Table Of ContentOdonatologica35(1):23-29 March 1,2006
Changesofbodytemperaturesin
Sympetrumfrequens(Selys) reproductivepairs
(Anisoptera: Libellulidae)
N.Ishizawa
1644-15Yamaguchi,Tokorozawa City,Saitamapref., 359-1145,Japan
[email protected]
ReceivedApril5,2005/ RevisedandAcceptedAugsut27, 2005
The reproductivebehaviour was dividedintofourphases:perching(phaseI),less
than 1min fromthestart ofcopulation(phaseII),morethan 3min fromthestartof
copulation(PhaseIII)andmorethan 1min fromthestartofoviposition(phaseIV).
Thebodytemperature(Tb)ofthe S washighestinphaseIII,while inthe $ Tbwas
notsignificantly different among phases. ThechangesofTbaredifferent between
thesexes,however,theyarebothinfluenced largelybythewind aswellasbytheair
temperature,andparticularlyinthe 9theeffectseemstobelargerthan inthe S,pos-
sibly because ofitssmallerbodysize.
INTRODUCTION
Therehave beenso farseveral reports madeon thermoregulation in dragon-
flies (DE MARCO&RESENDE, 2002; ISHIZAWA, 1998; MAY, 1977, 1998;
SINGER, 1987;TAGUCH1 & WATANABE, 1995). ISHIZAWA(1998) inves-
tigated thermoregulation in Sympetrumfrequens fromtheteneralstagetothere-
productive period andnoted thatthe body temperaturesofreproductive pairs
was particularly high.At thattimehedidnotexaminethebody temperaturesof
pairs atthelasthalfofcopulation, andhe only suggested theprobability ofthe
highest peak ofbody temperature atthatstage.
Thisdragonfly,indigenous toJapan,ismostabundantandinhabitsdominantly
rice paddies. Thisspecies wasdefinedas"autumnalspecies" by UEDA(1990) due
to itsprolongedreproductive periodinlateautumn(lateSeptembertoNovember).
Theaimofthisstudy is to clarify why S.frequens maintainhighbody tempera-
tures duringreproductive behaviour, particularly inthecourse ofcopulation.
24 N.Ishizawa
METHODS
STUDYSITES.- Field datawerecollectedatricepaddies(80ma.s.1.,locatedat35°46’N,139°26’E)
inthe SayamaHillsatYamaguchi,TokorozawaCity,SaitamaprefecturefromlateOctobertomiddle
November 2002 andlateOctober2003.Asthe reproductiveactivityismostlylimited inthemorning,
collection ofdata wasconducted from9:00h to12:00h.
FIELDTECHNIQUES. - Bodytemperatures(Tb) ofindividuals weremeasuredinthefollowing
fourphases;perching(phaseI),less than 1minfrom thestart ofcopulation(phaseII),morethan 3
min fromthestartofcopulation(phaseIII)andmorethan1minfromthestartofoviposition(phase
IV).Individuals ofmalesand femalesin phaseIwereperchingonleavesofweeds inthesunaround
theovipositionsite,and particularlyinthefemaledatawerescanty, becausemostofthemflewaway
fromthe site afteroviposition.InphaseIIImost ofdatawerecollected onpairscopulatingfor4or
5minand included those formorethan 5min.
ThereasonwhydataofphaseIVwerecollectedonlyonpairsovipositingformorethan 1min. isto
distinguishpairsingenuineovipositionfromthosesoonafterthearrivalattheovipositionsite,which
alwaysadopteddippingmovementsimilar togenuineovipositionfor scoresofsecondsbefore copu-
lation. ThisambiguousbehaviourwasnotedbyMILLERetal.(1984)and theauthor(ISHIZAWA,
1998)calledit trial oviposition.
Bodytemperaturesweremeasured asdescribed in thepreviousreport(ISHIZAWA, 1998),us-
inga0.05 mmdiameterchromel-alumel thermocoupleembedded in a0.3 mm hypodermicneedle.
Theprobewasinserted intothethorax ofperchingindividuals orpairsincopulaorinoviposition.
Inpairstakentogether,femaleswereprobedpriortomalesin rapidsuccession within 10s.Ambient
temperaturesattheheightofI m inthesun(Ta)weremeasured with anOmron HC-100thermister
(3mmdiameter)afterTbwasmeasured.
INDOOR EXPERIMENTS.- Theeffectbythewindonthebodytemperatureofspecimenswas
examinedasfollows:Tb ofspecimens wasraised upto 33°C(nearthemeanTbinnature)bya75W
halogenlamp atindoor temperatureof20°C, and theywereexposedtovaryingvelocities ofwind
(windless, 1m/s,2m/sand 3m/s),atthe sametimeasswitchingoffthelamp.TheloweringoftheTb
wasrecorded atintervals of30sfor3min using0.05mmchromel-alumel thermocouple,notembed-
dedinahypodermicneedle. Thewindwas generatedusingamini desk-fan(Senju 100,diameter,14
cm)poweredbyalkaline batteries.Wind speedwasmeasuredbyathermo-anemometer (CUSTOM,
CW-10)ofwhich resolution was0.1m/s.
RESULTS
BODY TEMPERATURE BY PHASE
Figure 1-A andTableIshow the changes in the meanTbof Sympetrumfre-
quensinphases I,II, IIIandIV.Tb inthemalestayed thesameinphases I(32.9
±2.7°C,n= 30)andII(32.9 ± 1.8°Cn=28), increasedtoreachthehighest peak
in phase III (34.2 ± 2.0°C, n= 27, z = 2.9559, p < O.OlMann-Witney U-test),
thenfellinphase IV(32.4 ± 2.9°C,n=29, z= 2.7806,p<0.01). Similarly,in the
female,Tb wasnot significantly differentbetweenphases 1(29.4 ± 5.2°C, n =5)
andII (27.9±2.5°C, n=29, z =0.8272, p>0.05),(although themeanwashigher
intheformer), increasedin phase III(28.9 ± 3.1°C,n=27, z = 2.3293, p<0.02)
andfellin phase IV(28.1 ± 3.2°C,n=26, z =2.0915, p< 0.02).
Bodytemperatureis influencedbyambienttemperatureandatlowTaTbtends
Bodytemperaturein Sympetrumfrequensreproductivepairs 25
TableI
Statisticscalculated fromleast squares linear regressionofTbonTain eachphase offree-ranging
S. frequens- [al=slope;r=correlation coefficient;p=probability;s.d.=standard deviation]
Phase Sex N al r P MeanTb±s.d. Range(°C)
(I) Perching 3 30 0.185 0.191 p>0.1 32.912.7 25.4-38.3
9 5 1.394 0.951 p <0.005 29.415.2 21.5-35.9
(II) Less than 1min from 3 28 0.367 0.595 p <0.005 32.911.8 29.1-38.3
thestartofcopulation 9 29 0.477 0.572 p <0.005 27.912.5 23.4-34.0
(III)Morethan 3min from 3 27 0.192 0.273 p> 0.1 34,212.0 31.7-39.5
thestartofcopulation 9 27 0.659 0.602 p<0.001 28.913.1 24.5-35.3
(IV) Morethan 1min from 3 29 0.682 0,726 p <0.001 32.412.9 25.4-37.0
thestart ofoviposition 9 26 0.851 0,759 p<0.001 28.113.2 22.0-35.0
tobelow. Figure 1-B shows thechanges ofthemeandifferenceT(b-a)between
TbandTa. Inthemale T(b-a)lowered significantly fromphase I(16.8 ± 3.5°C)
to phase II (14.6± 2.4°C, z = 2.5445,p< 0.02 Mann-Whitney U-test), then in
phase IIIT(b-a) raisedto the highest (17.5 ± 3.0°C, z =2.7535, p < 0.01) and
loweredinphase IV(14.3 ± 2.2°C,z = 3.239,p<0.01). Whileinthefemale, T(b-
a)tracedthe sameprocessas inthemalefromphase Ito phaseIII;phase I(11.6
± 2.1°C), phase II(9.4 ± 2.6°C, z = 1.8243, p>0.05), phase III(11.2 ± 3.9°C, z
= 3.4934, p< 0.001). However,T(b-a) raisedto thehighest inphase IV(11.9 ±
4.3°C, z = 0.3515, p> 0.05), though the differenceof T(b-a)betweenphase III
andphase IVwasnot significant.
During observationstandempairs cameover the rice paddies andconducted
Fig. 1.Sympetrumfrequens:A,changesofmeanTbbythephaseinthereproductivebehaviour;means
areindicatedby horizontal solid lines,and s.d.by vertical lines.Cl: within 1 min fromthestart of
copulation,C2:within 3min fromthestartofcopulation;- B,thechangesofthemeandifference
T(b-a)betweenTb andTa.
26 N.Ishizawa
trial oviposition forless than 1 min,thenmoved incopula to sunlitdepressions
adjacent to the rice paddies andcontinuedcopulation forseveralminutes.
DIFFERENCEOF BODY TEMPERATURE BETWEENBOTH SEXES
Differenceof the mean Tb between
bothsexes was significantly higherinthe
malethan inthe femalefromphase IIto
phaseIV(comparison betweenbothsexes
intandempairsexceptphase I).Thedata
of the pairs, in which eithersex escaped
werenot included, p<0.0001,Wilcoxon
Rank sum-test(seeTab. I &Fig. 2). The
differencewasenlarged fromphase II(5.1
± 1,4°C,n=26) tophase III(5.7 ±2.6°C,
n =26). However,inphase IVitfellto4.6
± 1,9°C(n=23). Butthedifferenceamong
phases was not significant.
Fig. 2.TherelationshipofTbtoTain pairs
in phaseIIIformorethanthree minfromthe Figure2 showstherelationofTbtoTa
startofcopulation.Datainclude Tb ofpairs in pairs copulating formorethan 3min.
andindividuals wherethepartnerescapedbe- Malesinpairs maintainedtheirTbhigher
fore Tb wasmeasured. Solidline and dotted than females. The regression coefficient
line areleast squaresregressionsofTbonTa; was generally smallerin themalethanin
in males(Tb=0.192Ta + 31.152,r=0.273,n
=27) and females (Tb=0.659Ta + 17.964,r the female, especially in phase I that of
=0.602,n=27). perching maleswas thesmallest(Tab. I).
EFFECTOF WINDSPEED ON BODYTEMPERATURES OF BOTHSEXES
Figure3showsthedecreaseofTbin3mininthespecimens cooledby thewind.
Thedifferenceof decreasing ofTb intheconditionofwindlesswas notsignifi-
cant between bothsexes (7.6 ± 0.4°C,n = 10 inthe male;7.9± 0.4°C, n= 9, in
thefemale,respectively, z = 1.4801,p>0.05,WilcoxonRank sum-test). Howev-
er,the differencewas significant intheconditionofthewindspeed of Im/s (9.8
± 0.3°C, n = 10, inthe male, 10.3 ± 0.4°C, n = 9,in thefemale, respectively, z =
2.4581,p<0.02),2m/s(10.5 ±0.3°C, n= 10; 10.9±0.3°C, n=9,z = 2.7027, p<
0.01). Butin theconditionoffasterthan 3m/s, thedifferencewas not significant
(11.1 ± 0.5°C, n= 8,in themale, 11.5 ± 0.3°C, n= 6, inthefemale, respectively,
z — 1.1109,p> 0.05).
Themaximumwindspeed attheoviposition siteoftenexceeded2.5m/sandthe
ovipositing pairs orientedto thewinddirectionusually atmorethan0.5m/s.
BodytemperatureinSympetrumfrequensreproductivepairs 27
Fig. 3.Bodytemperaturesrecorded in specimensofS.frequenscooledbythewind for 3rain. A: in
themale,B: inthe female. Tbofspecimenswasraised upto 33°Cbya75 Whalogenlampatindoor
temperature of20°C, and theywerethenexposedtovarious windspeeds(windless, 1m/s,2m/sand
3m/s)atthesametime asswitchingoffthelamp.The decreasein Tbwererecorded atintervals of
30sfor 3min.
DISCUSSION
Accordingto MILLERetal.(1984),pairs ofSympetrum depressiusculum that
is thevicariantofS. frequensmovefromtheirroostingsitestorice paddies intan-
demearly inthemorning andwaitthereuntiltheambienttemperaturebecomes
warm.Thiswaitingofpairs intandemisregarded asguarding femalesby males
fromrivalmales. On the otherhand, inS.frequens searching females by males
atthe roosting sitesstartsaround at7:00h(though thetimeprolongs as thesea-
son advances), and taking tandemformationwith femalesthere they move to
theoviposition sitesofrice paddies. As soonas arrivedthere theyconducttrial
oviposition forscores ofsecondsandmoveincopula to sunlitdepressionsadja-
cent torice paddies, wherethey copulate. Asmall numberofpairs remainedin
tandemwithoutcopulation forseveralminutes.However, inmostcases, as inS.
depressiusculum. therewas no waiting time.
ThefactthattheTbofbothsexesinS.frequens inphaseIIofthestartofcop-
ulationafterarriving attheoviposition sitewas thelowestsuggeststhatthepairs
lostTbon theflightfrom the roosting sites to the oviposition sites.As pairs in
tandemfly mostly towardsthe wind,theairspeed maybefasterthanthe appar-
ent speed. Theflight speed of pairs intandemwas not measured, however, itis
assumedtobearound2.5-3m/sfasterthanthenormalflightspeed insingle of2
m/s(ISHIZAWA, 1995; M1YAKAWA, 1994). As suggested by theexperiments,
theeffectof thewindonTbis large, andas thewind forceincreasesthelower-
ing of Tb becomes great. Consequently, the metabolicheatin thoraxmay not
compensatethelossofheatduringtheflightto theoviposition sites.Itisknown
28 N.Ishizawa
thatbody size influencesthermoregulatory ability in dragonflies (MAY, 1978),
andespecially inthe femalethethoracicmass issmallerby 20%thaninthemale
(ISHIZAWA, 1998;UEDA, 1993;MAY, 1998). InS. vicinumthe dry weight of
thoracicmass in thefemaleis 50% ofthatof themale(MAY, 1998). Thus, the
effectofthe windmaybe larger onthefemalethan on themale. Thisis shown
bythe factthattheregression coefficientis largerinthe femalethaninthemale
(ISHIZAWA. 1998; MAY, 1998).
ThedifferenceofTbbetweenthesexes tendstobe diminishedinphase IV,and
thisis dueto theelevationofTbofthe femalethatisejecting eggs(ISHIZAWA,
1998).Tbofthe femaleinsingle oviposition is as highas thatof themaleintan-
dem(ISHIZAWA, 1998), and thismay be becausewhen theTb ofthe female
is very high itmay be difficultforthe maleto form atandemwith thefemale.
SINGER(1987)notedthatinS. obtrusumtandemformationwasrarely adopted
whenTbofthe malewasless than 30°C.Thereasonwhy S.frequens andS. vici-
num(MAY, 1998) oviposit in tandemeveniftheirTbwas as low as 23°C,may
bethattheTbofthefemalesare lowerthanthoseof males.
Someof the pairs could not copulate soon after arriving at the oviposition
sites; thereforeTbofpairs may benecessary toberaised atsome extentbefore
they copulate. Thereason why theTbofthemaleinphase IIIreaches apeak is
assumedtobethepreparation forthemaintenanceofTbas highas possiblebe-
cause decreasing ofTbbythewindis expected atoviposition, inwhichthemale
takes the initiative.S.frequens prolongs copulation durationatlowTa, andthis
suggests that pairs wait untiltheirTbbecomes high enough. In S. danaepairs
thatcopulate early inthe morning prolong copulation duration(MICHIELS,
1992). MAY(1998) notedthatmalesof tandempairs in S. vicinum(thatrepro-
duceslateinautumn) maintainTb higherup to20°CthanTa(MAY, 1998),and
also inS.frequens malessimilarly maintaina highTb.
Thus, as S.frequens reproduces late in autumn,they are likely tobe affected
by thewindand theambienttemperature,andforthatthey maymaintaina high
Tb,particularly attheendofcopulation.
ACKNOWLEDGEMENT
Iwish tothankananonymous refereeforcorrection ofmy manuscriptandhis usefulcomments.
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