Abstract
The tragedy of the commons predicts social collapse when public goods are jointly exploited by individuals attempting to maximize their fitness at the expense of other social group members. However, animal societies have evolved many times despite this vulnerability to exploitation by selfish individuals. Kin selection offers a solution to this social dilemma, but in large social groups mean relatedness is often low. Sociable weavers (Philetairus socius) live in large colonies that share the benefits of a massive communal nest, which requires individual investment for construction and maintenance. Here, we show that despite low mean kinship within colonies, relatives are spatially and socially clustered and that nest-building males have higher local relatedness to other colony members than do non-building males. Alternative hypotheses received little support, so we conclude that the benefits of the public good are shared with kin and that cooperative investment is, despite the large size and low relatedness of these communities, kin directed.
Highlights
Understanding how individuals resolve conflicts over contributions to or exploitation of common resources remains a major challenge in ecological research
Using observations of behaviour and fine-scale population genetic structure, we have shown that male kin are spatially and socially clustered within the massive communal nests of
Non-building Building sociable weavers, and that the construction and maintenance of public goods in this species is predicted by the presence of kin despite the low average relatedness among members of a colony
Summary
Understanding how individuals resolve conflicts over contributions to or exploitation of common resources remains a major challenge in ecological research. When social interactions occur among relatives, kin selection may tip the balance in favour of cooperation; kin-selected fitness gains have been invoked as a key driver in transitions to sociality in many taxa (West et al 2002; Bourke 2011; Lukas & Clutton-Brock 2012; Fisher et al 2013). A study on Galapagos sea lions (Zalophus wollebaeki), for example, found that social ties between adjacent individuals in a network were positively related to genetic similarity (Wolf & Trillmich 2008) Another of the few studies that have investigated genetic sub-structuring of large social groups found no evidence that genetic relatedness predicted social interactions in guppies (Poecilia reticulata; Croft et al 2012). There is a paucity of studies describing the association between group size and composition and the benefit that group membership confers (Shen et al 2014)
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