Data from: Gene-dosage effects on fitness in recent adaptive duplications: ace-1 in the mosquito Culex pipiens

Gene duplications have long been advocated to contribute to the evolution of new functions. The role of selection in their early spread is more controversial. Unless duplications are favored for a direct benefit of increased expression, they are likely detrimental. In this paper, we investigated the case of duplications favored because they combine already functionally divergent alleles. Their gene-dosage/fitness relations are poorly known, because selection may operate on both overall expression and duplicates relative dosage. Using the well-documented case of Culex pipiens resistance to insecticides, we compared strains with various ace-1 allele combinations, including two duplicated alleles carrying both susceptible and resistant copies. The overall protein activity was nearly additive, but, surprisingly, fitness correlated better with the relative proportion of susceptible and resistant copies rather than any absolute measure of activity. Gene dosage is thus crucial, duplications stabilizing an ‘heterozygote’ phenotype. It corroborates the view that these were favored because they fix a permanent heterosis, thereby solving the irreducible trade-off between resistance and synaptic transmission. Moreover, we showed that the contrasted successes of the two duplicated alleles in natural populations depend on genetic changes unrelated to ace-1, confirming the probable implication of recessive sublethal mutations linked to structural rearrangements in some duplications.基因重复长期以来被认为是推动新功能演化的重要动力。然而，自然选择在其早期扩散过程中所扮演的角色却更具争议性。除非基因重复因提升表达量带来直接益处而受到青睐，否则这类重复往往会产生有害影响。本研究聚焦于一类因结合了已有功能分化的等位基因而受到选择青睐的基因重复案例。这类重复的基因剂量-适合度关系尚不明确，因为自然选择可能同时作用于整体表达量与重复基因的相对剂量。我们以研究充分的尖音库蚊（Culex pipiens）抗杀虫剂案例为研究对象，对比了携带不同ace-1等位基因组合的品系，其中包括两类同时携带敏感与抗性拷贝的重复等位基因。结果显示，整体蛋白质活性近乎呈加性模式，但令人意外的是，适合度与敏感和抗性拷贝的相对比例相关性更强，而非活性的任何绝对度量。由此可见，基因剂量至关重要，基因重复能够稳定一种“杂合”表型。这一发现证实了此前的观点：这类基因重复之所以受到青睐，是因为它们固定了永久的杂种优势，从而解决了抗性与突触传递之间不可调和的权衡难题。此外，我们还证实，两种重复等位基因在自然种群中截然不同的存续成功率，取决于与ace-1无关的遗传改变，这进一步印证了部分基因重复中与结构重排相关的隐性亚致死突变可能发挥了关键作用。