Evolution of sex differences in cooperation: the role of trade-offs with dispersal

Explaining the evolution of sex differences in cooperation remains a major challenge. Comparative studies highlight that the more philopatric sex tends to be more cooperative than the more dispersive sex, but we do not understand why. Here we test the two leading evolutionary explanations for this association for the first time in a wild cooperative bird, using a novel automated radio-tracking study. Our findings provide no support for the widely invoked philopatry hypothesis, which proposes that the more philopatric sex helps more as it gains a greater direct fitness benefit from cooperation. Instead, our findings support the lesser known dispersal trade-off hypothesis, which proposes that the more dispersive sex helps less because investments in extra-territorial prospecting for dispersal opportunities trade-off against cooperation. This simple explanation for the evolution of sex differences in cooperation could apply widely across taxa as it does not require that cooperation yields a direct fitness benefit. ### Competing Interest Statement The authors have declared no competing interest.