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中国有花植物的演化历史 精选

已有 2901 次阅读 2018-2-8 18:06 |系统分类:科研笔记

前几天的微信朋友圈被一则关于中国有花植物演化历史的消息刷屏,2018年的起始,中国的植物学同行在Nature上发文阐述了中国被子植物(即有花植物)的演化特点和规律,今天得空仔细品鉴了该研究论文Evolutionary history of the angiosperm flora of China,发现确实是一件好作品!

中科院植物所的Lu等基于中国26978种有花植物(代表着92%的中国维管束植物,即高等植物)的谱系关系,发现中国东部的植物区系分化时间可追溯到2200~2500万年前,而中国西部植物区系分化时间可追溯到1500~1900万年前。显然,西部植物更年轻,这点与学界普遍持有的观点一致:中国的西部,或青藏高原是中国植物的分化或起源中心。整体而言,66%属级水平的被子植物直到中新世(Miocene)才出现,中新世距今500~2300年。

最有意思的是,他们对种级水平被子植物平均分化时间(Mean divergence timesMDTs)的细致研究,作者发现,中国的西部是草本植物进化的摇篮,而东部则扮演着木本植物摇篮博物馆的双重角色;东部也可能是草本植物的博物馆。总之,东部更多地起到保存植物多样性的作用,而西部则是起源和物种形成中心。

作者把中国的植被分布格局从东西部的角度来审视,非常易于理解。更有意思的是,东西部植物区系分化时间上的分水岭貌似与500mm的等降水线重合,与决定中国经济、政治、文化和人口的黑河-腾冲线(大致是400mm的等降水线)有相似的走向,这种植被大格局给人一种豁然开朗、甚至不禁拍手叫绝的冲动。原来,科学如此多娇!(更多阅读:黑河-腾冲线的生态学本质之思考

这篇在Nature上的研究工作是以Letter形式发表的,通篇读下来感觉还有很多故事没有讲,让人不是很过瘾,特别是读到这种分布对保护能有什么启发时,给人一种戛然而止的感觉;另外一个缺憾是,作者在应该最精彩的部分东西部环境、地理格局时如何塑造这种植被大格局惜字如金,甚至守口如瓶。之后我又看了一下Lu & Chen发表在Nature Ecology & Evolution的推介性文字(https://natureecoevocommunity.nature.com/users/81922-limin-lu/posts/29798-evolutionary-history-of-the-angiosperm-flora-of-china),没能发现更详尽的解释。

那么,有哪些更有趣的点可以继续抒写中国植被大格局的故事呢?我觉得,可能是以下三小点(班门弄斧,权当读后思考之发散点记录好了):

(1) 古气候、古地理环境是如何影响东西部被子植物分化快慢的?这点牵涉到了物种形成的机理。作者虽然在文中也进行了当下气候因子与分化时间的相关性分析,但这种相关性显然不能作为一种因果关系。

(2) 当下的人类活动是如何影响东部被子植物分化时间的?西部的人类活动相对较弱,所采的植物样本可能就是自然演化出来的,但东部地区显然不是!个人感觉,人类活动可能是塑造东部植被格局的最关键因素,因此,忽略人类活动的植物区系演化关系推测可能是不客观的。

(3) 老生常谈,气候变化背景下东西部植物分化时间快慢比较。可结合(1)进行整合。


后记:这篇关于中国被子植物起源与进化的Nature Letter (Evolutionary history of the angiosperm flora of China)可结合今天刚发表的关于柑橘起源与进化的Nature Article (Genomics of the origin and evolution of Citrus)一起阅读!

   

Letter

Evolutionary history of the angiosperm flora of China

Abstract

High species diversity may result from recent rapid speciation in a ‘cradle’ and/or the gradual accumulation and preservation of species over time in a ‘museum’1,2. China harbours nearly 10% of angiosperm species worldwide and has long been considered as both a museum, owing to the presence of many species with hypothesized ancient origins3,4, and a cradle, as many lineages have originated as recent topographic changes and climatic shifts—such as the formation of the Qinghai–Tibetan Plateau and the development of the monsoon—provided new habitats that promoted remarkable radiation5. However, no detailed phylogenetic study has addressed when and how the major components of the Chinese angiosperm flora assembled to form the present-day vegetation. Here we investigate the spatio-temporal divergence patterns of the Chinese flora using a dated phylogeny of 92% of the angiosperm genera for the region, a nearly complete species-level tree comprising 26,978 species and detailed spatial distribution data. We found that 66% of the angiosperm genera in China did not originate until early in the Miocene epoch (23 million yearsago (Mya)). The flora of eastern China bears a signature of older divergence (mean divergence times of 22.04–25.39 Mya), phylogenetic overdispersion (spatial co-occurrence of distant relatives) and higher phylogenetic diversity. In western China, the flora shows more recent divergence (mean divergence timesof 15.29–18.86 Mya), pronounced phylogenetic clustering (co-occurrence of close relatives) and lower phylogenetic diversity. Analyses of species-level phylogenetic diversity using simulated branch lengths yielded results similar to genus-level patterns. Our analyses indicate that eastern China represents a floristic museum, and western China an evolutionary cradle, for herbaceous genera; eastern China has served as both a museum and a cradle for woody genera. These results identify areas of high species richness and phylogenetic diversity, and provide a foundation on which to build conservation efforts in China.

   

Article | Open

Genomics of the origin and evolution of Citrus

Abstract

The genus Citrus, comprising some of the most widely cultivated fruit crops worldwide, includes an uncertain number of species. Here we describe ten natural citrus species, using genomic, phylogenetic and biogeographic analyses of 60 accessions representing diverse citrus germplasms, and propose that citrus diversified during the late Miocene epoch through a rapid southeast Asian radiation that correlates with a marked weakening of the monsoons. A second radiation enabled by migration across the Wallace line gave rise to the Australian limes in the early Pliocene epoch. Further identification and analyses of hybrids and admixed genomes provides insights into the genealogy of major commercial cultivars of citrus. Among mandarins and sweet orange, we find an extensive network of relatedness that illuminates the domestication of these groups. Widespread pummelo admixture among these mandarins and its correlation with fruit size and acidity suggests a plausible role of pummelo introgression in the selection of palatable mandarins. This work provides a new evolutionary framework for the genus Citrus.



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