Sexual dimorphism in the alpine butterflies Boloria pales and Boloria napaea: differences in movement and foraging behavior (Lepidoptera: Nymphalidae).

Sexual dimorphism is a widespread phenomenon in Lepidoptera. It is reflected in differences in life history, behavior and morphology. Analyses of differences in behavior are mostly difficult and time-consuming, especially in high mountain ecosystems. To enhance our knowledge on sexual dimorphisms of alpine butterflies, we performed a mark-release-recapture study on 2 species common in the Alps: Boloria pales and Boloria napaea. We analysed movement and foraging behavior to investigate differences between sexes. Both sexes were mostly sedentary and the movement distances of males and females similar. However, obvious differences in dispersal behavior between the sexes were found in the movement patterns. Three different patterns were distinguished. Most males showed intensive flight activity, but mostly flew only in a limited part of the entire habitat (i.e., their individual home range) searching for females, whereas females were less flight active and flew only to find places for oviposition or feeding. The third pattern, where individuals flew larger distances, was only observed in a small number of males, which always returned to their home range. Nearly all feeding was observed on Asteraceae. However, males preferred the genera Leontodon and Crepis, while females preferred Leontodon and Carduus. Apart from this sexual difference in foraging, individuals of both sexes were found to be more or less specialised on nectar sources. Flight activity was generally greater in males than females. Therefore, we think that sex-specific requirements in nectar ingredients exist, that is, sugar for the intensive flight activity of males and amino acids for egg production of females.