Abstract
Testosterone is a key regulator of vertebrate social behavior. As such, testosterone can mediate and respond to social interaction dynamics.
Although experiments have demonstrated that testosterone signaling pathways can influence aggression and cooperation, no study has examined the links between hormone levels, behavioral phenotypes, and emergent properties of the social network. In other words, how do mechanisms underlying an individual’s social behavior scale-up to influence the emergent properties of the social network?
Here, we address this question by studying wire-tailed manakins, a species of bird in which males cooperate to court females at sites known as leks. Our previous experiments established that testosterone can influence the social behavior of individual male manakins. In the present study, we use an automated proximity system to monitor multiple manakin leks and measure the social network at each lek repeatedly through time. We also quantified the testosterone phenotype of all individuals in the lek.
Our analysis examines how the collective hormone phenotype of individuals within the lek affects three emergent properties of the social network: social specialization (the exclusivity of social relationships), network stability (the persistence of partnerships through time), and behavioral assortment (like associating with like). These three properties are expected to enhance the benefits of cooperation. We found that the manakin social networks with high-testosterone, dominant individuals were less specialized, less stable, and had more negative behavioral assortment.
These results provide evidence that hormones can act as an extended phenotype that shapes the broader social architecture of animal groups. High-testosterone groups exhibit collective behaviors that are predicted to impede the evolution of cooperation.
Footnotes
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