BACKGROUND AND AIMS Hosting several global biodiversity hotspots, the region of the Qinghai-Tibetan Plateau (QTP) is exceptionally species-rich and harbours a remarkable level of endemism. Yet, despite a growing number of studies, factors fostering divergence, speciation and ultimately diversity remain poorly understood for QTP alpine plants. This is particularly the case for the role of hybridization. Here, we explored the evolutionary history of three closely-related Gentiana endemic species, and tested whether our results supported the "Mountain Geo-biodiversity Hypothesis" (MGH). METHODS We genotyped 69 populations across the QTP with one chloroplast marker and 12 nuclear microsatellite loci. We performed phylogeographic analysis, Bayesian clustering, approximate Bayesian computation and principal components analysis to explore their genetic relationship and evolutionary history. In addition, we modelled their distribution under different climates. KEY RESULTS Each species was composed of two geographically distinct clades, corresponding to the south-eastern and north-western part of their distribution. Thus Gentiana veitchiorum and G. lawrencei var. farreri, which diverged recently, appear to have shared at least refugia in the past, from which their range expanded later on. Indeed, climatic niche modelling showed that both species went through continuous expansion from the Last Interglacial Maximum to the present day. Moreover, we have evidence of hybridization in the northwest clade of G. lawrencei var. farreri, which probably occurred in the refugium located on the plateau platform. Furthermore, phylogenetic and population genetic analyses suggested that G. dolichocalyx should be a geographically limited distinct species with low genetic differentiation from G. lawrencei var. farreri. CONCLUSIONS Climatic fluctuations in the region of the QTP have played an important role in shaping the current genetic structure of G. lawrencei var. farreri and G. veitchiorum. We argue that a species pump effect did occur prior to the LIG, thus lending support to the MGH. However, our results do depart from expectations as suggested in the MGH for more recent distribution range and hybridization dynamics.

中文翻译：

---

青藏高原龙胆属物种复合体的种群细分与杂交

背景和目标 青藏高原 (QTP) 地区拥有多个全球生物多样性热点，物种异常丰富，具有显着的地方性特征。然而，尽管进行了越来越多的研究，但对于青藏高原高山植物，促进分化、物种形成和最终多样性的因素仍然知之甚少。杂交的作用尤其如此。在这里，我们探索了三个密切相关的龙胆特有物种的进化历史，并测试了我们的结果是否支持“山区地理生物多样性假说”（MGH）。方法我们使用一种叶绿体标记和 12 个核微卫星位点对 QTP 中的 69 个种群进行基因分型。我们进行了系统地理学分析、贝叶斯聚类、近似贝叶斯计算和主成分分析来探索它们的遗传关系和进化历史。此外，我们模拟了它们在不同气候下的分布。主要结果 每个物种由两个地理上不同的进化枝组成，对应于它们分布的东南部和西北部。因此 Gentiana veitchiorum 和 G. lawrencei var。farreri 最近分道扬镳，过去似乎至少共享过一个避难所，后来它们的范围扩大了。事实上，气候生态位模型表明，这两个物种都经历了从末次间冰期最大值到现在的持续扩张。此外，我们在 G. lawrencei var 的西北进化枝中有杂交的证据。farreri，这可能发生在位于高原平台上的避难所。此外，系统发育和种群遗传分析表明，G. dolichocalyx 应该是地理上有限的独特物种，与 G. lawrencei var. 的遗传差异较低。法雷里。结论 青藏高原地区的气候波动在塑造 G. lawrencei var. 的当前遗传结构方面发挥了重要作用。farreri 和 G. veitchiorum。我们认为在 LIG 之前确实发生了物种泵效应，从而为 MGH 提供了支持。然而，我们的结果确实偏离了 MGH 中对更近期分布范围和杂交动态所建议的预期。结论 青藏高原地区的气候波动在塑造 G. lawrencei var. 的当前遗传结构方面发挥了重要作用。farreri 和 G. veitchiorum。我们认为在 LIG 之前确实发生了物种泵效应，从而为 MGH 提供了支持。然而，我们的结果确实偏离了 MGH 中对更近期分布范围和杂交动态所建议的预期。结论 青藏高原地区的气候波动在塑造 G. lawrencei var. 的当前遗传结构方面发挥了重要作用。farreri 和 G. veitchiorum。我们认为在 LIG 之前确实发生了物种泵效应，从而为 MGH 提供了支持。然而，我们的结果确实偏离了 MGH 中对更近期分布范围和杂交动态所建议的预期。