Mechanisms of Inbreeding Avoidance in a Wild Primate

Abstract

The deleterious effects of inbreeding have been well-documented in both captive and wild populations. Hence, animals are expected to engage in inbreeding avoidance. However, one recent meta-analysis of mate-choice experiments indicates that animals of many species do not avoid mating with kin in experimental settings, and another reports that behavioral inbreeding avoidance is likely to evolve only when kin encounter each other regularly and inbreeding costs are high. These important results call for more detailed data on the patterns and processes of encounter frequency and mating behavior between kin within natural animal populations. Here, we present the first detailed assessment of encounter frequency and behavioral inbreeding avoidance in multiple kin classes in a wild mammal population, the baboons of the Amboseli ecosystem in Kenya. We find that death and dispersal are very effective at separating opposite-sex pairs of close adult kin. Nonetheless, adult kin pairs do sometimes coreside, and we find strong evidence for inbreeding avoidance via mate choice in kin classes with relatedness ≥ 0.25. Notably, maternal kin avoid inbreeding more effectively than paternal kin despite having identical coefficients of relatedness, pointing to the problem of kin discrimination as a potential constraint on effective inbreeding avoidance. Overall, demographic and behavioral processes ensure that inbred offspring are rare in undisturbed social groups (1% of offspring). However, in an anthropogenically disturbed social group with reduced male dispersal, we find inbreeding rates 10x higher. Our study reinforces the importance of demographic and behavioral contexts for understanding the evolution of inbreeding avoidance.