基于线粒体基因组的深海热液阿尔文虾起源与演化研究

The deep-sea hydrothermal vent is one of typical extreme environments on Earth that assembles with the early life circumstance. It is important for elucidating the life origins and the relationships between geological change and biological evolution by exploring the origin and develop mechanisms of representative species in the hydrothermal vents. Shrimps of the family Alvinocarididae are vent-endemic species, and many species of genus Lebbeus from the family Thoridae also inhabit in hydrothermal vent. Taking alvinocaridid shrimps for research objects, we reconstruct a phylogenetic tree of Caridea based on mitochondrial genomes to determine if the vent-endemic species migrate from non-hydrothermal environments or they are the remnants of ancient species of hydrothermal. We implement the molecular clock method for dating analysis to determine the molecular divergence time of alvinocaridid shrimps and the thorid shrimps from hydrothermal vent. The results will help us understand whether the different vent organisms originated at the same time. The alvinocaridid shrimps not only the dominant species in hydrothermal vent environment, but also have a high proportions of endemic species. Different hydrothermal vent in Pacific, Atlantic and Indian Oceans populated with different Alvinocarididae species. The phylogenetic topology among generas in Alvinocarididae, as well as their geographical distribution pattern were combined to further clarify the evolutionary origin and history of the alvinocaridid shrimps. Furthermore, molecular divergence time was estimated to infer however the geological events, e.g. historical climate changes, ocean geographic patterns, sea-floor spreading, influence the distribution of alvinocaridid shrimps. Our findings will provide theoretical and practical evidence for revealing the origin and the evolution of the chemosynthetic-fauna in deep-sea hydrothermal vents.

深海热液区是地球上典型的极端环境，与地球早期的环境极为相似。开展热液代表性物种的起源与演化研究对探索生命的起源及地球环境演变与生物进化的关系有重要意义。阿尔文虾是热液的标志性物种，藻虾科Lebbeus属的多个物种也栖息于热液环境。本研究以阿尔文虾为主要研究对象，基于线粒体基因组构建真虾下目科间系统发育关系，明确热液特有物种是由非热液环境迁徙而来还是热液口古老物种的遗存。通过分子钟分析确定阿尔文虾和热液藻虾的起源时间，阐明不同热液生物类群是否同一时间起源；阿尔文虾不仅是热液的优势种，而且具有很高的喷口特有性。本研究基于线粒体基因组构建阿尔文虾科属间系统演化关系，结合阿尔文虾的地理分布格局，阐释其演化路径；通过分子钟分析明晰不同地质时期历史气候变化、海洋地理格局等重要地质事件对阿尔文虾分布的影响。为研究热液大型生物起源中心及扩散路径提供重要的理论依据。

阿尔文虾科隶属于甲壳动物亚门（Crustacea）十足目（Decapoda）真虾下目（Caridea），是热液生态系统的标志性物种，是进行深海热液生物起源与演化研究的理想实验材料。本项目获得了4个热液阿尔文虾物种，1个热液藻虾和9个海山真虾下目物种的线粒体基因组全序列，利用已获得的其它真虾下目物种的线粒体基因组数据，进行了线粒体比较基因组学，系统发育与起源演化分析。结果表明，4个阿尔文虾物种的线粒体基因组均编码37个基因（13个蛋白编码基因，2个rRNA基因和22个tRNA基因），具有相似的线粒体基因大小，碱基组成和相同的基因排列顺序。基于线粒体基因组构建的系统发育树支持热液特有物种是由非热液环境迁徙而来，并非是热液口古老物种的遗存；通过分子钟分析，明确了热液阿尔文虾起源于白垩纪和第三纪之间（61.39 Mya），支持灭绝-重生假说。通过对系统演化关系及阿尔文虾地理分布特征的分析，提出西南太平洋是阿尔文虾的起源中心，并经印度洋扩散到大西洋中脊。选择压力分析在8个基因中（atp6、atp8、cox1、cox3、cytb、nad2、nad4l和nad5）共筛选出22个正选择位点。本项目明晰了不同地质时期历史气候变化、海洋地理格局等重要地质事件对阿尔文虾起源与分布的影响，为阐明深海热液大型生物起源扩散及适应进化提供了重要的理论依据。