Paternal Investment in a Monandrous Butterfly, Pararge Aegeria

Abstract

The investment by male Pararge aegeria during mating was studied under laboratory conditions. Investment in the first copulation was significantly smaller than reported for other butterfly species. I propose differences in degree of sperm competition between species as a possible explanation for differences in male investment. Polyandrous species with high degree of sperm competition are expected to invest more than monandrous species with no sperm competition. Despite the small investment in the first copulation, the investment done by males during additional matings showed a dependence on days elapsed since the previous mating. The weight of the investment reached values of the same magnitude as in the first mating only after six to seven days. Thus, although the paternal investment on a weight basis is rather small in P. aegeria this study supports the view that males incur non-trivial costs in producing ejaculates. This observation together with the fact that multipel-mated males did not suffer reduced longevity, may indicate that the main cost incurred by males is to be measured in units of time.