The quantitative genetics of social behaviour

Overview How and when social behaviour evolves has long been a focus of study within evolutionary biology, yielding the entire subfield of sociobiology and behavioural ecology. Although social behaviours may be explored in the same way as any other type of phenotype, the genetics underlying social behaviours differ from traits that do not vary depending on the social environment in which they are expressed. Social behaviour is best described as an interacting phenotype: a phenotype that depends at least in part on interactions with social partners for its expression. Models of indirect genetic effects provide a quantitative genetic framework for understanding the sources of variation underlying interacting phenotypes. They also suggest a genetic mechanism for inheriting traits that are expressed among rather than within individual animals, and identify selection arising from the interactions (termed social selection). This chapter will first introduce the concepts of interacting phenotypes, indirect genetic effects, and social selection. We build a quantitative genetic model for interacting phenotypes and discuss how the evolution of such traits differs from non-interacting traits. We then explore the parameters of the model in more depth. We subsequently summarise existing empirical studies of indirect genetic effects, discuss the implications for the evolution of behavioural traits through social selection, and discuss transitions between quantitative genetic and molecular genetic approaches to studying behavioural evolution. Finally, we highlight potential future avenues of research.