Sex differences in helping effort reveal the effect of future reproduction on cooperative behaviour in birds

The evolution of helping behaviour in species that breed cooperatively in
family groups is typically attributed to kin selection alone. However, in
many species, helpers go on to inherit breeding positions in their natal
groups, but the extent to which this contributes to selection for helping
is unclear, as the future reproductive success of helpers is often
unknown. To quantify the role of future reproduction in the evolution of
helping, we compared the helping effort of female and male retained
offspring across cooperative birds. The kin selected benefits of helping
are equivalent between female and male helpers – they are equally related
to the younger siblings they help raise – but the future reproductive
benefits of helping differ because of sex differences in the likelihood of
breeding in the natal group. We found that the sex which is more likely to
breed in its natal group invests more in helping, suggesting that in
addition to kin selection, helping in family groups is shaped by future
reproduction.