Evolved changes in pheromone production underlie differences in larval social behaviors between closely related Drosophilids. Joshua D. Mast, David L. Stern. Janelia Farm Research Campus, HHMI, Ashburn, VA.

   Both the genetic and neurobiological mechanisms underlying the evolution of behavior are not well understood. Species in the melanogaster subgroup provide an opportunity to explore these mechanisms. While still closely related and amenable to traditional genetic analysis and techniques, these species occupy different ecological niches and have a variety of divergent behavioral traits. For example, we have found that larval social signaling in this species group has evolved. D.melanogaster and D.sechellia larvae are attractive to other larvae, while D.simulans larvae are not. We have identified both a novel attractive larval pheromone whose production has evolved between these species, and a single pair of gustatory neurons in D.melanogaster that are required to respond to this compound. By comparing the bouquet of compounds produced by larvae in these species, and then screening these molecules for attractive activity in behavioral assays, we identified a fatty acid monene pheromone. This attractive pheromone is produced by both D.melanogaster and D.sechellia larvae, but not by D.simulans. The attraction to this pheromone in D.melanogaster larvae is not affected by silencing chemosensory neurons expressing genes required in the adult fly to detect sex pheromones, namely Or83b, Gr66a and Gr33a. Rather, attraction is abolished by silencing a pair of gustatory neurons we identified in a targeted silencing screen using the Rubin fragment GAL4 collection.