Thermoregulation and Habitat Preference in Two Wing Color Forms of Mnais Damselflies (Odonata: Calopterygidae)(Behavior Biology)

7 Pages·1991·17.9 MB·English

by  Mamoru Watanabe

ZOOLOGICAL SCIENCE 8: 983-989 (1991) © 1991 Zoological Society ofJapan
Thermoregulation and Habitat Preference in Two Wing Color
Forms of Mnais Damselflies (Odonata: Calopterygidae)
Mamoru Watanabe
Department of Biology, Faculty ofEducation, Mie University,
Tsu-shi, Mie 514, Japan
—
ABSTRACT Thoracic temperaturesofMnaisdamselflieswith wingcolordimorphism (paleorange vs
hyaline) were compared with ambient and radiation temperatures. All sexually immature adults
remained on perches in sunflecks in deciduous forests. They controlled their thoracic temperature
against radiant heat load in similar manner. After maturation, territorial males, with orange wings,
were seen to spend much time perching in open streams, increasing the degree of thermoregulation.
They changed some physiological properties, probably due to the quantity ofhaemolymph because of
decline in watercontent ofthe thorax. Although there wasasimilardecline inwatercontentofmature
females, with orange wings, change in the body temperature did not show higher degree of
thermoregulation because oftheirperchingbehaviorformatingin open streams. Both sexesofmature
insects with hyaline wings were restricted to deciduous forests. Their water content ratio did not vary
with ageing. The response ofcontrolling thoracic temperature to ambient and radiation temperature
was similar to that in immature adults. The high degree of thermoregulation clearly allowed mature
insects with orange wings to be active under direct sunlight.
INTRODUCTION there was no evidence of heat transfer in the body
[7]-
Thermoregulation is an important behavioral The Japanese Mnais-species is regarded as a
activity in adult Odonata. Since they spend much percher. It shows a remarkable polymorphism
time in sunlight, in either open or closed habitats includingwingpolychromatism in both sexes and a
[1-2], any behavior that regulates body tempera- complicated geographical variation in Japan.
ture would be advantageous. Some peculiar post- Wing dimorphism and differences in habitat pre-
ures such as an "obelisk" are those used for ference have been considered to be an adaptation
regulation of thoracic temperature against solar for thermoregulation in Colias butterflies [8]. In
radiation [3]. In low temperatures they shiver or the present study, I compared wing polymorphism
whir their wings for basking [4). forthe thermoregulation againt solarradiation and
Based on the means of thermoregulation, ambient temperature in relation to ageing, and
"fliers" and "perchers" were recognized in Odona- discussed their habitat preference. The water
ta considering their active period on the wing [5J. content in their thorax is also measured as an
Soaring or gliding in high temperatures is com- indicator of the quantity of haemolymph.
monly seen in the former type of species. Their
heat transfer between abdomen and thorax by
MATERIALS AND METHODS
haemolymph was clarified [4]. The energy meta-
bolism for soaring flight was similar to the resting Two distinct forms with pale orange and hyaline
metabolism because wings are essentially im- wings in Mwv/.v-species have been recognized for
mobile [6], On the other hand, in the lattertype of both sexes inTsu, Mie Prefecture, central Honshu.
species perched under direct sunlight. However, Japan [9]. The orange-winged damselflies main!)
inhabit open fields where some males hold territor-
Accepted April 25, 1991 ies. They belong to M. prumosa nawai Yamamo-
Received Januarv 14. 1991 to. according to Asahina |10|. On the contrary.
984 M. Watanabe
hyaline-winged damselflies always stay in closed abdomen were recorded in order to obtain in-
habitats such as sunflecks on forest floors. They formation on ageing. In the present study, the
still have no scientific name (Mnais sp.) but have a damselflies were divided into two age classes:
Japanese name, Hiura-kawa-tombo [11]. They do sexually immature and sexually mature.
not show clear territorialism. Since it has been All the damselflies whose thoracic temperature
included insome different classificatorysystemsby was measured were brought to the laboratory and
certain taxonomists [10, 12], in this paper, I have their abdomen and hind wing lengths were re-
adopted the wing color division for referring to corded. Then, the thorax of each individual was
each group of Mrta/s-damselflies. removed and weighed (accuracy 0.1 mg) to assess
The survey area was located in Tsu, Mie Prefec- the water content of the body. The samples were
ture. It includes paddy fields and a deciduous then dried in a homoiothermal chamber under
forest with various sizes of sunflecks. Study plots 80°C for 8hr and re-weighed.
were prepared along a stream in the paddy fields
(300 m long) and in the forest (400m long). The
RESULTS
former is an open habitat, where the stream is 1 m
wide. Study plots with a 5 m width were set up on
either side of the stream. The latter is a shaded Size and water content ofthe damselflies
habitat, where the study plotswere set up 50m on Either body size or quantity of haemolymph
either side of a stream less than 1 m in width. may affect thermoregulation. Table 1 shows that
The field survey was made on 20 windless and orange-winged damselflies were larger than
sunny days between 28th April and 1st July, 1988. hyaline-winged ones in both sexes. The abdomen
Oneachsamplingday, Isurveyedalongthestream length of mature orange-winged males was signi-
and on the paths of the neighboring forest floor. ficantly larger than that ofimmature one, whereas
The thoracic temperature ofthe damselflies was theirhindwinglengthwasnotsignificatlydifferent
measured chiefly during the period between 08 00 in either stage.
:
and 17:00, because mature males arrived in the An orange-winged damselfly was heavier than a
stream or sunflecks from roosting sites after08 00 hyaline-winged one. Mature orange-winged males
:
and left at around 16:00 [13]. All the damselflies were the heaviest. With ageing, the dry weight of
found were captured by a net after recording their the thorax increased, and the water content ratio
perching postures. The thoracic temperature was ofthethoraxdecreased, particularlyintheorange-
measured within 10sec from the time of capture. winged form. In hyaline-winged damselflies, the
If the time from capturing to measuring exceeded water content ratios were similar in the two age
10sec, orifItouchedtheirthoraxorabdomen,the classes.
damselfly was marked and released without
measuring. A pocketable digital thermometer Thermal environment ofperching sites
(accuracy0.1°C) with athermocoupleprobe of0.5 During the surveyperiod, the ambient tempera-
mm in diameter was used for measuring the thor- ture in the open stream varied from 15.1°C to
acic temperature. Damselflies in the state of 29.2°C, andthatofthe radiationtemperaturefrom
feeding, flying, ovipositing or copulating were not 23.5°C to 42.7°C. The regression coefficient be-
recorded. tween the radiation and the ambient temperature
Immediately after measuring the thoracic was 1.40 (r2=0.98, n=112), which is significantly
temperature (about 1 min), ambient and radiation different from unity (P<0.001). This shows that
temperatures were measured at the same perching the rate of increase of the radiation temperature
point. An Assmann'saspiration psychrometerwas was higher than that of the ambient temperature.
used for measuring the former. A digital thermo- On the other hand, the ambient temperature at
meter with a sensor covered with black tape was the sunflecks in the deciduousforest was relatively
used for measuring the latter. low, rangingfrom 11.7°Cto28.7°C, andthatofthe
The degree of wing wear and the color of the radiation was from 14.4°C to 40.6°C. The radia-
Thermoregulation of Mnais Damselflies 985
Table 1. Size, dry weight, and water content of the thorax in different wing forms of the
A/wjw-damselrlies on aging. Eaeh mean was assesed bv ANOVA between the ages
Wing-form Sex Immature stage Mature stage
Oransze <? abdomen length (mm) 45.3±1.0 (40) 47.7±0.2 (54) P<0.01
hindwinglength (mm) 38.7±0.3 (39) 39.4±0.2 (54) n.s.
dryweight (mg) 66.9±4.4 (27) 108.8±2.1 (50) P<0.01
watercontent (%) 78.0±0.8 (27) 71.8±0.6 (50) P<0.01
$ abdomen length (mm) 41.3±0.2 (93) 41.9±0.4 (20) n.s.
hindwinglength (mm) 38.7±0.2 (94) 38.8±0.5 (20) n.s.
dr\ weight (mg) 61.3±2.3 (82) 73.7±3.4 (19) 0.05>P>0.01
watercontent (%) 78.7±0.5 (82) 73.8±1.4 (19) P<0.01
Hyaline <? abdomenlength (mm) 42.6±0.4 (41) 43.2±0.3 (37) n.s.
hindwinglength (mm) 34.1 ±1.8 (41) 34.7±0.2 (36) n.s.
dryweight (mg) 42.0±2.1 (35) 64.0±2.2 (37) P<0.01
watercontent (%) 78.3±0.8 (35) 77.1±0.6 (37) n.s.
* abdomenlength (mm) 38.9±0.3 (46) 39.2±0.4 (17) n.s.
hindwinglength (mm) 35.9±0.3 (46) 35.5±0.6 (17) n.s.
dryweight (mg) 45.4±0.2 (37) 61.3±3.7 (16) P<0.01
watercontent (%) 78.0±0.6 (37) 75.5±1.8 (16) n.s.
( ): Number of damselflies sampled.
Table2. Regression coefficient (b) and determination coefficient (r) of the thoracic on the ambient
temperature of different wing forms of the M^aw-damselflies on ageing. Each regression coefficient
was assessed bv a t-test with b=l
Immature stage Mature stage
Wing-form Sex Perching site
b r n b r2 n
Orange <? sunfleck 0.98 0.93 10 n.s.
open 0.95 0.82 22 n.s. 0.66 0.31 21 n.s.
? sunfleck 0.75 0.78 50 P<0.01
open 0.66 0.58 8 n.s.
Hyaline ' sunfleck 0.67 0.73 20 P<0.01 0.82 0.60 7 n.s.
$ sunfleck 0.73 0.74 24 P- 0.01 0.80 0.45 6 n.s.
n: Number of damselflies sampled.
tion temperature fluctuated more widely than that
ofthe open stream, according to the differences in Thoracictemperatureagainstambientandradiation
the size of sunfkcks and its surrounding vegeta- temperature
tion. The regression coefficient between the radia- Most damselflies with orange or hyaline wings
tion and ambient temperature was 0.98 (r=0.32, began toemerge in late April in the open stream in
n=120). which is near unitv. the Mudy area. They stayed only (Hie day there
before moving to deciduous forests near the
stream. Their sexually immature stage was to 2
I
986 M. Watanabe
-10
male
-15
5 Immature Stage Mature Stage
female
-
b= -0.30
r2= .12
-5
b= -0.63 o
^=0.59 •
10
•15 (P
20 25 30 35 40 30 35 40 45
CO
Tr (°C ) Tr
Fig. 1. The relationshipbetweentheradiationtemperature (Tr) andtheoddswiththethoracictemperature (Tr-Tt)
in the damselflies oforange-winged forms. An open circle represents a damselflyperchinginopensites; asolid
circle represents a damselfly perching in sunflecks.
weeks. After maturation, the orange-winged energy, the rate of increase of thoracic tempera-
males held territories in the open stream. Mature ture may be expected to be lowerthan that forthe
males of the hyaline-winged form flew around the radiation temperature. If so, the regression coef-
deciduous forest floorandoverthe shadedstream. ficient of the odds on the radiation temperature
Therefore, no encounter between the orange- and must be negative. Further, the regression coef-
hyaline-winged forms was observed in the study ficient itselfmaybe used as anindexofthermoreg-
area. ulation ability of damselflies.
The thoracic temperature was always higher In the immature damselflies of the orange-
than the ambient temperature (max. ca. 10°C) winged form, the regression coefficientwas almost
irrespective of perching postures. The relation —0.5 or —0.6, irrespective of the differences in
between thoracic and ambient temperatures was the condition ofperching point, eitherin sunflecks
almost linear (Table 2). However, all the regres- or at the open stream (Fig. 1). On the contrary,
sion coefficients were below unity, though two there is a salient sexual difference in mature indi-
thirds of the coefficients were not significantly viduals. Theregressioncoefficientinmaturemales
different from unity. was —1.20 (r2=0.40): the rate of increase of the
Radiantheat loadmighteffectivelycontributeto thoracic temperature with the radiation tempera-
increasing the body temperature of damselflies ture was the lowest. This means that the body
perchingunderdirect sunlight. Ifthereisacertain temperature is kept relatively low under high
mechanism for thermoregulation against radiant ambient temperatures. However, such a relation
Thermoregulation of Mnais Damselflies 987
V
X
b= -0 84 b= -0 95
r2=0 77 r2= 90
^ male
*
10-
V
-151-
Immature Stage Mature Stage
5
V ST"
•
b= -0 85 b= -0 85
L. -5 r2=0 90 \ r2=0 88
N
female
•:
-15
I L I I I L
15 20 25 30 35 40 20 25 30 35 40
TrCC) Tr('C)
Fig. 2. The relationshipbetween the radiation temperature (Tr) andtheoddswith the thoracictemperature (Tr-Tt)
in the damselflies of hyaline-winged forms perching in sunflecks.
^cure in females. ambient temperature. Therefore, the change in
The regression coefficients in the damselflies of the ambient temperature might affect the body
both sexes of the hyaline-winged form were smal- temperature ofdamselflies inhabiting the forest as
ler than those in the orange-winged one during the well as radiation. However, radiation temperature
immature stage of both sexes (Fig. 2). seemed to be more important for the damselfly
perching in the open stream than the ambient
temperature.
DISCUSSION
Although damselflies are poikilotherms, their
After emergence, damselflies take several days body temperature is probably regulated against
to mature [14]. Although the preferable habitats both ambient and radiation temperatures. Several
oforange- and hyaline-winged damselflies differ in works on thermoregulation have so far focused on
their mature stage [11. 15], they were both res- the radiant heat load obtained from a thcrmister
tricted to deciduous forests during their immature with a probe painted black [4. 16-18]. The be-
Most immatures perched in sunflecks. The havioral posture for thermoregulation againsl
size of sunfleck and its surrounding vegetation radiation was analyzed in many butterfly species
\aried as noted above [2]. The thermal environ- [18-19]. However, the perching posture of the
ment of the sunflecks. particularly radiation damselfly species, excepting the "obelisk", has not
temperature, varied according to different so far been studied from the aspect of thermoreg-
sunflecks. The change of radiation temperature ulation [3|. In general, conductive heal transfer
can. however, be roughly explained by the between the wing base and the thorax is negligible
988 M. Watanabe
[20]. irrespective of their previous behavior: some of
Other elaborate physiological adaptations, as them had just finished oviposition (the thoracic
well as perching behavior, also help odanate spe- temperature ofthe females might be relativelylow
cies to regulate body temperature [21-22]. Con- because they were sometimes sprayed by the
trol of haemolymph in thermoregulation may be stream during oviposition) and others were
important in damselflies as in some butterfly spe- oriented towards the territory to mate.
cies [19]. The "fliers" appeared to thermoregulate On the other hand, hyaline-winged damselflies
exclusively through controlling blood circulation did not change their water content ratio. The
[7]. In general, most flying insects have higher regression coefficients suggest that hyaline-winged
rates of metabolism, and hence heat production, damselflies have a relatively steady thermoregula-
than other animals [23]. Rapid rates of cooling, tion mechanism against high radiant heat load.
due to their small size, may preclude appreciable Such a mechanism seemed to be unrelated to age
endothermy. Since the Mnais damselfly is a per- because the regression coefficients at both stages
cher that stays under direct sunlight all day long, were not markedly different in either sex. In
controlling the radiant heat load may be a more Kyushu, however, male f. strigata with hyaline
important factorforbodytemperature than thatin wingsofM. p. pruinosasettledaroundtheterritor-
the fliers. They receive solar input onto the body iesoff. esakiiwith orangewingsofM. p. pruinosa
without heat loss due to wind. Furthermore, I in open streams [24-25]. Such males with hyaline
observednoendothermicbehavior, probablyasno wing must perch under direct sunlight. It is said
cool days occurred during the survey period. that a certain change in the body physiology of f.
Teneral damselflies thermoregulate poorly due strigata in respect to thermoregulation between
to their cuticle being incompletely hardened [4]. immature and mature stages seemed to occur.
This suggests that both orange and hyaline wing Thus, thermoregulation maybe influenceedbythe
forms might have the same thermoregulatory thermal environment of the mating sites of the
mechanism during their immature stages. This is damselflies.
subject to excessive water loss. The watercontent
ratio of the thorax in immature damselflies was ACKNOWLEDGMENTS
similar irrespective ofthe difference ofwingform,
though body size was significantly different. This study was supported primarily by grants from
It is reasonable to find that the relationship Nissan Science Foundation. I am especially indebted to
Mr. Ko'ichi Tanabe for his continued assistance in the
between thoracic temperature and radiation or
field. Drs. KazunoriHigashi, KunioSuzukiandKeisuke
ambient temperature was similar in both wing Uedareadearlierdraftsofthepaperandofferedhelpful
forms, if the water content simply reflects the comments. Mr. Naoyuki Ohsawa identified the damse-
haemolymph content. However, the water con- lflies. I also thankMr. MasaoTaguchiforusefuldiscus-
tent: thorax weight ratio decreased in mature
orange-winged males. Therefore, the growth rate
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