When boys want to be girls: effects of mating system and dispersal on parent–offspring sex ratio conflict

Question: How is parent–offspring conflict over the sex ratio affected by mating system and sex-specific dispersal? Methods: Inclusive fitness maximization models and dynamic simulations. Life cycle: Patch-structured diploid population, fixed number of adult females per patch, sex-specific dispersal of offspring, mating after dispersal, competition for breeding sites. The mating system is monogamous, polygynous or polyandrous. Results: In geographically structured populations, offspring can prefer a sex ratio more biased than that preferred by parents if the mating system is polygynous and dispersal is femalebiased. This can be understood from an inclusive fitness perspective: offspring have to balance the benefits of belonging to the minority sex – which enjoys a higher reproductive success than the majority sex – with the cost of increased competition between relatives. Simulations confirm these results and show that mating system and dispersal regime can determine the invasion prospects of feminizing or masculinizing genes, and hence may be important for the evolution of sex-determining systems.