连续分布广布种的种群遗传分化驱动机制—以小果冬青（Ilex micrococca）为例

Investigating population genetic differentiation pattern and identifying its drivers can promote understanding of mechanism of genetic diversification at early stage in speciation. Population genetic differentiation in widespread species with continuous distribution cannot be solely explained by geographical distance because these populations lack substantial geographic barriers and have gradual, environmental heterogeneity. Given several possible factors including geographical distance, vicariance in population history and adaptation, testing influences of these factors on population genetic differentiation in widespread species can benefit our understanding of mechanism driving the population genetic differentiation. As a series of features in Ilex micrococca that continuously wide distributes in subtropical forest in China and shows evidence of differentiation in its morphology, habitat and genetics, the species is good candidate to study the mechanism driving population genetic differentiation in widespread species. Hence, this study chooses I. micrococca as example to examine the influences of geography, vicariance in population history and adaptation on population genetic differentiation, which based on using a combination of population genetics, environmental niche modeling and adaptive characters measurements. This study will demonstrate the mechanism driving population genetic differentiation in widespread species, which will not only help uncover genetic basis of cosmopolitan distribution and high diversity in genus Ilex, promote theoretical advances of mechanism driving population genetic differentiation in widespread species with continuous distribution, but also serve as a reference for scientifically designing policies for conservation and utilization of biodiversity.

解析种群遗传分化空间异质性的驱动机制，将有助于理解物种分化早期遗传多样性产生的机制。由于种群间缺少明显地理隔离及其生境空间异质性连续变异等特点，连续分布广布种的种群遗传分化很难单纯被地理距离解释。综合地理距离、种群历史隔离和适应性分化等多种可能因素，分析它们对广布种的种群遗传分化的影响，有利于明确广布种遗传分化的驱动机制。小果冬青广泛、连续分布于中国亚热带地区，且发现其形态、生境和遗传有分化的迹象，是研究广布种种群遗传分化驱动机制的优秀材料。本项目拟选小果冬青为对象，整合种群遗传学、环境生态位模拟和适应性性状等多方面证据，比较地理、种群历史隔离及适应性分化等因素对种群遗传分化的影响，揭示连续分布广布种的种群遗传分化驱动机制。本项目结果将有助于揭示冬青属世界广布、物种丰富的遗传基础，促进连续、广布种种群遗传分化驱动机制的理论发展，又对建立科学的多样性保护、利用政策有重要参考价值。

解析种群遗传分化空间异质性的驱动机制，将有助于理解物种分化早期遗传多样性产生的机制。由于种群间缺少明显地理隔离及生境空间异质性连续变异等特点，连续分布广布种的种群遗传分化很难单纯被地理距离解释。综合地理距离、种群历史隔离和适应性分化等多种可能因素，分析它们对广布种的种群遗传分化的影响，有利于明确广布种遗传分化的驱动机制。小果冬青广泛、连续分布于中国亚热带地区，且发现其形态、生境和遗传有分化的迹象，是研究广布种种群遗传分化驱动机制的优秀材料。首先，本项目通过采集小果冬青主要分布区内43个种群、284个个体的材料，结合我们重头组装的染色体水平冬青参考基因组，系统发育分析结果支持小果冬青种群可以大致分为两组，大致对应小果类和多脉类。遗传主成分分析结果支持两类冬青种群之间存在少数杂交个体。种群遗传结构分析结果表明这些种群可分为9个祖先成分，分别对应不同的地理区域，且多个种群的个体由多个祖先成分混杂组成。随后，我们进一步针对分布于我国西南地区多脉类(即《中国植物志》中的多脉冬青)的21个种群、112个个体进行重点分析，系统发育分析结果表明这些种群被分为4个分支，分别对应不同的地理位置和海拔。种群遗传结构分析结果表明这些种群存在4个祖先成分，其中各有2个祖先成分对应低海拔(<1,500m)和高海拔(>1,800m)种群，中等海拔(1,500–1,800m)种群由低海拔和高海拔种群的祖先成分混杂组成。连锁不平衡衰减分析表明低海拔种群的连锁不平衡系数衰减速度最快，其次是高海拔种群，最慢的是中等海拔种群。选择消除分析共识别出34个受海拔选择的候选基因，它们的功能大多与谷胱甘肽合成、抵抗病原菌侵染等响应生物和非生物选择压力有关。综合各种结果，推测这些冬青种群遗传分化格局更符合适应隔离的机制。本项目的结果为冬青属园艺品种的分子育种与鉴定提供重要基础，更有助于进一步理解冬青属世界广布、物种丰富的分子机制，增进对中国亚热带常绿阔叶林植物适应和多样性演变机制的认识。