Immune melanization ability and male territorial status in Erythemis vesiculosa (Fabricius) (Anisoptera: Libellulidae)

2006·0.94 MB·English

by  Córdoba-Aguilar, A

Odonatologica35(2): 193-197 June I,2006
Immunemelanizationability
andmaleterritorial status
in Erythemis vesiculosa (Fabricius)
(Anisoptera: Libellulidae)
A.Córdoba-Aguilar* andV.Méndez
InstitutedeEcología,Universidad Nacional Autónoma deMexico,ApartadoPostal70-275,
Circuito Exteriors/n,MX-04510 Ciudad Universitaria,México,D.F.,Mexico
*[email protected]
Received June15,2005/ReviewedandAcceptedNovember 4,2005
Usinganylonfilamentimplantinsertedin thethorax,it wastested whether there
wereimmune ability and size differences betweenterritorial and nonterritorial 36
thatgatherinlenticaquaticsites.Itwasfoundthatterritorial 33mountedalarger
melanin-based immuneresponse than nonterritorial 33. This iscoherentwith cur-
rent resultsinother odon. andisinterpretedasterritorial 33beinginbettercondi-
tion than nonterritorial 3 3.However,there wasnosizedifference between theter-
ritorialand nonterritorial inidividuals. Thissuggeststhat sizemaybe apoorpredic-
torofimmuneability.
INTRODUCTION
Oneofthemostrecentemergingfieldsinecological theoryisthatofecological
immunity. Themainaimofecological immunity is tounderstandtheunderlying
forcesthatgive risetoandmaintainvariationin immunityas wellas theroleof
immunity indeterminingindividual’sfitness(ROLFF&SIVA-JOTF1Y,2003). A
basic tenet inecological immunity theory is thatimmuneresponses are costlyto
produce. Oneofthephysiological costsishowtheanimalwoulddivertresources
to the immunefunctionand otherfunctions(ROLFF & SIVA-JOTHY, 2003).
Given thispotential conflict ofresource allocation,only someindividualscould
afforddivertingresources to immunity. ,
Dueto theirsuitability formanipulation, oneofthe animalgroupsthathave
best served forecological immunityideasisthatofinsects. Insectimmunityrelies
oninnateresponses thatdonotapparentlyrecognise aparticularinvaderbutex-
ertsageneralised response(ROMAN, 1998).Withfairlylargeinvadingagents,a
194 A,Cordoba-Aguilar&V.Mendez
seriesof haemolymph cellsoftheinvertebrateimmunesystemadhere to thein-
truderencapsulating it.Theencapsulation processiseffectedby aseriesofenzyme
reactionswhichultimatelyinducethecellstobecomemelanized.Duetotherigid
properties ofmelanineandonceencapsulated, theinvaderisprevented fromfur-
ther development andis eventually eliminated(LAVINE& STRAND, 2002).
Recentstudiesininsectbehaviourhavesuggested alinkbetweensexualactivi-
tiesandimmunefunction.In damselflies, forexample, femalesthathaverecently
oviposited haveless intenseimmuneresponses,intheformof melanineproduc-
tion, thannon-ovipositing females(SIVA-JOTHY etal., 1998).Possibly thereis
amechanisticlinkbetween theeffort oflayingeggs(females submerge into the
water during this behaviour) and melanine production that compromises the
animalto divertmoreenergyto one functionthanto otherin situationsofen-
vironmentalstress.
Inthispaperweprovideevidenceofdifferencesinmelanineproduction aftera
non-pathogenic challenge interritorialandnonterritorialmalesofthe dragonfly
Erythemis vesiculosa.Malesofthisspecies gather ataquatic, lenticbody waters
that femalesuse foroviposition. Malesdefendthese places against nonspecific
malesby chasing themoutoftheterritory(ACA & VM, pers. obs.). Similarto
other©donates(forareviewseeCORBET, 1999),anumberofmalesare notable
to defendaterritoryand, instead, wandertrying to locateafemaleand, conse-
quently,endupwithalowermatingsuccess thanterritorialmales.Fortheactiva-
tionoftheimmuneresponse,weuseda nylon filamentwhichis astandardtech-
nique inimmunestudies(e.g. WIESNER& GOTZ, 1993). Wealso investigated
whethertherewas a differencein size inmalesusing differentterritorialtactics
and to seewhetheritwas related to immuneability.
MATERIALANDMETHODS
A largepopulationofE. vesiculosa wasstudied nearthe marshesatPalo Verde National Park,
Guanacaste,Costa Ricaon4and 5June2004,fromll-14h,thetimeatwhich dragonflyactivitywas
morepronounced.Thisspeciesinhabits pondsofvariable sizecoveredwithvegetation.Fourteenter-
ritorial and 14nonterritorial maleswerecollected.Thecriteria foridentifyingaterritorialmalewas
thattheindividual chasedawayconspeciflcmalesand remained inthesameaquaticplaceforseveral
minutes(ca 10min).Anonterritorial individual wasaway fromtheaquaticsitesand,therefore,did
notdefend aterritory.Animals weretakentothelaboratoryinglassineenvelopesandwithinablack
boxtoreduceinsects’activity.Seven males ofeachbehaviouralstatuswereimmunechallengedusing
a2mmlengthnylonfilamentwhich wasinsertedinthecentral,lateralregionofthesecond thoracic
sternite. Previous toinsertion,asmall holewasgentlymadewith apiece offorcepssothatthe fila-
mentinsertion waseasiertobe done.Thefilamentwasdirectlyinsertedin thethoracicmusclesand
left therefor 8hours,atime that hasbeendocumented asthe minimumforcompletinganimmune
responsein odonates (ACA,pers. obs.). Duringthistime andtoreducetheanimals’ activity(sothat
immuneactivitydoesnotbecomecompromisedwithotherpotentialenergetic-exhaustingactivities),
theanimalswereleft inthe glassinebagsand withinadarkcontainer. Theywerethen preserved in
ethanol(70%)and then thefilaments carefullyremoved usingdissectingforceps.Apictureofeach
filamentwasobtainedusingadissectingmicroscopeandadigitalcamera.Thesepictureswerestored
Immunemelanization inErythemisvesiculosa 195
inacomputerandtheimagesprojectedonthecomputerscreen,Asheetofgridlinesof5x5 mmwas
thenputonthescreen.Wecounted thenumber oftotalsquares thatthefilamentandcoveringmela-
ninefilledinandthenumber ofsquares ofthecoveringmelanine (thecriteria wasthat ifmorethan
halfofeach squarewasfilled,thenitcounted asonesquare).Therelative areacoveredbymelanine
wasthen obtainedtakingmelanine and thefilamentas 100%.
The 7 malesremainingfor each behavioural statusweremeasured (incm)fromthe basistothe
tipoftheright,anteriorwing.Wecomparedboth immuneresponses andsize ofbothterritorial and
nonterritorial animals. Means±STDareprovidedunlessstatedotherwise.
RESULTS
Immuneresponse was higher forterritorialmales (0.88 ± 0.29, N = 7) than
nonterritorialmales(0.47 ± 0.23; t-test = -4.04, P = 0.001, N = 7; Fig. 1). In
contrast, however, therewas no differenceinsize according to malebehavioural
status (territorial, 3.97 ± 0.21; nonterritorial, 3.97 ± 0.19; N = 7 each; t test=
0.072, P> 0.05).
DISCUSSION
Previous studies inOdonata havealready detecteddifferences in immune re-
sponses depending on the behaviouralstatus and reproductive activities (e.g.
SIVA-JOTHY etal„ 1998; SIVA-JOTHY, 2000; RANTALA et al„ 2000; KO-
SKIMAKI etal.,2004). Thesestudieshaveuseda rationaleofacost beingpaid
bythedifferenttacticsusinganenergetictradeoffscenario. Forexample,studies
ofaggression indamselflieshavesuggested thatmelaninproduction getsreduced
afterlonglasting,male-maleencountersandmalesusingaterritorialtacticusually
havealsobetterimmuneresponses(KOSKIMAK.I etal.,2004). Since oneofthe
costsoffightingisareductioninfatstoredinthethorax(where thewingmuscles
are inserted), somehowthe reductionoffatalsoaffects immuneability. Ourre-
sults are inagreementwiththeseotherstudies:malesthatare occupying theter-
ritories are better immuno-
competentthannonterritori-
almales.Possibly, onlymales
in good condition are able
both to defenda space and
dealwithpathogens, anabil-
ity that nonterritorialmales
donot have. Thephysiologi-
calbasis of this relationship
may lie on the reserves that
males have. It is likely that
Fig. 1. Melanine quantification(mean± SE)ofanimmune
nonterritorialmales are fat filamentchallengeinrelation toterritorial statusinErythemis
exhausted(e.g. old males) or vesiculosa.
196 A.Cordoba-Aguilar&V.Mendez
in theprocess of manufacturing this(e.g. youngmales) which meansthathave
not accrued enough resources which may also be used forimmuneresponses.
Possibly, fat directly affects melanineproduction so that animalswith less fat
are unableto produce a good immune response. The relationship between fat
andimmunity, however, maynot be directandbothmaybea consequenceofa
reducedincomeoffood thatthe animalhas obtained.A supportto thisis that
in beetles, recently-fed animals increasedtheir immuneresponses significantly
(SIVA-JOTHY & THOMPSON, 2002).
Theabsence ofsize effects inour comparison suggests thatthistraitis not an
indicatorof immuneability andmale territorial status.Interritorial odonates,
recently emerged males are fat depleted so that they startbuilding upresources
for reproductive activities (e.g. PLAISTOW & SIVA-JOTHY, 1999). In males,
fatis used toobtainanddefendaterritory. Once themalehasobtainedenough
fat, possibly, thereis apositive relationship between sizeand fatreserves (larger
size, morefatreserves). Thefact,however, thatfatgetsreducedwithtimeandde-
creases substantially whenthe animalis defeatedduring territorialcontest (e.g.
PLAISTOW&SIVA-JOTHY, 1996),makesthatthispositive relationship disap-
pears. Since somelargebutold malesthatwereonce territorialwillendupwith
lessfat,meansthatsizebecomesapoorpredictor ofterritorialstatus.Giventhis
andtherelationoffoodconsumption andimmunityininsects, suggests thatsize
maynotbea goodpredictor ofimmuneresponseeither.
ACKNOWLEDGEMENTS
ThiswaspartofanundergraduatesummercourseoftheOrganizationforTropicalStudies(OTS)
inCosta Rica.All studentsthatparticipatedinthis course kindlyprovidedhelpinthefield.
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