二型花柱向同型花柱演化转变的生态和遗传效应

Heterostyly is a specialized floral syndrome that promotes cross pollination and reduces sexual interference between female and male function. Phylogenetic studies indicate that heterostyly is often destabilized resulting in evolutionary transitions to a range of other sexual systems including gynodioecy, dioecy and other forms of gender specialization. However, the most frequent transition involves the evolutionary breakdown of distyly to homostyly and this represents a classic example of the evolution of predominant self-fertilization (autogamy) from outcrossing in the flowering plants. The shift from distyly to homostyly provide a rich, but largely untapped, source of experimental material for investigating the ecological and genetic causes and consequences of mating-system transition in plants.. Primula chungensis is of particular interest because it is comprised of populations that are either: 1) distylous (with long- and short-styled morphs); 2) monomorphic containing only homostylous individuals or 3) trimorphic in which all three morphs coexist. This species therefore provides an outstanding experimental system for investigating the ecological and genetic mechanisms driving mating system transitions. In this project we will address three questions: First, using phylogeographic analysis and studies of molecular diversity we will determine whether homostylous populations are derived from distylous populations. We will determine how many times this transition has occurred and whether the transition is associated with founder events and a loss of genetic diversity. Second, by investigating floral traits and mating systems using genetic markers in each of the three population morph structures we will determine whether increased rates of selfing are associated with changes in sex allocation and the evolution of the selfing syndrome as theory predicts. Finally, using molecular population genetic approaches and transcriptome sequencing we will determine the genomic consequences of transitions in mating patterns and test the hypothesis that the shift to selfing is associated with reduced molecular diversity and a reduction in the efficacy of selection in homostylous populations. This project will provide novel insights into how and why heterostyly breaks down to selfing and the genomic consequences of this transition. In addition the sexual polymorphic component of the study will provide valuable information on the role of historical and contemporary factors influencing diversity of primrose in Himalaya-Hengduan Mountains Region.

特化的异型花柱综合征呈现进化不稳定性。系统发育研究表明多数异型花柱植物类群蕴含向其他性系统发生演变的迹象，如雌全异株和雌雄异株。异型花柱向同型花柱的转变最为普遍，该过程伴随交配系统由异交向自交的急剧转换,花型转变的研究能够加深理解植物性别表型演化引发的生态与遗传效应。本项目以中甸灯台报春为研究对象，利用该物种具备二型花柱种群、同型花柱种群和混合三态种群在种内共存的特殊优势；在种群层面上开展分子生态学研究：1）通过种群谱系重建方法确证二型花柱而同型花柱的演化转变关系；2）通过繁殖性状和交配格局的比较研究，检验花型转变产生的繁殖生态效应，即“巩固自交”亦或“选择异交”；3）通过种群基因组学的比较研究检测交配系统转变导致的遗传效应。项目的实施有望为异型花柱植物性别表型的演化提供新的证据，开拓交配系统转变研究的新内容；同时，在性表型多态的层面上加深理解喜马拉雅-横断山区报春花植物多样性发生与维持。

特化的异型花柱综合征呈现进化不稳定性。系统发育研究表明多数异型花柱植物类群蕴含 向其他性系统发生演变的迹象，如雌全异株和雌雄异株。异型花柱向同型花柱的转变最为普遍 ，该过程伴随交配系统由异交向自交的急剧转换,花型转变的研究能够加深理解植物性别表型 演化引发的生态与遗传效应。本项目以中甸灯台报春为研究对象，利用该物种具备二型花柱种群、同型花柱种群和混合三态种群在种内共存的特殊优势；在种群层面上开展分子生态学研究 ：1）通过种群谱系重建方法确证二型花柱而同型花柱的演化转变关系；2）通过繁殖性状和交配格局的比较研究，检验花型转变产生的繁殖生态效应，即“巩固自交”亦或“选择异交”； 3）通过种群基因组学的比较研究检测交配系统转变导致的遗传效应。研究结果表明：1)中甸灯台报春在历史早期分化为西藏和四川两个多种群的谱系分支，两个分支中的同型花柱个体/种群为独立起源，其中西藏谱系分支中的同型花柱单态种群为原位竞争起源，而四川谱系分支中的同型花柱单态种群为奠基者扩散起源；2）同型花柱种群交配方式以自交为主，且在不同程度上发育出“巩固自交”的特征，同时也存在探出式和缩入式的异位形式；3）在异型花柱向同型花柱转变过程中，由于有效种群Ne的缩小，自交种群内轻微有害突变的积累量明显上升。本项目的研究首次以报春花的性系统转变为对象，揭示交配系统转变的生态和遗传效应，为理解我国西南地区生物多样性的起源和维持提供理论依据。