温带荒漠建群灌木红砂的生态物种形成研究

Temperature desert ecosystems are typical fragile ecosystems, in which Reaumuria soongarica, as one of the main constructive shrub species, plays important roles to keep their stability and species diversity. Global climate changes were believed to trigger the distribution shifts of plant species, and enhance the gene flow between populations by overlapping of their distribution regions or pre-zygotic isolation in the opposite way. Nevertheless, how the environmental changes drove the dynamics of gene flow during the ecological speciation was not well addressed so far. Our previous data strongly supported that R. soongarica had undergone intra-specific divergence and hybrid events, and this incipient speciation could supply us an ideal model to understand the ecological mechanism of plant speciation under climate changes. In this proposal, we aimed to investigate the differentiation of flowering phenology and habitat characteristics among the genetic clusters, and to elucidate the genomic divergence by genotyping the natural populations of this species based on RAD-seq technology. By describing the geographical genetic structure, constructing and optimizing its speciation models, and thoroughly profiling the dynamics of the gene flow during the evolutionary history which accompanied with paleo-climate changes and its ecological niche shifting as a consequence, this study could help us to illuminate the biological basis and ecological drivers of pre-zygotic isolation. This endeavor could supply a brand new example for us to address the ecological mechanism of plant speciation, and experienced data for modeling how the typical fragile ecosystems responded to global climate changes. On the other hand, this study could support new warning technology to mitigate the risk of sustainable development of fragile ecosystems in facing the conflicts of ecological civilization constructions for our country.

温带荒漠生态系统是典型的脆弱生态系统，而红砂是维持其稳定性和物种多样性的关键建群灌木之一。全球气候变化可导致植物分布区变迁，并促发基因流或配子前生殖隔离，但是基因流的历史动态变化如何受环境变化而驱动尚不明确。前期我们发现红砂进化历史过程中存在显著的种内分化和杂交事件，该物种形成的初始阶段为我们理解气候变化对植物物种形成的分子生态机制提供了绝佳模型。本项目拟结合红砂的花期物候和生境调查，基于RAD-seq技术对不同遗传支系进行基因分型分析，全面扫描其基因组遗传分化。通过刻画地理遗传结构，优化物种形成模型，全面解析红砂物种形成过程中基因流的动态变化，并结合干旱区古气候序列和生境分化模拟，阐明配子前隔离发生的生物学基础和生态环境驱动力。这将为我们理解植物物种形成的分子生态机制提供范例，同时为认识脆弱生态系统响应全球气候变化提供模型，并为我国生态文明建设中脆弱生态系统的可持续风险预警提供理论支撑。

红砂是维持温带荒漠生态系统物种多样性和稳定性的关键建群灌木之一，其内部经历过分化和杂交事件，是研究生态分化驱动物种形成的理想模型。为了解析红砂的生态物种形成机制，本研究通过物种范围采样，分析了不同遗传支系在表型性状和生态位上的差异；利用cpDNA片段和ITS探究了杂交支系的起源；并基于RAD-seq数据分析了红砂的群体遗传结构和物种形成历史。主要结果如下：. 1、通过野外观测和标本信息收集，发现北疆支系与其亲本东、西支系之间存在明显的表型分化和生境异质性。东西支系的花期几乎不重叠，北疆支系的花期介于两者之间，表明三个支系之间已存在一定程度的合子前隔离。北疆支系的叶长、叶宽和叶长宽比显著大于其他支系。三个支系之间的环境差异可能促进了上述的表型分化。. 2、cpDNA和ITS分子谱系数据显示，北疆支系中除WEH群体以外，其余群体均为东西支系杂交产生的后衍群体。北疆群体已明显分化为两组，靠近天山的南部分组（GuD-S）的遗传组分较为一致，母本为东部支系；远离天山的北部分组（GuD-N）的遗传组分混杂，不同群体的母本不同。除WEH群体以外，GuD-S和GuD-N的起源时间晚于0.5 Mya，与GuD沙漠的波动阶段吻合。. 3、基于RAD-seq数据的群体遗传分析显示，GuD-S起源于东西支系杂交，目前已演化成独立遗传谱系并处于生态物种形成的阶段。通过等位基因频率统计，找到了4个可能与GuD-S适应性分化相关的SNPs。GuD-N同时含有GuD-S和东部支系的遗传组分，这两种组分的比例在不同群体中不同，可能与东部支系持续的渐渗杂交有关。. 4、通过DNA C-值比对，发现GuD-S与东西支系的基因组大小存在差异，但倍性相同，表明GuD-S为同倍体杂交起源，而GuD-N中存在异源四倍体杂交种群。倍性差异导致了北疆红砂内部的生殖隔离。. 本项目理清了红砂的群体遗传结构、杂交起源和物种形成阶段，初步探讨了古气候变化及基因流对生态物种形成的影响，为理解生态物种形成初期的生态适应性分化和生殖隔离的产生等关键过程提供了研究范例，并为理解温带荒漠植物多样性的形成机制提供数据支持。