Kin discrimination in juvenile mandrills, Mandrillus sphinx

Kin selection theory predicts that the evolution of social behaviours will be promoted if these behaviours increase the inclusive fitness of the individuals that perform them, for example by positively affecting relatives. The ability to identify relatives may thus be crucial in maximizing overall fitness. In primate species, whether individuals discriminate paternal relatives and the mechanisms that might permit such discrimination are still the subject of debate. Some researchers have suggested that primates are not able to discriminate relatives in the absence of familiarity. However, recent studies have shown that paternal kin discrimination could emerge from both age proximity and phenotype matching. We investigated the effects of paternal and maternal kinship on the affiliation index of juvenile mandrills, in a semifree-ranging setting. Juveniles biased their behaviour according to kinship. First, when interacting with adult females, both paternal and maternal half-siblings showed more affiliation than unrelated dyads. Affiliation between juveniles and males was also higher among both father-offspring and maternal half-sibling dyads than among unrelated dyads. While these results suggest that juvenile mandrills are able to discriminate paternal relatives, other results do not. Maternal half-siblings had a higher affiliation index than paternal half-siblings and distant kin, the latter showing no significant differences. Finally, when the mechanisms involved in discrimination of paternal kin were analysed, we found no evidence to confirm either the phenotype-matching or the age proximity hypotheses. (c) 2006 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.