Evolution of plasticity in response to ethanol between sister species with different ecological histories (Drosophila melanogaster and D. simulans)

The contribution of phenotypic plasticity to adaptation is contentious, with contradictory empirical support for its role in evolution. Here I investigate the possibility that phenotype plasticity has contributed to adaptation to a novel resource. If phenotype plasticity contributes to adaptation, it is thought to evolve in a process termed genetic accommodation. Under this model, the initial response to the environment is widely variable due to cryptic genetic variation, which is then refined by selection to a single adaptive response. I examine the role of phenotypic plasticity in adaptation here by comparing two species of Drosophila that differ in their adaptation to ethanol (Drosophila melanogaster and D. simulans). Both species are human commensals with a recent cosmopolitan expansion, but only D. melanogaster is adapted to ethanol exposure. I measure phenotype plasticity in response to ethanol with gene expression and an approach that combines information about expression and alternative splicing. I find evidence for adaptation to ethanol through genetic accommodation, suggesting that the evolution of phenotype plasticity contributed to the ability of D. melanogaster to exploit a novel resource. I also find evidence that alternative splicing may be more important for the adaptive response to ethanol than overall changes in exon expression.