Multiple Mating, Sperm Utilization, and Social Evolution

Abstract

Allozyme data show that multiply inseminated honey bee [Apis mellifera] queens utilize the sperm of at least 3 males at any given time and that the sperm are, to some extent, mixing in the spermatheca. Statistical arguments based on the expected variance in brood viability among queens in a population, as a consequence of the genetic load imposed by the sex determination system of honey bees, suggest that queens are using the sperm of at least 5 or 6 males at a time, resulting in an average relatedness among siblings that approaches .hivin.r = 1/4. Assumptions of sperm clumping and high proportions of full sisters, leading to elevated relatedness values, are not justifiable. Polyandry does not introduce any special difficulties to the theory of social evolution by kin selection unless it is found to be more common in haplodiploid species than in diploids; or if both are found to have a low average relatedness among colony nestmates. This is especially true for incipient social species. Kin selection still relaxes the constraints imposed upon the evolution of altruism by individual selection, even with multiple insemination of females. Polyandry appears to be widespread in the Hymenoptera and may have evolved as a consequence of a sex determination mechanism that leads to the production of inviable or sterile diploid males. Polyandry results in a reduced variance in diploid male production among females and may be selected for or against, in different populations, depending upon population structure and life history strategy. The data for polyandry in the Hymenoptera are not systematic and do not provide an adequate test of this hypothesis.