The evolutionary fate of heterogeneous gene duplications: a precarious overdominant equilibrium between environment, sublethality and complementation.

Gene duplications occur at a high rate. Although most appear detrimental, some homogeneous duplications (identical gene copies) can be selected for beneficial increase in produced proteins. Heterogeneous duplications, which combine divergent alleles of a single locus, are seldom studied due to the paucity of empirical data. We investigated their role in an ongoing adaptive process at the ace-1 locus in Culex pipiens mosquitoes. We assessed the worldwide diversity of the ace-1 alleles (single-copy, susceptible S and insecticide-resistant R, and duplicated D that pair one S and one R copy), analyzed their phylogeography, and measured their fitness to understand their early dynamics using population genetics models. It provides a coherent and comprehensive evolutionary scenario. We show that D alleles are present in most resistant populations, and display a higher diversity than R alleles (27 vs. 4). Most appear to result from independent unequal crossing-overs between local single-copy al...