avoidance of inbreeding in small huntr gatherer tribes

Inbreeding may be tolerated ( 3, 4), however, if avoidance is costly, or if the costs of inbreeding are outweighed by the inclusive fitness benefits accrued from breeding with or interacting socially with relatives ( 5, 6). Inbreeding is generally maladaptive because it increases homozygosity and hence the unmasking of deleterious recessive alleles, which, when expressed, result in a reduction in fitness among inbred individuals termed 'inbreeding depression” ( 1, 2). Long-tailed tits are known to discriminate between the calls of close kin and nonkin, and they favor first-order kin in cooperative contexts, so we conclude that long-tailed tits use the same kin discrimination rule to avoid inbreeding as they do to direct help toward kin. Finally, we show that the similarity of vocal cues offers a plausible mechanism for discrimination against first-order kin during mate choice. We then compared relatedness within breeding pairs to that expected under multiple mate-choice models, finding that pair relatedness is consistent with avoidance of first-order kin as partners. First, we identified a positive association between heterozygosity and fitness, indicating that inbreeding is costly. Here we show that, in long-tailed tits ( Aegithalos caudatus), a cooperative breeder that risks inbreeding by living alongside opposite-sex relatives, inbreeding carries fitness costs and is avoided by active kin discrimination during mate choice. But, in many social animals, opposite-sexed adult relatives are spatially clustered, generating a risk of incest and hence selection for active inbreeding avoidance. Inbreeding is often avoided in natural populations by passive processes such as sex-biased dispersal.

Avoidance of inbreeding in small huntr gatherer tribes