Abstract
Progress in sociobiology continues to be hindered by abstract debates over methodology and the relative importance of within‐group vs. between‐group selection. We need concrete biological examples to ground discussions in empirical data. Recent work argued that the levels of aggression in social spider colonies are explained by group‐level adaptation. Here, we examine this conclusion using models that incorporate ecological detail while remaining consistent with kin‐ and multilevel selection frameworks. We show that although levels of aggression are driven, in part, by between‐group selection, incorporating universal within‐group competition provides a striking fit to the data that is inconsistent with pure group‐level adaptation. Instead, our analyses suggest that aggression is favoured primarily as a selfish strategy to compete for resources, despite causing lower group foraging efficiency or higher risk of group extinction. We argue that sociobiology will benefit from a pluralistic approach and stronger links between ecologically informed models and data.
Highlights
A major goal of sociobiology is to understand the extent to which adaptations are good for the individual and/or good for the group
An interesting test case has emerged in a highprofile study of the group-living spider Anelosimus studiosus, in which colony-level aggression has been interpreted as a group adaptation (Pruitt & Goodnight 2014a)
Pruitt & Goodnight (2014a) found that in low-resource sites, the proportion of aggressive females within a colony declines with colony size, whereas in high-resource sites, it increases with colony size
Summary
A major goal of sociobiology is to understand the extent to which adaptations are good for the individual and/or good for the group. We believe there is an urgent need to refocus these discussions on real biological systems, where alternative models can be evaluated with empirical evidence In this spirit, an interesting test case has emerged in a highprofile study of the group-living spider Anelosimus studiosus, in which colony-level aggression has been interpreted as a group adaptation (Pruitt & Goodnight 2014a). Pruitt & Goodnight (2014a) found that in low-resource sites, the proportion of aggressive females within a colony declines with colony size (number of females in the colony), whereas in high-resource sites, it increases with colony size They found that experimental populations with various colony sizes and compositions changed to resemble the site-specific patterns of naturally occurring colonies, and this was owing, in part, to the differential survival and extinction of groups. These results led to the conclusion that naturally occurring colonies exhibit the optimal aggressiveness for promoting group survival
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