Li Ju, Zhan Zifeng, Xu Kuidong
Department of Marine Organism Taxonomy & Phylogeny, Institute of Oceanology, Chinese Academy of Sciences, Qingdao, 266071, China.
Laboratory for Marine Biology and Biotechnology, Qingdao National Laboratory for Marine Science and Technology, Qingdao, 266071, China.
J Eukaryot Microbiol. 2017 Nov;64(6):850-872. doi: 10.1111/jeu.12420. Epub 2017 May 23.
A still challenging study on ciliate systematics is to clarify the taxonomic and phylogenetic confusions of the fascinating pigmented Pseudokeronopsis species because of their high interspecific similarities. We evaluated the identities and internal relationships within Pseudokeronopsis based on morphological descriptions in combination with the 18S and ITS-5.8S rDNA genetic distances, ITS2 secondary structures and phylogenetic analyses. Results showed that (1) Pseudokeronopsis pararubra, a species ever synonymized as Pseudokeronopsis carnea, is a valid species; (2) most Chinese populations identified as Pseudokeronopsis rubra represent a new species namely Pseudokeronopsis songi sp. nov.; (3) within Pseudokeronopsis, P. carnea branched early, while P. songi sp. nov., P. flava, and P. erythrina showed close relationships and formed a sister clade with P. pararubra; (4) compared to 18S and ITS2 rDNA, ITS-5.8S rDNA is more suitable for separating Pseudokeronopsis species, with pairwise distances of 0-0.0441 at the intraspecific level and 0.0635-0.1150 at the interspecific level; and (5) the core structure of Pseudokeronopsis ITS2 includes three helices, with helix III being the longest and showing an identical pattern in conspecific populations and small differences among species. Based on the evaluation, we clarify all misidentified and dubious 18S and ITS-5.8S rDNA sequences of Pseudokeronopsis in GenBank.
对纤毛虫系统学来说，一项仍具挑战性的研究是澄清迷人的色素伪角毛虫属物种的分类学和系统发育混乱，因为它们种间相似度很高。我们结合形态学描述以及18S和ITS-5.8S rDNA遗传距离、ITS2二级结构和系统发育分析，评估了伪角毛虫属内的物种身份和内部关系。结果表明：（1）曾被同义化为肉色伪角毛虫的副红伪角毛虫是一个有效物种；（2）大多数被鉴定为红色伪角毛虫的中国种群代表一个新物种，即宋氏伪角毛虫新种；（3）在伪角毛虫属内，肉色伪角毛虫分支较早，而宋氏伪角毛虫新种、黄色伪角毛虫和红色伪角毛虫显示出密切关系，并与副红伪角毛虫形成一个姐妹分支；（4）与18S和ITS2 rDNA相比，ITS-5.8S rDNA更适合区分伪角毛虫属物种，种内成对距离为0-0.0441，种间成对距离为0.0635-0.1150；（5）伪角毛虫属ITS2的核心结构包括三个螺旋，其中螺旋III最长，在同种种群中显示出相同模式，物种间存在微小差异。基于该评估，我们澄清了GenBank中所有错误鉴定和可疑的伪角毛虫属18S和ITS-5.8S rDNA序列。
