Societies of local populations in African great apes – dispersal, extra-group paternity, and intergroup relationships

Abstract

Little is known about the social systems of primates at the local population level. For a better understanding of the matter, African great apes are appropriate subjects because many studies have investigated multiple neighboring groups. Here, I reviewed patterns of dispersal, extra-group paternity, and intergroup relationships in African great apes. These three topics are relevant to the three components of primate social systems defined by Kappeler & van Schaik (2002): social organization, mating system, and social structure, respectively. Patterns of female dispersal are similar among African great apes, in that females usually immigrate into groups near their natal groups. In contrast, patterns of male dispersal, often observed in gorillas, are more variable; some males stay near their natal groups after dispersal while others disperse far from their natal groups. Extra-group paternity is rare in African great apes. This is likely because males actively guard females against extra-group males due to severe male-male reproductive competition. Furthermore, extra-group paternity is considered to be disadvantageous in male-philopatric species, as it weakens the degree of kinship among philopatric males within groups. Intergroup male-male relationships are typically antagonistic due to resource defense, although male gorillas sometimes show high degrees of tolerance toward extra-group males. In contrast, intergroup female-female relationships are much more tolerant and affinitive, likely because females typically remain near their natal groups even after dispersal, so that females of neighboring groups are sometimes related to each other. This review highlights that dispersal in both sexes and a scarcity of intergroup breeding shape the kin structure of local populations, which contributes to regulating intergroup relationships in African great apes. Future behavioral and genetic studies that target multiple neighboring groups and dispersing individuals are required to further develop our understanding of primate societies at the local population level.