Profiling caregivers: Hormonal variation underlying allomaternal care in wild red-bellied lemurs, Eulemur rubriventer

Neuroendocrine evidence suggests that paternal care is mediated by hormonal mechanisms, where hormonal changes in expectant and new fathers facilitate infant care. In species with obligate and extensive paternal care such as humans, androgen levels decline once males are paired and have offspring, and in direct response to offspring care. Facultative infant care is widespread in the Order Primates, but the underlying hormonal mechanisms are largely unknown. We found that wild, red-bellied lemurs living in family groups (two adults and their presumed offspring) varied in the amount of care they provided infants. The more fathers invested in helping infants (measured as a composite of carrying, holding, huddling, grooming, and playing), and specifically the more they huddled and groomed with infants, the higher their fecal androgen (fA) levels, contrary to expectations. Carrying was negatively related to fA levels. Helping by subadults and juveniles was not related to their own fA levels. Elevated fA levels during infant dependence have been observed in other vertebrate species, and are thought to reflect reinvestment in mating rather than investment in dependent offspring. However, red-bellied lemurs do not mate until after infants are weaned, and they have long-term pair-bonds, suggesting that elevated fA levels play a role in offspring care. These results support a growing body of research suggesting that elevated androgen levels do not inhibit protective infant care.