北温带中华蹄盖蕨复合体Athyrium sinense complex的物种分化

Genetic structure and speciation events of plants in the Northern temperate regions have been deeply influenced by the climatic oscillations since the Neogene. Compared to seed plants, ferns with heteromorphic generations, which possess a morphologically simple gametophyte generation, are very sensitive to environment and climate changes, and thus, may have evolved unique phylogeographic patterns and adaptive mechanisms. However, the lack of available single/low copy nuclear DNA markers hampers phylogeographic study in ferns to test the above hypothesis. Genomic phylogeography, based on high-throughput sequencing technology (Restriction-site Associated DNA Sequencing, RAD-Seq) opens the avenue to better untangle the species circumscription and evolutionary history within ferns. In this study, we select a diploid and widespread temperate fern species complex Athyrium sinense complex (Athyriaceae) to investigate its speciation mechanism. Species delimitation within this group has been long-term controversial due to complicated morphological variations. Based on evidence of single nucleotide polymorphisms (SNPs) from the whole genome using RAD-Seq, we aim to (1) analyze the genetic structure and relationships of DNA haplotypes using phylogeographic approaches; (2) estimate the spatio-temperal dynamic of populations and demographic history according to coalescent-based models and simulation-based approaches; (3) investigate the relationships between temperate fern diversity and Quaternary climatic oscillations; and (4) explore the natural circumscription of species within this complex based on population genetic and morphological evidence. With the incorporation of our pervious speciation studies on ferns from the Qinghai-Tibetan Plateau and subtropical Asia, we further aim to better understand mechanisms of fern diversification in Eastern Asia.

第三纪末期以来气候变化对北温带植物的物种分化和居群遗传结构产生了深远影响。蕨类植物具有独立孢子体和配子体世代，对环境和气候变化更为敏感，这些特征在居群遗传结构和地理分布上烙下深刻印迹。简化基因组测序技术弥补了蕨类谱系地理学研究中缺乏大量核基因信息的不足。中华蹄盖蕨复合体广布于北温带林下，主要以二倍体形式存在。该复合体的分类学性状变异复杂，在居群间甚至居群内存在过渡，传统形态分类学和以个体为单位的系统发育分析难以揭示其种间界限和相互关系。本研究将采用RAD-Seq技术获取基因组多态位点大数据，进行谱系生物地理学的分析，揭示复合体的遗传结构与居群动态历史；结合生态位模拟、形态学和地理分布等，探讨其物种形成过程及对气候变化的响应，进行科学的物种划分。综合分析青藏高原和东亚亚热带地区有关蕨类植物物种进化的研究，深入探讨东亚蕨类植物多样性的形成和演化过程，为物种多样性的保护和可持续发展提供理论依据。

蕨类在维管植物演化过程中占据重要地位，具有独立的孢子体和配子体世代，主要通过孢子随风传播。该生活史特征十分有利于群体间遗传交流的维持，被广泛用于解释蕨类植物较低的地域特有性，相反地，人们目前对该类群遗传分化的形成过程和维持机制了解甚少。中华蹄盖蕨复合体是一类主要以二倍体形式存在的草本蕨类植物，在北温带广泛分布，是研究蕨类物种分化的理想类群。本项目结合来自核基因组和叶绿体基因组的分子系统学证据，澄清了复合体中亚洲类群与欧美类群的亲缘关系；随后重点聚焦亚洲类群，基于RAD-seq技术获取的基因组层面的遗传变异，通过群体遗传学研究揭示了其在东亚35°N南北显著的遗传分化；针对形态特征和生态变量的统计检验表明，南北群体间同样具备显著的形态和生态位分化。群体历史和祖先分布区模拟的结果显示，该类群的分布区是在第四纪气候震荡下实现了向我国西南部高山地区的扩张。结合环境因子的统计检验则在支持该类群强扩散潜力的同时，表明 35°N南北的气候差异是造成现今分化格局的关键。研究结果为深入理解蕨类植物的时空演化历程提供了新的见解，并着重强调即便有强扩散潜力的存在，生境的异质性仍能有效地驱动物种的遗传分化。