Kim Taeho, Lee Yucheol, Kil Hyun-Jong, Park Joong-Ki
Division of EcoScience, Ewha Womans University, Seoul, Republic of Korea.
Animal Resources Division, National Institute of Biological Resources, Incheon, Republic of Korea.
PeerJ. 2020 May 13;8:e9108. doi: 10.7717/peerj.9108. eCollection 2020.
The infraorder Cephalobomorpha is a diverse and ecologically important nematode group found in almost all terrestrial environments. In a recent nematode classification system based on SSU rDNA, Cephalobomorpha was classified within the suborder Tylenchina with Panagrolaimomorpha, Tylenchomorpha and Drilonematomorpha. However, phylogenetic relationships among species within Tylenchina are not always consistent, and the phylogenetic position of Cephalobomorpha is still uncertain. In this study, in order to examine phylogenetic relationships of Cephalobomorpha with other nematode groups, we determined the complete mitochondrial genome sequence of , the first sequenced representative of Cephalobomorpha, and used this sequence for phylogenetic analyses along with 101 other nematode species. Phylogenetic analyses using amino acid and nucleotide sequence data of 12 protein-coding genes strongly support a sister relationship between the two cephalobomorpha species and (represented by a partial mt genome sequence) In this mitochondrial genome phylogeny, Cephalobomorpha was sister to all chromadorean species (excluding of Plectida) and separated from Panagrolaimomorpha and Tylenchomorpha, rendering Tylenchina non-monophyletic. Mitochondrial gene order among Tylenchina species is not conserved, and gene clusters shared between and . are very limited. Results from phylogenetic analysis and gene order comparison confirms Tylenchina is not monophyletic. To better understand phylogenetic relationships among Tylenchina members, additional mitochondrial genome information is needed from underrepresented taxa representing Panagrolaimomorpha and Cephalobomorpha.
头叶亚目是一个多样且在生态上具有重要意义的线虫类群，几乎存在于所有陆地环境中。在最近基于小亚基核糖体DNA的线虫分类系统中，头叶亚目与泛绕线亚目、垫刃亚目和钻线虫亚目一同被归类于垫刃下目。然而，垫刃下目内物种间的系统发育关系并不总是一致的，头叶亚目的系统发育位置仍然不确定。在本研究中，为了研究头叶亚目与其他线虫类群的系统发育关系，我们测定了头叶亚目的首个测序代表物种—— 的完整线粒体基因组序列，并将该序列与其他101种线虫物种一起用于系统发育分析。使用12个蛋白质编码基因的氨基酸和核苷酸序列数据进行的系统发育分析有力地支持了两个头叶亚目物种 和 （由部分线粒体基因组序列代表）之间的姐妹关系。在这个线粒体基因组系统发育中，头叶亚目是所有色矛线虫物种（不包括链环线虫目的 ）的姐妹群，并且与泛绕线亚目和垫刃亚目分开，这使得垫刃下目并非单系类群。垫刃下目物种间的线粒体基因顺序并不保守，并且 和 之间共享的基因簇非常有限。系统发育分析和基因顺序比较的结果证实垫刃下目并非单系类群。为了更好地理解垫刃下目成员间的系统发育关系，需要从代表泛绕线亚目和头叶亚目的代表性不足的分类单元中获取更多线粒体基因组信息。
