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.