Evolution of ABC transporters in herbivorous drosophilids

Herbivory has evolved in insects many times in spite of the costly adaptations required to overcome plant defenses including toxins, mechanical defenses, and camouflage. These adaptations in insects include changes in feeding behaviors and morphologies, digestion physiology, and detoxification. This study uses Scaptomyza flava as a study system due to its herbivorous lifestyle and its close relation to the well-studied Drosophila melanogaster. This research focuses on ATP binding cassette transporters (ABC transporters), a family of transmembrane proteins used to move various substrates out of the cell, such as plant toxins. ABC transporters have been shown to be evolving quickly in herbivorous species, such as the diamondback moth and spider mite, possibly in response to plant defense compounds. Thus, it may be possible that ABC transporters have evolved rapidly in response to plant toxins in S. flava as well. To study ABC transporter evolution, we obtained the ABC gene sequences from the assembly of the S. flava genome, and compared these sequences to three of S. flava’s closest relatives.  We found that S. flava had one loss in the C class of ABC transporters, and one gain in the G class. We also discovered that the A class of ABC transporters are likely evolving relatively rapidly. While these conclusions do support that there is rapid evolution occurring in the ABC repertoire within S. flava, future research will investigate the rate of evolution in each of the ABC transporter classes.