中国亚热带常绿阔叶林特有广布种三叶崖爬藤的亲缘地理学研究

Broad-leaved evergreen forest (BLEF) is the typical vegetation type in subtropical China at lower elevation, but how its constituents responded to past environmental change and the mechanisms underlying the intraspecific diversification remain largely unknown. Tetrastigma hemsleyanum (Vitaceae) represents a widespread component of BLEF in subtropical China (and Hainan Island), and its origin can be dated back to early Pliocene. Thus this species provides a good model with which to gain insights into the evolutionary histories of BLEF species since late Tertiary under conditions of environmental change over geological scales. Our previous study revealed that pre-Quaternary environmental changes appear to have had a persistent influence on the population genetic structure of this subtropical BLEF species, but due to the limitation of traditional markers, it failed to more rigorously elucidate the recent range dynamics of T. hemsleyanum and the potential role of environmental factors in shaping its population structure across subtropical China. In this study, we propose to utilize RAD-seq technique, and combine approaches from molecular phylogeography, landscape genetics and ecological niche modelling (i) to characterize the range-wide phylogeographical patterns based on plastid vs. nuclear data, (ii) to elucidate the spatiotemporal divergence and population dynamics using coalescent-based models and related simulation-based approaches, and (iii) to dissect the influence of historical events and contemporary environmental heterogeneity on patterns of population structure and lineage divergence. The outcome of these analyses will contribute to a better understanding of how BLEF species responded to historical environmental change, and provide new evidence for the evolutionary history of BLEF species and their forming mechanisms of genetic/lineage diversity.

常绿阔叶林是中国亚热带地区中低海拔分布的典型植被类型，但其林下物种对古环境变化的响应模式及其种内的谱系分化机制仍不清楚。三叶崖爬藤是中国亚热带常绿阔叶林下的特有广布物种，其起源可以追溯至早上新世，是研究常绿阔叶林物种自晚第三纪以来进化历史的理想模型。前期的亲缘地理学研究揭示了第四纪前的地质气候变迁对三叶崖爬藤遗传结构的长期影响，但由于分子标记的限制，未能充分解析其近期的群体动态历史和谱系分化的环境驱动力。本项目拟采用RAD-seq技术，通过亲缘地理学、景观遗传学和生态位模型的理论和方法，揭示三叶崖爬藤种内的谱系地理模式，阐明不同时空尺度的群体动态历史及谱系分化过程，解析历史地质气候变化和分布区的环境异质性对遗传结构和谱系分化的作用。本研究的成果将增进我们对中国亚热带常绿阔叶林物种如何响应古环境变化的理解，为揭示常绿阔叶林物种的进化历史以及谱系多样性的形成机制提供新的证据。

中国亚热带地区是生物多样性研究的热点区域，但该地区的常绿阔叶物种对古环境变化的响应模式及驱动和维持谱系分化的适应性进化机制目前仍不清楚。三叶崖爬藤是我国亚热带常绿阔叶林下的典型广布成分，是研究生态和进化之间相互关系的理想模式材料。本项目基于广泛的居群采样，采用转录组和简化基因组测序技术，整合多学科(群体基因组学、景观基因组学等)的研究手段，对三叶崖爬藤进行了系统的群体历史和生态适应研究。研究结果证实三叶崖爬藤种内存在中国西南部和中东部两大地理谱系，谱系分化时间可追溯至上新世中期。虽然谱系间分化程度高、起源早，但仅经历了局部的小规模扩张，谱系间仍存在低水平的基因交流。此外，本项目基于FST遗传分化和基因型-环境关联分析分别在三叶崖爬藤全基因组中检测到752和532个异常SNP，其中与季节性潜在蒸发系数、海拔和最湿月份降雨相关的位点数量最多。冗余分析和广义相异建模结果均表明在所有居群中，地理因素是影响遗传变异的主要因素，但在小尺度空间范围内（谱系内），气候因子的作用增大。本项目为了解常绿阔叶林组成物种的种群历史变化过程、探究生态适应的分子机理、推测其应对未来环境变化的能力奠定了重要基础。