Social behavior in context: Hormonal modulation of behavioral plasticity and social competence.

In social species animals should fine-tune the expression of their social behavior to social environments in order to avoid the costs of engaging in costly social interactions. Therefore, social competence, defined as the ability of an animal to optimize the expression of its social behavior as a function of the available social information, should be considered as a performance trait that impacts on the Darwinian fitness of the animal. Social competence is based on behavioral plasticity which, in turn, can be achieved by different neural mechanisms of plasticity, namely by rewiring or by biochemically switching nodes of a putative neural network underlying social behavior. Since steroid hormones respond to social interactions and have receptors extensively expressed in the social behavioral neural network, it is proposed that steroids play a key role in the hormonal modulation of social plasticity. Here, we propose a reciprocal model for the action of androgens on short-term behavioral plasticity and review a set of studies conducted in our laboratory using an African cichlid fish (Oreochromis mossambicus) that provide support for it. Androgens are shown to be implicated as physiological mediators in a wide range of social phenomena that promote social competence, namely by adjusting the behavioral response to the nature of the intruder and the presence of third parties (dear enemy and audience effects), by anticipating territorial intrusions (bystander effect and conditioning of the territorial response), and by modifying future behavior according to prior experience of winning (winner effect). The rapid behavioral actions of socially induced short-term transient changes in androgens indicate that these effects are most likely mediated by nongenomic mechanisms. The fact that the modulation of rapid changes in behavior is open to the influence of circulating levels of androgens, and is not exclusively achieved by changes in central neuromodulators, suggests functional relevance of integrating body parameters in the behavioral response. Thus, the traditional view of seeing neural circuits as unique causal agents of behavior should be updated to a brain-body-environment perspective, in which these neural circuits are embodied and the behavioral performance (and outcomes as fitness) depends on a dynamic relationship between the different levels. In this view hormones play a major role as behavioral modulators.