Cooperative investment in public goods is kin directed in communal nests of social birds

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.

Relatedness predicts multiple measures of investment in cooperative nest construction in sociable weavers

“…Specifically, we tested in this population whether males will show higher relatedness than females as a result of female-biased dispersal (as suggested in Covas et al 2006). Consequently, we predict that males in this population will show elevated cooperative nest construction (as reported in Leighton 2014b and van Dijk et al 2014) due to the higher relatedness. Males, however, may also show elevated nest construction since simply because nest construction in other weaver species is also male biased (Collias and Victoria 1978; Quader 2006).…”

“…We used sterile needles to draw ~50 μL of blood from the brachial vein into a sterile heparinized capillary tube as is typical for birds of similar mass (van Dijk et al 2014) and stored the blood in lysis buffer. We used styptic powder to stop bleeding along with sterile cotton pads.…”

“…van Dijk et al (2014) found that exterior nest construction was spatially associated with where relatives live in the nest, implicating indirect benefits as an important fitness component for the maintenance of this behavior. van Dijk et al (2014) ceased recording behavior at a nest when behavioral observations did not seemingly provide more information on nest chamber residence or whether an individual was an exterior builder. This stopping rule allows one to categorize a large number of individuals as exterior builders and determine what factors influence the decision to build.…”

“…Indeed, van Dijk et al (2014) used behavioral observations to classify individuals as those that built the exterior of the nest or did not build and determined whether individuals directed their exterior nest construction towards parts of the nest that housed related individuals. van Dijk et al (2014) found that exterior nest construction was spatially associated with where relatives live in the nest, implicating indirect benefits as an important fitness component for the maintenance of this behavior. van Dijk et al (2014) ceased recording behavior at a nest when behavioral observations did not seemingly provide more information on nest chamber residence or whether an individual was an exterior builder.…”

Cheating and punishment in cooperative animal societies

“…Although this finding was initially considered to be surprising, it now appears to be the rule rather than the exception. A growing number of studies have explicitly sought behavioural evidence for punishment and have failed to find it, even when laggards are obvious (for example, in lemurs [127]; chimpanzees [139]; dogs [126]; and sociable weavers [140]). …”