Genomic basis of latitudinal differentiation among North American populations of Drosophila melanogaster. Thomas Flatt^1,2, Daniel K. Fabian², Martin Kapun², Viola Nolte², Robert Kofler², Paul S. Schmidt³, Christian Schlötterer². 1) Department of Ecology and Evolution, University of Lausanne, Lausanne, Switzerland; 2) Institut für Populationsgenetik, Vetmeduni Vienna, Vienna, Austria; 3) Department of Biology, University of Pennsylvania, Philadelphia.

   Understanding the genetic basis of clinal adaptation is a major but still largely unresolved problem in evolutionary genetics. Drosophila melanogaster, an ancestrally tropical insect that has spread to temperate regions and become cosmopolitan, offers a powerful opportunity for identifying the population genomic basis underlying clinal differentiation. Here we have applied genome-wide next generation sequencing of DNA pools ("pool-seq") to three populations collected along the North American east coast (Southern Florida, Pennsylvania, Maine) in order to investigate patterns of latitudinal differentiation. Comparing the genomes of these populations is of particular interest since they exhibit strong clinal differentiation in a number of important life history traits, including body size, fecundity, lifespan and adult reproductive diapause. We document extensive latitudinal differentiation at the genic level, with many of the most strongly differentiated genes being involved in central signaling pathways such as the insulin/TOR, ecdysone, torso, EGFR, TGF/BMP, JAK/STAT, immunity and circadian rhythm pathways. Several of these pathways, and many of the candidates we have identified, have been previously implicated in the regulation of life history. Remarkably, the majority of our candidate genes and SNPs is located on chromosome 3R, especially within the inversion In(3R)Payne. Our results thus provide genome-wide evidence consistent with pervasive spatially varying selection along the well-known North American cline, with many candidates implicated in life history regulation and exhibiting parallel differentiation along the previously investigated Australian cline.