Proximate mechanisms of behavioural inflexibility: Implications for the evolution of personality traits

Abstract

Behaviour is often assumed to be the most flexible of traits, yet recent studies show a high repeatability of behaviour within individuals even across different functional contexts. Such consistent expression of behaviour may evolve either when selection favours its integration with less flexible components of the phenotype or when pleiotropic effects produce correlations between behaviours that have different optimal timing of expression. Examining the physiological mechanisms underlying correlated expression of behaviours provides powerful insight into the evolution of personalities by establishing the extent to which pleiotropic effects might limit the independent evolution of distinct behaviours. 2.Here, we investigated proximate mechanisms behind aggressive and non-aggressive personality types in western bluebirds, Sialia mexicana, to determine whether consistency in the expression of aggression is because of shared effects of plasma-circulating androgens on aggression and mating behaviour. 3.We found that androgen concentration was unrelated to variation in both intra- and interspecific aggression even though it was closely linked to variation in male mating behaviour. These results suggest that pleiotropic effects of circulating androgens are unlikely to cause consistent differences among individuals in aggression. 4.These findings suggest that decoupling of the activational effects of hormones on behaviour is an important step in the evolution of personality traits. © 2012 The Authors. Functional Ecology © 2012 British Ecological Society.