The evolution of social dominance in house sparrows

Abstract

Natural selection is a strong evolutionary force shaping those traits that determine individual fitness. Most animal social structures are organized hierarchically, with topranking individuals presumably monopolizing fitness. Although social dominance has been shown to positively correlate with fitness in many species, this relationship is absent in many others. Furthermore, little is known about the genetic basis of social dominance, and thus, about its evolutionary consequences. Social dominance has been suggested as a strong driver of conspecific variation in ornamentation. The status signalling hypothesis poses that some ornaments are used to signal dominance status, which would allow individuals to predict the outcome of a fight, and thus, to avoid unnecessary fights and their costs. Though this hypothesis has been tested often, literature reviews have highlighted large inconsistencies among studies. In this thesis, I studied the evolutionary consequences of social dominance. I developed a suite of tools to infer reliable dominance hierarchies and estimate their uncertainty. These tools were then used to test several hypotheses in relation to social dominance. First, I tested whether social dominance leads to conspecific variation in plumage ornamentation. I used a meta-analytic approach to test the validity of the status signalling hypothesis across populations of a classic textbook example, the bib of the house sparrow (Passer domesticus). Second, I tested the genetic basis of social dominance, and whether social dominance is under natural selection in a wild population of house sparrows. Third, I studied territoriality, an important predictor of fitness across animal species. For most of my studies, I used an age-structured and fully pedigreed wild population of house sparrows. The access to exhaustive longitudinal individual life-history data allowed me to disentangle effects otherwise impossible to unravel in most empirical studies.