冰期避难所隔离对蒙古栎-辽东栎复合体物种形成的影响

East Asia harbors the most diverse of the world's temperate flora. One hypothesis about the origin of this high diversity is that in East Asian repeated cycles of allopatry (habitat fragmentation), driven by Quaternary climate changes, accelerated the speciation of temperate forest species. In current research, we intend to test this hypothesis, by exploring whether and how the isolation of glacial refugia have motivated the speciation of Quercus mongolica and Q. liaotungensis (consist of two divergent geographical groups: west Q. liaotungensis and northeast Q. liaotungensis) complex, using 200 single copy nuclear gene loci..First, we will sequence 200 nuclear gene loci for 40 morphologically typical individuals for each of Q. mongolica, west Q. liaotungensis and northeast Q. liaotungensis, using the target sequences enrichment method, coupled with the next-generation sequencing technologies (NGS). Then, we use Approximate Bayesian Computation (ABC) method to simulate these sequence data under different speciation models, to estimate whether divergence between Q. mongolica and Q. liaotungensis was driven by isolation of distribution. And then, we will use IMa2 software to estimate the divergence time and historical gene flow between Q. mongolica and Q. liaotungensis, and between west Q. liaotungensis group and northeast Q. liaotungensis group, to infer whether their divergence meet a historical glaciation and what is the level of gene flow after their divergence. At last, ten most divergent loci will be sequenced for a total of 100 oak individuals from North China and Northeast China hybrid zones, where different reproductive barriers were found in our previous studies, to find the potential speciation gene, and then to try to infer how the two taxa keep divergence during their secondary contact. .The results from all above analyses would supply more evidence for the species status of Q. mongolica and Q. liaotungensis. Our research will not only detect whether populations were isolated and diverged during the glaciations, but also estimate whether the divergent populations experienced only limited gene flow, and how they remained genetically isolated after their secondary contact. Through detailing the speciation process of the Q. mongolica - Q. liaotungensis complex, we could further answer whether allopatric speciation driven by and Quaternary climate changes have attributed to the species diversity of temperate deciduous broad-leaved forest in North China.

东亚有着世界上最高的温带植物物种多样性，其多样性来源一直都是备受关注的话题。其中，是否第四纪气候变化导致的种群分布区隔离促进了该地区异域物种形成，是当前研究的热点。本项目拟采用第二代测序技术进行目标序列富集测序的方法，通过分析200个单拷贝核基因序列位点的变异，计算蒙古栎和辽东栎，及辽东栎不同地理支系间的分化时间和历史基因流情况，推断冰期避难所隔离对蒙古栎－辽东栎复合体物种形成的影响；同时通过比较种间分化位点的变异在种间繁殖隔离程度存在明显差异的华北和东北杂交带中的分布，查找地理隔离结束后种群再次接触时，继续维持种间分化的基因，从而试图探索栎树的物种形成基因，及其对应的适应性性状。以期通过解析蒙古栎和辽东栎的物种形成过程，探讨第四纪气候变化是否，并如何促进当前中国北部广泛分布的暖温带落叶阔叶林树种的物种形成，为东亚温带植物物种多样性来源提供实例。

栎树指壳斗科栎属所有物种，是我国温带森林的主要组成之一, 具有重要的生态和经济价值。栎属在中国大约有51种，其中白栎组纯种约10余种。然而，前期关于这些物种的种间遗传分化和杂交研究非常少。本研究采集了中国分布范围相互重叠的白栎组的槲栎，锐齿槲栎，槲树，白栎，大叶栎，辽东栎，毛叶槲栎蒙古栎，枹栎和短柄枹栎等10个物种的33个同域或异域种群，同时采用叶绿体DNA序列和单拷贝核基因序列分析这些物种的系统发育关系，并着重讨论蒙古栎和辽东栎的分化和基因流。利用5个叶绿体片段序列的分析发现, 中国白栎组物种的叶绿体变异并未反映出种间分化，而是与其种群所在地理位置有关；种间杂交广泛存在，从而导致同域或邻域分布的不同白栎物种共享叶绿体DNA序列变异。基于22个单拷贝核基因序列的贝叶斯分组分析表明中国白栎组物种有各自独立的核基因库，但是各物种间存在广泛杂交；系统发育树的结果显示各物种间分化程度都很低，分支节点的支持率低，表明中国白栎组各物种间分化时间较短。另系统发育树显示，蒙古栎和锐齿槲栎，而不是和辽东栎，有着更近的亲缘关系，与之前根据形态特征认定辽东栎和蒙古栎是近缘种的结论矛盾。近似贝氏计算推断，东北辽东栎可能是西部辽东栎通过花粉流反复与蒙古栎杂交后的结果，其中西部辽东栎的成分更高。IMa估计辽东栎和蒙古栎分化时间约为0.40百万年；辽东栎比蒙古栎有着更大的有效种群大小，前者到后者的基因流也更高。为进一步探讨蒙古栎是否存在多个北方避难所，我们利用19个微卫星位点和四个叶绿体片段分析了29个蒙古栎天然种群的遗传多样性和结构。研究表明，蒙古栎种在末次盛冰期可能在东北长白山地区、朝鲜半岛、渤海湾和俄罗斯远东沿海等地多处避难；另，在北部中-高纬度地区还可能零星分布着隐形避难所。这些研究将成为后期中国白栎组相关研究奠定重要基础，也将为中国栎树自然种质资源保护和遗传育种策略制定提供科学依据。