Paternity and relatedness in wild chimpanzee communities

The genetic structure of three contiguous wild chimpanzee communities in We st Africa was examined to determine the extent to which the community, the mixed-sex social unit of chimpanzees, represents a closed reproductive unit . An analysis of paternity for 41 offspring resulted in 34 cases of paterni ty assignment to an adult male belonging to the same community. Among the 1 4 offspring for which all potential within-community fathers have been test ed, one likely case of extra-group paternity (EGP) has been identified, sug gesting an incidence of EGP of 7%. This more extensive analysis contradicts a previous genetic study of the Tai chimpanzees that inferred 50% extra-gr oup fathers. We suggest, based on direct comparison of results for 33 indiv iduals at 1 microsatellite locus and direct comparison of paternity assignm ents for 11 offspring, that the error rate in the previous study was too hi gh to produce accurate genotypes and assignments of paternity and hence cau sed the false inference of a high rate of EGP. Thus, the community is the p rimary but not exclusive unit for reproduction in wild chimpanzees, and fem ales do not typically reproduce with outside males. Despite the inferred lo w level of gene flow from extra-community males, relatedness levels among t he community males are not significantly higher than among community female s, and the distribution of genetic relationships within the group suggests that, rather than a primarily male-bonded social structure, the group is bo nded through relationships between males and females. Kinship may explain c ooperative behaviors directed against other communities, but is unlikely to explain the high levels of affiliation and cooperation seen for male withi n-community interactions.