Balancing Cooperation and Competition in Callitrichid Primates: Examining the Relative Risk of Infanticide Across Species

Abstract

At least eight cases of infanticide by females other than the mother have been observed in wild groups of common marmosets (Callithrix jacchus), with several more cases described for captive groups. Infanticide by females other than the mother has not, however, been documented for wild groups of other callitrichid species. Why might such overt aggression toward infants be more likely in one species than in others? In the common marmoset, a variety of social, reproductive and ecological characteristics – including short inter-birth intervals (and the resulting potential for overlap of pregnancies and births), habitat saturation, small home ranges, and low cost of infant care (including decreased travel costs and short dependency periods compared to other callitrichids) – may contribute to an increased likelihood of two breeding females being present in a group, which in turn may give rise to the potential for competition between breeding females and, ultimately, to infanticide. These conditions are less common in wild groups of most other callitrichid species. All callitrichids balance the need for cooperative care of young with the reproductive competition that results from limited reproductive opportunities; however, ecological and social conditions appear to tip the balance toward infanticide more frequently in common marmosets than in other callitrichid species.