Mito-nuclear discordance with evidence of shared ancestral polymorphism and selection in cactophilic species ofDrosophila

Abstract

The Drosophila serido haplogroup is a monophyletic group composed of the following four cryptic and cactophilic species that are endemic to eastern Brazil: D. borborema, D. gouveai, D. seriema and D. serido. Here, we investigate the mito-nuclear discordance in these species found among the cytochrome c oxidase subunit I (COI) mitochondrial gene, the autosomal alpha-Esterase-5 (α-Est5) and the X-linked period gene (per). Our analysis indicates that shared polymorphisms in these three molecular markers may be explained by the maintenance of ancestral polymorphisms rather than introgressive hybridization. The primary structures of COI, per and α-Est5 genes evolve primarily under purifying selection, but we detected some sites that evolved under positive selection in α-Est5. Considering the high variability of cacti species in eastern Brazil and the role attributed to Drosophila esterases in digestion metabolism and/or the detoxification of several compounds found in cactus tissues, we conjecture about the role of natural selection triggered by host shifts as an important factor in the intraspecific diversification of the D. serido haplogroup.