Inter- and intra-species variation in the genome-wide gene expression of Drosophila in response to parasitoid wasp attack

Parasitoid resistance in Drosophila varies considerably, among and within species. Among species, resistance evolved in a subclade of Drosophila and was subsequently lost in at least one species within this subclade. Within D. melanogaster, resistance differs among geographic populations and can be experimentally selected to higher levels. While the mechanisms of resistance are fairly well documented in D. melanogaster, much less is known for closely related species. Here, we studied the inter- and intra-species variation in gene expression after parasitoid attack in Drosophila. We used RNA-seq after parasitization of four closely related Drosophila species of the melanogaster subgroup and replicated lines of D. melanogaster experimentally selected for increased resistance. We found a core set of genes that is consistently up-regulated after parasitoid attack in the species and lines tested, regardless of their level resistance.Another set of genes showed no up-regulation or expression in the species unable to raise an immune response against parasitoids. This set consists largely of genes that are lineage-restricted to the melanogaster subgroup, supporting the hypothesis that the ability to immunologically resist parasitoid attack is contingent on these new genes. Artificially selected lines did not show significant differences in gene expression with respect to non-selected lines in their responses to parasitoid attack, but several genes showed differential exon usage.