Partial brood care compensation by female breeders in response to experimental manipulation of alloparental care

In cooperative breeders, where nonparents participate in brood care, the investment of contributors to offspring care is predicted to be interdependent, reflecting a conflict of fitness interests between care providers. We experimentally manipulated the alloparental care of subordinate helpers in the cooperatively breeding cichlid Neolamprologus pulcher to test whether breeders compensate for reduced help, or whether brood care is additive. As predicted by recent theoretical models, breeder females only partially compensated for the reduced help of the subordinate by increasing their brood care effort. After being prevented from contributing to brood care, subordinates increased their brood care effort to a level exceeding that shown before the manipulation. Although this increased effort of helpers reduced the dominant female's workload, the clutch received more care in total post manipulation than during manipulation and before, that is, the brood care response was additive. These experimental results show that load-lightening effects and negotiation over brood care trigger behavioural decisions of dominants and subordinates, as suggested by a recent theoretical model. Together with previous evidence from birds, our results suggest that load lightening is taxonomically widespread in cooperative breeders.