Fecundity and oviposition in Mortonagrion hirosei Asahina, M. selenion (Ris), Ischnura asiatica (Brauer) and I. senegalensis (Rambur), coexisting in estuarine landscapes of the warm temperate zone of Japan (Zygoptera: Coenagrionidae)

2006·1.8 MB·English

by  Watanabe, M

Odonatologica35(2):159-166 JuneI,2006
Fecundityandoviposition
inMortonagrionhirosei Asahina, M. selenion (Ris),
Ischnura asiatica (Brauer) andI. senegalensis
(Rambur), coexisting inestuarinelandscapesof
thewarmtemperatezoneof Japan
(Zygoptera: Coenagrionidae)
M.Watanabe¹and S.Matsu’ura²
1GraduateSchool ofLife and Environmental Sciences,UniversityofTsukuba,Tsukuba,
Ibaraki305-8572,Japan;— [email protected]
2Graduate SchoolofEnvironmental Sciences,UniversityofTsukuba,Tsukuba,
Ibaraki305-8572,Japan
ReceivedMay11,2005/ RevisedandAcceptedNovember5, 2005
Adultsofthe 4spp.,inhabitinganestuarinelandscapethatincludesreedcommu-
nitiesandricepaddyfieldsestablished onwaterofvaryingsalineconcentration inMie
prefecture,Japan,werestudied.ThefecundityofIschnuraspp.washigherthanthatof
Mortonagrionspp.I.senegalensiscontained thelargestnumberofmature, submature,
andimmature eggswiththesmallestmature eggsize,whereasM.selenion contained
thesmallestnumber ofimmature eggswith thelargestmatureeggsize.Duringa3-
daylaboratoryovipositionexperimentwithoutfood,all 22 developedeggs,resulting
inagreaternumber ofmatureeggsthan wasoriginallycontained. Mostoftheeggs
thatdevelopedtomaturitywerelaidby M.selenion andI. asiatica,while M.hirosei
laidonlyhalf ofthenumberlaidbyeitherofthese. Theovipositionprocessofthe4
spp,isdiscussedfromtheviewpointoftheirlarvalhabitatselection.
INTRODUCTION
Estuarine landscapes provide a unique habitatfor Odonatain Japan, though
they are increasingly likely to containbrackish water.Ponds, rice paddy fields,
channelsand sewagedrains are themajorcomponentsoftheselandscapes and
containvarying degrees ofsalinewater,whichseems tobe disadvantageous for
the survival of odonatelarvae (CORBET, 1999). In Mie prefecture, Morton-
1Correspondingauthor
160 M.Watanabe&S.Matsu'ura
agrion hirosei, M. selenion, Ischnuraasiaticaand I. senegalensis are commonin
estuaries inwhich reed communitiesare dominant(MATSU’URA & WATA-
NABE, 2004). Although theywere foundinthesameestuarinelandscape, M. hi-
roseiisrestrictedto closed, densereedcommunitiesestablishedonbrackish wa-
ter (WATANABE& MIMURA, 2003), suggesting that theeggsand larvaeare
salinetolerant. INOUE & TANI (1999) reported thatin additionto M. hirosei,
Orthetrumpoecilops miyajimaensis and Tholymis tillarga inhabit seashorewith
lowsalinity, butthattheirdistributionis fairly limited. IWATA &WATANABE
(2004) showed thatyoungI.senegalensis larvae havesaline tolerancesimilar to
thatof M. hirosei. Becausethetwo Ischnuraspecies are regarded as beingpreda-
torsof M. hirosei(HIROSE& KOSUGE, 1973),thebehaviourandthe micro-
habitatof M. hiroseimustbe somewhatdifferentfromthat ofIschnuraspecies.
In fact, the two Ischnura species and M. selenionprefer open habitats, though
NISHU (1997) observedthatI.senegalensis adultsenterthe reedcommunityin
ordertoprey onM. hirosei. Inthisestuarinelandscape, manyadultsofthethree
species fly along themarginsof thedensereedvegetation inhabitedby M.hirosei.
Therefore, asastrategy forconserving M.hirosei whichisclassifiedas anendan-
,
gered species onthe IUCNred list, itwouldbe usefulto comparetheecologies
ofthesefourcoexisting species.
In general, odonatefemalesarelikelytodevelop eggscontinuously intheovaries
andto layeggs throughout theirlifetimesfollowing sexualmaturation(BICK et
al„ 1976;WAAGE,1978). BANKS&THOMPSON (1987)showedthatinperi-
odsof continuoussunnyweather, adultfemalesCoenagrionpuella cameto lay a
clutchofeggsevery day.By dissectionofwildfemales, WATANABE& ADACHI
(1987)clarifiedthefecundity ofLestes temporalis, L.sponsaandL. japonicus, all
ofwhich showedoviposition behaviourintandem, anditwas difficultto getfe-
malestolay eggs underlaboratoryconditions.However, inthepresentstudy, fe-
malesinallofthe fourspecies examinedoviposited aloneinplant tissues onthe
water,suggesting thatwithlittlestresstheycouldlayeggs onto awet filterpaper
inasmallpetri dish.Theclutchsize, definedas thenumberofeggsactually laid,
hasbeeninvestigated as anindexfor lifetimereproductive success inmanyspe-
cies(e.g.. THOMPSON, 1990;GR1BBIN& THOMPSON, 1990).
WATANABE& ADACHI(1987) classifiedeggsinovariesusingthreecatego-
ries;mature,submatureandimmatureeggs,buttheydidnotcount immatureeggs
directlyunderthemicroscope duetotheirsmallsize andthenumerousovarioles.
In this paper, weattempted to count the numberofeggs inall three categories
as anindexofthefecundity ofthefourcoexisting species by dissecting females,
andtocount thenumberofeggsartificiallylaidinorderto assess theoviposition
process. Thisinformationis anessentialcomponentfor reproductive strategyof
eachspeciesandwillfurtheradvancethe development ofa detailedconservation
strategy forthe endangered M. hirosei.
FecundityandovipositionincoexistingCoenagrionidae 161
STUDY AREAAND METHODS
Westudiedasmall,densereedcommunityinanestuarinelandscapeinMieprefecture,Japan,that
wasinhabited by M.hirosei.Thecommunitywasestablished onbrackish waterandthegrowthproc-
essofreedwasdescribedby MATSU’URA&WATANABE(2004).Surroundingthereedcommu-
nity,there wereabandoned ricepaddyfieldsthat weresuppliedbyfreshwater,resultingin shallow
pondswithshort emergentplantssuchasSchoenoplectusspp. andalso smallreeds. M.selenion and
thetwo Ischnuraspecies flew mainlyabove theabandoned rice paddyfieldsand alongthemargins
ofthedense reed community.
Justaftersexualmaturity,femalesofthe fourspecies,whichwereidentified mainlyby bodycol-
our,werecollected duringtheirflying season, fromlate Maytoearly August,in2003and 2004.All
femaleswerecapturedduringroostingin earlymorning,prior tothecommencementoftheir daily
oviposition.I.senegalensisfemalesaredimorphic.Wecapturedtheheteromorphs,becausetheywere
prevalentinthis population.Twenty-fiveM. hiroseifemaleswerecollected in thereed community,
and 17,28and46M.selenion,I.asiaticaand/.senegalensisfemales respectively,werecollectedalong
themarginsofthereed communityandintheabandoned rice paddyfields.
Somefemaleswereputinto50%ethylalcoholassoonastheywerenetted.Theabdomenlengthof
eachfemalewasmeasuredby usingamicrometer.Alldissectedfemales wereexaminedunderaster-
eomicroscopetodeterminethenumber ofeggsofeachtyperemainingintheovaries(WATANABE
&ADACH1, 1987).The number ofmature andsubmature eggswascounted directly.Since theim-
mature eggswerein ovarioles,thenumber oftotalovarioleswascounted. Thenumber ofimmature
eggsinanovariolewascountedbasedonfiveovariolesrandomlysampled,andthenthetotalnumber
ofimmatureeggs wascalculated. Thevolumeofamatureegg wascalculated asanoval.
Artificial(laboratory)ovipositionwasconducted atroomtemperatureinpetridishes(diameter9cm)
thatcontainedapieceoffilterpapersoaked indistilledwater.Theinsectinsertedeggsinto thefilterpa-
per.Afterthreedays,thenumberofeggslaidwascounted.The femaleswerethendissectedtocountthe
numberofmatureeggsremainingintheovaries.Theresultsarereportedasthemean± standarderror.
RESULTS
As shownin Figure 1, thenumberof ovariolescontaining immatureeggs in
thefourspecies variedwidely. Around150ovarioleswerefoundinM. hiroseiand
I.asiatica while M.selenionhad thelowest(ca 100) andI. senegalensis hadthe
,
highest (ca270) number, partly dueto the abdomensize (cf.Tab. I). In contrast,
thenumberofimmatureeggsperovarioleforeach species was relativelystable,
approximately 15forallspecies except I.senegalensis (ca 18).For M. hirosei,ap-
Fig. 1. Themeannumbers ofovarioles and ofimmature eggsper ovariole (±S.E.).The numbers
beside eachcolumnshow the samplesize. ***indicates asignificantdifferencefrom M.hiroseiata
probabilityoflessthan 0.001 (ANOVADunnett T3-test).
162 M.Watanabe&S.Matsu'ura
TableI
Femalebody size, thenumber ofeggs contained and the matureegg sizein thefourspecies studied
(+S.E.)
MM..hhiirroosseeii MM.. sseelleenniioonn II..aassiiaattiiccaa I/..sseenneeggaalleennssiiss
AAbbddoommeennlleennggtthh((mmmm)) 2244..77±± 00..44((1177)) 221U.1±100.2.2""•-((1133)) 2233..00±1 11..33 ((1166)) 2266..99+1 00..44“" ((1100))
NNoo..iimmmmaattuurreeeeggggss 22007744..33±1111144.2.2((1177)) 11662299.3.3±1 7766.1.1'’ ((1133)) 22555522..99±1118866..44 ((1144)) 44994400..99±1330011..33"*((1111))
NNoo..ssuubbmmaattuurreeeeggggss 1177..11±± 22..88((1144)) 1177..44±± 22..44 ((1177)) 3377.6.6±1 44..33""'((2288)) 4477..22±1 55..55*""'((4466))
NNoo..mmaattuurreeeeggggss 8833..44±1 1100..00((1144)) 8811..33111100..00 ((1177)) 112233..4411 1100..00”"'((2288)) 223399..0011 1166..44""*'((4466))
MMaattuurreeeeggggssiizzee 1122..7711 00..33((1177)) 1144..4411 00..44''((1133)) 1133..1111 00,,55 ((1166)) 1111..5511 00..22’’ ((1111))
((xxl!f(r>3'mmmm3’))
*,", significantlydifferencefromthose ofM.hiroseiwith probabilityat0.05,0.01 and0.001
(ANOVA Tukeyb-test),respectively.
(): number ofsamples.
proximately 2,000 immatureeggswerecontainedinafemale.Thelowestnumber
of immatureeggswas foundin M. selenion(ca 1,600)and the highest number
was foundin I.senegalensis (ca4,900).
TableI shows the abdomensize ineachfemale, M. selenionhadthe smallest
andI.senegalensis thelargest abdomen.Thesize differenceprobably accounts for
thenumberof immatureeggscontained.However, therewerenosignificant dif-
ferences inthe numberofsubmatureormature eggsbetweenM. hiroseiandM.
selenion(ca 17 andca80 forsubmatureand mature eggs,respectively). Inspite
of the similar sizeof I.asiaticaand M. hirosei,both thenumbers ofsubmature
andmature eggs in I.asiaticawere significantly greaterthanthoseinM. hirosei.
Furthermore,I. senegalensis containedthelargestnumberofsubmatureandma-
ture eggsamongthefourspecies, indicatingthe highest fecundity.
TableIalso shows the matureeggsize forfemalesofeach ofthe fourspecies.
M. selenionhad thelargest eggswiththe lowestfecundity, while I. senegalensis
hadthesmallesteggswith thehighest fecundity. Thefecundityandeggsize of /.
asiaticawere intermediatebetweenthoseofM. selenionand I. senegalensis, but
M. hiroseihad relativelylow fecundity withrelatively smallmature eggs.
During the3days spentinthepetri dishesforthelaboratoryoviposition experi-
ment, the femaleswere not given access to food, but nofemalesdiedandthere
werenofatbodiesintheabdomens, suggesting thattheyexploited theirenergyto
develop matureeggsforoviposition aswellas tomaintaintheirownbody.There
werefewsubmatureeggsinany femalesofany ofthespecies. Mostofthemature
eggmasseswerelaid,andothersremainedintheovaries.Figure 2showsthateach
M.hirosei, M. selenionandI. asiaticafemalehadcontainedtotalof200mature
eggs,indicating that,for eachfemale, thenumberofeggs developed to maturity
wasthe sameasthenumberofmatureeggsalready contained.Thesameeggde-
velopmental processwas observedinI. senegalensis, wherethe totalnumberof
mature eggs(ca 450) was twice the numberofmature eggs already contained.
FecundityandovipositionincoexistingCoenagrionidae 163
Althougheachfemale
developed during the 3
days alarge number of
mature eggs, M. hirosei
actually laid about65%
of the total number of
mature eggs (Fig. 2).
Then, a female laid 40
eggs daily,assumingthat
there was no peculiar
egg-laying rhythm dur-
ing the 3 days. On the Fig. 2.Thenumber ofeggslaid andthenumber ofmatureeggsin
other hand, M. selen- ovariesimmediatelyafterartificially oviposition ofthreedays(±S.
ionandI. asiatica actu- E.).Thedarkstripedareaandlightdottedareaindicaterespectively
ally laidmorethan90% thenumber ofeggslaidoverthree daysandthenumber remaining
tobe laid afterthisperiod.Thenumbers abovethe columns show
of the total number of
the samplesize. ** and *** indicate significant differences from
matureeggs, orapprox- M.hiroseiataprobabilityoflessthan 0.01 and0.001,respectively
imately 60 eggs daily. (ANOVADunnettT3-test).
I. senegalensis also laid
morethan80%ofthe totalnumberofmature eggs(120 eggs daily),suggesting
thatthe three species might havesimilaregg-developing and oviposition proc-
esses.Initially, artificiallylaideggs inthefilterpaperforeachspecies wereglisten-
ing white;they turnedgreyishbrownwithinone dayandeventually, becamedark
brown. Mosteggs werehatchedindistilledwaterwithinamonth.
DISCUSSION
Thesample dateoffemalesmayhaveaffectedthenumberofeggslaidbecause
ofthepatternofsunny, overcast and rainy days over theperiod ofreproductive
activity, as wellas thetimesincethey lastoviposited orthe inter-clutchinterval.
BANKS&THOMPSON(1987) foundthatthemostimportant determinantof
clutch size in Coenagrion puella was thetimesincetheprevious clutchwas laid.
GRIBBIN & THOMPSON(1990) alsoreported thatPyrrhosoma nymphula fe-
malesdidnotvisittheponds dailytobreed.Inthepresentstudy, however, nope-
culiarroosting sitesawayfromthewaterwereobservedforany ofthefourspecies,
suggesting thatthe femalesstayed by the water and were ableto oviposit daily
if they wished. M. hiroseistayed inthe understory ofthedensereedvegetation
during itslifespan andoviposited alone, ashasbeendescribedbyWATANABE
& MIMURA (2003, 2004). Femalesof the otherthree species also laidin the
plant tissuesoffloating leavesandsmallemergent plants,underdirectsunlight,
along themarginsofthereedcommunity (1WATA& WATANABE,2004). Fur-
thermore,allthecollectedfemaleswereidentifiedasrecentlymaturedindividuals
164 M.Watanabe&S.Matsu'ura
thatwere atthevery beginning oftheirreproductive activity.
Although MIZUTA(1985)countedmorethan 1,000ovarioles in Orthetrum
albistylum, nothingwasknown onthenumberofovariolesinany Zygoptera spe-
cies.If thereare noadditionalovarioles andifthereare no additionalimmature
eggs in theovarioleduring the lifespan, thenumberofimmatureeggs mustre-
flectthelifetimefecundity ofthefemale, andthusshouldbecomparable among
species. In thepresent study, despitethe relatively smallvariationin thenumber
of immatureeggsperovariole(ca 15inthreespecies), therewas avariationinthe
numberof ovariolesamongthe fourspecies. Thus, I. senegalensis, whichis the
largest ofour species, hadthe highestfecundity, whileM. selenionisthesmallest
andhad thelowest fecundity. Thisrelationship wasalso foundin thenumberof
mature eggscontained, suggesting thattheclutchsize maybelargeandsmallfor
I. senegalensis and M. selenion, respectively. I. asiaticamustbeintermediatebe-
tween I. senegalensis andM. selenioninviewpoint offecundity andthe number
of mature eggs contained.
Ingeneral, there is a trade-offrelationship betweeneggsize and the number
ofmature eggscontainedwhich isconditionedby thephysical spaceinsideafe-
male’sabdomen.Species that perform high (low) fecundity with small (large)
eggs areregarded asr-selected(K-selected) species (PIANKA, 1970). Although
femaleabdomensizes inM. selenionand inthetwo Ischnuraspecies were some-
whatdifferent, itis likely that M. selenionis a K-selectedandI. senegalensis an
r-selected species, becauseof theireggsize. I. asiatica seems tobeintermediate
between these. However, M. hiroseifemales hadapeculiar traitfortheirrepro-
ductive strategyamongthefourspecies. Although thefemaleabdomensize was
not very differentfromthatofI. asiatica, ithada relativelylowerfecundity.
During the3 daysof thelaboratory oviposition experiment, wedidnot know
whenthefemaleoviposited, thenumberofclutches, ortheoviposition duration
ofeachbout. In Coenagrion puella, initialclutchsizes ranged between 110and
250 eggs, whereafterthe femalehad 13mature eggs left (BANKS& THOMP-
SON. 1987). GR1BBIN & THOMPSON (1990)reported that atthe beginning
of a day’sreproductive activity P. nymphula laidasingle clutchof 350eggson
average. Inastudy ofChromagrion conditum, BICK etal.(1976) foundthateggs
weredepositedatarate of5.5perminute,resulting inanaverageof200eggsper
oviposition sequence. BENNETT& MILL(1995)alsoreported thattheaverage
clutchsizeofP. nymphulawas245eggsandthatthemeanlifetimeclutchproduc-
tionwas approximately 6.Inthe presentstudy, itis likely thatevenwhentheegg
maturationoccurred gradually overthe 3 days,almost all mature eggs could be
laidduring a day’soviposition by femalesofthefourspecies. Thelargestnumber
ofeggs was laidinI.senegalensis, though theclutchsizewas significantly corre-
latedwithbody size as inI. graellsii(CORDERO, 1991).
For M. hirosei, slowegg developmentwas foundanda smallnumberofeggs
was laid over the 3 days. Sincea mature eggin theovaries is definedas anegg
Fecundityand ovipositionincoexistingCoenagrionidae 165
ready tobelaid, thereare severalpossible explanations fortheremainingmature
eggs.If theenergywas exhaustedto develop egg maturation, the femalewould
not havehad the powerrequired to layeggs. Alternatively, the oviposition rate
mayhavebeen tooslowtoallowthefemaleto layallofhereggsin3 days.Inad-
dition,thespermaccumulationpriortocapturemaynothavebeensufficient,due
to,e.g.,thefemalematingbehaviourorto thesizeofbursacopulatrix, though in
thefieldmost femalesthatlay eggsinthe absenceofmaleshavesufficientsperm
mass storedfromprevious copulations (SIVA-JOTHY etah, 1995).
Oviposition sites are among themost important factorsin habitatselection
(CORBET, 1999).Theoviposition preference isinfluencedbywaterdepthinEnal-
lagma hageni (FINCKE, 1986), whichprefers the oviposition in deep water, in
orderto decreasetherisk theeggs woulddryupin thepools. Incontrast, inour
fourspecies, water depth didnot seemto beacriticalfactorinthechoiceofthe
ovipositionsite, sincethehabitathadaconstantwatersupply(e.g., MATSU’URA
&WATANABE, 2004). Femalesofthespecies withthehighest fecundity,I.sen-
egalensis, oviposit in varioussites irrespective of salineconcentration, such as
ponds, drainsandrice paddy fields,butthis isnot thecaseinthe other3species
coexisting inthe same estuarinelandscape. Although the eggsize of I. senega-
lensiswas thesmallest,thehatchabilitywas notsolow,andtheyounglarvae sur-
vivedeveninsalinewater,as inthecaseofM. hirosei(IWATA& WATANABE,
2004). Itwasobserved thatI.senegalensis preyedon M. hiroseiatboththelarval
andadultstages(HIROSE&KOSUGE, 1973; NISHU, 1997;INOUE& TANI,
1999). Predationon femalecoenagrionids by odonatelarvae hasbeen reported
previously(CORBET, 1999).On theotherhand,M.selenionandI.asiaticamight
becompetitorsforthehabitat,though theirsalinetoleranceinyounglarvalstages
wasnot as high as in M. hirosei(IWATA &WATANABE, 2004). WATANABE
& MIMURA (2004) studied the diurnalbehaviourin M. hiroseiby observing
individualscontinuously from sunriseto sunset,andpointed out thatin shady
perching sitesinthedensereedvegetation theirbody colourseemstobecryptic.
Therefore, the femaleoviposition siteselection and the larval habitatselection
inM. hiroseiare likely to maintainthepopulations withlowpredation risk. The
otherthreespecies, inopenhabitats, compensatefortheprobably higherpreda-
tion risk (from large dragonflies and small fish) by their high fecundity. Even
though itis aspecies withlowfecundity. M.selenionismultivoltine.Becausefe-
malesintandemoviposition arevulnerableto predation, laying eggs alone,as in
our fourspecies, might decreasetherisk of mortality. Inacomprehensive study
onthe mortality during oviposition in Zygoptera, FINCKE(1986) provided a
maximumestimate ofmortalityinEnallagma hageniat 13%peroviposition bout
inanopenhabitat.Femalesare certainlybeunderastrongselectionpressure to
oviposit in sites whichare unlikely tobe subjected toadverse conditionsduring
theperiod ofegg development andhatching. Furtherstudiesregarding thelife-
timeoviposition patternofthe fourcoexisting species are needed.
166 M.Watanabe &S.Matsu'ura
ACKNOWLEDGEMENTS
We thankY.MIMURA and S.IWATAfortheirfield assistance. Thisstudywassupportedin
part bythe Pro Natura Foundation.
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