Multi-male groups positively linked to infant survival and growth in a cooperatively breeding primate

Abstract

Abstract: Cooperative breeding is a system where helper individuals care for breeding individuals’ offspring. As a result, social environment is likely to play a key role in regulating reproductive success. In primates, cooperative breeding is only found in the family Callitrichidae. Callitrichid males typically provide more infant care than non-breeding females, and in many callitrichid species, the presence of multiple males has been linked to infant survival. Leontopithecus chrysomelas (the golden-headed lion tamarin) is an endangered callitrichid found in the Atlantic Forest of Brazil. We used long-term data for wild L. chrysomelas to assess the influence of social group composition on reproductive success. Our survival model found that infant survival was negatively associated with group size, but this cost was mitigated by the presence of multiple adult males vs a single adult male. We also found that infants raised in groups with multiple adult males exhibited faster growth rates and higher adult weights than infants raised with a single adult male. This study adds novel evidence for the positive influence of adult males on callitrichid reproduction, demonstrating that adult males influence infant growth, as well as survival, in wild populations of cooperatively breeding primates. We suggest that social group composition, particularly the presence of adult males, be considered in future conservation strategies given its importance for reproductive success. Significance statement: In cooperatively breeding species, group members care for breeding individuals’ offspring. Due to this care, group composition may have a strong influence on infant success. In cooperatively breeding primates, males often provide more infant care than females. We investigated the influence of group composition on infant success in a cooperatively breeding primate, the golden-headed lion tamarin. Using long-term field data, we found that infant survival decreased as group size increased. However, this effect was reduced when multiple adult males were present in the group compared to a single male. We also found that infants grew faster and reached larger adult weights in the presence of multiple adult males compared to a single male. Our results demonstrate the importance of group composition for cooperative breeders and provide new evidence for the positive influence of adult males on cooperatively breeding primate infants.