Kin-biased social behaviour in wild adult female white-faced capuchins, Cebus capucinus

Studies of kin bias in the distribution of social behaviour in group-living matrifocal species generally underline the importance of bonds among female kin. However, few studies examine either how kin bias may be affected by variation in the availability of kin or the relevance of paternal kin. In this study, we used genetic and behavioural data to analyse correlates of coalition formation, proximity, grooming and dominance relations among female white-faced capuchins over a 10-year period during which the number of adult females in the group varied from 6 to 10. Females sided with the most closely related of two opponents when joining coalitions. Both dominance rank and kinship influenced proximity and grooming patterns. In particular, when group size was small, mean relatedness high and interdyadic variation in relatedness low, rank distance was a better predictor of proximity and grooming than was kinship distance. However, when group size was large, mean relatedness lower and interdyadic variation in relatedness higher, females significantly biased their grooming and spatial proximity towards kin. Dominance rank was not so tightly associated with relatedness as in provisioned female-bonded cercopithecines; females did not follow the ‘youngest sister ascendancy rule’. Full sisters, maternal half sisters and mother–daughter dyads associated at statistically indistinguishable rates, and all associated significantly more often than paternal half sisters. Paternal half sisters did not associate more often than distantly related female–female dyads (r < 0.125). These and similar results call into question the general importance of paternal kin ties in wild primates.