Genetic relatedness in two-tiered plains zebra societies suggests that females choose to associate with kin

How kinship structures alter inclusive fitness benefits or competition costs to members of a group can explain variation in animal societies. We present rare data combining behavioural associations and genetic relatedness to determine the influence of sex differences and kinship in structuring a two-tiered zebra society. We found a significantly positive relationship between the strength of behavioural association and relatedness. Female relatedness within herds was higher than chance, suggesting that female kin drive herd formation, and consistent with evidence that lactating females preferentially group into herds to dilute predation risk. In contrast, male relatedness across harems in a herd was no different from relatedness across herds, suggesting that although stallions benefit from associating to fend off bachelors, they do not preferentially form kin coalitions. Although both sexes disperse, we found that most harems contained adult relatives, implying limited female dispersal distances and inbreeding in this population, with potential conservation consequences.