Kin preference in marmosets and tamarins: Saguinus oedipus and Callithrix jacchus (Callitrichidae, primates).

Field studies on callitrichid primates have suggested that some species may exhibit a communal breeding system in which two or more males mate with a single female and cooperatively participate in infant rearing. However, high levels of aggression have been observed between males under both laboratory and field conditions. In avian models for communal breeding, cooperating males are often closely related. In a laboratory test of a hypothesis of the amelioration of aggression based on kinship, four mated pairs of both Saguinus oedipus and Callithrix jacchus were introduced to both novel male conspecifics and to their own male siblings, from whom they had been separated for a minimum of 4 months. Significant differences (P less than .01) were seen in the responses of the two species to male conspecifics generally: S. oedipus males responded to intruders with overt aggression significantly more frequently than did marmosets while C. jacchus males more frequently scent-marked than did tamarins. Evidence of preference for kin males was seen in the significantly decreased frequencies of these behaviors in the presence of kin males over those observed in the presence of novel males. It is argued that, under field conditions, cooperation between male callitrichids may be facilitated by kinship. Further, twin births, short gestation lengths, and interbirth intervals seen in callitrichid primates all contribute to the number of socially familiar kin with which an individual animal might cooperate.