西北太平洋海域软骨鱼类分布格局形成的分子机制及其物种多样性：以魟属鱼类为例

Elasmobranches have been swimming the world's oceans for over 400 million years. They inhabit every ocean and play a vital role in maintaining the health of marine ecosystems. Among all 1000 species of extant chondrichthyan fishes, we have more than one-fourth of the species in China. However, there is still no phylogeography study of Elasmobranches in China. Genus Dasyatis belongs to Family Dasyatidae, Myliobatiformes, Batoidea,Elasmobranchii, comprising 40 valid species and about at least 5 unnamed species in the world. The biodiversity of Dasyatis is highest in the Northwestern Pacific. In addition, 73% of these species are endemic to this water area. Historically, the climatic oscillations produced severe changes in temperatures, current patterns, upwelling intensity and coastal habitats in this area, resulting in many famous geological events, such as the separation of proto-Japanese islands from the continent, the connection of Japan with the continent again at Kyushu Island, the emergence of the Taiwan-Ryukyu land bridge, and the shifts of continental lines and Kuroshio Current. Dasyatis bennetti and Dasyatis zugei are two closely related species and widely distributed along coastal water off China, Japan as well as some Southeast Asian countries. The combination of relative large spatial scale distribution and various habitat preferences of these two are regarded as a good link between the evolutionary history and the geological history of the landscape they occupy. In the present study, we aim to analyze population genetic differentiations and the population demographic history based on the analysis of combined mitochondrial DNA sequences, to understand how these fish responded to the severe climatic oscillations, and to reveal the molecular mechanism of distribution pattern of the two chondrichthyan fishes in Northwestern Pacific by the comparative phylogeography of D. bennetti and D. zugei. This study will fill the blank of understanding of elasmobranchs phylogeography in our country, advance our understanding of batoid elasmobranchs evolution. The results of the study can also provide scientific-based information for batoid elasmobranchs conservation and the fishery management. We hope we can boost regional research capacity and international cooperation on batoid elasmobranchs in the Western Pacific.

软骨鱼类为起源于4亿年前较原始的鱼类，在其进化过程中历经了海洋环境变迁和数次生物大灭绝,是大尺度研究海洋生物地理学的理想物种。在现生1000多种的软骨鱼类中，我国拥有238种软骨鱼类，约占世界总数的四分之一。本研究选取在西北太平洋地理分布上具有典型代表意义、生活史特征不同的黄魟Dasyatis bennetti和尖吻魟Dasyatis zugei为研究对象，利用系统发生生物地理学的理论和研究方法，以线粒体DNA数个基因联合分析魟属鱼类不同种群的遗传结构和种群动态；分别探讨黄魟和尖吻魟分布格局的历史成因及演化历程，比较二者谱系空间分布特征的异同点，从而客观地揭示西北太平洋海域重要地理历史事件对魟属鱼类多个物种分布格局的影响，并为该类群的物种多样性保护、资源可持续利用以及对气候变化的响应等方面提供科学的依据。

本研究以广泛分布于印度洋和西北太平洋的尖嘴魟Dasyatis zugei为研究对象，以筛选得到的10个微卫星位点和线粒体ND2及Cyt b基因同时作为分子标记，对采集自日本、中国大陆沿岸和泰国沿海的6个种群的173个个体进行扩增和测序，并对数据进行分析。本研究在尖嘴魟线粒体ND2和Cyt b基因中分别得到了59个和72个单倍型，总体单倍型多样性分别为0.926和0.953。ND2和Cyt b的总体核苷酸多样性分别为0.0189和0.0213。显示出单倍型多样性和核苷酸多样性都处于较高水平。尖嘴魟微卫星遗传多样性分析结果显示，整体的期望杂合度为在0.835~0.940之间。所有个体的全部等位基因数目为50.22，期望杂合度HE为0.940，观测杂合度HO为0.769，同样显示出较高的遗传多样性。经过54次计算得出29次明显偏离（P值﹤0.05）哈德温伯格平衡，显示出种群较高的偏离哈德温伯格平衡的比率。而近交检测结果显示6个种群都存在一定程度的近交。种群历史动态分析显示：Tajima和Fu's中性检验和Fluctuate计算增长系数g等均发现尖嘴魟种群处于增长状态中。而BEAST计算结果为尖嘴魟在10万年前出现了种群扩张。这可能是由于在间冰期时代，气候温和，海洋环境适宜，尖嘴魟种群有足够的生存空间和食物来源得以生长繁殖。而后大约在3万年前出现了种群分歧。这一时刻与即将进入1.5—2.8万年前的末次盛冰期的时间相吻合。尖嘴魟的种群结构和谱系地理学研究：基于尖嘴魟线粒体基因单倍型构建Network网络关系图，和利用Mega构建系统发生树，结果大致分为两个部分，中国大陆沿岸和日本种群聚为一组，泰国种群聚为一个大支；基于微卫星数据进行Structure聚类分析发现当K=2时，得到最大的ΔK值，这时JP种群与其他种群分离，而K=3时，泰国种群也与其他种群分开。并且Genetix计算种群遗传距离发现该种群与其他种群的遗传距离最远。结合分布和遗传结构特征，以及该物种的生物学特征，安达曼海、泰国湾、中国沿岸以及日本种群应该分别作为独立的保护单元。