喜马拉雅-横断山区三种五针松的物种形成和适应进化

Speciation is a fundamental question in evolutionary biology. Due to its extremely geological and geographical complexity and high plant diversity, the Himalaya-Hengduan Mountains at the southern and eastern fringe of the Qinghai-Tibetan Plateau offers us a natural laboratory to reveal the interactions of geography, climate, ecology and genetics in driving speciation and adaptation. The Himalayan white pine (Pinus wallichiana), Bhutan white pine (P.bhutanica)and the Chinese white pine (P. armandii) of the subsection Strobus (Pinus) are important forest trees endemic to the Himalayas and mountainous areas of central and western China. Their distributions show a pattern of geographic replacement to some extent from the west Himalaya to the Hengduan Mountains along longitude. Their ranges cross about 32 longitudes and 13 latitudes and exhibit distinct clinal patterns of environmental variables, in particular precipitation and temperature. In this project, we will employ the approaches of population genetics and comparative genomics to reveal the patterns of natural genetic variation in the three five-needle pines, their evolutionary histories, interspecific gene flow and ecological niche differentiation, and test the hypothesis of the homoploid hybridization of the Bhutan white pine. Also, we will elucidate the role of natural selection played in speciation and reveal the mechanisms underlying speciation and ecological adaptation in the three white pines based on analyses of intra- and inter-specific comparative transcriptome data and population genetics of some candidate genes tightly associated with ecological factors. Combined with the sugar pine (P.lambertiana) data in public databases, we will explore the genomic variation patterns and the mechanisms of speciation in subsection Strobus which is characterized with remarkable crossing behavior.

物种形成是进化生物学研究的核心问题。喜马拉雅-横断山区复杂的地史、多样的生境以及惊人的植物物种多样性为我们揭示地理、气候、生态和遗传等各种因素在物种形成和环境适应中的相互作用提供了天然实验室。乔松、不丹松和华山松是五针松亚组的重要森林树种，也是喜马拉雅山脉和我国中西部山地的特有种，在喜马拉雅-横断山区呈一定的水平地理替代分布。三个物种的分布区跨越了约32个经度和13个纬度，分布区内生态条件差异极为显著，尤其是降水量和温度。本项目拟利用群体遗传学和比较转录组学方法，揭示三种五针松的群体结构、进化历史、基因流和生态位分化，检验不丹松的同倍体杂交物种形成假说；通过种内、种间转录组的比较以及与生态因子密切相关的候选基因的群体遗传学分析，阐明自然选择在物种形成中的作用，揭示三种五针松的物种形成和生态适应机制，并通过与北美糖松的比较分析，探讨五针松亚组独特的杂交特性的形成机制和基因组水平的遗传变异式样。

物种形成和生态适应是进化生物学的核心问题。乔松、不丹松和华山松是三种重要的森林树种。乔松和华山松的分布区非常广阔，前者沿喜马拉雅山脉南麓从西喜马拉雅地区(阿富汗东部和巴基斯坦北部、克什米尔及印度北部山区)向东至尼泊尔及我国西藏自治区吉隆、亚东和错那呈狭长带状分布，后者则由北向南从秦巴山区至川藏地区和云贵高原广泛分布，显示出极强的生态适应性。不丹松是1980年发表的新种，分布区较为狭窄，主要分布在东喜马拉雅地区的不丹东部、中印边界及藏东南和云南独龙江一带。不丹松由于球果和种子形态与乔松相近，多被处理为乔松的变种，或被认为是与华山松和乔松的杂交种。本项目对这三种五针松进行了广泛的野外取样，基于群体转录组、系统发育基因组和细胞质基因群体遗传学分析，揭示了三种五针松的群体结构和进化历史，首次用遗传学证据确立了不丹松的系统位置，否定了不丹松与乔松的近缘关系及同倍体杂交物种假说，明确了不丹松是一个独立的物种，并与华南五针松和毛枝五针松成姐妹关系；通过对华山松整个分布区的野外调查和生态分析，系统深入的阐明了华山松南北群体的隐性物种形成和生态适应机制，揭示了横断山区松柏类植物物种多样性形成机制；由于五针松亚组具有独特的种间杂交特性，随着糖松基因组测序完成和数据释放，我们还对华山松、乔松、红松及糖松等物种开展了比较基因组分析，初步筛选出大量直系同源基因，后续分析仍在进行中。这些结果和数据不仅有重要的科学意义，同时对未来林木遗传育种和种质资源保护也具有重要的现实意义。