基于基因组学的巴山松群体进化历史与生态适应研究

The Qinling-Daba (Qinba) Mountains are an important climate and biogeographic boundary in China, which act as physical barrier for species expansion and genetic exchange corridor for isolated taxa. It has been the natural laboratory to investigate species boundary theory and various speciation models. Pinus henryi, an endemic pine in the Qinba Mountains, together with P. tabuliformis on the north and P. massoniana on the south, forms a sandwich-like geographic distribution pattern in this area. Here, we propose three models to elucidate this unique phenomenon: hybrid speciation, parapatric speciation, and introgressive hybridization. In this project, chloroplast, mitochondrial and nuclear genome data will be analyzed to investigate the genomic variation, gene flow and nature selection between species pairs. Our aims are: (1) to document the evolutionary history of Pinus henryi, (2) to know the mechanism of the geographic distribution of the three pines, (3) to screen genes possibly experienced with selection and local adaptation using genetic, ecological and morphological data. These works will not only help to understand the speciation mechanism of Pinus, but also provide clues to know the nature of biogeographic boundary of Qinba Mountains. They will also benefit the conservation and utilization of Pinus henryi, the rare and endemic species.

秦巴山区是我国气候与生物地理的南北分界线，它既是物种扩张的地理屏障，又是隔离物种基因交流的通道，该地区的生物地理特性使其成为研究验证物种边界理论以及多种成种模型的天然试验场。巴山松作为本地区特有针叶树种，与北方的油松和南方的马尾松形成独特的“三明治”式地理替代模式。为探究巴山松这一地理分布式样的产生机制，本项目利用二代测序技术，从群体水平出发，对三种松树父系遗传的叶绿体基因组、母系遗传的线粒体基因组和双亲遗传的核基因组进行测序分析，研究巴山松的群体遗传结构与种内种间基因流水平，阐明巴山松的群体进化历史。并结合表型与生态分析揭示物种分化与生态适应的遗传基础，探讨巴山松演化过程对邻域成种、杂交成种与基因渐渗等模型的符合程度。这些研究能够拓展我们对于物种形成理论的认识，为揭示秦巴地区生物地理过渡性的本质提供线索，也为巴山松这一珍稀特有物种的科学保护与合理利用奠定理论基础。

秦巴山区特有种巴山松与其近缘物种油松、马尾松形成独特的地理替代。为探究这一地理分布式样的产生机制，本项目利用群体基因组数据研究巴山松的群体遗传结构与种间基因流水平。结果表明，巴山松是5.15百万年前以油松为父本、马尾松为母本的古老杂交物种。历史上巴山松与油松存在较强的基因交流，而与马尾松基因交流水平较低。0.70百万年前秦巴山脉隆升导致的巴山松与油松间基因交流急剧降低，在巴山松成种过程中起到重要作用。由于不具备与亲本强烈的生殖隔离与生态隔离，导致巴山松成种后饱受亲本遗传侵蚀，在竞争中处于不利地位，未来有效群体大小可能会持续降低。巴山松群体遗传结构主要受迁移因素影响，生态因素影响不大。但选择压力分析仍能发现与环境相关的受选择基因，比如光合作用相关基因、细胞调控相关基因。这些研究结果首次揭示了巴山松成种过程与机制，拓展我们对于物种形成理论的认识，为揭示秦巴地区生物地理过渡性的本质提供线索，也为巴山松这一珍稀特有物种的科学保护与合理利用奠定理论基础。