中国三江并流区蜉蝣稚虫的分类研究

Mayflies are one of groups of ancient and common aquatic insects, whose nymphs are important bio-indicators for assessments of water quality and river health. The adults have short life span and weekly flight ability. The Three Parallel Rivers Region (TPRR) of the world natural heritage site is the only area that both having the Pacific river system (Mekong River and Yangtze River) and the Indian Ocean river system (Salween River) in China. The peculiar landforms of “three large rivers (Nujiang River, Lancang River and Jinsha River) parallel flow hundreds of kilometers without intersection” effectively restricted the spread and communication of mayflies among the three rivers, become the natural base for studying the isolation and differentiation of the mayfly species. According to the headwater origin hypothesis for aquatic insects, TPRR is likely to be one of centers of mayfly origin and differentiation in Oriental Region. However, the mayfly species diversity is poorly known in the TPRR. This project will focus on morphological taxonomic study with DNA barcode technology as a supplement, and the purposes of the project are: (1) try to ascertain the mayfly species compositions and the mayfly longitudinal distribution pattern along the three rivers by extensively surveys in the region; (2) to analyze mayfly fauna characteristics of three different watersheds in TPRR by means of DNA barcode technology, and (3) to discover and describe new mayfly taxa in TRPP. The results of the project will help to reveal the origin relationship of mayfly fauna between TPRR and its downstream watersheds, and to provide the important basis materials for the studies of mayfly geographical distribution and phylogeny in China as well as the river health assessment of TPRR. It has important scientific value and significance for exploring the mayfly isolation and vicariance as well as the mayfly faunistic specificity in the TPRR, and the origin and evolution of Ephemeroptera in the Oriental Region.

蜉蝣是一类古老而常见的水生昆虫，成虫寿命短且飞行能力弱，其稚虫是评价水质和河流健康的重要指示生物。世界自然遗产地三江并流区是我国唯一兼有太平洋和印度洋水系的地区，其“三江并流数百公里而不相交”的独特地形有效地限制了河流之间蜉蝣的扩散和交流，成为蜉蝣物种隔离与分化的天然基地。根据水生昆虫的河流源头起源假说，三江并流区很可能是东洋区蜉蝣起源与分化中心之一，但该地区蜉蝣的物种组成及分布状况知之甚少。本研究拟以形态分类研究为重点，通过对三江流域蜉蝣稚虫种类的系统调查，力争查清该区域蜉蝣稚虫的物种多样性及纵向分布格局；借助DNA条形码技术分析该地区各流域蜉蝣的区系组成，并建立一批新的分类单元。研究结果有助于揭示该区域与下游流域蜉蝣区系之间的渊源关系，为我国蜉蝣地理分布与系统发育研究及该地区河流健康评价提供基础材料。对探讨该地区蜉蝣物种隔离分化和区系特异性及东洋区蜉蝣的起源与演化具有重要的科学意义。

三江并流区不仅是全世界生态系统类型最多样化的地区之一，也是世界上生物多样性最丰富的热点地区之一。然而，长期以来三江并流区的蜉蝣目种类缺乏全面系统的调查。四年来，本项目对三江并流区及其邻近流域进行了广泛深入的调查，共采获8000多号蜉蝣标本。取得了以下成果：（1）共记述了三江并流区及其邻近流域蜉蝣141种（隶属13科45属），约占中国已知蜉蝣种类的40%。其中21种为中国新纪录种，已发表6个新种，尚有41个新种待发表；四节蜉科是三江并流区种类最丰富的类群，共发现13属63种，其中23个新种和8个中国新纪录种；扁蜉科的物种多样性次之，共发现扁蜉科28种，其中8个新种和10个中国新纪录种；（2）对全国200多个采样点的 316个花翅蜉属标本进行了测序，构建了中国花翅蜉属DNA条形码参考库。分子界定结果表明，中国花翅蜉属共有47种，其中37个为未知种。多基因系统发育分析表明，中国花翅蜉属可分为4个种团，兰坪花翅蜉（B. lanpingensis）、片鬃花翅蜉（B. spathae）和日本花翅蜉（B. japonica）所组成的种团与外群的Baetis、Liebebiella等属关系更密切，建议将其移出花翅蜉属以保持该属的单系性；（3）从全国169个采样点中选取了1130头高翔蜉属标本进行了测序。分子物种界定结果显示，高翔蜉属可划分为50个种，其中43个为未知种。基于COI序列构建的ML树和BI树显示，高翔蜉属中可划分为9个主要支系；（4）从全国53个采样点选取了101个蜉蝣属标本进行COI测序。分子界定结果显示，在本项目选取的标本中，可划分为5个分支29个种（含6个新种）。以绢蜉（Ephemera serica）线粒体基因组作为分子标记，初步探讨了蜉蝣目各科之间的系统发育关系。结果显示，蜉蝣科与河花蜉科和多脉蜉科聚为一支，绢蜉与红纹蜉（Ephemera rufomaculata）亲缘关系最为密切。