SEX-RATIO BIAS, RELATEDNESS ASYMMETRY AND QUEEN MATING FREQUENCY IN ANTS

HAMILTON's rule and the principle of inclusive fitness' provide a theo retical basis for understanding the evolution of social behaviour, and a framework for predicting reproductive characteristics of social ins ect colonies2-4. Sex allocation in social insects (especially ants) ha s become a central factor in tests of inclusive fitness theory5-9. The most powerful such test is the analysis of individual colonies where the predicted sex allocation varies depending on variation in worker f itness functions10,11. Recently developed models5,12 predict that work ers may enhance their inclusive fitness by biasing sex ratios in respo nse to the degree of relatedness asymmetry in each colony. Here I prov ide the first empirical evidence of facultative sex ratio biasing in r esponse to relatedness asymmetries caused by inter-colony variations i n queen mating frequencies. In a Finnish population of the ant Formica truncorum, colonies have a single queen mated to one or several males . Colonies show a bimodal distribution of sex ratios, with a significa ntly greater proportion of males in colonies headed by a multiply mate d queen.