BACKGROUND AND AIMS Hybridization and introgression play an important role in the evolution and diversification of plants. To assess the degree of past and current hybridization, the level of genetic admixture in populations has to be investigated. Ongoing hybridization and blurred species separation have made it challenging to assign European white oak taxa based on leaf morphology and/or genetic markers and to assess the level of admixture. Therefore, there is need for powerful markers that differentiate between taxa. Here, we established a condensed set of single-nucleotide polymorphism (SNP) markers to reliably differentiate between the three most common oak species in temperate European forests (Quercus robur, Q. petraea, Q. pubescens) and to assess the degree of admixture in a large set of selected Swiss populations. METHODS A training set of 194 presumably pure reference samples from Switzerland and Europe was used to assign 633 test individuals with two different approaches (population genetic-based/Bayesian vs. assumption-free/discriminative classifier) using 58 selected SNPs from coding regions. Admixture was calculated at the individual and population level with the Shannon diversity index based on individual assignment probabilities. KEY RESULTS Depending on the approach, 97.5-100% of training individuals were assigned correctly, and additional analyses showed that the established SNP set could be further reduced while maintaining its discriminatory power. The two assignment approaches showed high overlap (99%) in assigning training individuals and slightly less overlap in test individuals (84%). Levels of admixture varied widely among populations. Mixed stands of Q. petraea and Q. pubescens revealed much higher degrees of admixture than mixed stands of the other two taxon pairs, accentuating high levels of gene flow between these two taxa in Switzerland. CONCLUSIONS Our set of SNPs warrants reliable taxon discrimination with great potential for further applications. We show that the three European white oak taxa have largely retained their species integrity in Switzerland despite high levels of admixture.

中文翻译：

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一个物种歧视的单核苷酸多态性集揭示了在杂交欧洲白橡树（Quercus spp.）中保持物种完整性，尽管混合水平很高

背景和目的杂交和基因渗入在植物的进化和多样化中起重要作用。为了评估过去和现在的杂交程度，必须调查种群中的遗传混合水平。持续的杂交和模糊的物种分离使得根据叶子形态和/或遗传标记分配欧洲白橡树分类群并评估混合物水平变得具有挑战性。因此，需要区分分类群的强大标记。在这里，我们建立了一组浓缩的单核苷酸多态性 (SNP) 标记，以可靠地区分欧洲温带森林中三种最常见的橡树物种（栎树、Q. petraea、Q. pubescens），并评估在欧洲森林中的混合程度。一大群选定的瑞士人口。方法 使用来自瑞士和欧洲的 194 个可能纯参考样本的训练集，使用来自编码区域的 58 个选定 SNP，使用两种不同的方法（基于群体遗传/贝叶斯与无假设/判别分类器）分配 633 个测试个体。基于个体分配概率，使用香农多样性指数在个体和群体水平上计算混合物。关键结果 根据方法的不同，97.5-100% 的训练个体被正确分配，另外的分析表明，已建立的 SNP 集可以进一步减少，同时保持其区分能力。这两种分配方法在分配训练个体时显示出高度重叠（99%），而在测试个体中重叠略少（84%）。不同人群的混合水平差异很大。Q. petraea 和 Q. pubescens 的混合林分比其他两个分类单元对的混合林分显示出更高程度的混合，突出了瑞士这两个分类单元之间的高水平基因流动。结论 我们的 SNP 集保证了可靠的分类群区分，具有进一步应用的巨大潜力。我们表明，尽管混合水平很高，三个欧洲白橡树分类群在瑞士基本上保留了它们的物种完整性。