Z chromosome divergence, polymorphism, and relative effective population size in a genus of lekking birds

Sex chromosomes contribute disproportionately to species boundaries as they diverge faster than autosomes and often have reduced diversity. Their hemizygous nature contributes to faster divergence and reduced diversity, as do some types of selection. In birds, other factors (mating system and bottlenecks) can further decrease the effective population size of Z-linked loci and accelerate divergence (Fast-Z). We assessed Z-linked divergence and effective population sizes for two polygynous sage-grouse species and compared them to estimates from birds with various mating systems. We found lower diversity and higher FST for Z-linked loci than for autosomes, as expected. The πZ/πA ratio was 0.38 in Centrocercus minimus, 0.48 in Centrocercus urophasianus and 0.59 in a diverged, parapatric population of C. urophasianus, a broad range given the mating system among these groups is presumably equivalent. The full data set had unequal males and females across groups, so we compared an equally bala...

性染色体（sex chromosomes）对物种界限的贡献不成比例，因其进化速率快于常染色体（autosomes）且遗传多样性往往更低。其半合子（hemizygous）特性与部分选择类型，均可加速分化进程并降低遗传多样性。在鸟类类群中，其他因素（婚配制度与瓶颈效应）可进一步降低Z连锁位点（Z-linked loci）的有效种群大小（effective population size），并加快分化速度，即快Z效应（Fast-Z）。我们针对两种一雄多雌制的艾草松鸡属物种，评估其Z连锁分化程度与有效种群大小，并与不同婚配制度鸟类的相关估计值进行对比。结果显示，Z连锁位点的遗传多样性低于常染色体，而遗传分化系数（FST）更高，与预期相符。小艾草松鸡（Centrocercus minimus）的Z连锁位点与常染色体核苷酸多样性比值（π_Z/π_A）为0.38，大艾草松鸡（Centrocercus urophasianus的该比值为0.48，而其分化的邻域种群（parapatric population）的该比值为0.59；鉴于这些类群的婚配制度大概率一致，该比值跨度却相对宽泛。由于完整数据集各组间雌雄个体数不均等，因此我们对一个同等平衡的...