Experimental Introgression To Evaluate the Impact of Sex Specific Traits on Incipient Speciation.

Sex 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 in pheromonal communication: affects both the production and the reception of sex pheromones while is 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 express but only Zimbabwe strains show high expression. To evaluate the impact of sex pheromones, female receptivity and expression on the incipient speciation process between Zimbabwe and Cosmopolitan populations, we introgressed the Zimbabwe genome into a Cosmopolitan genome labeled with the mutation, 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 stable lines showing Zimbabwe-like sex pheromones, copulation discrimination and expression. Our study indicates that the variation of sex pheromones and mating discrimination depend of distinct-yet overlapping-sets of genes in each sex suggesting that their cumulated effects participate to reinforce the speciation process.