Group structure, kinship, inbreeding risk and habitual female dispersal in plural-breeding mammals

In most plural-breeding mammals, female group members are matrilineal relatives but, in a small number of species, all adult females are immigrants who are seldom closely related to each other. Some explanations of contrasts in female philopatry suggest that these differences are a consequence of variation in resource distribution and feeding competition, whereas others argue that they reflect variation in the risk of close inbreeding to philopatric females. However, neither explanation has been tested against quantitative comparisons. Here, we use quantitative comparisons and phylogenetic reconstructions to show that contrasts in female philopatry in plural breeders are associated with the risk that a female's father is reproductively active in her group when she starts to breed, supporting the suggestion that habitual female dispersal has evolved to minimize the risk of inbreeding.