正向选择驱动家蚕的快速Z进化
Positive selection drives faster-Z evolution in silkmoths
摘要：
与X或Z染色体相连的基因，在异配子性别中是半合子的，预计会以与常染色体不同的速度进化。这种快X效应可能是半合子的结果，这导致在异配子性别中对隐性有益突变的更有效选择，也可能是半合子染色体的有效种群大小减少的结果，这导致由于随机遗传漂变而增加的弱有害突变的固定。迄今为止的实证结果表明，虽然整个类群的整体模式是复杂的，在一般系统与男性异配显示更快的X效应主要归因于更有效的选择，而唯一的女性异配类群研究的日期（鸟类）显示更快的Z效应主要归因于增加漂移。为了测试鸟类中出现的快速Z模式的普遍性，我们对鳞翅目昆虫黄蚕蛾的基因组进行了测序，黄蚕蛾是家养家蚕家蚕<动>的近亲。我们发现，蚕蛾经历更快的Z进化，但与鸟类不同，更快的Z效应似乎是由于女性更有效的正选择。这些结果表明，单靠雌性异配不足以解释鸟类Z染色体选择效率的降低。相反，很可能是剂量补偿模式和总体有效种群大小以及其他因素的组合影响了更快Z进化的模式。
英文摘要：
Genes linked to X or Z chromosomes, which are hemizygous in the heterogametic sex, are predicted to evolve at different rates than those on autosomes. This faster-X effect can arise either as a consequence of hemizygosity, which leads to more efficient selection for recessive beneficial mutations in the heterogametic sex, or as a consequence of reduced effective population size of the hemizygous chromosome, which leads to increased fixation of weakly deleterious mutations due to random genetic drift. Empirical results to date have suggested that, while the overall pattern across taxa is complicated, in general systems with male-heterogamy show a faster-X effect primarily attributable to more efficient selection while the only female-heterogamy taxon studied to date (birds) shows a faster-Z effect primarily attributable to increased drift. In order to test the generality of the faster-Z pattern seen in birds, we sequenced the genome of the Lepidopteran insect Bombyx huttoni, a close outgroup of the domesticated silkmoth Bombyx mori. We show that silkmoths experience faster-Z evolution, but unlike in birds, the faster-Z effect appears to be attributable to more efficient positive selection in females. These results suggest that female-heterogamy alone is unlikely to be sufficient to explain the reduced efficacy of selection on the bird Z chromosome. Instead, it is likely that a combination of patterns of dosage compensation and overall effective population size, among other factors, influence patterns of faster-Z evolution.
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