Increasing our understanding of how evolutionary processes drive the genomic landscape of variation is fundamental to a better understanding of the genomic consequences of speciation. However, genome-wide patterns of within- and between- species variation have not been fully investigated in most forest tree species despite their global ecological and economic importance. Here, we use whole-genome resequencing data from four Populus species spanning the speciation continuum to reconstruct their demographic histories and investigate patterns of diversity and divergence within and between species. Using P. trichocarpa as an outgroup species, we further infer the genealogical relationships and estimate the extent of ancient introgression among the three aspen species (P. tremula, P. davidiana and P. tremuloides) throughout the genome. Our results show substantial variation in these patterns along the genomes with this variation being strongly predicted by local recombination rates and the density of functional elements. This implies that the interaction between recurrent selection and intrinsic genomic features has dramatically sculpted the genomic landscape over long periods of time. In addition, our findings provide evidence that, apart from background selection, recent positive selection and long-term balancing selection have also been crucial components in shaping patterns of genome-wide variation during the speciation process.

中文翻译：

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在胡杨物种形成过程中广泛选择以塑造基因组景观的证据。

增进我们对进化过程如何驱动变异的基因组格局的了解，对于更好地理解物种的基因组后果至关重要。然而，大多数林木物种尽管具有全球生态和经济重要性，但尚未对全物种范围内和物种间变异的全基因组模式进行全面研究。在这里，我们使用跨越物种连续体的四个胡杨属物种的全基因组重测序数据来重建其人口统计历史，并研究物种内部和物种之间的多样性和分化模式。使用毛果杨（P. trichocarpa）作为外来物种，我们进一步推断族谱关系，并估计整个基因组中三个白杨物种（P. tremula，P。davidiana和P. tremuloides）的古老基因渗入程度。我们的结果表明，沿着基因组的这些模式发生了实质性变化，这种变化是由局部重组率和功能元件的密度强烈预测的。这表明，长期选择和内在基因组特征之间的相互作用极大地雕刻了基因组景观。此外，我们的发现提供了证据，除了背景选择之外，最近的正选择和长期平衡选择在物种形成过程中也是塑造全基因组变异模式的关键组成部分。这表明，长期选择和内在基因组特征之间的相互作用极大地雕刻了基因组景观。此外，我们的发现提供了证据，除了背景选择之外，最近的正选择和长期平衡选择在物种形成过程中也是塑造全基因组变异模式的关键组成部分。这表明，长期选择和内在基因组特征之间的相互作用极大地雕刻了基因组景观。此外，我们的发现提供了证据，除了背景选择之外，最近的正选择和长期平衡选择在物种形成过程中也是塑造全基因组变异模式的关键组成部分。