Title: Behavioral thermoregulation in anisoptera
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 Material Information
Title: Behavioral thermoregulation in anisoptera
Physical Description: x, 217 leaves. : illus. ; 28 cm.
Language: English
Creator: May, Michael Love, 1946-
Publication Date: 1974
Copyright Date: 1974
 Subjects
Subjects / Keywords: Dragonflies   ( lcsh )
Boby temperature -- Regulation   ( lcsh )
Zoology thesis Ph. D
Dissertations, Academic -- Zoology -- UF
Genre: bibliography   ( marcgt )
non-fiction   ( marcgt )
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Thesis: Thesis -- University of Florida.
Bibliography: Bibliography: leaves 209-216.
General Note: Typescript.
General Note: Vita.
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Bibliographic ID: UF00098339
Volume ID: VID00001
Source Institution: University of Florida
Holding Location: University of Florida
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Resource Identifier: alephbibnum - 000582503
oclc - 14116860
notis - ADB0878

Full Text














BEHAVIORAL


THERMOREGULATION IN ANISOPTERA


By

MICHAEL LOVE MAY


A DISSERTATION PRESENTED TO THE GRADUATE COUNCIL OF
THE UNIVERSITY OF FLORIDA
IN PARTIAL FULFILLMENTS OF THE REQUIREMENTS FOR THE
DEGREE OF DOCTOR OF PHILOSOPHY


J













ACKNOWLEDGEMENTS


I gratefully acknowledge


the help of the many people who contributed


to this study.


Special


thank


are du


to Dr.


Brian McNab who first


kindled my interest in the physiological


responses of organisms to


their environment and who provided continuing assistance in the form


of equipment and valuable


riti


ism throughout this study.


I am also


indebted to Dr. Minter Westfall, who introduced me to the fascinating


possibilities of research on Odonata, and to Drs.


Johnson and


J. L. Nation who criticized the manuscript and were always ready with


their help.


I also wish to thank Dr


. James E


Heath and P. L.


Miller


for valuabi


discussions of some of the ideas


presented here.


It is impossible to enumerate all


of the faculty and students of


the Departments of Zoology and Entomology who have contributed to this


study by hours of discussion and physical


aid and by providing specimens.


To them I offer my sincerest thanks.


Johnson and Mr.


Ashley Wood


of the


Institute of Food and


Agricultural


fences, and Ms.


K Williams drew several


of the figures,


and Mr.


Paul


Laessl


of the Department of Zoology provided valuable


counsel


equipment which made poss


the completion of the others.


Ms. Donna Gillis typed the manuscript and aided in the final details of
Dreparation.


. Eri














TABLE OF CONTENTS


Page


Acknowledgements


List of Tabi


List of Figures


Abstract .

Introduction


Materials and Methods


Patterns of Thermoregulation


Discussion

Conclusions

References


Biographical


ketch















LIST OF TABLES


Table

1


Page


Species studied, with an indication of study
and basic activity pattern . . . . .


Frequency of various posture and wing position


combinations in


Pachy


diplax


Effect of wing position on equilibrium


dead


Pachydipt lax


Statisti


regression of
Odonata .


calculated from least squares


on Ta


linear


in free-ranging


Relation of
Erythemis


in tethered specimens of


. . . . a . a. . a a.


Species known to employ obelisk posture

Effect of humidity on cooling constant in


Tramnea


carolina


. . . . a . . a. 120


Cooling constant


of principal


temperate zone species


Warm-up rates and
in Odonata .


initiation of flight


Heat production during warm-up in Odonata


Effect of humidity on warm-up in
at T = 250C


Anax


junius


Minimum


for sustained flight in Odonata


Maximum voluntary tolerance
heat torpor in Odonata .


and thres


hold of


n S 4~,4 k,,4-an INC nr~r4-,arr~e nr'rn iaainht rli


vq-I nn 4-n WQ-inhf r a


_i r^ r^r\


^ ^













LIST OF FIGURES


Figure


Page


Male


Pachydip lax


longipennis


in obelisk


posture


Male Pachydiplax oriented perpendicular to the
sun with wings in the "down and forward"
position . . . . . . . . .


2A-B


Body positions in


Pachydip


that minimi


exposure to the sun


2C-E.


Body positions that maximi


Relation of
Pachydip lax


to?


exposure to the


in free-ranging


Frequency distribution of postu
of T, in Pachydiplax . . .


as a function


Posture as a function of


Pachydiptax


. . . 32


Frequency distribution of wing position


a function of


Pachy


plax


Frequency distribution of certain posture and


wing combination


Pachy


dip lax


A direct tracing from a recording of T in male
Pachydiptax heated with a 250 W lamp, showing
effect of obelisk posture . . . . . . . .


Relation of


in tethered


Pachydiplax


. . . 47


Relation o
Erythemis


f Tb andT
sipl liccoc


in free-ranging


Frequency distribution of posture a


a function









Perch height as a function of


Erythemis


simplicico ltis


Frequency distribution of wing position as a


function of

Relation of


simplicicollttis


Relation o
Erythemis


simp


in tethered


licicotlis


Erythemis


* * * 63


. . . . 65


to T
a *


2


. a a a . * * *

in free-ranging
* a a a a a


Frequency distribution of posture as a function


Erythemis


plebeja


Posture as a function of


E. pl


ebeja


. . . . 68


Frequency distribution of


free-ranging


Erythemis


pl


T.a
ebeja


in
. S S a * a S


As in A, tethered specimens of


Relation of

Relation of


plebeja


in free-ranging


in tethered


Libellttula


Libellula


Frequency distribution of posture
of T, in Libellula . . . .


as a function


Posture as a function of


Libet


tula


S. . 79


Overall position


as a function of


Libellula


Relatio
Tramea


n of T.b
carolina


in free-ranging


Relation of


Tramea


cophysaz


in free-ranging


Tramea


walker


S . S


Relation of Tb
Tauriphila argo


Relation of


in free-ranging


in free-ranging


Miathyria mrrcetIla


Relation of


ALa V7


in free-ranging


.7u lnus


Erythemis


f T to
pleoeja


1


. .


.


e n -*-<***/








Thoracic and abdominal


temperature recorded in


male Anax


gunzus


during


local


heating of the


thorax at ambient temperatures of 15C,


and 25C, and in the same
hours after decapitation


specimen at


20C,
5C four


S . . . . . . 1 03


As in A,


in a femal


Anax


at T


= 15C


. . . . . 105


As in A,


in a femal


Anax


at T


= 29C


A direct tracing from a recording of thoracic


abdominal


temperature during wing-whirring and


subsequent cooling in a female Anax


As in A


, in a second female


specimen


S . . . .. 108


Cooling constant a
in Anax junius .

Relation of T to
taeniolata . .


a function of air speed


in free-ranging


Cooling constant a


a function of thoracic


weight (W)


in dead temperate zon


Anisoptera


Cooling constant


weight in


= 15C


Cooling const


weight in


as a function of thoracic


living temperate zone Anisoptera


ant as a function of thoracic


living temperate zone Anisoptera


at T


= 20C


S. . . . . . . . . 127


Cooling constant


weight
at Ta


as a function of thoracic


living temperate zone Anisoptera


= 25C


Cooling constant


weight in


. . . . . . . . . .

as a function of thoracic


living temperate zone Anisoptera


= 300C


Thermal conductanc


as a function of weight in


varanid
insects


s, mammals, dragonflie


Cooling constant a


1 i'jilnn f nnIr.l


and other


a function of thoracic


nntpra at


= ?5


weight
S SA


Macromia


F-,\ !


I lf


\ .








Relation of warm-up rate and


of flight to


Macromia


T at
taenio


initiation


lata


Relation of


Anax


uniu a
junzus


at initiation of flight to
males and females . .


Relation of warm-up rate to T
Anax junius males and females


Duration of warm-up as a function of


several


species of dragonflies


That initiation of flight


as a function of


body weight in


Tramea


caro lina


Miathy


marcella


.. . . . . . a S S S


Tb at initiation of flight
weight in Anax junius and


as a function of body


Macro


mna


Warm-up rate as a function of thoracic weight
in various species of Anisoptera at Ta = 25C


Warm-up rate


. . . 173


as a function of thoracic weight in


Tramea


carolina


Miathyria marcelltta


Theoretical


relationship between warm-up rate


and weight in mammals and


insects


a . . . . . 178


Minimum Tb for sustained flight
body weight in Anisoptera .


as a function of
. . .B S S .


ria










Abstract of Dissertation Presented to the Graduate Council


of the University of Florida


in Partial


Fulfillment of the Requirements


for the Degree of Doctor of Philosophy


BEHAVIORAL


THERMOREGULATION IN ANISOPTERA


hael


March


Chairman:


Major Department


Love May

, 1974


McNab
Zoology


Several


speci


Anisoptera maintain their body temperature more


constant than ambient temperature.


Spec


ies that spend most of their


active period on perches and make only


hort flights


(perchers)


thermoregulate heliothermically,

adjustments and perch site select


primarily by means of postural

ion. Even the smallest species


probably obtain some thermal


advantage from postural


adjustments


Some of the species that fly continuously (fliers) are endothermic


regulator


during flight.


They regulate body temperature


largely by:


1) controlling metabolic heat production by alternately using gliding


or powered flight; 2) controlling heat


by altering circulation


between the thorax and abdomen.


well


Small


fliers are unable to regulate


because they are subject to high rates of convective heat


Cooling constants,


related to thoracic


as defined by Newton's


weight by a negati


loss.


law of cooling, are


power function over a wide








temperatures. The high cooling constants probably result from

increased rates of circulation at high temperatures.


Most fliers, and some


large perchers, are able to elevate


their body temperature endothermically by "wing-whirring."


species the rate of heat production apparently varn


to ambient temperature.


In some


in response


The body temperature at which flight i


initiated after warm-up is positively correlated with body weight.


probably because wing


body


loading increases with increasing


Warm-up rate is positively correlated with thoracic


weight up to weights of 0.5 g.

the weight dependence of metab


This relationship may result from


)olism and thermal conductance


The maximum voluntarily tolerated body temperature and the


threshold of heat torpor of


several


species


were determined


laboratory and field


tudi


Both parameters are correlated with


normal


environment.


The minimum temperature at which flight is


possible

tropical


1


positively correlated with body weight and is higher in


dragonflies than in temperate zone species.


Body temperature is more variable


relative to air temperature in


tropical


than in temperate zone species.


The ability of dragonflies


to maintain a relatively constant body temperature is determined


primarily by climate, body


size,


and behavior.













INTRODUCTION


Most of the so-called


"cold-blooded" vertebrates thermoregulate,


a view that began with the classical work of Cowles and Bogert


(1944).


Recently several workers have shown that this capability occurs in


certain arthropods as well


especially insects in the orders Lepidoptera,


Hymenoptera


, and Homoptera


(Cloudsley-Thompson,


1970)


Clench (1966)


Heinrich (1972e), Kevan and Shorthou


(1970), and


Vielmetter (1958)


howed that some butterflies bask in the sun and


orient these


so as to optimi


incident radiation.


Watt


(1968,


1969)


howed in addition that color in butterfli


correlated with thermal


environment.


adaptively


Heath and his co-workers


(Heath,


1967


Heath and Wilkin,


1970


Heath


et at.,


1971) have shown


that cicadas may also regulate body temperature by basking and shade-

seeking and that some types of their behavior occur only within narrow


ranges of body temperature.


During these


studies Heath deve


loped


effective field techniques for measuring body temperature of large


insects


(Heath,


1967


Heath and Adams,


1969)


Not all inse

body temperature.


cts depend on external


Early work


heat sources to elevate their


howed that a number of insects warm up


before flight by rapid contractions of the wing musci


("wing-whirring"


or "winq-shiver


inq"; Dotterweich


, 1928;


Krogh and Zeuthen


1941


,


l








during flight and warm-up in sphinx moths.


Hanegan and Heath (1970a,


b, c) extended this work to the saturniid,


Hyalophora


cecropz-a,


Heinrich (1970a,


1971a,


b) showed that the sphingid,


Manduca


sexta,


control


circulation between the thorax and abdomen during


flight.


When ambient temperature is


low there is


little


circulation


between the tagmata and the heat generated by the flight muscles


largely remains in the thorax, which is well


insulated by


low ambient temperatures thoracic temperature may


excee


scal


d ambient


temperature by as much as 30C.


When ambient temperature is high,


however, circulation


into the abdomen


increases greatly, and much of


the heat generated in the thorax i


abdomen


transferred to the poorly insulated


, where it can be dissipated easily to the air.


Heinrich has also demonstrated w


deve


loped endothermy in


bumblebees


(1972a


b, c, d) and was


to relate the energetic of


temperature regulation to pollination and reproductive behavior of


the bees


(see also Heinrich and Raven,


1972).


Regulation of hive


temperature in bees i


well


known (e.g., Chapman,


1969


Clouds ey-


Thompson,


1970)


Despite thi


growing


literature,


the number of insects known to


thermoregulate i


probably only a small


fraction of those that actually


do so.


Most studies have been restricted to groups having fairly


uniform responses to temperature.


studies are few, although Heath


Thus, meaningful comparative


(1971) drew some useful


a..4A%.,- Ct'.r.m ~ r.nnn~r4cnn n-F 4-ha ovrromoi~j diu'ornpnt d-r~tpnies








attention


so far in work on in


sects.


For example


what is the effect


of body


on thermoregulation in


insects?


This parameter i


very


important in mammals


(McNab,


1970)


but, except for the recent


papers of Bartholomew and Heinrich (1973) and Heinrich and Casey


(1973),


it has been practically ignored in insects.


How are


mechanisms of temperature regulation related to feeding and other


behavior?


To what extent is temperature response adapted to


environmental conditions, and to what extent i


morphology or evolutionary history


it determined by


These and other issues deserve


more investigation.


My purpose in the present work i


to demonstrate thermoregulation


in several


speci


of dragonflies


(Odonata, Anisoptera) and to compare


behavioral and physiological


adaptations that make this possible


in a number of different groups.


will


present some data from all


seven families of the suborder, mostly from members of the Libellulidae,


Macromiidae, and Aeshnidae.


The specie


comprise individual


ranging


in body weight over about one and one-half order


habitat from wooded streams to open field


of magnitude,


, and in the climate they


inhabit from warm temperate (Gainesv


ille, Florida) to tropical


(Panama


Canal


Zone).


As a result of thi


study I can propose partial


answers


to the questions raised above, although final con


lusions will


many ca


ses,


require additional


research


Little previous work has been done on dragonflies.


Corbet (1963)


FL.... C4tr4 4-n A ri-lEer lnnrwi-Ii 4-ho nneckfl4+Ane Cnr 4-hcnnmn.....








by wing-whirring was noted in Odonata


1957)


long ago


but has not been studied quantitatively.


(Moore,


1953; Corbet,


Hardy (1966)


howed


that in


Peri themis


tenera


posture relative to the sun i


orrelated


with air temperature,


ture.


but he made no measurements of body tempera-


Church (1960b) noted that the thoracic musculature of dragon-


is almost completely surrounded by superficial


sacs,


he showed that the air


sacs


substantially reduce heat


loss from the


thorax.


Adult dragonflies offer a number of advantages


in a study of


this kind.


They are


large and easy to observe


in the field.


Most


speci


are readily distinguishable in the field.


Although noted


for their acrobatic flight


many


peci


are reasonably


easy


to collect.


They occupy


variety of habitats, and some species


fly from dawn to dusk and from early spring to


thus encountering a wide range of thermal


late fall


conditions.


in Florida,


They are


diverse in


size


and some aspect


of behavior, but are similar


enough in general


body form and basic biology that comparisons of


body temperature, extent of thermoregulation, effect of body weight,

and many other factors are meaningful.














MATERIALS AND METHODS


Animal


Adult anisoptera were collected in the vicinity of Gainesville,


Florida, and in the Panama Canal


Zone during the period April


1971


September,


1973


Table


lists the species used in thi


study (see


also


Table 8)


The speci


for which I have extensive field and


laboratory data, and which are the primary subjects of this thesis,


are as follows


from Gainesville, Anax


j un-us


(Drury)


Eryt


hermis


simpti-


cicottis


(Say),


Libellula auripennis


Burmeister,


needhami


Westfall,


Macromia


taeniolata


Rambur,


Miathyria


marcel la


Pac hydiplax


longipennis


(Burmeister), and


Tramea


carolina


(Linn.)


from the Canal


Zone,


Erythemis


lebeja


(Burmeister),


Tauriphi


argo


Hagen,


Tramea


cophysa


Hagen and


walkeri


Whitehouse.


Of these speci


Pachydip


lax,


the two


themes


, and the two


Libel


tula


are "perchers," as defined by


Corbet (1963)


They spend most of their active hours sitting on


perches and intermittently make sallies to


atch prey or interact


with another dragonfly.


The remaining speci


are "fliers,


" i.e.


they remain on the wing almost constantly during their period of


activity.


Table


1 cl


ifies a


perchers or fliers the other species


studied.


specimens were collected with ordinary aerial


insect


- -- S 3* 3. t A -~ t I










Table


Species studied, with an indication of
study site and basic activity pattern.


Species


Site


Activity Pattern


Petaluridae


Tachopteryx


thoreyi


Florida


percher


Cordulegastridae
Cordulegaster


say


Florida


percher?


Aeshnidae


Anax junius
A. longipes
Coryphaeschna
C. perrensi
Epiaeschna he
Gynacantha gr
G. membranali


-ngens


Florida
Panama
Florida
Panama
Florida
Panama
Panama


ros


acitis
s


flier
flier
flier


flier
fl ier


nervosa
tibiata


Nasiaeschrma
Triacanthagy
T. dentata


Panama and Florida


pentacantha
na caribbea


trifida


Panama
Florida
Panama
Panama
Florida


flier
flier


Gomphidae


hylla wi
igomphus
mphus ca


lliamsoni
quadracies
vitlaris


dilatatus


G. m-nutus
G. pallidus
G. plagiatus


Progomphus


obscurus


Florida
Panama
Florida
Florida
Florida
Florida
Florida
Florida


percher
percher
percher
percher
percher
percher
flier?
percher


Macromiidae


Didymops
Macromta


transversa
taeniolata


Florida
Florida


flier
flier


Corduliidae


Epicordutia


regina
-v *


Florida
I-,*


r'. -1 -









Table


Continued


pecl e


Activity


Pattern


Libellulidae


credula


E?. plebeja
E. simplicicollis
Ladona deplanata


auripennis


L. needhami


Miathyria marceltta


Micrathyria
M. atra


aequalis


eximia


ocellata


Orthemis ferrugqinea
Pachydipclax longipennis
Pantata flavescens
Perithemis tenera


Tauriphi la


Panama
Panama
Florida
Florida
Florida
Florida
Florida
Panama
Panama
Panama
Panama


Panama and
Florida
Florida
Florida


argo


carolina


T. cophysa
T. walker


Panama
Florid
Panama
Panama


percher
percher
percher
percher
percher
oercher


flier


Florida


ercher
ercher
ercher
ercher
ercher
ercher


flier


rcher


flier


flier
flier


themes


Libellttula


Tramea


ammiIIIIII liI








rare occasions as many as four or five days


lapsed.


The animals


were not fed.


Only mature


individuals were used in both field and


laboratory work, except for a few general


specimens of


Anax,


noted below.


Description


of collection sites around Gainesville appear in


accounts of individual


species.


Most of the data on Panamanian


dragonflies


were obtained from


pecie


coll


ected


in the


laboratory


clearing of the Smithsonian


Tropical


Research Institute field


station on Barro Colorado


Island


(BCI).


Other species were taken


in the forest on BCI or at two small, artificial


ponds at Summit


Gardens, a botanical


garden in the Canal


Zone.


Field Techniques


The procedure in field studies of body temperature was a

modification of that used by Heath and his coworkers on cicadas


(e.g., Heath


, 1967;


Heath and Adams,


1969)


Body temperatures


were determined either with a


Yellow Spring


Instrument Co.


hypodermic


thermister probe, #524, equipped with a handle


of bal


a wood and


polyethylene tubing, or with a hypodermi


design of Heath and Adams


probe made following the


(1969) and using Veco #32A130 ultra small


thermistors as the


sensing


element.


Temperatures were read to the


nearest 0.1


C on a


YSI Telethermometer, Model


43TD


Each probe was


calibrated


in water against a


laboratory mercury thermometer


each was recalibrated at intervals of a few months.


In one


case








Each dragonfly was netted and quickly placed,


still


in the net,


on a square of light colored styrofoam.


The net was stretched tightly


over its body and the probe


inserted into the thorax


If the period


from capture to measurement exceeded 10 second


(estimated) or if I


touched the insect,


the reading was discarded.


Generally insertion


of the probe was


lateral, but


sometimes


dorsal


or even ventral


insertion was necessary to obtain a reading within 10 seconds.


depth of insertion depended on the


size


of the


insect.


I made an


effort to reach the approximate center of the thorax,

necessarily involved some uncertainty.


but this


The activity of each


specimen was


noted at the time of capture.


In those that were perched the following were recorded:


orientation


relative to the sun and to the ground, position of wings relative


to body, and in many


cases


, perch height and type of perch.


Activities


preceding capture were recorded


if they seemed relevant to the thermal


balance of an


individual


The activity of flying dragonflie


not analyzed further unl


they were engaged in some special


behavior


such as territorial


patrol,


sexual or aggressive encounters, or


oviposition.


Ambient temperatures were measured with


thermometers.


laboratory mercury


were calibrated against a NBS calibrated Parr


bomb calorimeter thermometer and were accurate to at


least 0.5C.


In the field they were


supported on a wooden rack


feet from the


..n-VI+nrr~A +kcrninrra+or h,,nn -Frnrn i-hp rack anti was


- .~ .


sh


added








held with adjustable


was in a plane normal


lamps and positioned so that their


to the direction of the sun.


long axi


One of these


the bulb partially shielded from wind by an aluminum tube painted

flat black and closed except for a rectangular window permitting


exposure of the bulb to the sun


The entire assembly was positioned


in an exposed location within the collecting area.


Ambient temperatures were usually recorded at


interval


15-30 minute


In estimating ambient temperature at the time of each


capture of a dragonfly,


I assumed that ambient temperatures changed


linearly between readings and that captures were evenly distributed


in time between determinations of


have


These assumptions probably


little effect on the accuracy of ambient temperature estimation


during most of the day but


during the early morning and lat


temperatures were changing rapidly


should substantially improve accuracy


afternoon when air and black bulb

. On some occasions, particularly


when working with


large flier


like


Anax


Macromia,


the ambient


temperatures were noted immediately after each capture, since


interval


between captures were generally


long.


Occasionally


, air


temperature was measured at the


of capture with the hypodermic


probe.


In these instances


tried to insure equilibration of the


probe by waving it in the air for


0-60 seconds after reading.


Other weather condition


were noted


as seemed appropriate but were


not quantified.


Cloud


cover


rated on a subjective scale of 1


(wurv linht ha7rl tn


(dark clouds comoletelv obscurina sun)


- J


*








over the back, and


suspended from the thermometer rack.


long


axis of the body of the exposed specimen was oriented approximately

normal to the rays of the sun. These controls were run only for


perchers,


since it seemed that


little could be


learned from tethered


fliers, which do not bask.


Several


sources of error are


inherent in these methods.


First,


since the animals are quite small,

probe might affect the reading. H


the initial


eath and Wilkin


was not true for their probes used on


cicadas.


mperature of the

(1970) found that


However,


smallest dragonfly studied h


ere,


Pachydip lax,


has a


thorax about


the mass of that of


icada


and the commercially manufactured


probes used initially may have a substantially higher heat capacity


than Heath'


probe.


Therefore the effect of one of these probes was


tested on tethered specimens of


Pachy


dip lax.


Temperatures were


simultaneously determined


in the field under varying exposures to


solar radiation by implanted


read on a


opper-constantan (Cu-Cn)


Thermo-Electric Mini-Mite thermocoupl


thermocouples,


reader, and by the


thermister probe.


regression,


These


sets of temperatures were related by a


equation for which was


the probe reading and


the thermocoupl


= 1.02


reading


linear


- 0.1, where I

. The reading


are not


significantly different, although the probe tends to giv


lightly higher reading,


presumably because


it warmed when


exposed to


the sun.

precaution


This error appears to be unimportant, although


took care not to


as an added


leave the probe on or near the ground


I








might change between the time of capture and the time of measurement.


Since there was usually


substantial differential


between air and


body temperature there must indeed have been some


change in body


temperature.


Heath and Adams


(1969) and Heath and Wilkin


(1970)


specifically cautioned that th


time interval


between capture and


measurement


should be


limited to 5 seconds.


Working alone with such


agile insects as dragonflies I


found that this was impracticable,


but as already mentioned, a


10 second limit was maintained.


Captured


insects were also kept out of the direct sun, so the greatest


differential


to which they were exposed was between body and


shade


temperature.


Pachydipt lax


difference wa


maximally about


15C.


The cooling constant


. 119)


of this


species


generally between 0.4/min and 0.5/min, meaning that


- T
a


=- 15C,


should drop not more than


1.25C in


10 seconds.


In fact,


there was


probably even


error than this in most cas


since this calculation


assumes the extremes of temperature differential and conductance.


addition,


the probe was often


left in place for more than


10 seconds


after initial


insertion, and a change


a degree was never observed.


Thus,


of more than a few tenths of


probably reasonable to


assume that for


Pachydipt lax


the measured body temperature was within


1C of the true temperature in the great majority of cases.


error


should be no greater in the other species studied since they


are all at


least


large.


It may be noted that this type of error


should tend to obscure thermorequlation if


it occurs, since the greatest








Another way in which

with the experimenter. H


might be altered is by heat exchange


eath and Wilkin (1970) emphasize that they


kept their hands at


least


10 cm from their animals.


Again this proved


impracticabi


for me.


However,


laboratory tests,


the body tempera-


ture of a


Pachydip


changed no more than a few tenths of a degree in


10 second


when my hand was


only 2-3 cm from it, although


rose


rapidly if the thorax was actually touched.


Finally,


if the specimen struggled in the net after capture


could raise its temperature by internal

rate of warm-up ever observed in labor


heat production.


tory studies was ab


The fastest

out 8C/minute,


indicating a maximum


levation of 1.30C


in ten seconds.


Since


fast


warm-up rates were seen only in fliers, which normally already were


producing heat rapidly in flight when collected,


probably much


there usually was


elevation of temperature.


Determination of Minimum Flight


Temperature


The minimum temperature at which

was determined for the species listed


flight can be


Table


sustained


by the method of


Heath and Adams


(1969)


Specimens were cooled in a refrigerator,


then repeatedly tossed into the air until


they could maintain


level


flight for


several


feet.


Then they were quickly netted and body


temperature was measured with the thermistor probe already desc


Each individual was rel


ribed.


eased at room temperature before cooling to


ascertain that it could fl


y at that temperature.


No individual








to fly even at room temperature.


For that reason specimens were only


cooled a few minutes.

replaced and cooled a


If they could fly immediately,


litti


they were


longer.


Determination of Upper Limits of Tolerance


The body temperature of dragonflies was continuously monitored


with fine wire Cu-Cn thermocouples to study the upper


limits of


tolerance


The wire, obtained from Omega Engineering,


either 0.003" diameter,


Teflon insulated,


Inc., was


or 0.002" diameter, un-


insulated.


latter was coated either with Insul-X lacquer or


fingernail


poli


h before use.


Thermocouple junctions were made by


twisting the wires together and melting the tips in a Bunsen burner


until a


mal


bead formed


Readout wa


either continuously recorded


on a Honeywell


Electronic


19 two-channel


chart recorder, or in the case


of species studied in Panama,

Mini-Mite thermocouple reader


recorded by hand fr

The thermocouple


Thermo Electric


leads were connected


to the chart recorder through a Con-Ohmic thermocouple reference


junction


output could be read to 0.1C with the recorder and to


0.5C with the Mini-Mite.


Each junction wa


calibrated against a


mercury thermometer,


in rare ca


often at


several different temperatures


the departure from the nominal


value of 40 pv/C


Except
(Weast,


1966-1967) wa


insignificant over a range of 20-30C.


At most it


amounted to 0.5C.


The thermocouple readings of water bath tempera-


tures were stable and reproducibi


to 0.1C over at


least five hours








0-60C.


At a given setting temperature fluctuated sinusoidally


with an amplitude of about


15C,


1C and a period of 1


the coolest temperature normally used,


minutes.


the room temperature


elevated about 0.4-0.5C when the investigator was in the room.


Relative humidity was uncontrolled and varied from 20-60% on occasions


when it was measured.


Air velocity near the insect was


than 0.25


m/second.


No such facility was available in the Canal


Zone.


Experiment


there were performed in an air conditioned laboratory at


Temperature was held within this rang


and judiciously selecting time of day when thi


by adjusting the air conditioner


temperature was easily


attained.


The junction wa


implanted to a depth of 1-5 mm in the thorax


through a pinhole in the


left metepisternum.


The depth of insertion


depended on the


size


of the dragonfly


Dissection of


several


pecimens


revealed that this mode of insertion


left the junction within the mass


of flight muscle


es, usually in the metathorax.


The junction wa


held


in place either with a drop of beeswax-paraffin mixture or with a small


amount of Elmer


After an animal


contact cement.


No anesthesia was used.


had recovered from the implantation,


released from restraint and placed on a vertical


stick.


it was

It usually


hung quietly while


minute.


being heated with a 250 W heat


At some point the


lamp at


insects avoided further heating,


1-4C/


either


h, mrn inn r+n fhQ chrIort ci fe nf thP Cti


attilmlna


C nor


i a Cl %tliI h t l L *


nostures -


U l I t I








rates of 1-7C/minute


(usually 1


-4C/minute).


The point at which


motor control


lost was also noted.


Heating was then dis-


continued and the animals invariably recovered after cooling.


The principal


causes


of error in the measurement of upper


temperature tolerance


ance or paralysi


lie in the difficulty of deciding whether avoid-


had occurred and whether the dragonfly had been


disturbed.


These are related problems.


Avoidance reactions were


usually obvious and the associated body temperature could be


determined to within 0.5C, except when the animal


stick.


flew off the


Because flight could have been caused by disturbing the


specimen, avoidance


was scored in these c


ases


only if the animal,


after being cooled a


little and replaced on the


tick


, flew again


at a

mean


within 2C of the temperature of its previous flight.


was taken


as the point of avoidance.


Recognition of paralysis


was often more difficult.


With


continued heating,


three ph


ases


of response could often be discerned:


coordinated struggling,

coordination, and feeble


vigorous movement with progressive


uncoordinated movements.


loss of


tried to record


the beginning of the


ast phase


as the point of paralysi


Individual


determinations might on occasion be inaccurate by as much a


but normally the accuracy was probably within


Since I


had to


be close enough to watch both the dragonfly and the record of Tb


rather carefully,


1 ..........- "


ne-ne .illarmiew m


no attempt was made to conceal myself from the


iinhicrdccarw 2nYA ciiSMrlon mnfomchntc iloro \n1rAold


-* + J








Investigation of Warm-Up and Conductance


In measuring these parameters the techniques of environmental


control and temperature recording described above were used.


After


implantation of a thermocouple a specimen was allowed to cool, if

its temperature was above ambient as a result of its struggling, to


within 1lC of ambient.

on a vertical stick.


Then the wings were freed and it was placed

If wing vibration did not begin spontaneously,


I pinched the end of the abdomen gently with forceps and repeated


this stimulation for up to 10 minutes.


If no warm-up behavior was


initiated within this period, this was noted and stimulation dis-


continued.


If the animal began to warm up by wing-whirring it was


permitted to continue undisturbed until takeoff.


If it stopped


without taking off, it was pinched again until it either began to


warn: up again or flew off the perch.


In the latter event, takeoff


was not considered spontaneous and the associated


was not used


to character


the temperature of spontaneous flight


Warm-up


rate was determined by measuring the maximum slope of the trace


of Tb


vs. time.


In most


cases


warm-up was virtually linear with time


throughout most of its course (


. 149-150).


After warm-up the specimen was placed on a wooden perch in a

metal box or glass desiccator in the dark and allowed to cool.

Usually relative humidity was maintained at near 100% with wet

paper toweling or distilled water in the well of the desiccator.


mine


r012+f,,n kimt-it/ wnc 1nbU n.,ro -i-n near n"Y with flrinritp








is assumed that the change in body temperature follows Newton's


of cooling,


constant.


i.e.3


d /idt


Thus a plot of


= K(Tb
A b/At


- Ta), where


vs. 2'


is the cooling


has a slope approximately


equal


to the cooling constant


Points were


selected from the continuous


record at one minute interval


beginning only after the dragonfly had


cooled several


degrees.


ince recording apparatus was not available


in Panama, cooling curves were determined by timing with a stopwatch


one to four degree decrements of body temperature.

were essentially the same except that time interval


Calculations


were unequal


In instances where the dragonfly would not warm up by


hovering,


or where it warmed too


little to obtain a good cooling curve,


it was


placed in a pasteboard box under a 250 W lamp and heated to at


least


10C above ambient.


It wa


then allowed to cool


as already described.


When cooling constants of dead specimens were determined,


heated in thi


they too were


way.


Several authors


(Krogh,


1948


Heinrich,


1971a) have pointed out


that significant heat may be


lost from insects through the


leads of


implanted thermocouples,

the rate of cooling. Th


reducing the rate of warm-up and increasing


ie possibility was tested in two ways on


specimens of


Pachydip


Perithemis


tenera.


First cooling curves


were run on dead individual


with one and then two sets of 0.002"


diameter


lead


implanted.


increase in cooling rate was apparent


with two


sets.


Second,


living specimen of


Pachydip


with


leads


- S I I I U - .i.... L i. 1.


"t _ L .... .. . .. .-----.- 1.- JLl








diameter leads were not tested in this way, but since they were


insulated and were used only on species


larger than


Pachy


diplax,


it seems unlikely that they had any greater effect.


I always


remained


least several


decimeters from the specimen except during implan-


station and brief periods of stimulation to prevent heat transfer

from myself to the specimen.


Newton


law of cooling describes temperature change in a body


with a uniformly warm core surrounded by an insulating shell


of zero


heat capacity


model


may apply when warm-up is endogenous.


However, when an object is warmed from the outside,


then cooled,


surface will


initially be warmer than the core.


For this reason all


specimens were permitted to cool


a few degrees to reverse


temperature gradient before using the data for cal


ulation of


conductance.


In any


case


almost al


plots of


AIIAt


vs. T


gave fairly good straight


lines


extrapolating near zero,


so the


lopes


gave an adequate inde


to cooling rates.


Other aspects of thermal


conductance in


Anax


received some


attention.


A series of experiments investigated the relation of


cooling constant to air speed.


Dead specimen


Anax


were suspended


with the wings held vertically over the back in a wind tunnel.


tunnel


had a closed working section of 5


cm X


0 cmX


0 cm and was


equipped with an entrance cone and baffl


produced by a centrifugal


air stream was


fan driven by a belt and pulley system


.~... ... -' 1 ,-. -I- ~. *. r- ni r *4- ,"' "~


,'-,n C:-


nanA ~A!kA rh ~n'.r10rl hcrhwc~nn fl inH








usual


strictly


controlled


normally was


about


5C.


Another


group


riments


was intended


idate


possible


effect on


lymph


thermal


from


condu


thorax


tance of


abdomen


thora


Living


circulation


pecimens


haemo-


Anax


were


prepared


as described


above


except


that


thermocouple wa


implanted


laterally


abdomen


, usually


second


or third


segment,


as wel


as in


thorax.


These


specimens


were


heated


with


lamp


10-15


above


ambi


Cooling


curves


both


thorax


abdomen


were


means


ured


on each


individual


ambi


tempera-


tures


of 15


Then


lamp,


made


narrow


spring


metal


strip


held


their


each


hort


ngth


tubing,


tened


tightly


across


abdominal


segment,


determination


were


repeated


same


ambient


temp


ratures.


Finally,


lamp


removed,


imen


killed


the cooling


curves


repeated


again.


Cooling


constant


of both


thorax


abdomen


were


calculated


as usual


possibility


that


contact


with


metal


clamp


acce


rated


cooling


cannot


altogether


counted,


effect


should


depend


on ambient


temperature


so any


diff


erence


between


conductance


should


other


causes.


same


said


possible


injury


abdomen


clamp


or t


thermocouple.


Local


Heating


Experim


ents








shaded by a small


piece of aluminum foil


fastened to a cork.


microscope


light,


which could be focused on an area of less than


cm2,


was shone on the thoracic dorsum so that the thorax


rapidly heated.


This was repeated at several air temperatures.


Near the end of some experiments, while the thorax wa


elevated temperature,


held at an


the base of the thorax was pinched with forceps,


so that most circulation between thorax and abdomen was cut off.
After a few minutes the abdomen was released and body temperature


measurements were continued for several


more minutes


Investigation of Role of Wing Position


The influence of variations


in wing positions on body temperature


Pachydiplax


was investigated


as follows.


An incadescent


lamp was


fixed on an arm that could be rotated about a fixed bolt and clamp


through approximately


in a vertical


plane.


The angle of the


arm was determined with a carefully handmade cardboard protractor


centered on the axis of rotation.


A dead specimen of


Pachy


was mounted with contact cement on a thin wooden dowel


and positioned


at the center of rotation with its


long axis parallel


to the axis of


rotation. Th

thermocouple.


toracic temperature wa


monitored with an implanted


The wings were positioned either in a horizontal


or pushed forward and well
run at both wing positions.


positions often seen in the field


below the horizontal.


plane


Each specimen was


positions approximate natural


. The wings were held








In addition to possibi


effects of the glue,


the possibility


exists that the position of the thorax was not exactly the same


relative


to the


light during run


at the different wing positions.


Secondly, at times


it was diffi


ult to position the wings in a


completely natural and symmetri


al way, and at times they shifted


positions


lightly


as the glue contracted.


Since several


replications


were made,


these errors should have no consistent overall


effect.













PATTERNS OF THERMOREGULATION


This section presents an overall


picture of thermoregulation in


each speci


that was investigated extensively.


The following accounts


are based primarily on fi


Id data but results from laboratory


experiments supplement the analyses.


Pachy


lon gipennis


long ago


99 Williamson remarked on the peculiar posture


that


Pac r:dip


sometime adopts, with the abdomen pointed almost


straight up


(Figu


1A and 2A).


Corbet (1963)


spec


ulated that a


similar po


sture, which he described


as an


"obeli


k," in certain


tropical


spec


the surface


ies might serve a thermoregulatory function by minimizing


area intercepting radiant energy.


Although elevation of the


abdomen


in Pachy


dip lax


may hav


more than one signifi


chance,


it clearly


reduces the radiant heat


load


in many c


ases.


Figure


is a plot of


vs. T


in this


pecies.


Specimens were


collected primarily at breeding sites, at small


ditches, but many were also taken in open area


sunny pond


away from the water.


This figure


excludes all


general


specimens and those


adults to which


un was not available, since thi


speci


heliothermic, as will


hown


shortly.


They may remain acti


in th


absence of sun, however,


psnpiallv in warm wea


t, ,I I


lml | I






















Figure 1A.


Male


Pachydiplax


longipennis


in obelisk posture.


Figure IB.


Male


Pachydiplax


oriented perpendicular to the sun


with wings in the "down and forward" position; sun
is above the plane of the paper and slightly to the
viewer's right.












25


















































































































































*S+
"i .... ..

*1i--x: Wx







... ..


**

ygt txx
139 xx xxx ^^ /i^^ ^.

xx KK K^ xKK KK K


:' x 'P .x x xx
x <














Figure 2A-B.


Body positions in


exposure to the sun.


Figure 2C-E.


Pachydip lax


that minimize


Wings not shown.


Body positions that maximize exposure to the sun;
stippling indicate sun above or behind plane of
paper (modified from Hardy, 1966).




27















A


*** 9.
**. ***



.*. ****

0* *


























Figure 3.


Relation of Tb to Ta in free-ranging Pachydiplax.
Thin straight line indicates line of thermal
equality, dashed lines the levels of critical


temperature


as determined


- heat torpor


erance, MF


in the


laboratory


- maximum voluntary tol


- minimum flight temperature), and the


line the


specimens above the


range of Tb (see t
field measurement,


follows:


aenil r r e r e s s i o n o f


gi


lower


ext).


nn p


limit of th preferred
Each point represents one


and postures are indicated a


- perpendicular to sun, X


postures maximizing radiant heating, A


- other
- obelisk,


- other postures minimizing radiant heating,


- all


flight.


other perched specimens,


- specimens in


heavy

















45






40





S35

I-



30






25





20








involved are shown in Figures


Those that appear to reduce


the surface area exposed to the sun are the obelisk, already mentioned,


and that shown in Figure 2B,


in which the individual


faces the sun


with the abdomen and thorax depressed.


In a variation of the obelisk,


which may occur during times when the sun azimuth is relatively


but the heat


load is still


high,


the specimen faces away from the


un with the abdomen partially elevated and pointing directly at


the sun.


Of these postures,


the typical


obelisk i


the most common


In the most common posture that appears to maximize solar heat input,


the insect perched horizontally with the


long axis of the body normal


to the horizontal


direction of the sun's rays


perpendicular position; Figures


1B and 2C).


(referred to as the

Less common positions


placed the specimen facing the sun with the thorax and abdomen elevated,

or facing away from the sun with the abdomen and thorax depressed

(Figures 2D and E respectively).

Figure 4 presents the frequency distribution of postures of


perched specimens as a function of Tb


It is clear that the


obelisk and other positions that could reduce solar input occur only


when Tb


is high and at very high Tb


are the only perching postures


observed.


Postures that presumably increase solar input are the only


ones observed below Tb


of about 300C,


but they are


also seen at


intermediate and high Tb.

more closely related to 3


However,


it appears that postures are


than to T


Fin~rn S


hnw<; that wina nosition is also stronalv


orrelated


I


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and promotion varied greatly and this position sometimes was in-


distinguishable from the


"flat" position.


In the


"elevated" position


the insect raised its wings well


Figure


above the plane of the terga, as in


Clearly there is a tendency to hold the wings down and


forward at


low Tb


and elevated at high Tb


These wing positions are


associated with certain postures


(Table


but the down and forward


position, at


least,


independently correlated with


Figure


hows that individual


perched perpendi


ular with wings down and


forward have


lower body temperatures than those perched perpendicular


with wings flat or elevated.


Individuals perched parallel


to the


un's rays,


or in an intermediate position, are


less


likely to have


the wings down and forward if


high.


In addition, when dead


specimens with their wing


positioned down and forward were heated


with a


lamp,


they tended to equilibrate at higher


than specimens


with wings in the flat position, except when the


lamp was exactly


horizontal


(Table 3)


In natur


, dragonflies


would


seldom encounter


a situation where incident sunlight


ame in exactly a horizontal


direction


because the true horizon i


normally obscured by vegetation


or slight elevations of land.


The elevated wing position may


decrease heat


load in itself,


but it may also simply


assist in


maintaining balance in the obelisk posture.


Two aspects of the result


in apparent disagreement with


the conclusions of others.


Johnson


(1962b)


showed that the bluish-


white pruinescence on the abdominal dorsum in mature male


Pachydiplax










Table


Frequency of various posture and wing position


combinations in


Pachnydiptax.


wing position


Posture relative to sun


down


flat


Perpendicular

Intermediate

Parallel

Obelisk








Tabi


Effect of wing position on equilibrium


dead


Pachydip


ranged from 5


tax.
- 28


Absolute values of
C.


- T
a


Lamp Position
(degrees above horizontal)


(oC)b


- 0.34

1.63

1.24

1.42


a number of specimens


in which equilibrium


was higher


with wings depressed.
b mean difference between equilibrium
and Tb with wings flat.


with wings depressed








dragonflies elevate their abdomen


in order to display the white


signal.


Male


Pachydiplax


often rai


their abdomen during aggressive


encounters with other males, espec


ially when they meet in flight or


when a male on a favorite perch is approached by a flying mal


Also,


many dragonfli


raise


and curl


their abdomen when touched or approached,


particularly if tethered in the


laboratory or otherwise prevented from


flying.


On one or two occasions a


Pachydip


in the field was seen to


abruptly rail


its abdomen when approached.


Neverthel


ess,


the function


of the raised abdomen


is often thermoregulatcryas is shown by the


fact that the obelisk posture is always associated with a high


Furthermore,


the position


is often assumed by femal


and by mal


away from breeding


ites.


Also,


if an individual


in an obelisk i


haded,


e.g.


by a cloud or an


insect net,


it will


lower its abdomen


to a horizontal


position


When the


hade 1


removed,


it resumes the


obelisk in a series of jerky movements.


have repeated this obser-


vation many times without any exceptions to this pattern.


Finally,


individual


heated with a


lamp in the


laboratory will


often assume an


obelisk or equivalent posture at high


If they are perched on the


ide of a vertical


support and the


lamp i


directly behind rather than


above them,


they will


assume a posture that


looks identical


to the


typical obelisk except that it


rotated 90 in a vertical


plane.


The abdomen of th


insect still


points almost directly at the


light.


action is in fact effective


I r.!-..... r


in preventing or slowing further rise


nr 'I' I~I] rlIIYO U~ I


























Figure 6.


A direct tracing from a recording of Tb in male
Pachydiplax heated with a 250 W lamp, showing effect


of obelisk posture.
sequence of events:
raised about 45, 3


Arrows indicate the following
1) lamp turned on, 2) abdomen


) full


obelisk,


specimen


lowers


abdomen and walks a short distance away from light,
5) full obelisk, 6) specimen in same location as 4)


and 5)


but with abdomen forced down to horizontal


position.

































































































































































































*








temperature in order to shade their thora


Corbet,


1963).


Johnson (1962b) and Paulson


(1966)


specifically associated wing


depression with elevation of the abdomen in


Pachydip lax.


suggestion seems reasonab]


a prior,


it receives support from


Heath's (1967) observation that Magicicada cassinix can obtain some


shading from its transparent wing


However, my data refute the


idea


in the present case.


First,


the distribution in Figure 5


clearly


hows the connection of wing position and


only once hav


I seen a Pachydiptax in a definite obelisk with dep

specimen was perched on an exposed twig in a gusty,


vress


ed wings.


This


shifting breeze.


It depressed its wing when the wind blew from behind it and held them


flat or elevated at other times.


Second,


lowered wings in dead


specimens actually facilitate heating.


The reason for the disagreement is not clear.


It may be that


previous workers failed to distinguish functionally different postures.


My data


how a number of instances


in which the wings were depressed


and the abdomen slightly or moderately


elevated


The mechanism by


which


lowering the wing


involve alteration of th


permits higher


thickness of the


is also obscure.

insulating air s


It may


acs


surrounding the thorax.


It i


now possible to draw the following picture of the behavioral


responses of


Pachydip lax


to temperature under field conditions.


cool


temperatures, particularly early and late in the day when the sun


L t '1 -- ri


-1- L - -


q* t I'l *" P Il I f rfl F, iCfl i il, n r i i I w i nlar T nCis L i


on-c ~eciimn h~cLinn nnet;iroc


1 -_ .


__i __ __ 1- ^


1 n i_








of about 30-35C,


Pachydiplax


begins to assume other postures, often


without regard to their orientation relative to the sun.


Many con-


tinue to use the perpendicular position, however, up to about


rarely 40-410C.


9C,


Above about 37C postures that minimize radiant


heating appear, and at higher temperatures they predominate.


It is interesting that


Pachydip lax


ordinarily does not


seek


shade to avoid overheating


On only two occasion


were individuals


apparently seeking shade,


both when


exceeded


4C.


In one


instance a femal


was hanging vertically in the shade of a twig and


in the other a mal


perched beneath a


layer of tall


water hyacinth


leaves.


In both instances other individuals remained active


in the


SPachydiplax


may remain active at


individuals have been taken in th


as high as


but not in


Other


assoc


iation with


particularly high temperatures.

One may now ask how effective are these behavior patterns in


maintaining a constant


Body temperatures occur outside of


(most


often below) the preferred range either because physical


are inappropriate or because


condition


has not had time to reach an equilibrium.


Most body temperatures


resulting from these condition


should not be


used in


valuating the precision of temperature regulation, because


in all


heliotherms


must vary from equal


to T


at night to some


maximum valu


near midday.


To eliminate inappropriate value


for Tb


those taken from


baskina individuals


were


ot used.


. I .


solid line of Figure


I I











































-D
0
ctS



ed











r3


0) C)



4 -)



"J-



c >ci


ien c
. r0
,- ^


. a
in n < n
0 O00



000
CMO0) t
* a


rOrN



* a a
000


tAO L


d- Io<- rd-


CO tO- CO
* a *

CO) COCOO


CM 0 (N -
N- 't- (0 Lfl
* a a






* a
0000


co) 't CM N-


O 0


t:j-wzj-


CM N- L n- O


0303 car-
co co co co)


N CM( 0 0 0 L


co r



00
* S




r -
c90
* a
300


co LA LA 't U)
co c co co (V


tg- C3O N-
CM i- CM ^
ft* a C



N- On CM co
03 N- On CM
Un Ln Ln CM
* a a
0000


in LA N CMr-CM CM


* S .a a a . a
NtOen 'toLm 't- CM
CC'J CMCCMC% CJC' CM


000


CM 0CM
'CC M


in 00o n0
CM 0 CMJ Ln

0000


0000
o cO (o in
On CM jD CM


On-

00

00

o nC


* *
o .- On co
c on CM


C N M l
' On N-
CM r- CM
* t t
0000



CM CM O) <0
N0 i- 'i -


'c1i On0en
CM CM CM
a N a
0C M 00


ON-
* *







0CM
* *




CM C
co

0LO
**




00
a






00~

NO)



100






O **
'OO


V O


000-
O r-


o -" Ln N- (0
N- co Cr3 o 0^
CM CM CM CM CM
aaa aN a

0000 0
00000


I '


S0 0 0

00000


bO+


bo+












4J? 0
edLo
LA
,E


C-


CO 0


to Ln On an


O 0r
01- CM 0


CnO


C0 LO
co r


,- c o r-.i
0- N- to
0000 ^ r


00


,--, 0 ,.
* * 1
^- fl C,,C\J
cJ CMj CI C'


0c9nm
- an Cl


r-'LO
Id-- LO
'JNt--
ctU-)


r-0








regression coefficient represents the overall


dependence of


and the standard error of estimate is a rough measure of the


preci


ion of regulation at any one


These


indices of thermoregulatory


ability are analogous to tho

regulation in bats. They do

resulting from imprecision i


McNab (1970) used to describe thermo-


not distinguish between variation of T

n active temperature responses and variation


due to the passive physical


characteristics of the insects.


Some other


workers (e.


Heath,


1965) defin


thermoregulatory ability of ectotherms


primarily in terms of the preci


thermoregulation will


ion of active responses.


be discussed in a


This aspect of


later section.


It 1


clear that in


Pachydiplax


is, to a considerable extent,


independent of T


under favorable conditions.


Figure 7


shows tempera-


tures of specimen


tethered in the sun or in the shade.


In both


cases


the slope of the regress


ion of


on T


significantly


although


slightly,


less than


Neverthele


ss, T


obviously depends much more


strongly on


than


in free-ranging individual


Evidently th


latter


do thermoregulate, and they must do so


largely by varying posture and


wing position,


as suggested above.


Pachydip


can e


levat


endogenou


heat production if forced to fly or struggle in the


l abora-


tory, but this


seldom results in a temperature differential of more


than 2-3C.


No evidence


indicates that activity contributes to thermo-


regulation since these dragonfl


are usually more active


at high


Table


4 reveal


that the


sexes


regulate


equally well, despite the


fact that males devote appreciable


time to territorial


defen
































Figure


Relation of Tb and Ta in tethered Pachydiplax.
Thin straight line indicates line of thermal


equality, heavy lines the regression of


on Ta


in exposed (Tb,
(TC = 0.84 T.


= 0.81


+ 12.84) and shaded


+ 7.65) specimens.






































20 25 30 35


(oc)








obtained from general


Pachydip


with those from other speci


, but the data available, coupled


, indicate that general


thermoregulate


poorly and tend to have


lower


than adults.


The great majority of


Pachydiptax


found in deeply


haded areas are general.


This i


also


true of the other


libellulid perchers studied here.


occasionally perch in full


hade.


Adults only


propensity of general


shade and cool


temperatures i


probably related to the fact that


their


uticle is incompletely hardened and therefore subject to


excess


ive water


loss.


In a few populations of


Pachydipt lax


,both tenerals and adults,


seem to spend a


larg


proportion of their time in the


hade


several of the


large


cypress-bordered lakes in the Gainesville area,


large concentration


Pachydip lax


breed among the emergent and


floating vegetation under the cypresses, where only patche


of sun-


light are present.


Therefore


the adult


of these


populations must


often perch in the


hade and consequently probably have


lower or


less


well-regulated body temperatures than populations in more open areas.

Of course, the former may experience a narrower range of ambient

temperature. The ability of these groups to exist under what appear


to be substantially different thermal


of the species emphasis


conditions from most populations


the facultative nature of thermoregulation in


these insects.


Such opportunism i


characteristic of many


aspects of


the behavior of Odonata


(Corbet


1963


Paulson


, 1966)


Although


J.L~a..n~nn..1,%4nr wm+knr emmrv-neefii1~, in mnct citi,~tinnct








themis


spp.


Erythemis


simplicicottllis


is a small


to medium sized


(mean body


weight


- 0.270 g)


libellulid, common in the Florida fauna.


Most


specimens were taken in an open field where there was no breeding


activity


Figure 8 i


a plot of Tb


in this


species.


As with


hydip


tax,


only mature


pecimens with


unlight available are plotted.


Variations in perching posture are not


frequency i


hown as a function of both


hown in thi


figure, but their


in Figure 9.


individual


in the genu


Erythemes


was seen to assume an obeli


posture.


Speci


observed included


E. credula,


haematogastra,


peruvzana,


plebeja,


simplicicotlis.


However


, Needham and Westfall


(1955)


describe


peruvvana


as perching with "flaming red abdomen erected


and held steadily aloft,


like a miniature obelisk.


Erythemis


simp


licicotllis


rarely el


vated


its abdomen at all


(three out of ninety-


four observations in whi


ch abdominal


orientation was


scored)


Various other postures were ob


served in thi


species.


In the


perpendicular orientation


thorax below the horizontal,

actually exposed to the sun.


Erythemis


frequently holds


its abdomen and


thus probably reducing the surface area

In a posture that more definitely


indicates active basking


E. simpli


cicol


exposes its dorsal


surface


to the sun by facing away from it with the abdomen and thorax horizontal


or depressed.

Pachydiplax,


posture i


but it is rare


like that


in th


shown


latter speci


in Figure 2E for


and common in


F -F cr 4 .14f


anne


L i i V r | |r i r


nf the nnsture i


orpatpst when the


| II -" t--


1 | r-L


-1
































Figure 8.


Relation of


simplicicottis.


points


a in free-ranging


The thin broken


in chronological


order.


lines connect
Open circles were


not included in the calculation of the regression


of Tb on


(see text).


Other symbol


as in


Figure 3 except that postures are not differentiated.


Erythemis


I





















HT ---------------------------------------- --


MVT S*.
-a* a


SO ..* *.


035
o


A'


^*


A A | ----


















C
-aic
-,
co DE~ 0'-
o cni-..t- 0a--
* *r-- .v -c cn +

*TU
00 O4- O-C n





3: oi c~oc
*^ o, o3 t--
*r- 0 0 <-
rC 4-) a -,-
-- 0 0
*00) Wr




0C S-
rS --r -o.,- u ui

Zs tf -0ed0 4-'
s. O r- 0 r- 0)
Sa r- a 4-











0 I r0.. C -0 0)
*1L 3fO (a L=
Im.0
4 -a4 ]a 4-
0 0 0 ,.













o ,- 4- ",-,r>
4-0 0 C0 0 -

0 C4- 3












Ou. >rdE)-O( ,---
c- (0 tr- O0 -r- a
C i r0 ,- .- __
*r 0 0 C) 4) v-




4f3 0...C 0 S0 0
* 4-) C


O L) U) UI ** **
CL 0O34-'a






fltl4-rcf r'J
on >n.Co .-4


*r- O C *Gr- -t>0
niroCro CO




r- O S- 0





4-) r- &U U) 4^i> a0
03 W-S -OO
*Q- 0r + r 0i *r
a* ..C .- p *fl

S- Q. >n C 0 O *3



o^v a* floW 4-
oi c ge*t0 C -
r0 0

Ol04-r 44
r 4 rO >0 00
=3 0- -3
CamC






00) I *



-EO >vr4-) xo
r-(^- -r ** A x


























4.
I ~~~~~ ~ ~ .. I.. i -- | |^' -- --





V"




*.* .











i------|. ..







* *

-S4






Ep


CD -














I--
m im
































m


N









image of the one just described.


Individuals face the sun more or


directly and depress the abdomen and thorax.


is similar


to Figure 2B, except that


themis


often perches on the side of a


straight stem rather than at the top,


so they may actually be partially


shaded by the stem.


Figures 9A and B


how that these postures correlate with temperature,


as expected.


Orientations that minimi


associated with high


regardless of


radiant heat


load are


The individual


facing the


sun with Tb


in the


interval


31-32C was one of the rare specimens with


an elevated abdomen.


20).


It probably was maximizing heat


load (see Figure


Postures that presumably maximize solar input are about


correlated with


as with


as well


however.


themis


simp lici


collins


somewhat unusual


among the Libellulidae,


although by no means unique,


in that it frequently perches directly on


or very near the ground


From


shortly after


unri


until about


sun-


set, ground surface temperatures are


likely to be substantially


higher than the temperature of the air a meter or two above ground


(Lowry,


1969).


Furthermore,


there is


little air movement at ground


level,


so heat


loss by convection


is reduced.


Thus,


themis


can,


effect,


select a body temperature by perching an appropriate distance


from the ground


Figure


10 suggests that they do thi


Erythemis


tends


to perch at higher


as T


measured in the usual way by a


thermometer about two feet above ground,


increases.


The actual


. * S I I 1 t I I

































Figure 10.


Perch height as a function of T


Erythemis


simplicicollis.


Open circles represent individuals


perched on broad, flat surfaces in the sun above


the ground (see text).


Elevations were estimated.





















































*f


* *


- - --


G ee el w m MMOM MM = = = -


(0C1


i








moderate


of 37.9C.


Three specimens were perched high at


below 25C,


but of these one was on a


large,


horizontal,


light-


colored log and another was on a broad leaf with its back to the


sun.


Thus, when ambient conditions are generally cool


there


definitely appears to be a preference for broad surfaces,


which


may have a boundary


layer of relatively warm air.


The trend


especially evident because


most observations were made in an area


with extensive


patches of bare ground.


Other observations


indicate


that


simp


icico


will


perch on the surface of lawns or


litter at higher air temperatures than


There i


as seen in Figure


hown here.


some relation between wing position and temperature,


Again the wings tend to be depressed at


At high Tb


they are generally flat,


seldom elevated.


siap


licicottis


a more or


less effective regulator than


Pachy


dip lax?


A comparison of the regressions of


on T


(Table 4)


suggests an answer,


but the result is equivocal


for two reason


First, many


Pachydip


, unlike most


Erythemis,


were taken at breed-


ing sites,


where reproductive activity may reduce the time


spent in


thermoregulation.


Second, somewhat different criteria were used in


calculating the


regressions for the two genera.


This stems from the


facts that


data were available for


Erythemis


and that no posture


in that species was recognized


as being a neutral


response to


temperature.


Thus,


is difficult to define satisfactory behavioral


criteria


r of a n i m a l s t ha t ha v e


less than optimal


I


temperatures.


































CO
*^



to-S



c



4-,
0
C
0
4-



cC



f0-




ac



4J -

o *-


c rE


.0
S-


0 1

Co"


W02.

ar




































1Z2r


r~r


Ir rJJ


JfJ


>^^^^^^^








The time of measurement wa


used to separate body temperatures


that represent initial warming from nighttime


represent a regulated level.


level


The thin irregular


from those that


on Figure


connects,


in chronological


order, points representing specimens


collected from 0800 to


1030 on


12 August


The early points


indicate that Tb


was rising much faster than


At about the time


indicated by the transition from open to closed circles


became much more constant and thereafter rose


(0900), Tb


rapidly than


although all


perched individual


were still


in postures scored as


increasing incident solar radiation until


about


1000.


Therefore,


all measurements taken before 0900 were


excluded from the regression


of Tb


on T


The change in the relation of


seen at about


0900 may be due to some


ubtl


behavioral


change that was not detected


by direct observation, but


as Heath


1964)


shown,


this conclusion


can be misleading and can be accepted only with some reservation.


However, since certain postures in


themes


are clearly correlated


with temperature, and


mince the break in


the Tb


vs. T


curve i


fairly


harp,


opposition seems to be justifi


Of cour


length


of time the insects must


pend basking will


vary with latitude,


season,


cloud cover, and other factors,


so no particular hour will


be the


proper cut-off point


in all


cases.


If the regression equations of Tb


on T


are accepted at face


value,


simp


licico


llis


appears to thermoregulate a


little better than


PachudinZam:


i t al


A.i tj r mA i 41 L' t A r~ i tJ LA .a


has a body temperature about


I


C higher than the








a bit more precisely than males


(Table 4)


are also usually


smaller than females,


and there


some


indication in


Table 4 that


large specimens regulate better than small


ones.


Tethered


individuals


how no sign of regulation


(Figure


12).


Erythemis


plebeja


a tropical


speci


es, slightly smaller than


licicol


tis,


and these sp


ecies


are s


similar in their habit of


perching on or near the ground and in the perching postures they


assume.


Ery themis


lebefja


differs strikingly from


simp


licicollis


in two respects.


First,


females tend to perch in or near shaded


areas much more than males.


Second,


the bodies of mature mal


completely black.


The mal


are also somewhat more


slender than


simplicicottllis.


, mostly away from breeding


the data presented here pertain to


tes.


Erythemis


plebeja


was studied at BCI, a


lowland tropical


location


at which air temperature varied very little.


the thermal


example,


This does not mean that


conditions experienced by this dragonfly are constant.


the temperature registered by a shielded black bulb thermometer


ranged from 30.9C


to 47C, and that of an unshielded black bulb about


one cm above the ground varied from 29.500C to 53C.


scatter normally found in behavioral


However, given the


thermoregulators, a wide range of


is required to demonstrate thermoregulation, so it is not surprising


that a plot of Tb


VS. T


(Figure


13) does not convincingly demonstrate


temperature regulation.


Some evidence


uaaests that


ntabeda


.JLIIII: I- V .Li tl. tj, l1lJAU .C L.f Il *L L, JLI. L ftCr//C'. LA.


emolovs thermoreaulatorv































Figure 12.


Relation of


to Ta


in tethered


Erythemis


simplicicollis.


specimen in the sun


Symbols


as in Figure 7.


= 0.99


for specimens in the shade
r = 0.983.


+ 6.61, r


= 0.98


= 0.917;


+ 2.69,





































25 30 35


(c)


































Figure 13.


Relation of 'Tb to Ta
Symbols as in Figure


in free-ranging
8.


Erythemis


plebeja.























4 -_MVT ow.""_ll I _


0
o
^ 35
1-P


20 25 30 35








males appear to perch almost exclusively


in the sunny patches.


Erythemis


plebeja


also


hows a tendency to perch either perpendicular to


or with the dorsal


surface exposed to the sun at


low temperature


(Figure


There did not appear to be any clear-cut heat avoidance


posture, nor was there any evident relationship between perch height

and temperature.


There i

may occur.


another line of evidence to


Figure


suggest that thermoregulation


15 shows the frequency distribution of body and


air temperature for


pecimens tethered


in the


un or free-ranging.


The variance of

specimens, n =


of


is similar for both groups


33; 2.03 for free-ranging, n


is much higher for tethered


individual


(1.65 for tethered


= 54), but the variance


(7.12) than for free-


ranging ones


(4.24).


The value of the ratio of variance i


Fisher index, F


which indicates that the variances


of these two populations are significantly different (p


=-- 0.95)


The mean Tb


for free-ranging


ebeja


(38.6C)


is about


C higher


than in tethered specimens


(35.8C) despite almost identical mean


This observation may reflect the fact that free individuals


perch near the ground while tethered on


were held three feet above


the ground.


The difference


in height


should tend to reduce the


difference in variance


if anything


becau


as already discussed,


is generally more variable near ground level.


Examination of tethered specimens may


also indicate the


influence


on T


of the black color of


plebeja.


Table 5


hows that although


I,


























Figure 14A.


Frequency distribution of posture as a function of


plebeja.


perpendicular posture,


Symbols are as follows: E


- postures in which the specimen


faced away from the sun with the adbomen depressed,


exposing its dorsal surface,


- all other postures.


Figure 148.


Posture as a function of
as in A.


plebeja;,


otherwise


in Erythemis




68






10 A




5 /




-C
- 35 40
"*- Tb(C)
o b
o




5




25 30
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Table 5.


Relation o


themis;
themis


f Tb to
Erythem
plebeja


in tethered specimens of


is simplicicollis is green,
is black.


Mean


Species


simplicicollis


+ S.D.


30.2 + 3.41


28.9 + 1.29


Mean TBB
+ S.D.


Mean Tb -
+ S.D.


46.0 + 5.08


.9 + 4.12


Max.


STa


8.0

12.3


6.32 + 1.47a

6.84 + 2.23a


a Probability that mean of E. simplicicollis
is about 0.85 (one-tailed Student's t test)


is less than that of


E. plebeja


Erythemis

Erythemis


plebeja


T








E. plebeja


exceeded


greater extent.


Some of the difference in


mean black bulb temperature is due to cooling of the imperfectly


shielded bulb by the almost constant trade wind at BCI.


will


The dragonflies


be cooled by the wind also, of course, but not necessarily to the


same extent.


Nevertheless,


it appears


likely that the black color of


ebeja


results in a greater elevation of


above T


than the


mostly green


E. simplici


coll


can maintain under similar circumstances.


Maximum voluntarily tolerated temperature and the temperature at


which heat torpor occurs ar


both


lightly


lower in


E. plebeja


than in


simplicicotLis


(Table


13).


Note,


however,


that


E. plebeja


is more


likely in the field to exceed its maximum voluntary tolerance and to


approach the effective


lethal


temperature than is


simple


icico


llis.


suggests that the black color of


plebeja


is thermally dis-


advantageous and therefore probably evolved in response to some other

selection pressure.


Libelluta


The following account refers to the two


ibling


species


(Paul son,


1966), Libellula


auripennis


needhami,


which are treated together.


They are usually indistinguishable


in the fi


Id, although they can be


readily separated in the hand


. Through an oversight they were not


distingui


hed in collections mad


1972.


However, all


data are


from the same site, an open field where no breeding activity took


place.


Since all collections made in


1973 comprised at


least








between adults of the two spe


cies,


nor have I


so c


conclusions about


one are probably equally applicable to the other.


The species are


about the same


(body weight


- 0.495 g)


Figure


16 i


a plot of


Libellttula.


Again,


general


and individuals taken when sunlight wa


not available are excluded.


is immediately evident that


is substantially


less variable than


Figure


shows that if thes


dragonflies are tethered either in


sun or shade,

Libellttula


temperature regulation is abolished.

accomplishes regulation with behavior patterns similar


to those of


Erythemis.


Figures


18A and B are the frequency distributions


of various


described for


body postures.


themis.


These postures are similar to those already


Postures maximizing solar exposure may be


maintained over a wide range of


but th


are mostly restricted to


Heat avoidance postures


are strictly associated with high Tb


These dragonflies


were


also scored in


different way (Figure


18C).


Individuals recorded as perching on the


"sun side" were on the


ides


of erect stems facing almost directly away from the sun, with their


abdomens and thoraxes dep


ress


thus maximally exposing their thoracic


dorsum.


Those scored on the


"shade


" were in the corresponding


mirror image position and were partially


haded by their perch.


This


divi


ion of postures makes


possible a


harper distinction between


individual


actively


seeking or avoiding radiant heat input.


Libellula


evident


never


perches on the ground, and there seems to be


no correlation between temperature and perch height.


There is also no































Figure 16.


Relation of


in free-ranging


Symbols as in Figure 8.


Libeltuta.









50






45






40






y 35

I--
































Figure 17.


Relation of T to
as in Figure .


Tb = 0.92
the shade


in tethered


Libe lula.


Symbols


For specimens tethered in the sun
For specimens tethered in the sun


+ 11.12,
= 1.00 1


r = 0.888; for specimens in


+ 2.74, r


= 0.975.











































20-.
20


25 30 35


(oc)





























O a

-o
camn3S-



r>. 0
*Oa
0 O
a)

-c 0
+j +Ji


O O


(U C
- E *r-

T to
a <'






qr"O
--O T-
t-" ('-lt4
O~ C
-* r- O
in .0







Q *r- C
C
Z rd


O-- OL
rlOO
Es -o

4- 0 S-
o 0
CC")
Ow










0 0"J
*r- E4 4
4->*r- 0
OUC
CC)
3 CQ. <
4- ta) tol

nfOI -C
0


amI

rC'
*.- at
*r- OE
t/1 r- (U
0 r-- *!-
0- 0 OS-
4- (U

r-- O 0 +

ec 0
0 0)-0 <
> S *-.r.C
0 "3 en -



C-)


c cn
0
-r-
S-LI-
.Q CD

4-)
r r
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CTr-
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I I I


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the departure from the flat position was usually small.


The regression of


onT
a


was cal


ulated


in the same way as


Erythemis,


except that the cut-off time for excluding data from


the calculation was 0930.


lightly


later time may be due to the


fact that

and thus i


Libelluta


does not usually perch on or very near the ground


restricted to


The data from 11


July


rapidly warming air strata.


1972 illustrate that the heterogeneity of


the habitat is another complicating factor in measuring


thermo-


regulatory behavior.


Note that on thi


date


determinations


howed


an initial


sharp rise,


followed by an almost equally precipitous fall,


followed by another rapid increase


. The fall


record


occurred


as I worked my way across


the field.


This field i


surrounded by


trees, so in early morning the west side receives sunlight before the


east side.


Dragonflies on the west side could therefore attain el


before those on the east side.


Clearly the individuals in the


vated

haded


areas could elevate their body temperature


by flying to the sunny


region, since they can fly if disturbed and the field is only 45 to


50 m across, but they apparently do not do so.


Erythemis


simplZi


cico His


in the same field doe


tend to be somewhat more concentrated in the


sunny areas, although many individual


remain in the shade.


Libellula


apparently remain on their nocturnal


perches on grass stems, oriented


randomly, until


sunlight reaches them.


From about mid-morning on, only


general s


are found in the shade,


indicating that adults avoid


hade


f+o thhov hornmp full v Crtivft


on thp


vprv hnttest days there seems








Table 4 shows that at


least from mid-morning to


thermoregulates much better than either


late afternoon,


Pachy


Erythemis


both in terms of the


independence of


and of the


the variation in Tb

better than females


at a given


, but thi


appear to regulate somewhat


may be misleading.


Males are much more


wary than females,


especially at high temperatures, so fewer of the


former were collected.


Trameinae


Five speci


of this subfamily,


belonging to the genera


Kiathyria,


Tauriphi la,


Tramea, were studied.


They were generally collected in


feeding swarms in which there was no reproductive activity.


dragonflies are quite uniform


hese


tructurally and behaviorally and are


very different from the other


libellulids considered


o far.


most important difference


in terms of their thermal


relations i


that


they are fliers, although they will


perch occasionally.


They al


can elevate their body temperature


by wing-whirring, an ability which


the previously di


scussed


ecies


lack


the trameines have their


hind wings expanded basally


Taur


less so than the others), and


are primarily diurnal


although


Tramea


carolina


may fly at dusk.


Figures


show the relationships between


in these dragon-


flies.


In these four figures all


data on non-teneral


pecimen


included, whether or not sunlight was available


during sunless periods, a


pecimens taken


as those not in flight, are indicated.


Libellula































Figure 19.


Relation of


Symbol s


in free-ranging


as in Figure 8 except


in flight in sun,


available,


- specimen


follows:


carolina.
- specimens


in flight with sun not


- specimen perched.


Tramea
































Figure 20.


Relation of
cophysa and
Figure 19;
unavailable


in free-ranging


Tramea


walker.


Tramea


Symbols as in


- specimens perched with sun



















45







40







0
35
.0


eta a- S. a -
































Figure 21.


Relatio


argo.


n of Tb to Ta in free-ranging
Symbols as in Figure 19.


Tauriphi lta











50







45







40





C-)
o
0
35
.0


m ....































Figure


Relation of


marcella.


Tb to Ta in free-ranging
Symbols as in Figure 19.


Miathyrta
















45






40






a
.0
I-




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