P450 gene family mediates allelochemical detoxification and tolerance to alkaloids in cactophilic Drosophila

Cacti are characterized by the extensive production of a broad variety of toxic metabolites as an anti-herbivore strategy but nevertheless cactophilic Drosophila spp. (Diptera: Drosophilidae) feed and breed on decaying cacti. The family of cytochrome P450 is a group of enzymes involved in the detoxification metabolism, which are critical for the adaptation of phytophagous insects, especially populations of Drosophila exploiting cacti. In this context, Drosophila buzzatii Patterson & Wheeler and Drosophila koepferae Fontdevila & Wasserman (Drosophilini), constitute an excellent model for the study of the genetic basis of tolerance to cacti allelochemicals. These closely related species allow testing to what extent a relatively small set of genes can explain host use patterns and their role in the divergent evolution of specialization. We evaluated the role of the P450 genes in the adaptation of these species to the use of one of their hosts, the columnar cactus Trichocereus terscheckii (Parm.) Friedrich & GD Rowley (Cactaceae). Experimentally evolved strains exhibiting different degrees of cactus specialization were exposed to artificial rearing media enriched with cactus allelochemicals and piperonyl butoxide (PBO), an inhibitor of P450 family activity. Our analyses showed a significant viability reduction in the presence of PBO, in the non-tolerant strains of both species as well as in the strain historically subjected to mild concentrations of allelochemicals (the soft strain) of D. koepferae. We confirmed the key role of P450 genes for the evolution of cactus specialization but also found evidence for the evolution of other detoxification pathways.