栎属物种多样性与气候关系的进化成因

Evolutionary process, such as speciation, extinction and dispersal, can directly change species diversity. Climate could have influence on species diversity through these evolutionary process. Therefore the species diversity-climate relationship may be originated from evolution history. Early studies mainly focused on species diversity-climate relationship and proposed many hypothesis to explain the spatial variation of species diversity. Recent researches on spatial variation of species richness proposed new hypothesis based on evolutionary history, such as evolutionary rate hypothesis, time-for-speciation hypothesis and niche conservatism hypothesis etc. However, what drives the species diversity-climate relationship and the link between evolutionary history and species diversity-climate relationship is still poor studied. By incorporating a phylogenetic perspective, this question may be best studied. Here we will use a phylogenetic approach to address the causes of species diversity-climate relationship in Oaks (Quercus L.) by combining data on distribution, leaf habitat, climate, Quaternary climate and phylogeny. Specifically, we are aiming to answer the following three key questions to address the origin of oak species diversity-climate relationship..1).How the historical event or historical climate change influences the evolutionary rate, niche evolution, leaf habitat evolution and species diversification of oaks? Dose the historical event influence species diversification by speed the evolutionary rate, hence force promote the niche and leaf habitat evolution?.2).Does evolution history drive the species diversity-climate relationship? If it is true, which hypothesis plays a key role in the origin of species diversity-climate relationship, the evolutionary rate hypothesis, time-for-speciation hypothesis or niche conservatism?.3) Dose evolutionary history have influence on the relationship between species diversity and Quaternary climate change? Using the clades with different evolutionary history, we will compare the effects of Quaternary climate change on species diversity among clades and identify which clade in which area is easily to be affected by climate change.. This project aims to enhance the understanding of mechanisms of the species diversity patterns; especially the influence of evolutionary history on the species diversity-climate relationship. Taking into evolutionary perspective, the achievements of this project could be used in the conservation policy plan under global climate change.

物种多样性格局的形成和维持机制是生物多样性保护的基础，因此一直是生态学的核心研究问题之一。以往关于物种多样性格局的假说多基于物种与气候关系而提出，而关于进化是否以及如何影响物种多样性格局及其与气候的关系仍然研究较少。其本研究拟以栎属为例，通过结合分子系统进化树与气候、物种属性和分布数据，研究：1) 关键地质事件对栎属分布与多样性格局的作用；2) 进化历史如何影响物种多样性与现代气候的关系；3）评估不同类群物种多样性对第四纪气候变化响应的差异。栎属是北半球亚热带和温带森林的重要树种，揭示进化过程和第四纪气候变化对其多样性格局影响，将加深对北半球森林起源和演化的理解，并将为栎属多样性保护提供科学依据。

栎属约450种，广布于北半球，是温带和亚热带森林生态系统的重要组成物种。本研究以栎属为研究对象，通过建立栎属物种分布数据库和涵盖主要类群的时间校准的栎属分子系统进化树，确定栎属各类群的进化历史，分析各类群物种多样性与环境的关系，研究物种多样性与气候关系的进化起源以及末次冰期以来气候变化对栎属物种多样性的影响。本项目的研究结果主要有以下几点。（1）北美的墨西哥和中国西南部地区是栎属物种多样性的分布中心，栎属物种多样性从北纬25度左右向赤道和北极地区物种多样性逐渐降低。（2）渐新世时期北美分枝的平均进化速率高于欧亚分枝，而中新世时期欧亚分枝的进化速率高于北美分枝。（3）栎属系统进化树的分枝长度与分枝祖先节点与子孙节点间的降水和温度的变化范围呈显著正相关，年龄越古老，对降水和温度变化范围的适应越广，而分枝的进化速率与该分枝降水的变化范围没有显著关系。同时，北美分枝进化速率越快，降水的变化范围越大。（4）区域历史对栎属物种多样性与气候关系的影响是不显著的。不同的水分和温度因子对栎属物种多样性的影响在东亚、欧洲和北美之间没有显著性差异。（5）东亚分布的类群生态位最为保守，物种多样性与环境关系最强，而欧洲分布的主要类群生态位最不保守，物种多样性与环境的关系最。祖先生态位及其保守性可能是栎属物种多样性与气候关系差异的主要原因。（6）末次冰期以来温度变化范围越大，则温度变化范围物种多样性的解释率越高，但是过去温度变化对物种多样性的斜率没有显著性影响，即过去温度的变化限制了栎属各类群的物种多样性。北美分枝中，降水的变化与降水对多样性的解释率是正相关的。东亚分枝中，降水的变化与降水对多样性的解释率是负相关的。本项目所构建的进化树只涵盖了40个物种，取样不全可能也会影响进化分析结果的可靠性，这是本项目的主要局限性之一。