One, two, and many--a perspective on what groups of Drosophila melanogaster can tell us about social dynamics.

In the natural world, interactions between individuals occur in groups: an individual must recognize others, identify social opportunities, and discriminate among these options to engage in an interactive behavior. The presence of the group is known to exert an influence on individual group members, and this influence may feed back through the individual to affect behavior across the group. Such feedback has been observed in Drosophila melanogaster, for example, when mating frequency increases in groups composed of mixed strains compared to homogenous groups (Krupp et al., 2008 and Billeter et al. 2012). A working hypothesis is that social processes-to recognize, identify, discriminate, and engage-are innate. They rely on a combination of genetic inheritance, molecular interactions, and cell circuitry that produce neural and immunological responses. Here, we discuss studies that emphasize social interactions in four categories in Drosophila melanogaster: learning, circadian clocks, aggression, and mating. We also speculate that a systems-level network approach to the study of Drosophila groups will be instrumental in understanding the genetic basis of emergent group-level behavior.