Detoxification Genes Differ Between Cactus-, Fruit- and Flower-Feeding Drosophila.

We use annotated genomes of fourteen Drosophila species covering diverse host use phenotypes to test whether five gene families which often have detoxification functions are associated with host shifts among species. Bark, slime flux, flower and generalist necrotic fruit feeding species all have similar numbers of carboxyl/cholinesterase, glutathione S-transferase, cytochrome P450 and UDP-glucuronosyltransferase genes. However, species feeding on toxic Morinda citrifolia fruit and the fresh fruit feeding D. suzukii have about 30 and 60 more respectively. ABC transporters show a different pattern, with the flower feeding D. elegans and the generalist necrotic fruit and cactus feeder D. hydei having about 20 and >100 more than the other species, respectively. Surprisingly, despite the complex secondary chemistry we find that three cactophilic specialists in the mojavensis species cluster have variably fewer genes than any of the other species across all five families. We also find 82 positive selection events across the five families, with the terminal D. suzukii and M. citrifolia-feeding D. sechellia branches again having the highest number of such events in proportion to their respective branch lengths. Many of the genes involved in these host-use-specific gene number differences or positive selection events lie in specific clades of the gene families which have been recurrently associated with detoxification. Several genes are also found to be involved in multiple duplication and or positive selection events across the species studied regardless of their host use phenotypes; the most frequently involved are the ABC transporter CG1718, which is not in a specific clade associated with detoxification, and the α-esterase gene cluster, which is.