Whole-Genome Expression Plasticity across Tropical and Temperate Drosophila melanogaster Populations from Eastern Australia

The genotypic signature of spatially varying selection is ubiquitous across the Drosophila melanogaster genome. Spatially structured adaptive phenotypic differences are also commonly found, particularly along New World and Australian latitudinal gradients. However, investigation of gene expression variation in one or multiple environments across these well-studied populations is surprisingly limited. Here, we report genome-wide transcript levels of tropical and temperate eastern Australian populations reared at two temperatures. As expected, a large number of genes exhibit geographic origin-dependent expression plasticity. Less expected was evidence for an enrichment of down-regulated genes in both temperate and tropical populations when lines were reared at the temperature less commonly encountered in the native range; that is, evidence for significant differences in a directionality of plasticity across these two climatic regions. We also report evidence of small scale neighborhood effects around those genes significant for geographic origin-dependent plasticity, a result consistent with the evolution of high level, likely chromatin based gene regulation during range expansion in D. melanogaster populations.