Siblicide and life-history evolution in parasitoids

Parasitoid wasps exhibit a stark dichotomy in larval behavior and developmental mode. In gregarious species, siblings developing together tolerate each other; hence more than one individual can successfully complete development. In contrast, solitary species have intolerant larvae that will engage in siblicide, leading to only one individual successfully completing development. Previous theoretical and empirical work has suggested that females from species with intolerant larvae should reduce their relative investment in reproduction. We tested this prediction by measuring investment in survival and reproduction in a pair of sister species from the genus Aphaereta (Hymenoptera: Braconidae). With increasing body size, divergent patterns of investment exist in the two species. Females of the solitary A. genevensis allocate additional resources almost exclusively toward greater fat reserves, resulting in enhanced longevity. Females of the gregarious A. pallipes invest relatively more in reproduction and hence have lower fat reserves, reduced longevity, and greater egg loads than A. genevensis. These differences reflect a trend toward greater investment in survival relative to reproduction in the solitary species, as predicted. We discuss the implications of these findings for the development of sibling rivalry and life-history theory. Copyright 2002.