A common pattern observed in temperate tree clades is that species are often morphologically distinct and partially interfertile but maintain species cohesion despite ongoing hybridization where ranges overlap. Although closely related species commonly occur in sympatry in tropical ecosystems, little is known about patterns of hybridization within a clade over time, and the implications of this hybridization for the maintenance of species boundaries. In this study, we focused on a clade of sympatric trees in the genus Diospyros in the Mascarene islands and investigated whether species are genetically distinct, whether they hybridize, and how patterns of hybridization are related to the time since divergence among species. We sampled multiple populations from each of 12 Mascarene Diospyros species, generated genome-wide single nucleotide polymorphism data using 2bRADseq, and conducted population genomic and phylogenomic analyses. We found that Mascarene Diospyros species diverged millions of years ago and are today largely genetically distinct from one another. Although hybridization was observed between closely related species belonging to the same subclade, more distantly related species showed little evidence of interspecific hybridization. Phylogenomic analyses also suggested that introgression has occurred during the evolutionary history of the clade. This suggests that, as diversification progressed, interspecific hybridization occurred among species, but became infrequent as lineages diverged from one another and evolved reproductive barriers. Species now coexist in partial sympatry, and experience limited hybridization between close relatives. Additional research is needed to better understand the role that introgression may have played in adaptation and diversification of Mascarene Diospyros, and its relevance for conservation.

中文翻译：

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RAD 测序揭示了多样化和杂交模式，以及部分同域热带岛屿树木进化枝中生殖隔离的积累

在温带树木进化枝中观察到的一个常见模式是，物种通常在形态上不同且部分不育，但尽管在范围重叠的情况下正在进行杂交，但仍保持物种凝聚力。尽管密切相关的物种通常出现在热带生态系统中，但对进化枝内随时间推移的杂交模式以及这种杂交对维持物种边界的影响知之甚少。在这项研究中，我们专注于Mascarene 群岛Diospyros属的一个同域树分支，并调查了物种在遗传上是否不同、它们是否杂交，以及杂交模式与物种间分化以来的时间有何关系。我们从 12 个 Mascarene Diospyros 中的每一个中采样了多个种群物种，使用 2bRADseq 生成全基因组单核苷酸多态性数据，并进行种群基因组和系统发育分析。我们发现 Mascarene Diospyros物种在数百万年前发生分化，如今在遗传上大体上彼此不同。尽管在属于同一分支的密切相关物种之间观察到杂交，但关系更远的物种几乎没有显示出种间杂交的证据。系统基因组分析还表明，在进化枝的进化历史中发生了基因渗入。这表明，随着多样化的进展，物种之间发生了种间杂交，但随着谱系彼此分化并进化出生殖障碍，这种杂交变得不频繁。物种现在以部分相似的方式共存，并且在近亲之间经历有限的杂交。需要进一步研究以更好地了解基因渗入可能在 Mascarene 的适应和多样化中发挥的作用Diospyros及其与保护的相关性。