近缘种间的遗传渐渗对松属植物适应气候变化的影响

The genetic introgression is thought to be ubiquitous in the process of evolution and has important effect on species differentiation and adaptive evolution. However, there is still no clear understanding of the ability of species’ and populations’ to respond to climate change through adaptive introgression. Pinus represents an important group in the world’s forest ecosystems, and the extensive hybrid zones in Pinus with broad climate range and genetic variation making it an ideal group to understand the effect of the adaptive introgression upon species adaptability to climate change. In this study we use three closely related pine species, which cover the climate-space and range of habitats occupied by Pinus. We will use multidisciplinary methods: firstly, using Genotype-by-Sequencing methods on the population level to get a better genetic background of the introgression direction、extent and scale of populations across the hybrid zone; Secondly, apply niche modeling and hindcasting to investigate the ecological niche variation during the past climate change between the taxa and introgressed populations; Thirdly, conduct the reciprocal transplantation experiments in three sites which represented the typical habitat of three species to evaluate the phenotype and fitness differentiation among introgressed populations; Finally, using population transcriptome analysis combining introgressive gene expression variation levels for phenotypic differentiation and environmental factors to explore the ecological evolutionary function of adaptive introgressive genes. Thus, through the “genetic－environment－phenotype－ecological function” multi-level cross validation to provide a fine-scale picture of how the scale and complexity of genetic introgression across this ecological hybrid zone affects their adaptability to climate change, which will provide a model to make the genetic strategy to protect other tree species under the dramatic climate change.

遗传渐渗被认为是物种进化过程中的普遍存在形式，对物种分化及适应性进化有着重要影响。然而，遗传渐渗规模如何影响物种应对全球气候变化挑战，至今知之甚少。作为全球森林生态系统的重要类群，松属近缘种间存在大量自然杂交渐渗带，跨越较大的地理区域，蕴含丰富的遗传变异，是进行此类研究的理想材料。本项目针对三种分布呈现气候梯度性差异的近缘种松树，首先通过群体遗传学分析揭示群体间渐渗的遗传基础，重建群体渐渗历史；其次利用生态模拟检验渐渗群体最适生态位及种间生态界限随气候变化的变异幅度；再次通过交互移栽实验验证渐渗群体的表型适合度差异；最后利用群体转录组学通过渐渗基因的表达变异水平结合表型适合度分化和环境因子探讨适应性渐渗基因的生态进化功能。从而实现从“遗传－环境－表型－生态功能”多层面相互验证，系统地探讨遗传渐渗对物种应对气候变化适应能力的影响，对物种应对急剧气候变化保护策略的制定具有重要的指导意义。

本项目针对亚热带分布的云南松和热带分布的卡西亚松的遗传渐渗及其对物种分化及适应性进化的重要影响开展研究。首先，通过群体遗传学方法结合细胞质基因片段及核基因组信息揭示在云南松和卡西亚松分布的重叠区产生了杂交群体，该区域群体的核基因组分以卡西亚松为主，而线粒体基因组受到云南松的显著渐渗，叶绿体基因组主要来自卡西亚松。云南松与卡西亚松的祖先群体的分化大概在15.5个百万年，卡西亚松分布的中心区域与渐渗区的分化时间大概在0.065个百万年。其次，利用生态模拟检验到影响两种松树生态分化的最重要的气候因子是温度季节性。在未来气候情景下，云南松的分布范围预计将进一步向东北部移动，而卡西亚松的分部范围将急剧减小且高度分散。我们筛选到两种松树与各自分布环境的气候因子的显著适应性关联位点，并且基于这些适应性遗传变异与未来气候变化的响应模拟分析表明卡西亚松受威胁的程度更重，发生遗传渐渗的群体在新的扩散边缘区域因为要适应新的环境，也具有较高的遗传脆弱性，需要重点保护。此外，森林树木的形态特征和适应性可能会因环境条件和其他进化因素（例如，群体历史、基因渐渗等）而发生变化。我们通过比较亲本种和渐渗群体的种子及针叶性状变异和同质园种子萌发适合度，表征了种子和针叶性状的环境梯度特征，进而探讨基因渗入的遗传背景和生态进化结果。结果表明，种子宽度在三种松树间存在显著差异，所有的种子性状均与纬度梯度呈显著负相关关系，与最干旱和最潮湿地区的平均温度呈显著负相关。渐渗群体的萌发适应性对低温的耐受性较高，表明杂种个体在萌发过程中对温度胁迫的适应性优于亲本物种。结果表明，环境因素影响松复合体的种子的表型变异，遗传渐渗对种子萌发适合度有显著影响。本研究系统地探讨了遗传渐渗对物种应对气候变化适应能力的影响，对物种应对急剧气候变化保护策略的制定具有重要的指导意义。