生殖隔离形式及物种形成连续性探究

Speciation is characterized by the evolution of reproductive isolation among groups of organisms. To understand the process of speciation, it is crucial to quantify various barriers to reproductive isolation, to dissect the genetic mechanisms that contribute to those barriers and to determine the forces driving the evolution of those barriers. Pinus densata is an ecologically successful homoploid hybrid pine inhabiting vast areas of heterogeneous terrain on the south-east of the Tibetan Plateau. Population genetic studies have revealed a strong spatial genetic structure for P. densata populations. The origin of P. densata was initiated in the northeastern periphery of its range, it then colonized the plateau by migrating westwards, during which consecutive bottlenecks strongly affected the population composition. The direction and intensity of introgression from parental species varied among geographical regions. This study proposes to use P. densata as the study system, to comprehensively assess the strength and patterns of multiple prezygotic and postzygotic reproductive isolating barriers contributing to the divergence of P. densata populations. Under the context of "Speciation Continuum" which emphasizes the continuous nature of divergence during speciation, the regional populations of P. densata are regarded as representing different stages of speciation and divergence. In this project, we shall carry out controlled crosses to examine the genetic compatibility in the species complex. We shall investigate flowering phenology along the ecological and genetic transitions of P. densata and its parental species Pinus tabuliformis and Pinus yunnanensis. We shall also conduct common garden experiments in both central and species boundary regions of the three species to evaluate the strength of ecological selection. Results from the project will shed light on the relative roles of different isolation barriers in the process of divergence. It will also contribute to our understanding on the origin and maintainance of biodiversity in Qinghai Tibetan Plateau.

生殖隔离的建立是物种形成的关键。揭示种间生殖隔离的存在方式、形成过程及遗传机制是进化生物学研究的重要课题。高山松（Pinus densata）起源于油松和云南松的天然杂交，不同的高山松群体拥有各自独特的遗传组成和进化历史；高山松杂种起源可追溯到青藏高原的隆起；不同地域的高山松群体可被看做是高山松与亲本种间生殖隔离建成这个连续过程不同阶段的代表。本项目计划在物种形成连续性的理论体系下，将彼此独立、遗传差异显著的高山松地域性群体做为对高山松成种连续过程的不同时段的模拟，以此分析物候、生态选择及遗传分化等隔离机制在物种形成不同阶段的作用和重要性，探讨近缘种分化的连续性过程。本项目整合遗传学、生态学理论和方法，探讨多重生殖隔离机制的相对作用和进化，该研究结果不仅有助于理解生殖隔离和适应性分化对物种形成的作用，也有助于理解青藏高原生物多样性产生及维持机制。

生殖隔离的建立是物种形成研究的关键问题之一。种间生殖隔离的存在方式、形成过程及遗传机制是进化生物学研究的重点。高山松（Pinus densata）起源于油松和云南松的天然杂交，不同的高山松群体拥有各自独特的遗传组成和进化历史；高山松杂种起源可追溯到青藏高原的隆起；不同地域的高山松群体可被看做是高山松与亲本种间生殖隔离建成这个连续过程不同阶段的代表。本项目在物种形成连续性的理论体系下，将彼此独立、遗传差异显著的高山松地域性群体做为对高山松成种连续过程的不同时段，分析了物候、生态选择及遗传分化等隔离机制在物种形成不同阶段的作用和重要性，探讨了近缘种分化的连续性过程。（1）多地点的物候观察表明，尽管开花和传粉物候存在着种间差异，且随不同地理和环境而改变，但种间重叠区的物候特征介于种间，开花物候不足以构成种间生殖隔离；（2）人工杂交实验显示三个高山松群体（四川康定、米亚罗、云南香格里拉）与亲本种油松可配性差异明显，川西群体与油松可配性高于云南西北部群体与油松的可配性，这个发现刚好与物种形成连续性理论预期相符；（3）大尺度的移栽实验显示种间存在着强烈的生境选择。本项目突破了物种概念，着眼于群体，探讨多重生殖隔离机制的相对作用和进化。该研究整合遗传学和生态学理论和方法，不仅有助于理解生殖隔离和适应性分化对物种形成的作用，也有助于理解青藏高原生物多样性产生及维持机制。