横断山区大王马先蒿复合群物种分化机制研究

Pedicularis is a genus of adaptive radiation in the Hengduan Mountains, with more than half of species endemic to this small region. Pedicularis exhibits striking diversity and variety in the Hengduan Mountains, however, we less know about the reasons and processes of speciation and species divergence. In this project, we will choose Pedicularis rex complex as the subject to investigate speciation process. This complex includes P. rex, P. thamnophila and P. cupuliformis, and their systematics and pollination biology is resolved well. Therefore, this complex is an ideal exampler to study the issue of speciation. Previous results showed that the rex complex corresponds to three of four criterions for sympatric speciation: (i) they are monophyletic group and sister species, (ii) their distributions are completely overlapped, and (iii) floral divergence mediate effectively reproductive isolation. The main goal of this project is using the phylogeographic approaches to explore whether their biogeography and evolutionary history are sympatric or not allopatric or parapatric. In order to clarify this issue, population samplings of all taxa covering distribution region could be included. Two or three chloroplastic genes will be selected to sequence, and five and six SSR loci to amplify for all population samples. Meanwhile, cytologic karyotype and ploidy are also investiged as population level, and hand hybridizations between taxa and/or populations are conducted in selected populations. The haplotypic data of DNA sequences are used to analyze evolutionary history of species and populations, and using the Cytologic data to examine whether speciation is associated with chromosomal variation. Gene flow caculated by SSR data, and fitness of hybrids can evaluate whether reproductive isolation is completed, as well as the importance of floral isolation inducing reproductive isolation. Whether speciation of Pedicularis rex complex is sympatric or not, this study will provide a valuable case for origin of endemic species in the Hengduan Mountains.

在横断山区马先蒿属植物是辐射分化的典型类群，大多数种类为该地区特有，但是到目前为止，如此丰富多样的马先蒿物种的形成和分化机制尚不十分清楚。本研究选择该地区特有的斗叶群中大王马先蒿复合群为研究对象，包括了大王马先蒿、灌丛马先蒿和杯状马先蒿，它们是研究物种分化机制的理想材料。该复合群满足了同域物种形成中的标准：1）该复合群是一个单系群，物种间是姐妹关系；2）分布区完全重叠，且存在同域分布居群；3）有效的花部隔离机制。本研究将利用谱系地理学研究方法，检验该复合群的生物地理和进化历史，验证同域物种形成可能性的这一标准；结合细胞核型的分布式样，探寻染色体重组或多倍化是否在物种分化过程扮演了重要角色。利用共显性的SSR分子标记和人工杂交试验，评价种间基因流强度和种间生殖隔离指数，评估物种形成所处的阶段和花冠分化在物种形成中的作用。以期为横断山区马先蒿属物种形分化和多样性保护提供重要理论依据。

横断山区是世界生物多样性热点地区之一。该地区是受青藏高原的抬升和东西伸展的影响，变为了物种分化和新物种形成的天然实验室。马先蒿属植物在横断山区发生了快速分化，形成物种的现代多样化中心。该属中的斗叶组是该属中少有的单系群，其中大王系种间关系复杂，即大王马先蒿复合群。本研究借助谱系地理学的研究方法分析该复合群居群扩展历史，重建物种分化过程，寻找出可能驱动物种分化的因子。并同时借助形态和分子证据，对复合群内部的种间关系进行了重新界定。并在整个属的系统发育关系上，对斗叶组和大王系的系统位置进行了再确定。.基于大尺度取样和四个基因片段，重建马先蒿属系统发育关系表明斗叶组是一个单系群，其姐妹种为互生叶类群。斗叶类组分为两个主要分支：无喙型短管型的大王系和有喙或长管类的华丽马先蒿+拟斗叶马先蒿+斗叶马先蒿。进一步对斗叶组进行广泛的取样，系统发育分析强烈支持大王系是一个单系群；核基因ITS得到的拓扑关系与传统分类具有较高的一致性，而四个叶绿体基因片段联合分析表明一些样本的叶绿体是捕获而来，或存在不完全的谱系分选或基因渐渗，在复合群中可能更为普遍。随后，我们利用基于NGS技术的GBS数据对复合群物种间的关系。研究结果确认灌丛马先蒿、大王马先蒿立氏和原亚种+洛氏变种单系，并支持未知物种作为独立种。基因流检测表明单系类群间的基因流较弱或不显著，暗示灌丛马先蒿、未知马先蒿和大王马先蒿之间的分化已基本完成。基于8个花部性状，以及种子等形态特征也支持复合群内4-5个分类群的划分。盔高、花冠管长和下唇长形成有效的机械隔离机制。.对复合群75居群748个个体的叶绿体rpl32-trnL片段进行测序和分析，共获得39种单倍型。其中多个主要单倍型存在种间广泛共享，这可能是祖先多态性的继承，或基因渐渗或叶绿体基因组捕获所造成。通过对种群扩张时间进行推算，暗示灌丛马先蒿和未知种与大王马先蒿原亚种的分化可能是间冰期扩张和/或冰期退缩所造成，灌丛马先蒿偏爱湿冷的高寒环境，未知种偏好于温暖的干暖河谷地带。基于SSR数据估算的基因流表明，大王马先蒿原亚种和立氏亚种之间的基因流最强，其次是大王马先蒿原亚种与未知马先蒿和洛氏变种；灌丛马先蒿和未知马先蒿之间的基因流相对较弱一些。研究进一步证实灌丛马先蒿、未知马先蒿和大王马先蒿原亚种之间的生殖隔离机制完全，而物种间的基因型共享可能是不完全谱系筛选或古杂交的结果。