The X chromosome, being hemizygous in males, is exposed one third of the time increasing the visibility of new mutations to natural selection, potentially leading to different evolutionary dynamics than autosomes. Recently, we found an enrichment of hard selective sweeps over soft selective sweeps on the X chromosome relative to the autosomes in a North American population of Drosophila melanogaster. To understand whether this enrichment is a universal feature of evolution on the X chromosome, we analyze diversity patterns across six commonly studied Drosophila species. We find an increased proportion of regions with steep reductions in diversity and elevated homozygosity on the X chromosome compared to autosomes. To assess if these signatures are consistent with positive selection, we simulate a wide variety of evolutionary scenarios spanning variations in demography, mutation rate, recombination rate, background selection, hard sweeps, and soft sweeps, and find that the diversity patterns observed on the X are most consistent with hard sweeps. Our findings highlight the importance of sex chromosomes in driving evolutionary processes and suggest that hard sweeps have played a significant role in shaping diversity patterns on the X chromosome across multiple Drosophila species.

中文翻译：

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与六个果蝇物种的常染色体相比，X 染色体上的硬扫描富集。

X染色体在男性中是半合子，有三分之一的时间暴露，增加了新突变对自然选择的可见性，可能导致与常染色体不同的进化动力学。最近，我们发现北美果蝇种群中 X 染色体相对于常染色体的硬选择性扫描比软选择性扫描更富集。为了了解这种富集是否是 X 染色体进化的普遍特征，我们分析了六种常用果蝇物种的多样性模式。我们发现，与常染色体相比，X 染色体上多样性急剧下降和纯合性升高的区域比例增加。为了评估这些特征是否与正选择一致，我们模拟了各种进化场景，涵盖人口统计学、突变率、重组率、背景选择、硬扫描和软扫描的变化，并发现在 X 上观察到的多样性模式与硬扫描最一致。我们的研究结果强调了性染色体在驱动进化过程中的重要性，并表明硬扫描在塑造多个果蝇物种的 X 染色体多样性模式方面发挥了重要作用。