蔷薇科物种丰富度分布格局研究

Explaining the species richness patterns across the tree of life is one of the great challenges in evolutionary biology. Two major hypotheses - clade age hypothesis and diversification rate hypothesis - have emerged in recent years, and have been used to explain the disparity of species richness among major clades of the Tree of Life. However, we have no idea if these two hypothesis can work among clades of family. Rosaceae is an excellent group for investigating the processes that determine species richness patterns because they are a diverse group with c. 90 genera and 3000 species and a nearly global distribution, and they show a huge disparity in species richness across major lineages. The absence of a comprehensive time-calibrated phylogeny for Rosaceae has precluded efforts to disentangle the evolutionary processes that explain species richness patterns in this group. Until recently, the phylogenetic relationships in Rosaceae have been fully resolved with plastomic and transcriptomic data, respectively, though the deep phylogenetic incongruence was detected. In this project, DNA sequences from three genomes produced by genome skimming technology will be applied to reconstruct the phylogeny of Rosaceae and the deep incongruence will be revealed. This robust phylogenetic frame will be applied to infer the origin and divergence time and the diversification rate of Rosaceae and its major clades, and explore their rapid diversification period and according trait(s) evolution. Rather than simply testing individual traits as before, our research will focus on comparing how much variation in diversification rates is explained by different types of traits. This project will provide novel insights into whether patterns of species richness among clades across family are explained primarily by diversification rates or clade age. This project will supply the theoretical basis for studies of origin, evolution and other biological disciplines in Rosaceae and promote studies of genomic structure and evolution in Rosaceae.

解析物种丰富度的分布格局及其形成过程是进化生物学的重要研究内容。分支年龄假说和多样化速率假说是被广泛用来解释物种丰富度分布格局的两种假说。然而，到目前为止，两种假说在科下等级的适用程度尚缺乏检验。蔷薇科分支间物种丰富度极度不平衡，是被子植物多样性最丰富的一个科，也是系统发育关系较为清楚的类群，是检验两种假说的极好模式。因此，本项目以蔷薇科为研究对象，利用浅层测序技术获得较为完整的叶绿体基因组、部分线粒体基因组和核基因组18S-5.8S-26S区段数据，重建蔷薇科的系统发育树，分析拓扑结构冲突原因。结合化石推算主要分支的起源分化时间和多样化速率，分析分支年龄和多样化速率与物种丰富度的相关性，剖析促使多样化速率改变的性状，并着重解析每个性状的影响程度。项目的实施将检验两种假说在科下等级的适用程度，为解析物种丰富度分布格局形成过程提供参考，并为研究蔷薇科的起源、进化历史和物种多样性保护奠定基础。

对项目的背景、主要研究内容、重要结果、关键数据及其科学意义等做简单概述，800字以内，含标点符号)：..解析物种丰富度的分布格局及其形成过程是进化生物学的重要研究内容。分支年龄假说和多样化速率假说是被广泛用来解释物种丰富度分布格局的两种假说。然而，到目前为止，两种假说在科下等级的适用程度尚缺乏检验。为了解释物种丰富度在蔷薇科各主要分支上的分布差异，本项目收集了1581个叶绿体全基因组数据，通过分析叶绿体基因组结构变异，比较全基因组和蛋白编码基因编码区建树差异，探究样品数量和长枝等因素对系统树的影响，重建了一个高度解析的蔷薇科系统发育树，从而厘清了所有亚科和族的范畴和关系。基于102个属的代表种构建的系统树结合化石推算蔷薇科起源于白垩纪晚期，三个亚科的分化时间在距今70至96百万年前。多样化速率分析表明桃亚科在距今40到30百万年前的始新世晚期和渐新世早期经历了1次明显的多样化速率加快事件。与此同时，其祖先的生境、生活型和果实类型也发生了改变。综合以上结果，我们认为蔷薇亚科和仙女木亚科物种丰富度产生的原因更符合分支年龄假说，但显然仙女木亚科的多样化速率更慢，而桃亚科更符合多样化速率假说，虽然在分化早期桃亚科也经历了长时间的物种多样性积累过程；晚始新世和早渐新世全球温度持续变冷导致的北半球植被由亚热带植被类型向落叶阔叶林过渡，为适应冷凉气候的木本类蔷薇科植物提供了快速分化的条件，促使蔷薇科整体物种丰富度的提高。本项目的实施不仅检验了两种假说在蔷薇科下等级的适用程度，为解析物种丰富度分布格局形成过程提供参考，并为研究蔷薇科的起源、进化历史和物种多样性保护奠定了基础。.