我国新记录海链藻属物种的形态学和系统学研究

THE MORPHOLOGICAL AND PHYLOGENETIC STUDIES ON TWO NEWLY RECORDED THALASSIOSIRA SPECIES FROM CHINA

  • 摘要: 为了廓清我国海链藻属的物种多样性, 并丰富其分子生物学信息, 为后续的系统学研究提供基础数据, 从我国沿海分离并建立了海链藻的单克隆培养株系, 利用光学显微镜和电镜技术进行了形态学研究, 同时还对其核糖体大亚基的高变区序列进行了扩增和测序分析。结合形态学和分子生物学数据, 鉴定了我国海链藻属的2个新记录种: 狭线形海链藻Thalassiosira anguste-lineata (Schmidt) Fryxell & Hasle和碟形海链藻T. minicosmica Lee & Park。对它们的形态学特征进行了较为详尽的描述, 并与相似种进行了比较研究。此外, 还基于核糖体大亚基高变区的碱基序列信息, 分析了它们的分子系统学位置。在分子系统树上, 狭线形海链藻和碟形海链藻均不与该属模式种——诺氏海链藻T. nordenskioeldii 聚在同一分支上, 显示它们与典型海链藻属物种之间具有较大的遗传差异。分子系统树还显示, 目前基于形态学建立的海链藻属并非自然类群, 而是被骨条藻属Skeletonema、小环藻属Cyclotella、漂流藻属Planktoniella等邻近属种分隔成多个分支, 这预示着现存的海链藻属应该是一个并系类群, 在后续的系统学研究中, 或许会有较大的系统学调整, 但目前有限的分子生物学信息是相关研究推进的重要限制。

     

    Abstract: To investigate the species diversity of Thalassiosira in China and provide molecular data for further phylogenetic studies, monoclonal strains have been isolated and established from some representative sites in Chinese coast. The morphology was studied using light and electron microscopy, and the hypervariable D1‒D3 region of the nuclear large subunit ribosomal RNA-encoding gene region (LSU rRNA gene) was amplified and sequenced. Two newly recorded Thalassiosira species (T. anguste-lineata (Schmidt) Fryxell & Hasle and T. minicosmica Lee & Park) for China were reported based on the combination of morphology and molecular data. Their detailed morphology were described and compared with allied taxa. The results of molecular phylogenetic tree based on sequences data of D1—D3 region of LSU rRNA indicated that neither T. anguste-lineata nor T. minicosmica were clustered with T. nordenskioeldii, the type species of the genus Thalassiosira, suggesting great genetic difference is present among Thalassiosira taxa, and that the present morphology-based genus Thalassiosira is not a natural group because it is separated by some other allied genus, such as Skeletonema, Cyclotella, Planktoniella. These results revealed that the present reported Thalassiosira species should be paraphyletic group and will be gradually revised into multiple independent genera in future phylogenetic study. However, it is difficult to carry out specific taxonomic revisions because of limited molecular data that is an important constraint for the advancement of related researches.

     

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