Meeting Abstract

62.1  Jan. 7  Evolution of avian personalities: adaptive variation or hormonal constraint? DUCKWORTH, R.A.*; SOCKMAN, K.W.; University of Edinburgh; University of North Carolina rad3@duke.edu

The correlated expression of behavior across different contexts can reflect constraints to the independent evolution of behavior or a suite of behaviors favored by selection. Behavioral constraints are thought to result from the pleiotropic effects of hormones that simultaneously affect the expression of multiple behaviors. We tested the idea that testosterone, by affecting the expression of aggression across multiple contexts, underlies variation in aggressive personalities of western bluebirds (Sialia mexicana). Here, we show that testosterone levels are unrelated to males� aggressive phenotypes and instead vary closely with mating behavior. Moreover, male aggressive behavior was associated with distinct dispersal strategies � highly aggressive males are superior competitors and are more likely to disperse, but invest very little in parental care, whereas non-aggressive males acquire low quality territories, are philopatric and invest highly in parental care. Thus, distinct aggressive personalities of western bluebirds are favored because they ensure that the trait necessary for success in a new environment � aggression � is reliably associated with the propensity to disperse. These results suggest that selection can decouple hormonal and behavioral variation when inflexibility in the expression of behavior is adaptive.