The genome of Drosophila innubila reveals lineage-specific patterns of selection in immune genes

Abstract

Viruses make up a considerable proportion of the pathogens infecting animals. They can spread rapidly between hosts, and sicken or even kill their hosts to promote their own proliferation. Due to this strong selective pressure, antiviral immune genes are some of the fastest evolving genes across metazoans, as highlighted in mammals and insects. While Drosophila melanogaster are frequently exposed to pathogenic RNA viruses, little is known about D. melanogasters ecology in terms of viral exposure, or if they are representative of other Drosophila species. Here, we sequence and assemble the genome of a highly diverged, mushroom-feeding Drosophila species, Drosophila innubila, a species frequently exposed to a highly pathogenic DNA virus. We investigate the evolution of the immune system and find little evidence for rapid evolution of the antiviral RNAi genes, though we do find rapid evolution of several other pathways, suggesting alternate means of viral resistance. This contrasts with D. melanogaster, and suggests that evolution of resistance to DNA viruses differs greatly from that of RNA viruses.