角毛藻属硅藻的种类多样性和分子系统学研究

Chaetoceros Ehrenberg is a very species-rich diatom genus with more than 500 described taxonomic units, mainly based on morphological features, although it is assumed that only a fraction “no more than one-third to one-half” is still valid. Meanwhile our present knowledge about some key Chaetoceros taxa is insufficient, and the reexamination is needed. Chaetoceros species are globally distributed and are ecologically important as they often make up a major part of the phytoplankton community and form blooms. They are therefore an excellent choice as model species to study the species diversity of diatoms. Routine examination of Chaetoceros species relies presently mainly on the morphology. But some key characters are shown to be varied, so the morphological taxonomy of Chaetoceros has thus become more difficult and challenging. Moreover, recent phylogenetic analyses inferred from 28S rDNA sequences have indicated the existence of several well-supported clades in this group, but proved less successful in resolving the within-clade relationships. So far, the paraphyly of Chaetoceros is strongly supported, and better resolution of the within-group relationships may be possible based on the combination of morphology and molecular data from more and more Chaetoceros strains. .In present proposal, the taxonomy and systematic studies of Chaetoceros species are recommended to be conducted based on the combination of morphological methods and molecular analyses synchronously. On one hand, following contents and aims will be achieved using morphological methods: (1) Establish a detailed morphological database of Chaetoceros taxa, including on vegetative cells and resting spores; (2) Clarify the variations of some key morphological characters and analyse their stability within taxa; (3) Reestimate the taxonomic values of key morphological characters for delineation of taxa; (4) Establish/verify the morphological taxonomical criteria among Chaetoceros species and the systematic relationships within Chaetoceros based on morphological data. Simultaneously, molecular phylogenetic analyses will be carried out based on different target genes from the chloroplast and nuclear genomes, such as SSU, LSU, ITS, rbcL, etc. Finally, the following key taxonomic and systematic questions will be answered through the combination and comparison between morphological data and molecular results: (1) How many different paraphyletic clades exist in Chaetoceros and Chaetocerotaceae; (2) Which morphological characters reveal shared derived traits in the morphological and molecular trees and which ones show mainly homoplasy; (3) Does morphologically perceived species constitute clades and (4) Do these clades contain genetically distinct groups of specimens. Above studies will provide progress and important new knowledge in the taxonomy and systematics of Chaetoceros, and may hence serve as a baseline study for future studies.

角毛藻是全球海域常见的优势浮游植物和藻华生物。该属种类繁多，已报道500多个分类单位，但普遍认为只有1/3至1/2的种名是有效的，需要开展二次研究和修订工作。本项目拟以角毛藻及其系统学邻近属种为研究对象，采用形态学和分子生物学技术相结合的手段开展分类学和系统学的专题研究。一方面，利用形态学方法研究营养细胞和休眠孢子的特征，建立完善的形态学数据库和图像资料库，充分研究关键特征，并评估其分类学价值，筛选有效而稳定的特征，建立基于形态学的分类标准和系统关系；另一方面，利用基因序列分析等分子生物学技术开展分子分类学和分子系统学研究，构建系统进化发育树。最后，综合考虑形态学和分子生物学的结论，澄清角毛藻属内现存的多个系统学类群，提炼各个类群的共享特征，明确模式物种，构建分类依据和分类标准，对现有分类学和系统学体系进行修订，澄清同种异名，以及重要种类的分类学信息，并对（拟）隐形种进行二次研究和修订。

项目执行期间，共计参加了15个国家基金委共享航次，覆盖渤海、黄海、长江口、东海、台湾海峡和南海北部海域，此外还在中国沿海设计了多个站位，从北到南涵盖我国沿海的不同地理区域，以及不同生境区域，定期开展活体样品采集工作，共采集自然水样300余份。利用毛细管显微操作法，共计建立隶属于41个角毛藻物种的821个培养株系。结合光镜和电镜下的形态学观察，以及基于核糖体大亚基和小亚基的分子生物学数据，开展了形态特征二次评估、物种信息界定、多样性澄清、相似物种划分、系统学归类等工作。分子系统学结论发现：（1）以往依据角毛是否含有色素而建立的亚属中，有色角毛亚属的种类相对集中在一个分枝上，表现出较好的单一起源，但是无色角毛亚属的种类却聚类在三个分枝上，表现出较为丰富的多起源；（2）以往“单纯依据某些相似形态学特征来划分亚属之下组”的方法是不准确的，需要二次研究或修订。本项目对洛氏角毛藻复合群、窄隙角毛藻复合群、柔弱角毛藻复合群等重要类群进行了专题研究，廓清了关键物种的鉴定信息，如并基角毛藻、窄隙角毛藻和柔弱角毛藻，报道了优美角毛藻、平孢角毛藻、曼纳角毛藻、稀疏角毛藻、容纳角毛藻、美丽角毛藻、千足角毛藻、二叉角毛藻、短刺角毛藻、钢盔角毛藻等10余个新种，修订了华丽角毛藻、异常角毛藻、威尔角毛藻等多个已知物种，明确了短孢角毛藻和拟短孢角毛藻的物种差异，评估了相邻角毛基“并行融合”特征的分类学价值。本项目丰富和重塑了重要角毛藻物种的分类学信息，丰富了该属的物种多样性，厘清了相似物种之间的分类界限，构建了该属的系统学关系，可为角毛藻相关研究提供重要而准确的物种信息。