All of life is social! Organisms have an inherent drive to form groups, which is explained by the fitness benefits individuals accrue from group membership. Such benefits include greater survival and higher chances of reproduction. However there is a limit to these benefits because overcrowding results in resource over-exploitation. This balance of costs and benefits determines the ability of species to invade new niches, the likelihood of their extinction and the optimal exploitation of their environment. Because of the importance of density-dependent fitness effects of group size, there must be strong selection for optimal strategies on whether individuals should join a group or go elsewhere. Surprisingly, how individuals assess optimal group size and whether, why and how plasticity in joining/avoidance behaviour evolves are poorly understood processes. This is due to the lack of studies integrating both ultimate and proximate approaches to aggregation.
Here we aim to combine our unique expertise on evolutionary and behavioural genetics, ecology and social behaviour to understand the mechanisms and evolutionary processes underlying group formation in the fruit fly Drosophila melanogaster. The genetic basis and evolvability of group formation will be studied with an evolve-and-resequence approach, complemented by a genome-wide association study. The fitness consequences of aggregation will be studied by determining frequency dependent fitness effects in flies selected for different aggregation strength. Building on our theoretical work, we will construct ecological and evolutionary models specifically tailored to Drosophila life history, experimental group size, and the genetic architecture and mechanisms of aggregation uncovered by our study. Thus, by integrating theory and experiments, as well as mechanisms and experimental evolution, we will advance our understanding of how evolutionary processes and neuronal mechanisms determine when individuals should stay in or go away from a group.