengenderedtheproperecologicalcontextforsuchcharacterreversals.Forthis
tobetrue,itwouldhaverequiredsuchmarkedecologicalsimilaritiesbetweentheSicilianbiotopesandthe
main Europeanpartofthespecies' rängethatallthetraitscharacterizingpersonawouldhavebeensubject
to strong directional selection to obtain a "new' donünnia on the Island. Nonetheless, the number of the
charactersinvolved,aswellastheirgenetic/ontogeneticindependence,makeagainapreciseturningback
todo)ninnln fromperso)iaa highly improbableevent.
As for the remaining hypotheses, the proposal ofa vicariance model would require an exageratedly
complicated theoryofcrustalmovementsand landbridges,notsupportedbythetertiaryandquaternary
geological history ofthe Central Mediterranean (cf. Azzaroli & Cita 1980, Catalano et al. 1995). As the
ScarletTigerMothisabsentinthecentralandsouthernIberianPeninsulaandthewholeofNorthAfrica,a
colonization of Sicily from the south can reasonably be excluded. The species is also absent from other
Mediterranean islandsand in the Hast Mediterranean itshowsa differentcombination ofcharacters. The
possibilityofaccidentalintroductionisalsolessened,astheSicilianrecordsarenotfromcoastalareasnear
portsandtowns,butfromwellpreservedinnermountainzones. Itshouldalsobenoted thatthelarvaedo
notfeed upon treesused inreforestation.
Accordingtothe'shiftofthein-betweenmodel",theNebrodipopulationswouldrepresentthedescend-
antsofnormalredunmelanicdominulawhich,spreadingfromthenorth,colonizedwholepeninsularItaly
andSicilv.Infact,severalnorthernspeciesreachedSicilythroughtheApenninicrängeandcurrentlysurvive
ontheIsland"smountainmassiveswithrelictpopulations.OncethecolonizationofSicilywasassessed,it
wouldhavebeentheApenninicgroupofpopulationsthatdiverged,givingrisetoVnepersonaphenotypes.
Therefore, instead ofclaiming highly improbable theories in order to Interpret the presence ofnominate
dominulainSicily,thequestionbasicallymovestotheoriginofpersonainpeninsularItaly,amoreparsimo-
nioushypothesiswhichwillbetentativelvdiscussedinthenextparagraph.
4.1 Melanism and the shift red-yellow in Apenninic day-flying moths
TheoriginoipersojwinpeninsularItalystillneedsadequateexplanation;nevertheless,somebizarrecongru-
enceswhichoccurintheApenninesthrowsomelightonthephenomenon.IntheItalianPeninsula,infact,
two otheraposematicday-flying mothsreplaced an archaicred/black-unmelanic pattern (R/m), widely
spreadinthenorthernareasoftheirranges,withayellow/black-melanicone(Y/M),namelyZi/gaenaephialtes
(Li.WAELS,1767)andZ.transalpina(Esper,1782).ThefactthatinbothspeciestheY/Mpatternismorerecent
thantheR/monecaneasilybeinferredthroughoutgroupcomparisonwiththepatternscharacteristicofother
Zygaenaspecies,particularlvthosemorerelated phvlogenetically.Asamatteroffact,bothZygaeiiadori/enii
OcHSENHEiMER, 1808 (sister species of Z. ephialtes) and Z. angeticae Ochsenheimhr, 1808 + Z. hippocrepidis
(Hüb.ner, [1799]) (making up an Artenkreis together with Z. transalpina) (cf. Naumann & Tremevvan 1984,
HiLLE & Naumann 1992) show the pattern R/m.
In Zygaena ephialtes thearchaic R/m pattern is widespread from Francetocentral Asia, even though
populationswithindividualsbearingaY/mpatternarefoundoccasionally.WiththeexceptionoftheTurkish
populations(R/m),themelanicpatterns(R/MandY/M)arecharacteristicofthesouthernpartofthespecies"
ränge,fromSpaintosouthernRussia. However,thefourmainpatternsoiephialtes(R/m,R/M,Y/M,and.
87
scarcer, Y/m) coexist over large extensions, the species showing also many more types of pattern in
particularcontactzones,e.g. intermediatemelanicsororangespecimensduetomultiallelism withdiffer-
ential penetrance and the disruption ofdifferently coadapted genotypes (Bovey 1941, 1966, 1983, Reichl
1958, 1959, Dryja 1959, Bullini et al. 1969, Gabriele 1990).
As for Italy, the Situation is rather simple throughout the peninsula. Apart from some "relictuar
presenceoftheR/M pattern inNorthTuscany(Verity 1930),allalongtheApenninesmonomorphicY/M
populations occur (the polymorphism relevant to the number of forewing spots not being considered
here). Thedistribution ofthe colourpolymorphism in North Italy is more mosaic-like, with Y/M, R/M,
and, occasionally in the western Alps, even R/m populations (Gabriele 1990) (fig. 2).
TheSituationoiZygaenatransalpinainItalyis,onthecontrary,remarkablycomplexasthecontactzone
between northern (R/m) and southern patterns (Y/M) is somehow streaked along the Apennines. R/m
patternscharacteristicofcentralEuropeandtheAlpsdoapproximatelyoccurovermostofNorthandCentral
ItalyuptotheTiberValley. Itisnoteworthythat,likeiordojuimila,inFriulipolymorphicpopulationswith
red/yellow and unmelanic/melanic individuals occur (Reiche 1962, Bovey 1981) (interestingly, in the
surroundingsofTarnovaalsoZ.tvigclicncshowspopulationswithabundantY/mindividuals,L.Morinpers.
comm.).FromCentralItalysouthwards,theR/mpatternbecomesprogressivelyrestrictedtoinnermountain
andeasternzones,leavingoutthewesternpartofthepeninsula.Accordingly,Y/Mand R/Mpatternsare
increasinglyfrequent from thewestern hillsofcentral Italyto themountains ofSouth Italy (fig. 3).
Because of the spacial heterogeneity due to the orientation of Apenninic ridges, Isolation effects or
geographicallyasymmetricgeneflow,aswellasthepolygenicnatureofthemelanismandmultiallelismfor
backgroundcolouration(Bovey1981,Reiche1992),eachtransalpinapopulationshowsinpracticeapeculiar
combinationofphenotypic freciuenciesofcolour forms. Highly polymorphic populations with all sortof
intermediatesareparticularlyfrec]uentalongthesouthernhalft^fthePeninsulawherethetwomainbulks
ofpopulations meet.
Twomoreaspectsdeservefurtherattention,i.e.thepresenceofR/Mpopulationschieflylinked tolow
altitudeareasfromLiguriatoTuscany,similartomanyotherspeciesofZi/gaena,andmainlyconsistingof
stout-bodied individuals (Costantini 1916, Verity 1930, Burceff 1951, Alberti 1971), and of relict R/m
offshoots ofthese populations in somelittoral localities ofcentral Italy.
Despitethecomplexity ofthecolourpolymorphism ofthe Italian transalpina, thereislittledoubt that
theY/MpatternsrepresentapurelysouthernSituation,thepresenceofyellowandofmelanicphenotypes
beingpositivelyassociated with warmerand southernareas. Thisisalsodemonstrated bya transectina
favourable area at the border between Latium and the Abruzzi, where two parallel mountain ridges,
respectivelywestandeastofRovetoValley,showaNW-SEorientation. Atthesouth-westernfoothillsof
bothridges,noticeablywarmerthanthenorth-easternones,Y/Mindividualsprevail.Thefrequencyofyellow
specimens, as well as melanic ones (both R/M and Y/M),decreases goingup themountains. On the top
and onthecoolernorth-easternslopesofboth ridgesR/m individualsaredistinctlymoreabimdant.
Theecologicalbackground allowingtheshiftofthe R/mpatternofZi/gacnaephialtcstoward theY/M
onewasidentifiedasachangeoftherelativeabundanceoftwoMüllerianmimicryringsduringthePleistocene
period.Accordingtotheproposedmodel,inSouthItalycpJiialteswouldhavedivergedfromamainEuropean
ring,involvingseveralspeciesoiZygaenasharingaR/mpattern,andenteredintoamoreMediterraneanring
basedonaY/Mpattern,inwhichthemostabundantcomimicsarethermophilousspeciesbelongingtothe
genusSyntomis(Bullinietal.1969,Turner1971,Sbordonietal.1979).Thereisstrongevidencethatthesame
basicphenomenonhasoccurredmZygaenatransalpi)m,althoughincompletely.
ThegeneralappearanceoiCalliinorpliadoininiilaobjectivelylooksquitedifferentfromthatcharacteristic
oftheZygaenaortheSyntomisspecies,particularlyinsize.Nevertheless,biochemical,eco-ethological,and
colourpatterncongruences(Frazer&Rothschild1960,Rothschild1961,1985,Kayetal. 1969)suggestthat
theyareall involved in thesameMüllerian rings. As a matteroffact, Rothschild& Lane (1960) showed
thatsomeinsectivorousspeciesofbirdsareunabletoperceivethedifferencebetweenC.domiindaandspecies
oiZygaenaandTyriajacohaeae(Linnaeus,1758),sothebirds,havingexperiencedthelatterspecies,trytoreject
orevenescapewheneitherdominulaorspeciesofZygaenaareoffered to them.
InpeninsularItaly,thetwoalternativemimicryringsarenotmutuallyexclusive,butcoexistoverlarge
extensions.However,asthereisadistincttrendfortheY/Mringtobecomeprogressivelyscarcernorthwards
orathigheraltitudes,itcanbesupposedthatitattaineditscurrentspeciescomposition,includingancestral
dominulapopulationswhichoncewereredunmelanic,inxerothermicrefugialareasofsouthernItalyduring
thePleistoceneglaciations.ItisnoteworthythatSicilyremainedunaffectedbytheshiftR/m-Y/M,apparently
because of unsuccessful colonization by some species. In fact, if is compared the lepidopteran species