THERMOREGULATORY DIFFERENCES BETWEEN PHENOTYPES IN THE SPECKLED WOOD BUTTERFLY - HOT PERCHERS AND COLD PATROLLERS

Males of the speckled wood butterfly Pararge aegeria L. (Satyrinae), a ctively search for females (''patrolling'') or wait for them at partic ular places (''perching''). Darker males are more likely to patrol tha n pale ones, which are mainly territorial perchers. We studied whether this morphological variation relates to thermoregulatory differences. The relationship between thoracic temperature and ambient temperature differed between the colour types under natural conditions: darker ma les had on average lower body temperatures than paler males. Different activities (e.g. resting, flying) and behavioural strategies (perchin g or patrolling) were associated with differences in thoracic temperat ure: patrolling males which mainly engaged in long nights and periods of basking afterwards, had lower thoracic temperatures than perching m ales which engaged in very Short fight, fights and basking. When resti ng for a while thoracic temperatures did not differ between males prac tising different strategies. Under laboratory conditions, darker males heated up faster than pale males but there was no difference in the t horacic temperature at which they started to By. These results indicat e that thermal requirements (or general conditions) differ between the behavioural strategies, and that behavioural differences between phen otypes (colour types) relate to differences in thermal ecology. This s upports the idea that darker males are better adapted to patrolling. T here is no evidence that one mate-locating strategy is always superior to the other. which coincides with the observation that both strategi es co-exist. More generally, this study shows that relatively small di fferences in colour can have a considerable effect on thermoregulation and hence on the behavioural strategies a heliothermic insect will ad opt.