Oviposition high above water in Micrathyria dictynna Ris (Anisoptera: Libellulidae)

5 Pages·1998·1.5 MB·English

by  Förster, S

Odonatologica27(3):365-369 September1,1998
Oviposition highabovewaterinMicrathyria
dictynnaRis (Anisoptera: Libellulidae)
S.Förster
ZoologischesInstitutderTechnischen UniversitätBraunschweig,Fasanenstrasse 3,
D-38092 Braunschweig, Germany
Received November 18, 1997/Revised andAcceptedJanuary28, 1998
A 9 wasobserved toattach eggsontotheundersideofaleafhangingmorethan2
m above the waterlevel ofasmall rainforest streamin Costa Rica. Itwasfound that
theeggsusuallyremain in thispositionuntilthe larvaehatch.Thistype ofoviposition,
thefirstrecorded in amemberofthe subfamilyBrachydiplactinae,issimilartothatof
someOld WorldTetratheminae and it issuggestedtobe acaseofconvergence due to
similarenvironmental conditions. Its adaptivesignificanceisdiscussed briefly.
INTRODUCTION
Regarding the behaviouralecology ofthe subfamily Brachydiplactinae sensu
FRASER (1957), theonly species studied so farare Nannophya pygmaeaRambur
(TSUBAKI&ONO, 1986)andEleuthemisbuettikoferiRis (LEMPERT, 1988)from
theOldWorld,aswellassix speciesoftheneotropicalgenusMicrathyria:M.aequalis
(Hagen), M.atra(Martin),M.hageniKirby,M.mengeriRis,M.ocellataMartinand
M.schumanniCalvert(NEEDHAM, 1943;PAULSON, 1969;DUNKLE, 1995).Ac-
cording to PAULSON (1969) the genus Micrathyria shows a great inter- and
intraspecific variabilityof ovipositionbehaviour.Indetailhedistinguished sevendif-
ferenttypes including 'dropping eggs fromabove', 'tapping the water', 'tapping ex-
posed leaves'as wellas 'egg-laying whilesettled'onmud orfloatingleaves (seealso
NEEDHAM, 1943).SomeofthesemethodsarequiteunusualamongtheLibellulidae,
whichmostlyovipositby washingtheireggsoffinflight,by tappingthewatersurface
or floating vegetation (CORBET, 1962). However, since Paulson'swork littlewas
addedtoourknowledge aboutthebehaviouralplasticityinthegenus.Theaimofthis
paperisthereforetodescribeamodeofoviposition hithertounpublished forMicrathyria
orotherneotropicalOdonata.
366 S.Forster
STUDYSITE
Theobservation wasmade onDecember 12, 1996,atasmall rainforest streamnorth ofthetrailmark
“SUA 350” in La Selva BiologicalStation (OTS), 2.5km S Puerto Viejode Sarapiqui,Province
Heredia,Costa Rica (10° 26' N,83° 59' W,40-45 m alt. atSUA350).The streamwas 1-2m wide,
with a maximal depthofabout 50cm and a negligablecurrent velocity.Itwaslocated within dense
primaryforest.There wasnovegetationinthestreamoralongthewater'sedge.However, manypalms
and fernsstood nearbyandoverhungthe water.Aspossiblepredatorsforaquaticinsects many small
fishes wererecorded inhabitingthe stream.
The average annual precipitationatLa Selvais 3,962mm withaperiodofleastprecipitationfrom
FebruarytoApril. The average monthlyairtemperatureis 25.8 °C withadiurnal range of6- 12 °C
andalessthan3°C average monthlychange(alldata fromSANFORDet. al., 1994).
Theovipositingfemalewascollected andlateridentifiedfromphotographsandadescriptionby Dr
S.W. Dunkle.
OVIPOSITION BEHAVIOUR
At 10:20(CST) afemaleMicrathyria dictynna visitedthestream. Sheflew be-
tween0.5and3 mabovethewaterthrough thevegetation searching forasuitable
oviposition site. I saw herhovering in front ofthe tip ofseveralpalm leaves. In
each case she made one dipping movement to the undersideofthe leafwithout
laying eggs,thenchanged toanewsite.
Aftersomeminutesofsearching thefemalebegan todepositeggsinflightonthe
undersideofapalm leafnearitstip, about2.3 mabove themiddleofthestream.
Theway shewas doing so is illustratedinFigure 1.Thefemalehoveredin frontof
the tipoftheleafandextrudeda clearly visible mass ofeggs, lasting about5 s.
Thenshebenttheabdomendownandtapped theundersideoftheleaftoattachthe
eggs. Following this she again hovered, extruded eggsand attached them to the
samesite.Altogethersherepeated thisprocess 4timesbeforeIcaught her.Inhand
sheextrudedmoreeggsandInotedthattheeggshadaratherliquidglutinous layer.
Although Icouldn'tseethe
positionofthelegs atthemo-
mentthefemalewas deposit-
ing her eggs due to an unfa-
vourable angle of view and
the rapidity ofmovement, it
is likely thatshe usedthesec-
ond andthirdpairforaslight
contact withthe substrate, as
Fig. 1: Process ofoviposition in Micrathyria dictynna: the shown inthefigure.
female extruded eggs whilehoveringin front ofaleaf, fol- Beforeandafteroviposition
lowedbyattachingtheeggs totheundersideoftheleafwhile
inflight,probablyusingthesecondandthirdpairoflegs for no Micrathyria malewas re-
a slightcontact with the substrate (according to J. Lempert, cordedalong thestream sec-
pers. comm.). tion. Butonthenext day two
Ovipositionin Micrathyriadictynna 367
males probably ofthe samespecies
were observed perching on leaves
abovethewater,butnofurtherfemale
appeared.
Alonga 10msectionofthestream
aroundtheoviposition siteIfound4
more clutches ofeggs, all of them
locatednearthetip on theunderside
ofleaves(Fig. 2), hanging between
0.3 and 1.2 m above the water sur-
face.Oneclutchwithfullydeveloped
embryos wasbroughthomeinaplas-
ticfilmbox, together withsomewa-
terdrops fromthestream.Afterabout
two hourswithoutexaminationofthe
eggmass Irecorded someprolarvae
crawlingaroundonitssurface.When
I placedthem intowaterthey imme- Fig. 2: Egg mass ofMicrathyriadictynna. hanging
diately hatched into the first larval about2 m above the middle ofa small rainforest
streamonthe underside ofapalm leaf, containing
stage.
eggs ofdifferentdevelopmentalstages.
Twoeggmassesmeasured 15x9.5
mm and 17 x 9.5 mm, containing approximately 1,100 and 1,400eggs respec-
tively. Conspicuously they containedeggsof different developmental stages. In
general, attheperiphery theeggswere mostly well developed, often withclearly
visible embryos andof lightbrown coloration, whereas around the centre they
mainly were poorly developed andof milkywhitecoloration.Thecovering layer
ofeggsalso consistedof poorly developed ones,butincontrast tothecentraleggs
they were darkbrown.Thealcohol-preserved eggsmeasured0.56mm(range 0.52-
-0.6 mm; SD=0.02;N=16)x 0.34mm (range 0.3-0.38mm; SD=0.02;N=16) and
were elliptically shaped.
DISCUSSION
ThebehaviourofMicrathyriadictynna describedabove probably represents the
firstrecorded case ofepiphytic oviposition high above the water in NewWorld
Odonata. Itresemblesindetailtheoviposition behaviourdescribedfortheAfrican
Malgassophlebia aequatoris Legrand (LEGRAND, 1979) and M.bispina Fraser
(LEMPERT, 1988),whichbelong tothesubfamilyTetratheminae(FRASER, 1957).
Within thissubfamily epiphyticoviposition high(!) abovethewateris frequently
encounteredalso inthepool breeding species oftheOldWorldgenusTetrathemis
(CLAUSNITZER, 1995;CLAUSNITZER &LEMPERT, 1998; FRASER, 1952;
LEMPERT, 1988;McCRAE& CORBET, 1982),which incontrast to Malgasso-
368 S.Forster
phlebia spp.oviposit whilesettled.
Micrathyria ocellata was the only species for which PAULSON (1969) men-
tionedthetapping of exposed leaves (Typha)justabovethewater surface, which
couldbeviewedas anevolutionary stageonthewaytooviposition likeM. dictynna.
Similarbehaviourcombinedwith gluing eggs tothe substratewas alsorecorded
for Brachythemis lacustris (Kirby) and B. leucosticta(Burm.) (CORBET, 1962;
MILLER, 1982), Old World membersofthe Sympetrinae (FRASER, 1957), as
wellas forsomeTetratheminae(CLAUSNITZER, 1995;LEMPERT, 1988).
Threedifferentsuggestions were madeto explain the adaptive significance of
epiphytic oviposition above the water in libelluliddragonflies of the tropics. It
couldserve topreventtheeggsfrom(1)anoxic conditionsonthebottomofstand-
ing waters(McCRAE&CORBET, 1982),(2) being washeddownstream(MILLER,
1982), or (3) predation by fish (MILLER & MILLER, 1985;LEMPERT 1988).
However,1 suppose thatthere is no universally validexplanation forthephenom-
enonandthatallthesevariantsapply wellforspecific cases.Thisimplies thatfor
M. dictynna thedecisivefactors havetobescrutinizedcriticially.
Theconditionsinthedescribedstreamresembledmoreor less those ofstagnant
water. Becauseofa negligible currentvelocity therewas athick layerofsoft, an-
oxic bottomdeposits.Toseparatetheeggsjustfromthisanoxic conditionitshould
besufficientto depositthem into shallowwater oron asubstratenearthewater's
edge. So there wouldbe noevident reason to evolvesuch specialized behaviour
like oviposition highabovethewater. Thereforeitseemslikely thatpredation risk
by fishesis amorerelevantfactorforthereproductive strategy ofM.dictynna.This
hypothesis is supported by theoccurrence ofmanysmall fishesinthestreamwhich
wereobserved toreact quickly toallobjects droppingonto thewater surface.Un-
der this high potential predatory pressure the multi-layered egg masses of M.
dictynna couldbeadvantageous becauseofthe differentdevelopmental stagesof
theeggsandtheirdifferenthatching times.
Incomparison tootherlibellulidswitheggdepositionabovethewater,M. dictynna
seems to lay more eggs, as indicatedby the twoexamined clutches. LEMPERT
(1988)recordedforthe similarsized Malgassophlebia bispina an averageclutch
sizeofonly 417 eggs(range 60-730). In thelarger Tetrathemispolleni, McCRAE
& CORBET (1982) counted between 200 and 780 eggs per mass and they de-
scribed the eggs to be about0.7 mm long. It is unlikely that egg masses of M.
dictynnacontainedeggsfrommorethanonefemalebecausenooverlapping clumps
couldberecognized.
Oviposition inM. dictynna was not relatedto thebeginning ofthe rainy season
andthereforeeggmasses were morelikely to suffer fromrainless periods during
development. Thusthegreat clutch size could simply be amethod to prevent at
leastpartoftheeggsfromdryingup. Inthiscontext itwouldalsobeofparticular
interestifthereareany differencesinthehatching success ofeggspositioned ex-
perimentally above andinthewater atlocationswherethisbehaviouroccurs.
Ovipositionin Micrathyriadictynna 369
The describedbehaviourin Micrathyria couldbe consideredto be a case of
convergencebetweenTetratheminaeandBrachydiplactinae. Itis recordedin this
special mode only for tropical rainforest inhabiting Malgassophlebia spp. and
Micrathyria dictynna. Thusitis probably causedby similarenvironmentalcondi-
tionsin suchforestsofboththeOld andNewWorld.
ACKNOWLEDGEMENTS
I am gratefultoANDREAS MARTENS and JOCHEN LEMPERT forhelpfulcomments on the
manuscriptandstimulating discussions. I wish tothank SIDNEY W. DUNKLEforidentification of
the specimenand criticalreadingofthemanuscript.Ialsothank theLASELVABIOLOGICALSTA-
TIONcrew, Costa Rica,forprovidingexcellent research facilities.
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