Key Laboratory of the Ministry of Education for Coastal and Wetland Ecosystem, College of the Environment and Ecology, Xiamen University, , Xiamen 361102, People's Republic of China, Department of Biology, North Carolina Central University, , Durham, NC 27707, USA, State Key Laboratory of Marine Environmental Science, College of Ocean and Earth Sciences, Xiamen University, , Xiamen 361005, People's Republic of China, Department of Biological Sciences, University of Ulsan, , Ulsan 680-749, Korea.
Proc Biol Sci. 2013 Oct 2;280(1771):20131177. doi: 10.1098/rspb.2013.1177. Print 2013 Nov 22.
Vorticella includes more than 100 currently recognized species and represents one of the most taxonomically challenging genera of ciliates. Molecular phylogenetic analysis of Vorticella has been performed so far with only sequences coding for small subunit ribosomal RNA (SSU rRNA); only a few of its species have been investigated using other genetic markers owing to a lack of similar sequences for comparison. Consequently, phylogenetic relationships within the genus remain unclear, and molecular discrimination between morphospecies is often difficult because most regions of the SSU rRNA gene are too highly conserved to be helpful. In this paper, we move molecular systematics for this group of ciliates to the infrageneric level by sequencing additional molecular markers-fast-evolving internal transcribed spacer (ITS) regions-in a broad sample of 66 individual samples of 28 morphospecies of Vorticella collected from Asia, North America and Europe. Our phylogenies all featured two strongly supported, highly divergent, paraphyletic clades (I, II) comprising the morphologically defined genus Vorticella. Three major lineages made up clade I, with a relatively well-resolved branching order in each one. The marked divergence of clade II from clade I confirms that the former should be recognized as a separate taxonomic unit as indicated by SSU rRNA phylogenies. We made the first attempt to elucidate relationships between species in clade II using both morphological and multi-gene approaches, and our data supported a close relationship between some morphospecies of Vorticella and Opisthonecta, indicating that relationships between species in the clade are far more complex than would be expected from their morphology. Different patterns of helix III of ITS2 secondary structure were clearly specific to clades and subclades of Vorticella and, therefore, may prove useful for resolving phylogenetic relationships in other groups of ciliates.
钟形虫包括 100 多种目前公认的物种，是纤毛类中分类最具挑战性的属之一。迄今为止，对钟形虫的分子系统发育分析仅使用了编码小亚基核糖体 RNA（SSU rRNA）的序列；由于缺乏类似的序列进行比较，只有少数几个物种使用其他遗传标记进行了研究。因此，属内的系统发育关系仍不清楚，而且由于 SSU rRNA 基因的大多数区域高度保守，因此很难进行形态种之间的分子区分。在本文中，我们通过对来自亚洲、北美和欧洲的 28 个形态种的 66 个个体样本的额外分子标记（快速进化的内部转录间隔区（ITS）区域）进行测序，将该纤毛类群的分子系统发育推向了种下水平。我们的系统发育树都具有两个强烈支持的、高度分化的并系分支（I、II），包含了形态定义的钟形虫属。I 分支由三个主要谱系组成，每个谱系的分支顺序都相对清晰。II 分支与 I 分支的明显分歧证实了前者应被视为一个单独的分类单元，这与 SSU rRNA 系统发育一致。我们首次尝试使用形态学和多基因方法阐明 II 分支内种间的关系，我们的数据支持了一些钟形虫种与 Opisthonecta 之间的密切关系，表明该分支内的种间关系比从形态学上预期的要复杂得多。ITS2 二级结构的 III 螺旋的不同模式明显是钟形虫的分支和亚分支特有的，因此可能对解决其他纤毛类群的系统发育关系有用。
