Colour variation in female Lestes disjunctus Selys: a second example of a polymorphic lestid (Zygoptera: Lestidae)

2006·1.1 MB·English

by  Robb, T

Odonalologica35(1):31-39 March I.2006
Colourvariationin female
Lestesdisjunctus Selys:
asecond exampleofa polymorphiclestid
(Zygoptera: Lestidae)
T.Robb¹*,H. Van Gossum² andM.R.Forbes¹
1DepartmentofBiology,Carleton University, 1125 Colonel By Drive,Ottawa,
Ontario,K1S 5B6, Canada
2EvolutionaryBiologyGroup,UniversityofAntwerp,Groenenborgerlaan171,
B-2020Antwerp, Belgium
Received January25, 2005/Revised andAcceptedSeptember1,2005
Coexistence ofdiscrete 9 colourmorphsisacommoncharacteristicofmanyodon.
species. Surveys have found thatforsomeNorth American and Europeangenera,
half ormore ofthespp. show female-limited polymorphism,while inother genera,
9polymorphismappearsfarlesscommonamong spp.One suchgenusisLesteswith
reportedly only onesp. (L. sponsa)beingpolymorphic. Here aredescribed andro-
morphsandheteromorphsforL. disjunctus.Female-limited polymorphismmightbe
morecommon,eveninthisgenus,than isperceivedcurrently. 9 morphfrequencies
wereestimated for4consecutive yr.:andromorphsconstitute approximately 16%of
mature 9 9sampledandthisproportionisfairlyconsistentbetweenyears.Similarto
otherpublishedreportsonother spp.,andromorphsandheteromorphsinthis study
populationdid notdifferinwinglengthormass.Seasonal patternsinrepresentation
ofdifferent morphssuggest thatfurtherresearch shouldbe doneontimingofemer-
gence ofandromorphsversusheteromorphsinthisand perhapsotherspp.
INTRODUCTION
Many species of damselfliesand dragonflies exhibit discrete female colour
morphs (e.g. FINCKE, 2004). Most typically, two (or sometimesthree) mature
femalecolour morphs are foundincoexistence.Onefemalemorph (furtherre-
ferredto as heteromorph) is distinctively colouredcompared to themale, while
theothermorph (andromorph) shows similarcolorationandsometimespattern
* Corresponding Author; Tonia Robb, Tel: [phone] x4491; Fax; 613-520-3539; E-mail:
[email protected]
32 T.Robb,H.vanGossum&MR.Forbes
as theconspecific male.
Laboratory crossing experiments havebeencompleted forfivespeciesandindi-
categeneticinheritanceoffemalepolymorphism(e.g. ANDRES&CORDERO,
1999;SANCHEZ-GUILLEN et al„ 2005). Morph typeappearsdeterminedby
Mendeliangenetics, withanumberofallelesequal tothenumberoffemalecol-
our morphs andallelesare likely situated on asingle autosomallocus. Further,
randomgenetic processes (e.g. genetic drift, foundereffects) are insufficientto
explain maintenanceoffemalemorphs (i.e. female-limitedpolymorphism is un-
derselection; ANDRESetal., 2000,2002; WONGetal„ 2003).
Femalemorphdifferencesare notrestrictedto variationinbody colorationor
pattern.Indeed, severalstudieshavedemonstrateddifferencesinbehaviouralrep-
ertoiresbetweenandro-andheteromorphs (e.g.ROBERTSON, 1985;FORBES
etal., 1997).Forexample, heteromorphsoftenoccupy densevegetationandavoid
unwantedcopulations byflyingaway fromanapproaching male,whereasandro-
morphs use moreopenhabitat, donot fly large distancesanddirectly facemales
inapparentagonistic interactions(e.g. FORBESetal., 1997;VAN GOSSUM et
al.,2001). Severalresearchers havenot founddifferencesinbody size measures
betweenfemalemorphs(CORDERO, 1992;THOMPSON, 1989;FORBES,1994;
LAJEUNESSE &FORBES, 2003). CORDERO etal.(1998), however,reported
andromorphs were on averagelarger compared to heteromorphs intheir study
on Ischnuraelegans, indicating the possibility thatmorphs for somespecies or
somepopulations may differinmorphometries.
In the majority of species where variationin femalemorph frequencies has
been examined, thefrequencyofandromorphs appearsrelativelyconstant with-
in a population (FORBES et al., 1995;CORDERO & EGIDO PEREZ, 1998;
SIROT, 1999). McKEEetal.(2005) reviewedallcurrent literature,andconcluded
thatvariationinandromorph frequencies betweenpopulations islimitedandhas
been reported mainly intheorderof 10-30%,with somevariation dependenton
species. Additionally, WONG etal. (2003) showedconsiderablestability or ho-
mogeneity of morph ratioswithinafewsites across years. Ithas beensuggested
thatselectioncontributestothemaintenanceofsimilarmorph frequencies across
nearby populations (ANDRES etal.,2000). However, onenotableexception is
the damselfly I. elegans, forwhicha survey of morph frequencies in NW Spain
showedinter-population variability inandromorph frequencies ranging from4-
-91%(SANCHEZ-GUILLEN etal.,2005).
Recently, FINCKE (2004) reviewed the distributionof female-limitedpoly-
morphismthroughout suborder, familyandgenus fortheNorth Americanand
European species. Heroverview indicatesthatsuch polymorphism isthreetimes
morecommoningeneraofZygoptera compared to Anisoptera.Second, insome
species-rich damselflygenera,noteworthy Ischnura, Enallagma and Argia,about
50%ormoreoftheNorthAmericanandEuropean species show female-limited
polymorphism.FINCKE(2004)excludedtwo polymorphic species(Lestessponsa
Colourvariation infemale Lestes disjunclus 33
andLibellulajesseana) fromheranalysis becauseeachrepresented less than5%
ofotherwisemonomorphic genera.
Here,wereportonfemale-limitedcolourpolymorphism infemaleLestesd.dis-
junctus Selys (hereafter referred to as L. disjunctus).Wedescribe thephenotype
oftheandromorph incomparison to theconspecific maleandtheheteromorph.
Wealso provide informationon thefrequency ofandromorphs in onepopula-
tion forfourconsecutiveyears,and examinewhetherandro-andheteromorphs
differ inwing length and/ormass. The approximate age of heteromorphs and
andromorphs wasalsoassessed to determinewhetherthis colourvariationis in-
deedatypicaladultcolourpolymorphismorsimplyanageeffect withsomeolder
femalesacquiring pruinosity. Finally, wenotedwhenandromorphs andhetero-
morphs wereobserved first during theseason, inthreeyearsofstudy.
METHODS
Lestesdisjunctus isa widelydistributed species in Canada and is somewhatsmaller than other
Lestes species(WALKER, 1953).Thespeciesfrequentspermanent marshesorbogsand isoneof
nine Lestes speciescommontocentral Canada. Atemergence,malesand femalesappearsimilarin
colour showinga bronzecoloration with thepaleareasbeingadull yellowishcolour (WALKER,
1953).L. disjunctusmaturation occursinjustover2weeks afteremergencewith females takingon
average2 dayslongerthan male conspecifics(SAWCHYN&GILLOT, 1974).Itisatmaturitythat
males developabluish pruinositynotpreviouslydescribed forfemales(WALKER, 1953).
Allsurveys andcollectionswerecompletedatBarb'sMarsh,located neartheQueen’sBiologySta-
tion (45°37’N,76°13’W).Asdescribedby ANHOLT(1997),themarshalsohasaseasonallyflooded
areaandbothmarshandfloodedareaarebounded byahayfieldand mixedwoods. Wefound Lestes
species inallstages ofmaturityprimarily in theseasonallyflooded areaaswell assomeindividuals
in thesurroundinghayfield. Thus,all surveyswereconcentrated in theseareas.AtBarb’s Marsh L.
disjunctusemergenceusuallybeginsattheend ofJune andadultscanbe observedaslateas1 Au-
gust.Both L.rectangularisand L. congeneralsoemerge fromthemarshbut arenotasabundant(T.
Robb,unpublisheddata).
Dailysurveys,foradultsofallLestesspecies,whichwereonehourinduration(1100-I200h),were
conducted inthesurroundingareaofthemarsh in2002,2003 and2005. Surveyswerenot complet-
edondayswhenitrained between 1100-1200h. Webeganconductingtheone-hour surveys on29
June throughto 1Augustin2002 (13surveys intotal),28 June throughto 19July,2003 (17surveys
in total)and4Julythroughto 31 July,2005 (21surveys intotal).Thedate oftheinitial surveycor-
respondedtowhenthefirstyoungadultL. disjunctuswas observed.Duringsurveys, allL. disjunctus
observedwerenetted. Uponcapture, thesex, ageofthe adult(teneral,youngormatureadult)was
recorded,accordingtoWALKER (1953).We alsomeasured thedistancebetweennodusand distal
endofpterostigmaoftheright forewingfor eachindividual (tothenearest 0.01 mm),usingMitu-
toyo®digitalcalipers. Ifanindividual wasfemale,wenotedwhether she displayedandromorphor
heteromorphcharacteristics(seeResultsectionfordescriptions).Priortorelease,each damselflywas
givenamarkon oneofthehindwingstopreventrecaptureonthat day. Markingwasdone with a
permanentmarker(Stanford®fine pointSharpie)andcolourcombinationswereuniquetodateof
marking.Recapturesonsubsequentdayswerenoted.
In2004,wedid notsurvey.However,wecollected matureadultL. disjunctusbetween 11 Julyand
19July.For allindividuals collected,werecorded sex, lengthoftherightforewingasaboveand also
mass(tothe nearest0.001 g),usingaMettlerSAE100DigitalScale,Foradultfemales,werecorded
34 T. Robb,H.vanGossum& M.R.Forbes
if theyhadandromorphorheteromorphcharacters.
Foreachdamselflysurveyed,wealsocounted thenumberofparasiticwatermites(Arrenuruspol-
lictus)and wescoredengorgementforeachmite.Theparasiticmites thatwerefoundonL. disjunctus
engorgethroughoutthehost’smaturationperiodanddropofftheirhostsduringboutsofreproduc-
tioncentredatappropriatewaterbodiesormarshes(cf.SMITH,1988).Thusthedegreeofengorge-
mentcanprovidesomeindication oftheageofthehostfollowingMITCHELL(1969)andSMITH
&COOK(1991).Inaddition,mite scarsindicatethatengorgedmiteshave droppedoffrecentlysug-
gestinganindividual has had atleast onebout of reproduction.The degreeofengorgementwas
scored usingasimilarscale,previously used forarelated mite species(FORBES elat, 1999).Mite
engorgement scoreswere0, 1,2,3,4or5where0wasgivenifthemitebody wasflatwith nosepara-
tionbetween ventralscleritesand thedorsal plate(noengorgement)andascore of5was givenfor
fullyengorgedmites.Averagemiteengorgementscoresfor eachdamselflywerecalculated.
Statisticalanalyseswerecompletedin R(version2.1.1,IHAKA&GENTLEMAN, 1996).
RESULTS
Weobservedtwo distinctLestes disjunctusfemalemorphswithinonlythema-
ture individuals.For visualexaminationofthefemalemorphs andmales, digital
images may be obtainedupon request from [email protected]. Hetero-
morphs never showed blue coloration, and were lighter in appearancewitha
similarcolorationto conspecific males prior to pruinosity (WALKER, 1953).
Typically, andromorphs had severalmale-likecharactersintermsofcoloration.
Andromorphs hadbluecolorationontherearofthehead,pronotum,lowerparts
ofthepleura ofthe pterothoraxandonabdominalsegmentsI, IXandpartially
onsegment X. Thegreenish colouredantehumeralstripe ofandromorphs also
was similarto males, however, similar to heteromorphs, the mid-thoracicand
humeralstreak was broaderthanthoseobservedonmaleconspecifics. WALK-
ER(1953) previously describedthatonly mature malesshowedthe bluishprui-
nosity on specific areas ofthebody, most notablyatthe rearofthehead, sterna
andlowerpartsofthe pleuraofthepterothorax, andabdominalsegmentsI, II,
VIII, IX andX.
Wereportonnumbersoffemalemorphsforonlymatureindividualsas weonly
observedandromorph characteristicson mature femalesinall surveys. During
2002weobservedatotalof228mature individualsofwhich69werefemaleand
159 were male.During 2003we observed 231 mature individuals, ofwhich 28
werefemaleand203weremale.Although wehadmoresampling days in2005we
observedonly 174individualsofwhich116werefemaleand58weremale.Ofthe
133mature individualscollectedin2004, therewere53 femalesand80males.
Thefirstandromorph appeared in oursurveys on 16 July in2002and6 July in
2003whilemature heteromorphs andmaleswereobservedbeforethosedates(Fig.
1).Andromorphs wereobservedonthe firstdayofcollection, 4 July,along with
bothmature heteromorphs and males during the 2005surveys (Fig. 1).Andro-
morph frequencies were 15.9%, 17.9%and17.2%forthesurveyscompleted during
theyears2002,2003and2005,andforthecollectionin2004theandromorph fre-
Colour variation in female Lestesdisjunclus 35
quency was 13.2%.
Thefrequency of an-
dromorphs was not
different between
years(x2=0.79,df=3,
p=0.85).
There were very
few recaptures over
thecourse ofthesur-
veys in2002(2 recap-
tures)andin 2003 (4
recaptures)anditwas
only malesthat were
recaptured in both
those years. How-
ever we did recap-
ture 36 individuals
in 2005, of which 19
were heteromorphs
and 7 were andro-
morphs. In support
of our hypothesis
heteromorphs recap-
tured between 1 and
18 days past initial
capture datestill ex-
hibited heteromorph
characters. We ob-
servedwornwings as
wellassomepruinos-
Fig. 1.Daily frequenciesofandromorphs (opensquare)andhetero-
ityontheventralsur- morphs(closedsquare)observed duringthesurveysconductedin2002,
faceof thethoraxon 2003 and2005.Theinitial datecorrespondstothefirstdayofthesur-
the individuals col- veysforthatparticularyear.
lected during the last
two surveysof2005indicatingtheendoftheflight season. We didnotnoteworn
wings during the2002and2003surveys.
Wereporton miteengorgementandmitescars only fortheyear2005as this
hadthegreatestnumberofdayswhenbothheteromorphs andandromorphs were
observedwithmites(Tab. I). Theaveragemiteengorgementscores didnotdiffer
betweenandromorphs andheteromorphs (Tab.I;W =\l\,p- 0.68). Mitescars
were observedon6ofthe 20(30%)andromorphs observedwiththefirstandro-
morph to havemitescars observedonthe 8 July2005. Of the96 heteromorphs
36 T.Robb, H.vanGossum &M.R.Forbes
Table I
Medians(interquartileranges inbrackets)oftheaveragemiteengorgement scoreondateswhenboth
heteromorphsandandromorphswereobserved duringthe2005 survey.Onlydamselflieswith mites
wereused incalculation ofmedians andforcomparison
Andromorph Heteromorph
Date n Median n Median
4July 2 2.99 (2.98-3.00) 2 2.50(2.00-3.00)
5July 1 3,97 5 2.88 (2.25-3.50)
6July 2 4.02(4.00-4.03) 6 4,00(2.82-4.02)
7July 1 4.00 11 4.08(4.00-4.20)
8 July 1 3,40 7 4.16(4.00-4.71)
11 July 1 5.00 1 4.17
20July 3 4.08(4.00-4.42) 2 3.43(3.00-3.86)
observed 16(16.7%) hadscarswiththefirst heteromorph to havemitescars ob-
servedonthe 11 July2005.
There were no differencesin size (wing length) between andromorphs and
heteromorphs surveyed in2002,2003and2005(Tab. II;2002.W=394,,p=0.22;
2003, W= 77.5,p = 0.24;2005, W = 1048,p= 0.85). Neitherwere therediffer-
ences inwinglength or massbetweenandromorphs and heteromorphs collected
in2004(Tab. II;winglength, W = 196.5,p= 0.36;mass,W = 150,p =0.78).
DISCUSSION
Two distinctfemaletypes, oneheteromorph andoneandromorph, werefound
to occur fora Lestes disjunctus population in central Canada. Andromorphs
were similarincolorationto maleconspecifics, howeverpattern(both themid-
thoracicandhumeralstreak)was similarto heteromorphs. Thefrequency ofan-
dromorphswas similarbetween allyearsexaminedand ranged between 13.2%
in2004to 17.9%in2003.Thisrangeoffrequencies andsimilarity betweenyears
iscomparable tootherodonatespecies exhibiting female-limitedpolymorphism
(e.g. McKEEetal., 2005).
Wefoundno body size differencesbetweenheteromorphs andandromorphs
forallyearsnor didwefinddifferencesinbody massforthe individualscollected
in 2004.Although there are instanceswhere femalemorphs differinbody size
(CORDERO etal., 1998) therehas beenseveralstudiesindicatingno differenc-
es inbody size between femalemorphs (e.g. LAJEUNESSE & FORBES, 2003
andreferencestherein).
Andromorphs were firstobservedmid-to late-seasonin2002andmid-season
in2003.Whilein2005andro-andheteromorphs wereobservedonthefirstdayof
thesurvey. Anearlierstudyfoundthatsexually matureEnallagmaborealeandro-
morphs appeared inthepopulation earlierinthe seasonthandidheteromorphs
Colourvariation infemale Lestesdisjunctus 37
Table II
Femaleandromorphand heteromorphmedian winglength(mm)andinterquartileranges (IQR)for
individuals surveyedduring2002,2003and 2005. Median and IQRofwinglength(mm)and mass
(g)forfemale andromorphsandheteromorphscollected during2004arealsopresented(see textfor
statisticalcomparisons)
Andromorph Heteromorph
Median IQR Median IQR
2002 13.85 13.40-14.26 14.20 13.90-14.76
2003 14.63 14.23-14.66 14.88 14.43-15.22
2005 14.63 13.96-14.98 14.60 14.17-14.98
2004
-winglength 14.65 14.05-15.24 14.99 14.50-15.56
-mass 0.638 0.613-0.733 0.648 0.571-0.708
(FINCKE, 1994). In thatstudy, FINCKE(1994) suggested thatif thegenesfor
body colourandtiming ofemergencewerein linkage disequilibrium, thenthis
linkage disequilibriumcouldexplain andromorphs appearingearlier.Ifanything,
itseemsandromorphs areappearing atthesametimeorlaterthanheteromorphs
inL. disjunctus. Itwouldbenecessary,however, toobtainactualemergencedates
forthedifferentmorphs toaddressFINCKE’s (1994) idea, adequately.
This studyprovides asecondspecies fromtheLestidfamily to display female-
limitedpolymorphism. Itis unlikely thatthis isa case ofage-related colourpol-
ymorphism(all femaleswouldacquire themalelikecolourationas they age) for
several reasons. First both andro-and heteromorphs were foundwith similar
miteengorgementscores throughout the flight period suggesting that andro-
morph characters develop early on in maturationandonly for some individu-
als. We also foundfullyengorged parasitic mites on the thoraxofboth andro-
morphsandheteromorphs. Mitescarswereobservedonbothheteromorphsand
andromorphs beginning at similartimesofthe flightperiod. If bluepruinosity
developed afterreproductive maturationwewouldexpect to findandromorphs
only late in the season and withmite scars. During our2005 survey werecap-
tured several females with heteromorph charactersand none showed any sign
of developing andromorph characters(one individualwas caught 18 daysafter
the initialcapture date). We also didnot observe anincreasein the numberof
andromorphs over thecourse oftheseason. Takentogether, thesedatasuggests
thatandromorphs andheteromorphs areofsimilarage.
Wehaveyet toaddressany behaviouraldifferencesbetweenandromorphs and
heteromorphs forthisspecies. AmoreintenseexaminationofotherLestes species
and other odonatespecies maybe necessaryto appreciate betterhowcommon
female-limitedpolymorphism is fordamselfliesand dragonflies. Itis interesting
to notethat,although notreported, andromorphs ofL. disjunctus wereobserved
during a previous study onthe same population (B. Anholt, pers. comm.)- De-
38 T.Robb, H.vanGossum&M.R. Forbes
spite earlierintensive work on many damselfly species, the presenceoffemale-
-limitedpolymorphism whethergeneticor age-related may havebeen observed,
butnot documented.
ACKNOWLEDGEMENTS
Wethank MARC LAJEUNESSE, SILVIALAIMGRUBER, and JAMIEMacDOUGALL for
assistancewithboth surveysandfieldcollections.We alsothankDENNIS PAULSONforcomments
and suggestionsonthe manuscript,HVGisa postdoctoralfellowwith theFund forScientific Re-
search-Flanders (FWO).
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