苦槠和钩锥的基因组异质性分化和渗透研究

Speciation proceeds with the origin of barriers to gene flow. In some taxa, such as Family Fagaceae, whole-genome isolation has not yet been achieved. Levels of genetic differentiation can be highly variable across the genome, loci under divergent selection and those tightly physically linked to them may exhibit stronger differentiation than neutral regions with weak or no linkage to such loci. Exceptionally differentiated regions are often assumed to experience reduced introgression. Outlier loci with extreme patterns of introgression relative to most of the genome can be identified by estimating genomic clines. Castanopsis tibetana and Castanopsis sclerophylla are sympatric divergent species of family Fagaceae. Hybrids between C. tibetana and C. sclerophylla are found in natural population, suggesting on-going gene flow still exist between these two species. Hybridization in natural populations provides a unique opportunity to study speciation and the genetics of reproductive isolation. In this study, RAD-seq technique will be explored to estimate locus-specific divergence and introgression between C. sclerophylla and C. tibetana, to reveal highly divergent region and barriers to gene flow, and to assess the relationships between locus-specific divergence and locus-specific introgression. These results will facilitate our understanding of porous species boundaries in Castanopsis.

壳斗科植物生殖隔离常常是不完全的,就是说基因组是可以被种间基因交流穿透的，进而表现出基因组的异质性分化和渗透。壳斗科锥属植物苦槠Castanopsis sclerophylla和钩锥Castanopsis tibetana是两个近缘且分布区重叠的物种，现有的杂交个体说明这两个分化物种目前还存在基因交流。本项目拟利用简化基因组测序从群体基因组水平开展苦槠和钩锥的基因分化和基因渐渗研究，揭示苦槠和钩锥基因组的异质性分化和渗透。检测那些受歧化选择影响而表现出异常高的种间分化的基因位点，以及受生殖隔离影响而呈现出异常低的种间渐渗的基因位点。通过分析基因组上高度分化的区域是否也呈现出异常的基因渐渗式样，为探讨歧化选择与生殖隔离的关联提供理论基础。这些研究结果预期能够帮助我们全面了解苦槠和钩锥的物种边界、物种分化和物种间基因交流，并且能够为基因流存在下的物种分化提供新的资料和证据。

壳斗科植物生殖隔离常常是不完全的,也就是说基因组是可以被种间基因交流穿透的。壳斗科锥属植物苦槠Castanopsis sclerophylla、钩锥Castanopsis tibetana是亚热带常绿阔叶林的优势树种。这两个物种近缘，分布区重叠，且推测有种间基因流发生。为了验证两物种间的基因流以及了解这两个物种的遗传边界，我们利用核微卫星标记和RAD-seq研究了苦槠、钩锥的遗传多样性、群体结构和分化历史。研究结果表明苦槠、钩锥都在东西方向存在显著的群体分化，罗霄山脉所在的中部地区其群体具有较高的遗传多样性水平。进化场景模拟检测显示雪峰山脉、罗霄山脉和武夷山脉的隆升对苦槠、钩锥群体产生了强烈的隔离作用，驱动了苦槠、钩锥在东西方向上的群体分化，随后隔离分化的分支在中部地区发生二次接触导致了中部群体产生较高的遗传多样性水平。中国植物志上曾记载分布于岳麓山的苦槠钩锥（Castanopsis× kuchgouzhui）疑似源于两个物种杂交。我们利用核微卫星标记和叶绿体基因变异验证了岳麓山的苦槠钩锥（Castanopsis× kuchgouzhui）是天然杂交个体。现存的杂交个体说明这两个分化物种近期还存在基因交流，但苦槠、钩锥间的天然杂交个体非常非常罕见，我们在这两个物种同域分布的其它群体中并没有检测到另外的杂交个体。我们进一步利用简化基因组测序更深入开展苦槠、钩锥的遗传分化和基因交流研究，发现两个物种间的遗传边界很清晰，等位基因混合程度很低。这些结果说明苦槠、钩锥存在完整的物种边界，两物种生殖隔离较强。这一研究为深入理解壳斗科植物的物种分化、物种间基因交流、以及遗传多样性的产生和维持机制提供了新的资料和证据。