Generation-dependent female choice: behavioral polyphenism in a bivoltine butterfly

Climatic and biotic circumstances vary as seasons shift, and different cohorts of multivoltine species are likely subjected to different selection regimes. The bivoltine butterfly Leptidea reali (Réal's wood white; Lepidoptera: Pieridae) appears during May and June in central Sweden and has a partial second generation in late July. We manipulated both generations to appear simultaneously and performed laboratory mating experiments that showed the presence of a behavioral polyphenism in mating propensity, which is induced during the developmental stages. Females of the summer generation expressed higher mating propensities than spring generation females. Spring females showed an increase in mating propensity with increasing age, whereas summer females accepted most matings already when they were only 1 or 2 days old. It is likely that larval time constraints, a lower abundance of males and a lower risk of accepting a male of their univoltine sister species Leptidea sinapis (wood white), have relaxed selection on mate discrimination among summer generation females. A major challenge for future research is to further investigate the developmental pathways causing the polyphenism and the adaptive implications of cohort-dependent behaviors. Copyright 2007, Oxford University Press.