School of Life Science, Luoyang Normal University, Luoyang, P. R. China.
Institute for Biology and Environmental Sciences, Carl von Ossietzky University Oldenburg, Carl von Ossietzky Strasse, Oldenburg, Germany.
Ann Bot. 2020 Mar 29;125(4):677-690. doi: 10.1093/aob/mcaa003.
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).
We genotyped 69 populations across the QTP with one chloroplast marker and 12 nuclear microsatellite loci. We performed phylogeographical 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.
Each species was composed of two geographically distinct clades, corresponding to the south-eastern and north-western parts 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.
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 Last Interglacial Maximum, 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.
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，特有程度极高。然而，尽管已有越来越多的研究，但对于 QTP 高山植物促进分化、物种形成和最终多样性的因素仍知之甚少。特别是杂交作用的影响。在这里，我们研究了三个密切相关的报春花属特有种的进化历史，并检验了我们的结果是否支持山地生物多样性假说（MGH）。
我们利用一个叶绿体标记和 12 个核微卫星标记对 QTP 的 69 个种群进行了基因型分析。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，以探讨它们的遗传关系和进化历史。此外，我们还模拟了它们在不同气候下的分布。
每个物种都由两个地理上不同的分支组成，分别对应于其分布的东南部和西北部。因此，最近分化的报春花属 Veitchiorum 和 G. lawrencei var. farreri 似乎至少在过去共享了避难所，之后它们的分布范围扩大了。事实上，气候生态位模型表明，这两个物种从末次间冰期到现在一直经历着连续的扩张。此外，我们在 G. lawrencei var. farreri 的西北分支中发现了杂交的证据，这可能发生在高原台地上的避难所。此外，系统发育和种群遗传分析表明，G. dolichocalyx 应该是一个具有地理局限性的独特物种，与 G. lawrencei var. farreri 的遗传分化较低。
QTP 地区的气候波动在塑造 G. lawrencei var. farreri 和 G. veitchiorum 目前的遗传结构方面发挥了重要作用。我们认为，在末次间冰期之前确实发生了物种泵效应，从而支持 MGH。然而，我们的结果与 MGH 所预期的最近的分布范围和杂交动态有所不同。
