Live long and prosper: durable benefits of early-life care in banded mongooses

Abstract

Kin selection theory defines the conditions for which altruism or ‘helping’ can be favoured by natural selection. Tests of this theory in cooperatively breeding animals have focused on the short-term benefits to the recipients of help, such as improved growth or survival to adulthood. However, research on early life effects suggests that there may be more durable, lifelong fitness impacts to the recipients of help, which in theory should strengthen selection for helping. Here we show in cooperatively breeding banded mongooses (Mungos mungo) that care received in the first three months of life has lifelong fitness benefits for both males and female recipients. In this species adult helpers called ‘escorts’ form exclusive one-to-one caring relationships with specific pups (not their own offspring), allowing us to isolate the effects of being escorted on later reproduction and survival. Pups that were more closely escorted were heavier at sexual maturity, which was associated with higher lifetime reproductive success for both sexes. Moreover, for female offspring, lifetime reproductive success increased with the level of escorting received per se, over and above any effect on body mass. Our results suggest that early life social care has durable benefits to offspring of both sexes in this species. Given the well-established developmental effects of early life care in lab animals and humans, we suggest that similar effects are likely to be widespread in social animals more generally. We discuss some of the implications of durable fitness benefits for the evolution of intergenerational helping in cooperative animal societies, including humans