Adaptive trait dissection in non-model Drosophila: Using next-gen sequencing to fine-map a naturally-occurring polymorphism in the sexually-selected cuticular hydrocarbons of D. serrata. Stephen F. Chenoweth, Bosco Rusuwa, Francesca Frentiu. Biological Sciences, University of Queensland, Brisbane, Queensland, Australia.

   A fundamental goal of evolutionary genetics is to establish links between the phenotypes that have facilitated adaptation, and their underlying genetic basis. The fly Drosophila serrata has proven to be an apt model system in which to investigate the evolution of traits affected by not only natural selection but also sexual selection. The cuticular hydrocarbons (CHCs) of D. serrata, function in mate and species recognition and also vary clinally along a latitudinal gradient, suggesting they are sensitive to climatic variation. However, the precise genetic underpinnings of CHC expression in D. serrata are yet to be determined. One conspicuous feature of the cline is a major-effect variant that segregates in tropical populations of D. serrata and declines in frequency towards temperate populations. To dissect this variant we have performed 1) a de novo genome assembly, 2) classic QTL mapping, supplemented with 3) next-generation bulked segregant analysis of advanced intercrosses and, 4) resequencing of multiple mutant and wild-type genomes. We isolate a small region a small region on 3R of the D. serrata genome enriched for sets of tandemly duplicated desaturase and elongase genes, each with likely functions in the CHC biosynthetic pathway. This region is then further interrogated using expression analysis. Fitness assays from polymorphic populations show that the variant likely has sexually antagonistic fitness effects - decreasing the mating success of males but increasing female desiccation resistance. Our results suggest that the polymorphism may be maintained though a balance between opposing natural and sexual selection.