THE CONSEQUENCES OF SEXUAL DIMORPHISM IN BODY SIZE FOR BUTTERFLY FLIGHT AND THERMOREGULATION

In Euphydryas phaeton (Lepidoptera: Nymphalidae), females are twice the size of males, with greater wing loadings throughout most of their lives. Males can fly at lower body temperatures than females, but multiple-regression analysis of body temperature as a function of weather variables reveals that females are better able to maintain elevated body temperatures against short-term thermal fluctuations. Males perch in exposed sites where they are more vulnerable to convective cooling; heat loss is counteracted by basking for the majority of the daylight hours. Females inhabit a warmer, more sheltered microenvironment and spend less time basking. The flight of females is argued to be sluggish and more constrained by environmental conditions than that of males due to their greater wing loading, yet despite the difference in the degree of environmental constraint, males and females spend an equal amount of time in flight. -Author