Sex determination and the evolution of polyandry in honey bees (Apis mellifera)

Many hypotheses attempt to explain why queens of social insects mate multiply. We tested the sex locus hypothesis for the evolution of polyandry in honey bees (Apis mellifera). A queen may produce infertile, diploid males that reduce the viability of worker brood and, presumably, adversely affect colony fitness. Polyandry reduces the variance in diploid male production within a colony and may increase queen fitness if there are non-linear costs associated with brood viability, specifically if the relationship between brood viability and colony fitness is concave. We instrumentally inseminated queens with three of their own brothers to vary brood viability from 50% to 100% among colonies. We measured the colonies during three stages of their development: (1) colony initiation and growth, (2) winter survival, and (3) spring reproduction. We found significant relationships between brood viability and most colony measures during the growth phase of colonies, but the data were too variable to distinguish significant non-linear effects. However, there was a significant step function of brood viability on winter survival, such that all colonies above 72% brood viability survived the winter but only 37.5% of the colonies below 72% viability survived. We discuss the significance of this and other "genetic diversity" hypotheses for the evolution of polyandry.