Kin selection and the problem of sperm utilization in social insects

Abstract

The evolution of social behaviour has posed a special problem for natural selection theory since Darwin. Sociality entails at least a partial loss of personal reproduction by some individuals, a seeming contradiction to the expectation that it be maximized by natural selection. The theory of kin selection^1,2 seeks to explain social evolution by reference to high degrees of genetic relatedness among cooperating individuals. In the most diverse and conspicuous of social organisms, the social Hymenoptera (ants, bees, wasps), kin selection theory has been especially attractive because the malehaploid genetic system of the group leads to potentially high relatedness among female nestmates^3–5. Multiple mating by queens poses a serious difficulty for kin selection, however, in that it reduces nestmate relatedness unless sperm from different males are used non-randomly^6–10. This possibility has been investigated in only one highly social insect, the honey bee Apis mellifera, where the absence of suitable genetic markers has necessitated the use of artificial insemination^10,11. In this first study of long-term sperm utilization in natural populations of highly social insects I show that queens of two social wasp species use sperm from different males in relatively constant proportions through time, resulting in consistently low relatedness among female nestmates. I also show that workers do not supplement their inclusive fitness by reproducing directly in colonies in which the mother queen is present.