Colony sex ratios vary with queen number but not relatedness asymmetry in the ant Formica exsecta

Split-sex-ratio theory assumes that conflict over whether to produce predom inately males or female reproductives (gynes) is won by the workers in hapl odiploid insect societies and the outcome is determined by colony kin struc ture. Tests of the theory have the potential to provide support for kin-sel ection theory and evidence of social conflict. We use natural variation in kinship among polygynous (multiple-queen) colonies of the ant Formica exsec ta to study the associations between sex ratios and the relatedness of work ers to female versus male brood (relatedness asymmetry). The population sho wed split sex ratios with about 89% of the colonies producing only males, r esulting in an extremely male-biased investment ratio in the population. We make two important points with our data. First, we show that queen number may affect sex ratio independently of relatedness asymmetry. Colonies produ cing only males had greater genetic effective queen number but did not have greater relatedness asymmetry from the perspective of the adult workers th at rear the brood. This lack of a difference in relatedness asymmetry betwe en colonies producing females and those producing only males was associated with a generally low relatedness between workers and brood. Second, studie s that suggest support for the relatedness-asymmetry hypothesis based on in direct measures of relatedness asymmetry (e.g. queen number estimated from relatedness data taken from the brood only) should be considered with cauti on. We propose a new hypothesis that explains split sex ratios in polygynou s social insects based on the value of producing replacement queens.