Socioendocrinology of Cooperative Offspring Care

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Exclusive offspring care by females is the norm among mammals, but among a small set of species, males and other group members also play an important and potentially crucial role in the nurturing of dependent offspring. Among marmosets and tamarins, primates of the New World, care by all group members, including the mother, father, and nonbreeding juveniles and subadults, is the norm for social groups. Results from previous NSF funding have revealed important differences in levels of effort in infant care by mothers and fathers, with mothers playing a large role in infant care in the first two weeks of life, and fathers and helpers playing a central role in the 3rd and 4th weeks of infant life and beyond. These changes are associated with variations in testosterone (T) concentrations in mothers and fathers: T is reduced in mothers in the first 2 weeks post partum and in fathers during the second 2 weeks post partum, which corresponds to the highest rates of infant care. The studies outlined in the current proposal will utilize both observational and experimental approaches to the possibility that variation in testosterone concentrations helps regulate responsiveness to infants in marmosets, and whether T mediates a trade-off in effort in infant care versus reproductive and/or aggressive behaviors, which may be incompatible with infant care. The results will shed light on the possibility that complex affiliative and caregiving behaviors in social primates may, in part, be influenced by biological states, as well as experience-related factors.