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Sexual Differences in the Thermoregulation of Thymelicus Lineola Adults (Lepidoptera: Hesperiidae)
Author(s) -
Pivnick Kenneth A.,
McNeil Jeremy N.
Publication year - 1986
Publication title -
ecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.144
H-Index - 294
eISSN - 1939-9170
pISSN - 0012-9658
DOI - 10.2307/1939825
Subject(s) - thermoregulation , wing , biology , mating , beak , ectotherm , ecology , radiant heat , zoology , physics , materials science , composite material , thermodynamics
Sexual differences in thermoregulation and activity under different weather conditions were observed in field populations of the European skipper, Thymelicus lineola. The proximal causes of these differences were studied under both field and laboratory conditions and their possible importance for the mating strategy of this species was examined. Males had a longer daily period of activity than did females, which was related to the ability of males to fly in cooler conditions than females. In the laboratory, in the absence of a radiant heat source, both sexes began basking at body temperatures of 19°—25°C. However, males were able to fly at body temperatures 3° lower than females, which we attribute to a lower wing loading in males. Male mass is 42—62% of female mass, while their wing area is 86% of that of females. This difference should theoretically allow males to fly with a lower wingbeat frequency, and hence, at a lower temperature, since wingbeat frequency is temperature dependent. The body temperature of both male and female dead T. lineola pinned in the basking position rose faster and to a higher level than that of individuals pinned in the resting position with the wings folded, when exposed to an artificial radiant heat source. The thoracic temperature of males at equilibrium was °4° higher than that of females, despite their smaller size. Males also had higher heating and cooling rates, particularly of the abdomen, which heated and cooled two to four times faster than the female abdomen. In the field, females spent more time basking than males, yet female and male thoracic temperatures did not differ significantly. However, abdominal temperatures, which were always lower than thoracic temperatures in both sexes, were higher in females than in males. As a result, the difference between thoracic and abdominal temperatures was smaller in females than in males. The greater thorax—abdomen temperature differential in males can be explained by their higher rate of abdominal cooling and lower incidence of basking. We suggest that these sexual differences reflect sexual selection favoring males that have superior flight capability in marginal weather conditions.