横断山区近溪蟹物种多样性形成机制的研究

The Hengduan Mountains Region (HDMR) lies in the southeastern part of Qinghai-Tibet Plateau (Q-T Plateau). This region can be treated as a unique geographic unit, and has been referred to as the core area with high levels of biodiversity and endemism of a global biodiversity hotspot. The unique topography and well-established geological history have made HDMR an excellent natural laboratory for testing the competing hypotheses of spatiotemporal history associated with climate change and/or tectonic events influence species diversification. Primary freshwater crab assemblages are recognized as components of tropical and subtropical fauna and are characterized by signally abbreviated life history along with poor dispersal ability. Our early investigations have shown 70 freshwater crab species from 18 genera and two families ranged in HDMR. The fauna exhibits extraordinary high levels of richness of the Potamidae, including 68 species and 17 genera. It is characterized by high concentrations of endemic species (90%) and genera (76%) with a narrow distribution range. This has lead to a hypothesis that potamiscine endemism in HDMR should reflect origination in situ. Also, we further postulated that the potamiscine species diversification was driven by the appearance of new habitats or ecological niches in association with mountain uplift, which is, accompanied with the uplift of Q-T Plateau. The hot-dry valleys spread throughout all the valleys of this region are most likely acting as barriers for their dispersals and expansions, as well might subsequently constrain further species formation. Despite this theoretical presumption, nevertheless, up to now the case has yet been made for any convincing estimates of diversification rates on HDMR groups owing to the absence of densely sampled, robust and fully resolved phylogenies. In this project, in order to test our hypothesis and to decipher the evolutionary history of early potamiscine species diversification in HDMR, we will 1) present comprehensive molecular phylogeny for members of Potamiscinae in HDMR based on multiple nDNA and mt DNA loci under a multi-species coalescent framework; 2) collect 3D geometric morphometrics (GM) of the male first gonopod (G1) and the female vulva, which are the so-called structure of “lock-and-key”, and other related issues. And further use the phylogenetic tree as an evolutionary framework for reconstructing the ancestral states of the morphological characters; 3) examine recent and historical distribution patterns of potamiscines, in addition to patterns of species diversification in HDMR. Collectively combine our data analyses and achieved results, we plan to investigate on the evolutionary history and species diversification processes of potamiscines in HDMR. This project will make a full use of the third generation sequencing combined with the high-resolution three-dimensional tomography GM. By performing present molecular dating, ancestral region and ancestral state reconstruction, distribution patterns, and rate of diversification, we reveal an explanation that species formation of potamiscines in response to the formation of new habitat, which is associated with the uplift of HD Mountains. Our results are expected to provide a representative typical case in revealing evolution of biodiversity of HDMR, Q-T Plateau. By peering into a new insight of the evolutionary drivers and historical events that are responsible for the formation of extant high richness of freshwater crab biodiversity, these progresses may as well contribute to a breakthrough on the evolution theory. Our data can also provide important conservation implications for the protection of freshwater crab biodiversity in HDMR hotspot, and in China as a whole.

横断山区是青藏高原隆升形成的、全球独具特色的地理单元和生物多样性热点地区，也是多样性进化研究的焦点。区内独特的地貌格局、水热条件和复杂多样的山地生态环境为喜湿暖的淡水蟹类繁衍分化创造了条件，极大地丰富了区内特有的近溪蟹物种多样性。由此奠定了中国淡水蟹物种多样性居世界首位。然而，横断山区高度集中的近溪蟹多样性之形成机制至今尚不清楚。推测其多样化过程伴随青藏高原隆升，受横断山脉不断抬升造成的新环境与生态位驱动而加剧和加速。本项目通过跨全分布区域野外考察和分类单元采样，采用第三代测序获得多座位核DNA数据，构建横断山区近溪蟹物种进化关系；整合新技术获取其“锁-钥”结构等几何形态分析数据，解析物种多样性进化的过程，探讨其快速成种机制。该结果有望在揭示青藏高原横断山区生物多样性进化方面提出有代表性的典型例证；在淡水蟹多样性进化理论上取得新突破；为最大限度地保护横断山区淡水蟹类生物多样性提供科学依据。

横断山区是独具天成的多样性进化研究“实验室”。本项目对横断山区近溪蟹物种多样性形成机制的研究，内容包括：横断山区近溪蟹亚科的分类和物种多样性分布的研究；基于多分子数据构建横断山区近溪蟹物种系统进化关系；解析与生殖隔离相关的形态分歧在支系分歧上的多样化过程；综合分子和形态分析数据、探讨物种多样性形成的进化过程。项目执行期间，通过野外调查采集，获得覆盖该区域近溪蟹亚科全部已记述淡水蟹类属和90%以上物种的1000余号标本；通过高通量测序获得54条DNA多座位分子标记序列，联合20余项几何形态等定量形态数据，深入解析了物种多样性形成的生态与进化驱动机制。研究获得的重要结果包括：1）发现和描述淡水蟹类3新属、11新种，2个中国新记录属和1个新记录种，丰富了横断山区淡水蟹类的物种多样性和本底资源；2）首次重建了中国横断山区及其周边地区的近溪蟹亚科淡水蟹类强健的系统发生关系；3）联合近缘化石种等类群及冲绳海槽开放的地质事件校准，首次推断和构建出横断山区近溪蟹亚科淡水蟹类多样性发生及其进化历史的时间框架，将横断山区淡水蟹类发生时间追溯到第三纪早期；4）首次提出研究证据，表明始新世晚期以来的本地物种多样化塑造了横断山区近溪蟹亚科物种多样性热点的时空演化格局，发展形成区域特有属种支系；5）联合分子钟和祖先分布区重建，推断第三纪以来高原的阶段性隆升以及与之相应的东亚季风发育和形成驱使近溪蟹亚科淡水蟹类开创新的山地生境适应，区内独特的“干热河谷”与“空岛效应”加剧了物种的多样化进程；6）联合线粒体基因组和多座位核基因分子系统发生研究，初步提示“走出横断山区”很可能是中国近溪蟹亚科淡水蟹类多样性热点形成的生物历史地理背景。本研究在淡水蟹类多样性进化理论上取得了新突破，并为揭示横断山区生物多样性进化提出了以淡水底栖大型无脊椎动物为典型代表的研究例证。项目研究成果为最大限度地保护横断山区淡水蟹类生物多样性提供了科学依据。