Joseph Manson: UCLA Department of Anthropology

Inbreeding reduces fitness in various taxa, and several behavioral and physiological mechanisms have evolved that inhibit fertile matings between close kin. Most commonly, members of one or both sexes disperse before breeding. In primates, males usually disperse and females often benefit from lifelong relationships with maternal kin within the group. Females thus risk breeding with their father if the tenure length of the dominant male, who usually sires most group offspring, exceeds the time it takes daughters to mature. Attempts to determine whether such co-resident father-daughter pairs systematically avoid inbreeding have produced equivocal results, and no published studies have addressed this question by genetically ascertaining paternity in a wild population. We determined paternity for 117 wild white-faced capuchins (Cebus capucinus) born into our study population. As expected, alpha males dominated reproduction. However, while siring the great majority (79%) of the offspring born to unrelated females, alphas sired only 6% (1 of 17) of the offspring conceived by their daughters during their tenures, providing evidence for effective inbreeding avoidance without female dispersal.