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Kinship and Incest Avoidance Drive Patterns of Reproductive Skew in Cooperatively Breeding Birds

Author(s): Riehl, Christina P.

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Abstract: Social animals vary in how reproduction is divided among group members, ranging from monopolization by a dominant pair (high skew) to equal sharing by cobreeders (low skew). Despite many theoretical models, the ecological and life-history factors that generate this variation are still debated. Here I analyze data from 83 species of cooperatively breeding birds, finding that kinship within the breeding group is a powerful predictor of reproductive sharing across species. Societies composed of nuclear families have significantly higher skew than those that contain unrelated members, a pattern that holds for both multimale and multifemale groups. Within-species studies confirm this, showing that unrelated subordinates of both sexes are more likely to breed than related subordinates are. Crucially, subordinates in cooperative groups are more likely to breed if they are unrelated to the opposite-sex dominant, whereas relatedness to the same-sex dominant has no effect. This suggests that incest avoidance, rather than suppression by dominant breeders, may be an important proximate mechanism limiting reproduction by subordinates. Overall, these results support the ultimate evolutionary logic behind concessions models of skew—namely, that related subordinates gain indirect fitness benefits from helping at the nests of kin, so a lower direct reproductive share is required for selection to favor helping over dispersal—but not the proximate mechanism of dominant control assumed by these models.
Publication Date: Dec-2017
Citation: Riehl, Christina P. (2017). Kinship and Incest Avoidance Drive Patterns of Reproductive Skew in Cooperatively Breeding Birds. The American Naturalist, 190 (6), 774 - 785. doi:10.1086/694411
DOI: doi:10.1086/694411
ISSN: 0003-0147
EISSN: 1537-5323
Pages: 774 - 785
Type of Material: Journal Article
Journal/Proceeding Title: The American Naturalist
Version: Final published version. Article is made available in OAR by the publisher's permission or policy.

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