喜马拉雅-横断山区白珠树属小叶类群的“空中岛屿”分布格局和遗传分化

As considered to be windows into evolutionary process, the distinct sky-island natural habitat for organisms provides a natural experiment lab for understanding the species diversity, genetic divergence and adaptive mechanism to environment change. The tectonic uplifts of the Qinghai-Tibet Plateau and its environmental effects on organisms and ecosystem since the late Cenozoic as a worldwide research has long been debated. In this project, a monophyletic group that originated at the late Cenozoic, characterized by narrow endemic distributions, highly isolated populations and rapid radiation within genus Gaultheria L. (Ericaceae) from the Himalaya-Hengduan Mountains region, i.e., G. ser. Trichophyllae, is ideally selected for a further study on genetic differentiation mechanisms in the ‘sky-island’ complexes of the Himalaya-Hengduan Mountains region. More than one hundred and thirty populations of all twenty-one species within the G. ser. Trichophyllae will be collected for: 1) understanding the differentiation patterns of genetic structure at both inter-specific and infra-specific levels with the methodologies of molecular phylogenetics, population genetics, and phylogeography by using the Sanger sequencing for chloroplast genes and the next-generation sequencing for the nuclear genome; 2) revealing the dynamics of the geographic distribution by the Ecological Niche Modeling, and the geographic or climate drives for the patterns of genetic differentiation by statistics analyses. This project may provide some biological insights on understanding the geologic history of the Himalaya-Hengduan Mountains region.

生物独特的“空中岛屿”（sky island）状分布格局被认为是研究生物演化过程的窗口，为揭示生物多样性及其对环境变化的适应机制提供了理想的天然实验场。晚新生代以来青藏高原隆升伴随气候变化的生态效应一直是生物地理学研究焦点之一。本研究立足喜马拉雅-横断山区“空中岛屿”群，以该地区杜鹃花科白珠树属一个晚新生代起源、狭域分布、种群间高度隔离、经历辐射演化的单系群，即小叶类群Gaultheria ser. Trichophyllae全部21个种130余个种群为研究对象，开展遗传分化机制研究。通过叶绿体基因Sanger测序和核基因简化基因组测序技术，利用分子系统学、种群遗传学和谱系地理学等多学科手段检测该类群遗传结构和分化式样，在种间和种下共同追溯基因流。通过生态位模型和环境因子分析，推测该类群分布格局变迁式样与成因，剖析不同环境因素对其遗传格局的影响，为该地区自然环境变迁史提供重要的生物学证据。

本项目以喜马拉雅-横断山区纵深峡谷区域分布的杜鹃花科白珠树属小叶类群Gaultheria ser. Trichophyllae为研究对象，利用分子系统学、种群遗传学、谱系地理学、景观遗传学、进化生态学等多学科手段检测该类群遗传结构和分化式样，在种间和种下共同追溯基因流，解析其“空中岛屿”状分布格局成因及规律。取得以下成果：（1）完成了小叶类群物种及种下单元的分类学修订，修订后小叶类群物种数量从6种增至21种，为进一步研究该类群打下了扎实的分类学框架。（2）构建了小叶类群叶绿体全基因组系统发育树，明晰了小叶类群的种间关系，筛选出8个分子序列变异热点区域。（3）基于低拷贝核基因和叶绿体基因联合分析，揭示了小叶类群是在11Ma至6Ma期间杂交起源的类群，异源多倍化是其适应“空中岛屿”分布的重要演化手段之一。（4）对小叶类群21种84个居群和伴生种铜钱叶白珠19个居群开展种群遗传学研究，揭示了各种的居群具有高遗传多样性、高私有单倍型、高遗传分化等特点，但仅广布种刺毛白珠具有明显的谱系地理结构。第四纪冰期、季风气候（西南季风）、严格生境隔离在遗传格局形成中扮演了重要的角色。各种的繁殖器官和营养器官均在遗传背景下受到了自然选择压力。（5）小叶类群这样具有蓝紫色果实的谱系，具有较高的物种分化速率，天蓝色果实色素为飞燕草素衍生物，被认为有助于保护植株免受更强烈的紫外线辐射，促使小叶类群能够在高海拔的“空中岛屿”强紫外辐射生境下适应，为其发生短期内辐射演化提供重要的保障。