Cost, risk, and avoidance of inbreeding in a cooperatively breeding bird

Amy E. Leedale, Michelle Simeoni, Stuart Sharp, Jonathan Green, Jon Slate, Robert Lachlan, Elva J.H. Robinson, Ben J. Hatchwell

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Inbreeding is often avoided in natural populations by passive processes such as sex-biased dispersal. But, in many social animals, opposite-sexed adult relatives are spatially clustered, generating a risk of incest and hence selection for active inbreeding avoidance. 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. First, we identified a positive association between heterozygosity and fitness, indicating that inbreeding is costly. 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. Finally, we show that the similarity of vocal cues offers a plausible mechanism for discrimination against first-order kin during mate choice. 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.
Original languageEnglish
Pages (from-to)15724-15730
Number of pages7
Journal Proceedings of the National Academy of Sciences of the United States of America
Issue number27
Early online date22 Jun 2020
Publication statusPublished - 7 Jul 2020


  • kin discrimination
  • Inbreeding
  • cooperative breeder
  • mate choice

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