Genetic Variation and its Influence on Drosophila Social Behaviour

Abstract

Social interactions can have profound influences on an individual’s fitness. As part of a long-term research program on the mechanisms and functions of social behaviour in fruit flies (Drosophila melanogaster), we addressed two main questions. First, we asked whether social behaviour is positively correlated between the larval and adult stages. We quantified genetic variation in social behaviour by measuring aggregation among larvae and adults taken from each of 29 inbred, wild-derived lines. We found significant genetic variation in social behaviour in both larvae and adults. While these lines also showed significant genetic variation in baseline locomotor activity, it had no significant influence on social behaviour. We found that neither social behaviour nor activity were correlated between larval and adult flies. This is consistent with the hypothesis that metamorphosis adaptively decouples the expression of genes between distinct life stages in animals with complex life cycles. That is, genetic variation in social behaviour during each life stage may reflect adaptation to the specific ecological settings during that stage. Our second question was whether social behaviour in adult flies was influenced by indirect genetic effects (IGEs), defined as the effect an individual’s genotype has on the phenotype of an interacting partner. IGEs can have profound effects on the rate of phenotypic evolution. We found that groups of 6 focal males maintained shorter inter-individual distances among themselves when interacting with 12 males from a line previously identified as highly social than when paired with 12 males from the least social genotype. Overall, our results indicate that heritable genetic variation influences an individual’s predisposition to engage in social behaviour as well as its effect on social interactions among other individuals it encounters.