Appearance and sweep of a gene duplication: Adaptive response and potential for new functions in the mosquito Culex pipiens

Evolution of a new gene function is a fundamental process of adaptation. Ge ne duplication followed by divergence due to relaxed selection on redundant copies has been viewed as the predominant mechanism involved in this proce ss. At a macroevolutionary scale, evidence for this scenario came from the analysis of sequences of genes families. However, even if several genetic m odels have described the different potential microevolutionary scenario for a new function to evolve, little is really known about the initial evoluti onary dynamics of such processes. We analyze such early dynamics in natural populations of the mosquito Culex pipiens polymorphic for a duplication at Ace. 1, a locus involved in insecticide resistance. The date of occurrence and the selective advantages of the duplication were estimated using frequ ency data. We propose a scenario where the spread of a duplication is drive n, from the very beginning, by selection due to insecticide treatment.