落叶松属红杉组的物种形成、自然变异和适应性进化

Speciation and adaptation is a fundamental issue in evolutionary biology and ecology. Larix, with unparalleled ecological and economical importance, is a prominent component of the boreal, montane and subalpine forests in the North Hemisphere and is the principal source of the world’s wood for pulp, paper and solid-wood products. Traditionally, Larix was divided into sect. Larix and sect. Multiserialis according to the morphological traits. China is the most larch species-rich region in the world. Because of the contrasting environmental adaptability, the geographical distribution of Larix in China follows the rule that Sect. Multiserialis never extends northwards over the Qin Ling Mountains and sect. Larix never passes southwards across Huang River. Species of sect. Multiserialis are mainly distributed in Qinling Mts. and Himalayas-Hengduan Mts., the well-known biodiversity hotspots in China and the world. Due to the rapid diversification of sect. Multiserialis, the phylogenetic relationships among species and the evolutionary history remain unresolved, and the spatial pattern of natural genetic variation is also needed to investigate. In this project, we will take advantage of the next generation sequencing technology to shed new insights into speciation processes, clarify the species relationships and evolutionary history of sect. Multiserialis and reveal the spatial patterns of natural variation of wild populations. Combined with the comparative transcriptome analysis of the cultivated species from sect. Larix, we will screen candidate genes for environmental adaptation and growth rhythm and then using population genetic analysis to test the patterns of these candidate genes in the wild populations and explore the evolutionary mechanisms of adaptation in Larix. This project would benefit the conservation and utilization of larch genetic resources and the study of speciation of conifers in Hengduan Mountains, the biodiversity hotspot in the world.

物种形成和适应机制是进化生物学和生态学的核心问题。落叶松是北半球寒温带、温带和高山及亚高山针叶林的主要组分和重要的造林树种，具有极高的生态和经济价值。中国是落叶松属物种分布最丰富的地区。传统上，该属根据形态分为落叶松组和红杉组。后者除北美两个种外，其余物种均分布在我国秦岭和喜马拉雅―横断山区及少数周边地区。由于生态适应性不同，落叶松在我国的地理分布遵循着“红杉组北不越秦岭，落叶松组南不过黄河”规律。由于快速辐射分化，红杉组物种遗传分化低，种间关系和进化历史仍不清楚，地理变异也有待研究。本项目拟基于转录组数据，利用系统发育重建和群体遗传学的方法，澄清红杉组物种的系统关系和进化历史，揭示红杉组物种的自然变异和物种形成机制。结合同质园（植物园）栽培的落叶松组物种的比较转录组分析，筛选与环境适应和生长节律相关的候选基因，通过在野生群体中的群体遗传学分析，阐明红杉组和落叶松组物种的适应性进化机制。

物种形成和适应机制是进化生物学的核心问题。落叶松是北半球寒温性针叶林的主要组分和世界造林树种，具有极高的生态和经济价值。本项目以全球落叶松属所有物种为研究对象，首次基于转录组和叶绿体基因组数据构建了该属物种最全、分辨率最高的系统进化树。在此基础上，通过分化时间估算、祖先分布区和形态性状重建以及环境因子分析等多种方法，阐明了落叶松属的时空演化和现有分布格局的形成过程，发现隔离分化是落叶松属物种形成的重要方式。谱系基因组学分析高度支持落叶松属分为高纬度的环北方支系和低纬度的青藏高原支系，这也是首次在落叶松属发现南北间断的遗传式样。这两个支系在生态位上有显著分化，主要体现为温度和水分的季节性变化以及温度的年变化。结合化石记录，我们推测落叶松属可能起源于高纬度的高海拔地区，并在始新世末期约35.5 Ma分化形成环北方和青藏高原两个支系。始新世-渐新世之交的全球气候变冷导致高纬度的环北方支系进一步分化形成北美和欧亚北部两个地理分支，而渐新世至中新世青藏高原剧烈的造山运动则促进了喜马拉雅-横断山区物种的快速分化。结合细胞质基因和群体转录组数据，我们进一步对中国分布的所有落叶松属物种共40个群体、598个个体进行了群体遗传分析，揭示了北方和西南山区物种不同的进化历史和遗传变异式样；北方群体的遗传变异式样和群体结构受第四纪受冰期影响显著，而青藏高原隆升驱动的造山运动促进了西南山区物种的快速分化，高黎贡山是横断山和喜马拉雅两个地理分支重要的地理屏障。我们的结果明确了西南山区红杉组物种的系统位置和物种界定，为落叶松属物种的分类修订提供了可靠证据。此外，对同质园（植物园）的落叶松个体不同时期的比较转录组分析发现生物钟和物候期相关的基因可能在落叶松属物种适应环境变化中起着重要作用。