Kin competition drives the evolution of sex-biased dispersal under monandry and polyandry, not under monogamy

The relation between mating system and sex-biased dispersal has been debated for three decades. However, the relative importance of the processes involved in this relation remains poorly known. In this study, we paid special attention to kin competition. We built an adaptive individual-based model fixing three mating systems (monandry, polyandry, monogamy) in a metapopulation, and allowing dispersal across patches to evolve independently for males and females. Our simulations showed that a difference in the number of mates can determine the evolution of sex-biased dispersal. Dispersal appears male biased under monandry and polyandry, but balanced under monogamy. By contrast, we showed that inbreeding can influence but does not promote sex-biased dispersal, and that the primary sex ratio does not qualitatively affect the evolution of sex-biased dispersal under monandry and polyandry. These results are driven by the interaction of two factors: the variation in reproductive success between patches in the metapopulation and kin competition. These two factors are influenced by the mating system, which modifies both the competition for access to partners and the mean relatedness between individuals. To ascertain that kin competition actually drives sex-biased dispersal, we made simulations with destruction of any genetic structure in the metapopulation, and we found that in this case dispersal was not sex biased.