The Effects of Dispersal and Reproductive Patterns on the Evolution of Male Sociality in White-Faced Capuchins

Abstract

In many mammalian species, philopatric females reside with female kin with whom they form long-lasting cooperative bonds, whereas dispersing males rarely form strong bonds with other males. However, males may have the opportunity to disperse and form long-lasting bonds with paternal male kin in species with high male reproductive skew and parallel male dispersal. We used 54 group-years with demographic and genetic data to investigate how male dispersal and reproductive patterns affected the distribution of male kin in the Santa Rosa white-faced capuchins (Cebus capucinus imitator). During 41 of 54 group-years, there was a high degree of reproductive monopolization by either the alpha or a subordinate male. Natal males often co-resided with paternal brothers of similar age. The likelihood of parallel dispersal from the natal group increased with age similarity and paternal sibship. Some males may possibly gain inclusive fitness benefits by engaging in parallel dispersal and forming long-term cooperative bonds with other males. However, only one of three groups displayed a positive association between male-male relatedness and time spent co-resident in the breeding group. Inbreeding avoidance between alpha males and their daughters also gives subordinate males an opportunity to gain direct fitness benefits and may provide a strong incentive for cooperation among males that are not close kin. These findings suggest that cooperation between related and unrelated males likely evolved due to different reasons. Subordinate males related to the alpha male may gain inclusive fitness benefits, while only unrelated subordinate males gained reproductive opportunities and direct fitness benefits from cooperating.