Table Of ContentOdonatologica25(3): 307-311 SeptemberI,1996
Pre-flight warmingup of
maturingAeshnamixta Latreille
(Anisoptera: Aeshnidae)
R. Stoks¹²’’³,M.Santens¹,L. De Bruyn¹ andE.Matthysen²
1 EvolutionaryBiologyGroup,DepartmentofBiology, University ofAntwerp (RUCA),
Groenenborgerlaan171,B-2020 Antwerpen,Belgium
2 LaboratoryforAnimal Ecology, DepartmentofBiology,University ofAntwerp (UIA),
Universiteitsplein1,B-2510 Wilrijk, Belgium
5 e-mail address: [email protected]
Received January9, 1996 /Revised andAcceptedFebruary 15, 1996
Itis shown that maturingA.mixtacan useshivering asapre-flight warmingup
strategy,which givestheinsects the capacitytoswitch between pureectothermy and
acombination ofectothermy andendothermy.So farthis has been evidenced in ma-
ture odonates only. Since this strategy opens the way to eocrepuscular flight in
immatures,this maybeacueinexplainingtherole oftwilightzoneflight.Forthe first
timetherelationshipbetween ambient temperature(T_) and shiveringon the duration
ofthe pre-flightperiodwas investigatedundernatural conditions. The duration of
shiveringwasnegatively,butjust notsignificantly, correlated with the ambient tem-
perature. The duration ofshiveringandT_didnoteffectthedurationofthepre-flight
period.Shiveringintensity,however, significantlyreduced thetimepriortotake-off.
Theobservationssuggestthatabdominal shiveringmayrepresentpartofanendothermic
strategy.
INTRODUCTION
In dragonflies, as in other flying insects, the thoracic temperature(T) has to
reach a certainlevel beforeflightis possible (MAY, 1976;VOGT& HEINRICH,
1983).Largeaeshnidsdonot takeoffbeforetheyreachaT ofatleast30°C(VOGT
h
&HEINRICH, 1983).According toCORBET(1962, 1980)Aeshnidae are ‘fliers’:
species thatfly continuously duringtheiractive phase. All ‘fliers’ areableto ac-
tivelyincreasetheirthoracictemperatureendothermically byshivering (HEINRICH
&CASEY,1978;VOGT&HEINRICH, 1983;HEINRICH,1993butseePOLCYN,
1994).
308 R. Stoks, M.Santens, L. deBruyn&E. Matthysen
WithinthegenusAeshna,shiveringpreceding take-offhasbeenobserved inadults
ofA. grandis and A. cyanea (or A. mixta, theauthor could not discriminatebe-
tweenthese two species) (POND, 1973). BROWNETT (1992), on the contrary,
reported thatmaturing individualsofA. mixtaprepared forflightby basking, with
the wings motionless.He never observed wing-whirring prior to take-off. This
possibly indicates an ontogenetic switch in thermoregulatory behaviour as was
already foundin otherdragonflies (WATANABE, 1991;MARDEN, 1995).
Becauseshivering increasesT itis expected thatthisalsoreduces theduration
h,
ofthepre-flight period. To ourknowledge, thisprediction hasnever been tested.
Sincetherate ofT increaseis positively relatedto theambienttemperature(T )
h
(VOGT & HEINRICH, 1983),we also expected a negative relationbetween the
durationofshivering andT.
The objective ofthis study was to testwhether(1) maturing A. mixtaalso use
shivering as a warming-up strategy ; (2) the durationof shivering is negatively
correlatedwithT and(3) shivering decreasesthedurationofthepre-flightperiod.
a
MATERIALANDMETHODS
MaturingA.mixta werenetted intree-lined lanes and woodland edgesnearAntwerp(Belgium)on
7 sunny andwindless days inSeptember1993. Immediatelyaftercapture each individual wasplaced
inalight-proofcontainerwhereitwasstored atapproximately4°C for30 minutes. Thenitwasposi-
tioned onasmall stick(50 cm) perpendiculartothe sun. We measured thepre-flightperiod (time
between release and take-off),the durationofwing-whirring,the ambienttemperature (inthe sunata
heightof50 cm), and noted thebodyparts used forshivering(forwings,hindwingsorabdomen).
The effects ofshiveringduration,
theshiveringintensityand T onthe
t
duration ofthepre-flightperiodwere
analyzed using a backward multiple
regression procedure with normally
distributed errors and the identitylink
using the statistical package GLIM
(CRAWLEY, 1993).Shiveringinten-
sity was defined asafactorwithfour
levels: nomovements, only abdomi-
nal shivering,whirringwithtwowings
and whirringwith four wings.To test
for different effects ofthe levels of
shiveringintensity we used thecon-
trast procedure(CRAWLEY, 1993).
RESULTS
Of the tested 27 animals, 8
did not shiver after being
placed on the stick. Four of Fig, 1. Duration ofthe shivering period in function ofthe
these had whirred with their ambienttemperature(T).
a
Pre-flightwarmingupin maturingAeshna mixta 309
wings duringtheirstay inthecontainerandwereexcludedintheanalysis.Thepre-
flightperiod lastedon average200±180s(range 0-871 s). Only a minority(0.15)
ofimmaturesdidnot useanyshivering.Twoanimalsshiveredonlywithtwo wings,
whileoneanimalonly usedtheabdomen.Wing whirring was not always continu-
ousbutranged from 9%to 100%ofthepre-flightperiod (87±73 s).
Therewas atendency for animalstoshiverforashorter timewithincreasing T
a
(without twooutliers,r=-0.42,
F ,=4.1, p=0.058) (Fig. 1).
u
Becauseoftherather low co-
efficient of determination
R2=0.17) the problem of
collinearity (PHILIPPI, 1993)
is smalland bothfactors will
be usedin theanalysis as in-
dependent factors.
Themaineffects T andthe
a
duration ofshivering had no
effect on the durationofthe
pre-flightperiod(Tab. I).Ani-
malsthatshiveredhadamuch
shorterpre-flight period than
animalsthatdidnot (R2=0.64;
Fig. 1;Tab.I). Shivering with
the abdomen only was less Fig.2.Duration ofthepre-flightperiodforfourlevelsofshiv-
successful in shortening the eringintensity(none=nowhirring,- abdomen =onlyshiver-
timetotake-offthanshivering ingwith the abdomen, - 2(4) wings= whirring with 2(4)
withthewings. Therewas no wings).
significant differencein thedurationofthepre-flight period ofanimalswhirring
withtwo orfour wings (Fig. 2).
DISCUSSION
Ourresults show that maturing A.mixtaare abletothermoregulate not only by
basking (cf. BROWNETT, 1992)
Table I
Multipleregression analysis ofthe effectsofshivering butalsobymetabolicheatproduc-
intensity,durationofshiveringandT ontheduration of tion through shivering. So these
t
thepre-flightperiod- [NS =notsignificant] animals can switch between a
combination of ectothermy and
Maineffect df F p-value
endothermy and pureectothermy
Shivering intensity 3,17 5.24 0.0096 (forafurtherdiscussionseeMAY,
Duration ofshivering 1,17 0.012 NS 1978 and POLCYN, 1994). As
T 1,17 0.0625 NS predicted, shivering hadasignifi-
310 R.Stoks, M Santens,L, deBruyn& E.Matthysen
cantshortening effecton thepre-flightperiod.
JODICKE(1993)consideredthespecies aseocrepuscular (flying inthetwilight
period beforesunriseandaftersunset). Becauseheonly studiedanimalsatapond,
he probably only observed adults (CORBET, 1980). BROWNETT (1992) saw
maturingindividualsflying aftersunset. Ourresults indicatethatflightbeforesun-
rise isalsophysiologically possible inimmatures(seee.g.CORBET, 1957).Infor-
mationonitseffectivepresenceorabsenceinthisstagewouldbeanimportantcue
in determining whethertwilight zoneflight plays a role in odonatereproduction
(as suggested MAY, 1977, 1978;JODICKE, 1993, 1995)or whetheritis merely a
way ofpreventing overheating in fliers(MAY, 1987).
As expected, therewas a negative, although not significant,correlationbetween
T and thedurationofshivering. On the otherhand, ourresults suggestthat the
a
durationofthepre-flightperiod is unaffectedbyT Perhaps theheatproduced by
.
shivering in these animals hasa greater impact on theirthermalbalancethan the
environment.An alternativeexplanation is thatthe observed rangeof T ’s meas-
a
uredwas too narrow and/ortoo high to detecta significant effect. The observed
lowlevelsofshivering intensity (only abdomenandtwo wings) can probably also
beexplained by theratherhighobserved T ’s.
a
NotallA.mixta whirredwith bothwing pairs, using themetabolicheatofboth
setsofflightmuscles.POND (1973) alsoobservedthatanA.grandisusedonly the
mesothoracicmusclesto warmup.The positive effectofabdomenshivering was
surprising.Thesemovements wereclearly distinguishedfromabdominalpumping
because theentireabdomenshivered andmovements were ata higherfrequency
than pumping movements. Because this shivering was donewithout any wing
movementsweexcludethepossiblity thatitis areflectionoflow-amplitudeflight-
-muscleshivering. Thisisthefirstreportonthepossible useoftheabdomenduring
endothermic warming up(see HEINRICH, 1993). Further research is however
neededtoclearly demonstratethethermogenic nature ofthisactivity.
ACKNOWLEDGEMENTS
We thank HANS VAN DUCK and ananonymousreferee for valuable criticism. This study was
partly supported by the BelgianNational Fund forScientific Research (RS is Research Assistant,
LDBisSeniorResearchAssistant andEM is ResearchAssociate).
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