华溪蟹属分子系统发生与物种多样性形成的驱动机制

True freshwater crabs are benthic macro-invertebrates and this important functional group plays a key role in the self-repair of inland freshwater ecosystems because of their high species richness. The genus Sinopotamon Bott, 1967 is endemic to China and the most species-rich freshwater crab assembly globally. The group comprises 84 species and subspecies and is distributed across 17 provinces in China. This striking species diversity and broad distribution suggest that diversification and historical biogeography in this genus is closely related to habitat shifts resulting from complex geological events and past climate and environmental change. This genus is therefore an ideal freshwater crab system for (1) understanding the history of current assemblages dependent on freshwater habitats in China, and (2) determining evolutionary processes underlying freshwater species diversification and biodiversity more broadly. However, phylogenetic affinities among Sinopotaomon are poorly understood and because of this it remains unknown how a high diversity and wide distribution evolved in this group. Here we test the hypothesis that paleoclimatic and paleoenvironmental changes, including geographic events acted as a potent force for evolutionary diversification of Sinopotamon freshwater crabs. To our knowledge, this is the first study of Sinopotamon phylogeny to combine mitochondrial DNA and a comprehensive suite of nuclear DNA using high-throughput sequencing, extensive taxa representatives (80% of named species and subspecies) across the entire distribution of this genus, and morphological and geographic characteristics of each species and subspecies. The objectives of this project are to: estimate current diversity of Sinopotamon based on field surveys and specimen-level distributional databases; clarify molecular phylogenetic relationships of Sinopotamon species; assess the accuracy of current taxonomies of Sinopotamon based on reexamination of species delimitation; analyze the tempo and mode of species diversification and infer the biogeographic history of this group; analyze the impact of habitat shifts resulting from past climate and environmental changes; and to investigate the role of extrinsic factors and evolutionary innovation in driving peak episodes of species diversification. For historical reasons, mainland China is one of the world's best-studied zoogeographical regions but there has been no attempt to analyze rates of diversification in genera with exceptional endemic species richness in its freshwater ecoregions. Our reconstruction of evolutionary histories using extant species data and rates of diversification in this genus will further research into the diversification of freshwater benthic macro-invertebrates in China and yield a more comprehensive understanding of the evolutionary drivers and historical events responsible for extant freshwater biodiversity.

真淡水蟹类是大型底栖无脊椎动物功能类群的代表，其物种多样性对内陆淡水生态系统自我修复起到重要调节作用。华溪蟹属是全球物种最丰富的淡水蟹类，有84种和亚种；为我国特有，在中东部、西南部及部分南部的17个省境内分化衍生。这提示该类群的多样化和生物地理历史与我国地史时期复杂的地质事件和气候环境变化所导致的栖息地变迁有密不可分的联系。这一类群为我们深刻理解现代淡水生态系统的生物多样性格局及进化过程提供了理想的淡水蟹模型系统。本项目基于跨全分布区域的野外调查和分类单元采样，对华溪蟹多样性进行准确评估；联合核和线粒体DNA数据，综合形态分类特征，重建华溪蟹属系统发生；推断属内各支系分歧和最近成种的年代序列，及物种多样化发生的生物地理历史；结合相关研究资料，解析气候环境变化等引起的栖息地变迁对其多样性形成的作用，探讨驱动华溪蟹物种多样性发生的机制。其结果将促进我国淡水底栖无脊椎动物多样性及其进化的研究。

华溪蟹属Sinopotamon Bott, 1967作为东亚淡水蟹类多样性最高的真淡水蟹代表类群和我国特有的淡水底栖大型无脊椎动物的重要功能类群，其丰富的物种多样性和广阔的地理分布在维持我国内陆山溪、河流等淡水生态系统多样性和“青山绿水”健康发展起到关键的作用。然而，在此之前一直缺少全属水平分子系统学与多样化研究，严重限制了我们对这些内陆特有蟹类多样性及其进化历史的认识。本项目通过跨全属地理分布区的野外调查和标本采集(覆盖该属已知物种约80%)，首次重建了华溪蟹属的分子系统发生关系，并基于分子测年、祖先分布区重建、祖先性状状态重建等方法构建了该属进化历程的时空框架；结合几何形态学分析，推断其物种多样性起源和辐射进化的生物地理历史，揭示物种多样性形成的驱动机制，科学评价华溪蟹物种多样性状况。研究揭示：(1) 华溪蟹属可能起源于四川盆地及其外围山地，随后沿长江流域向中部和东部地区扩散拓殖；(2) 更新世以来的气候转型触发了该属物种多样性近期的快速辐射；(3) 性选择和锁钥结构共进化机制共同促使华溪蟹的生殖器快速分歧，进而驱动了近期的物种多样性爆发；(4) 发现并描述1新种，保康华溪蟹Sinopotamon baokangense Chu, Zhou & Sun, 2017; 为城口华溪蟹Sinopotamon chengkuense Huang，Luo & Liu，1986指定新模；(5) 对90%以上的物种多样性状况重新评估，受胁13种，占比达16.7%，超过全球淡水蟹受胁种平均占比。据此认为，华溪蟹物种多样性在更新世近期的快速辐射，促使淡水蟹这类高生物量大型无脊椎动物拓展进入新的生境，增加了当地淡水底栖生物集群的组成体量，改善了山地水域生态系统的功能结构。可以说，华溪蟹属物种多样性发生促成了中国山地水域生态系统特有的生物多样性及其发育，为维持内陆山水生态系统健康发展起到关键作用。鉴于现有的华溪蟹物种受胁状况，考虑到国内其他淡水蟹类群可能存在的类似受胁情况，我们提倡开展跨全国分布范围的淡水蟹类生物多样性评估与保护研究，以期建立合理合法的淡水蟹类保育管理措施，有效保护我国山水生态系统的生物多样性与可持续发展。