Data from: Evolutionary melting pots: a biodiversity hotspot shaped by ring diversifications around the Black Sea in the Eastern tree frog (Hyla orientalis)

Hotspots of intraspecific genetic diversity, which are of primary importance for the conservation of species, have been associated with glacial refugia, that is areas where species survived the Quaternary climatic oscillations. However, the proximate mechanisms generating these hotspots remain an open issue. Hotspots may reflect the long-term persistence of large refugial populations; alternatively, they may result from allopatric differentiation between small and isolated populations, that later admixed. Here, we test these two scenarios in a widely distributed species of tree frog, Hyla orientalis, which inhabits Asia Minor and southeastern Europe. We apply a fine-scale phylogeographic survey, combining fast-evolving mitochondrial and nuclear markers, with a dense sampling throughout the range, as well as ecological niche modelling, to understand what shaped the genetic variation of this species. We documented an important diversity centre around the Black Sea, composed of multiple allopatric and/or parapatric diversifications, likely driven by a combination of Pleistocene climatic fluctuations and complex regional topography. Remarkably, this diversification forms a ring around the Black Sea, from the Caucasus through Anatolia and eastern Europe, with terminal forms coming into contact and partially admixing in Crimea. Our results support the view that glacial refugia generate rather than host genetic diversity and can also function as evolutionary melting pots of biodiversity. Moreover, we report a new case of ring diversification, triggered by a large, yet cohesive dispersal barrier, a very rare situation in nature. Finally, we emphasize the Black Sea region as an important centre of intraspecific diversity in the Palearctic with implications for conservation.

种内遗传多样性（intraspecific genetic diversity）热点对于物种保护具有首要重要性，这类热点常与冰期避难所（glacial refugia）——即物种在第四纪气候振荡（Quaternary climatic oscillations）中得以存续的区域——相关联。然而，催生这类多样性热点的直接机制仍是一个悬而未决的问题。一种观点认为，多样性热点反映了大型避难所种群的长期存续；另一种假说则提出，它们可能源自小型隔离种群之间的异域分化（allopatric differentiation），后续这些种群发生了基因混合。本研究以广泛分布于小亚细亚与欧洲东南部的东方雨蛙（Hyla orientalis）为研究对象，对上述两种假说进行检验。我们采用精细尺度系统地理调查（fine-scale phylogeographic survey）策略，结合快速进化的线粒体与核分子标记（mitochondrial and nuclear markers），对该物种的整个分布范围开展高密度采样，并辅以生态位建模（ecological niche modelling）分析，以阐明塑造该物种遗传变异的关键驱动因素。研究结果显示，黑海周边区域存在一处重要的遗传多样性中心，该区域包含多组异域或邻域分化类群，其形成可能受更新世气候波动与复杂区域地形的共同驱动。值得注意的是，这类分化形成了环绕黑海的环状分布格局：从高加索经安纳托利亚延伸至东欧，其末端类群在克里米亚地区相互接触并发生部分基因渐渗。我们的研究结果支持"冰期避难所不仅是遗传多样性的宿主，更能够催生遗传多样性，并可作为生物多样性的进化熔炉"这一观点。此外，本研究报道了一例由大型且统一的扩散障碍所引发的环状分化新案例，这类情况在自然界中极为罕见。最后，我们强调黑海区域作为古北界（Palearctic）内重要的种内多样性中心，其对于物种保护具有重要的启示意义。