Helping in cooperatively breeding long-tailed tits: a test of Hamilton's rule

Inclusive fitness theory provides the conceptual framework for our current understanding of social evolution, and empirical studies suggest that kin selection is a critical process in the evolution of animal sociality. A key prediction of inclusive fitness theory is that altruistic behaviour evolves...

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Published in:Philosophical transactions of the Royal Society of London. Series B. Biological sciences 2014-05, Vol.369 (1642), p.20130565-20130565
Main Authors: Hatchwell, Ben J., Gullett, Philippa R., Adams, Mark J.
Format: Article
Language:English
Subjects:
Aegithalos caudatus
Altruism
Animals
Biological Evolution
Cooperative Behavior
Genetic Fitness - genetics
Inclusive Fitness
Kin Selection
Models, Genetic
Nesting Behavior - physiology
Passeriformes - physiology
Relatedness
Social Evolution
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Summary:Inclusive fitness theory provides the conceptual framework for our current understanding of social evolution, and empirical studies suggest that kin selection is a critical process in the evolution of animal sociality. A key prediction of inclusive fitness theory is that altruistic behaviour evolves when the costs incurred by an altruist (c) are outweighed by the benefit to the recipient (b), weighted by the relatedness of altruist to recipient (r), i.e. Hamilton's rule rb > c. Despite its central importance in social evolution theory, there have been relatively few empirical tests of Hamilton's rule, and hardly any among cooperatively breeding vertebrates, leading some authors to question its utility. Here, we use data from a long-term study of cooperatively breeding long-tailed tits Aegithalos caudatus to examine whether helping behaviour satisfies Hamilton's condition for the evolution of altruism. We show that helpers are altruistic because they incur survival costs through the provision of alloparental care for offspring. However, they also accrue substantial benefits through increased survival of related breeders and offspring, and despite the low average relatedness of helpers to recipients, these benefits of helping outweigh the costs incurred. We conclude that Hamilton's rule for the evolution of altruistic helping behaviour is satisfied in this species.
ISSN:0962-8436
1471-2970
DOI:10.1098/rstb.2013.0565