Optimality, plasticity and selective regime in fig wasp sex ratios

Abstract

In thirteen species of fig-pollinating wasps the sex ratios of broods with one or two foundress mothers show qualitative agreement with the optimal sex ratios predicted by local mate competition theory. The deviations from these predictions are not random: for a given number of foundresses, the deviations are least in the wasp species that naturally encounter that number of foundresses most frequently. Furthermore, the difference in sex ratio between broods with one and broods with two foundresses is greatest in those species of wasp in which broods of both type commonly occur. These results show the importance of the selective regime in shaping the evolution of sex-ratio adjustment, and suggest that adaptive behavioural plasticity is more developed in species subject to more variable selective regimes.