Experimental introgression to evaluate the impact of sex specific traits onDrosophila melanogasterincipient speciation

Abstract

ABSTRACTSex specific traits are involved in speciation but it is difficult to determine whether their variation initiates or reinforces sexual isolation. In some insects, speciation depends of the rapid change of expression in desaturase genes coding for sex pheromones. Two closely related desaturase genes are involved inDrosophila melanogasterpheromonal communication:desat1affects both the production and the reception of sex pheromones whiledesat2is involved in their production in flies of Zimbabwe populations. There is a strong asymmetric sexual isolation between Zimbabwe populations and all other “Cosmopolitan” populations: Zimbabwe females rarely copulate with Cosmopolitan males whereas Zimbabwe males readily copulate with all females. All populations expressdesat1but only Zimbabwe strains show highdesat2expression. To evaluate the impact of sex pheromones, female receptivity anddesatexpression on the incipient speciation process between Zimbabwe and Cosmopolitan populations, we introgressed the Zimbabwe genome into a Cosmopolitan genome labelled with thewhitemutation, using a multi-generation procedure. The association between these sex-specific traits was determined during the procedure. The production of pheromones was largely dissociated between the sexes. The copulation frequency (but not latency) was highly correlated with the female—but not with the male—principal pheromones. We finally obtained two stablewhitelines showing Zimbabwe-like sex pheromones, copulation discrimination anddesatexpression. Our study indicates that the variation of sex pheromones and of mating discrimination depend of distinct—yet overlapping—sets of genes in each sex suggesting that their cumulated effects participate to reinforce the speciation process.