Department of Aquatic Animal Medicine, College of Fisheries, Huazhong Agricultural University, Wuhan, Hubei Province, 430070, People's Republic of China.
Hubei Engineering Technology Research Center for Aquatic Animal Diseases Control and Prevention, Wuhan, Hubei Province, 430070, People's Republic of China.
Parasit Vectors. 2018 Jul 9;11(1):399. doi: 10.1186/s13071-018-2943-0.
Myxozoans are a group of cnidarian parasites, the present taxonomy of which favors a more comprehensive characterization strategy combining spore morphology, biological traits (host/organ specificity, tissue tropism), and DNA data over the classical morphology-based taxonomy. However, a systematist might again run into a taxonomic dilemma if more than two of the following exceptional cases were encountered at the same time: extensive intraspecific polymorphism, interspecific morphological similarity, identical interspecific biological traits and blurred small-subunit (SSU) rDNA-based species boundaries. In the present study, spores of a species of Myxobolus Bütschli, 1882 with two morphotypes (wide type and narrow type) were collected from the gills of common carp Cyprinus carpio Linnaeus. Confusingly, the wide type was found to be identical to Myxobolus paratoyamai Kato, Kasai, Tomochi, Li & Sato, 2017 in spore morphology and SSU rDNA sequence, which confidently suggested their conspecificity; while the narrow type, was highly similar to Myxobolus toyamai Kudo, 1917 based on spore morphology and SSU rDNA sequence and thus could not be easily classified. This discordance between wide type and narrow type has caused a taxonomic dilemma. To address this problem, a hypothesis about the conspecificity of the narrow type and M. toyamai was addressed.
It was found that if the narrow type is conspecific with M. toyamai, it would be paradoxical for the SSU rDNA sequence of the narrow type to be more similar to M. paratoyamai (99.3%), Myxobolus acinosus Nie & Li, 1973 (98.6%) and Myxobolus longisporus Nie & Li, 1992 (98.7%) than to M. toyamai (97.6%). According to the results of the above what-if analysis, the narrow type and M. toyamai were considered to be different species. All in all, the present dual-morphotype species is estimated to be conspecific with M. paratoyamai Kato, Kasai, Tomochi, Li & Sato, 2017. Considering that this species name was preoccupied by Myxobolus paratoyamai Nie & Li, 1992, the replacement name Myxobolus pseudoacinosus nom. nov. is proposed.
This work addresses the taxonomic dilemma in polymorphic myxozoans and demonstrates that M. pseudoacinosus is a distinct species with two morphotypes. The present study may serve as a baseline for future studies that encounter similar classification complexities.
粘孢子虫是一类刺胞动物寄生虫，目前的分类学更倾向于采用一种更全面的特征描述策略，将孢子形态、生物学特性（宿主/器官特异性、组织嗜性）和 DNA 数据结合起来，而不是基于经典形态的分类学。然而，如果同时遇到以下两种以上的特殊情况，分类学家可能会再次陷入分类困境：高度的种内多态性、种间形态相似性、相同的种间生物学特性和模糊的小亚基（SSU）rDNA 种间界限。在本研究中，从鲤鱼（Cyprinus carpio Linnaeus）的鳃中采集到粘孢子虫属（Myxobolus Bütschli，1882）的两个形态型（宽型和窄型）的孢子。令人困惑的是，宽型在孢子形态和 SSU rDNA 序列上与 Myxobolus paratoyamai Kato、Kasai、Tomochi、Li 和 Sato，2017 完全相同，这表明它们是同一种；而窄型在孢子形态和 SSU rDNA 序列上与 Myxobolus toyamai Kudo，1917 高度相似，因此难以分类。这种宽型和窄型之间的不匹配导致了分类困境。为了解决这个问题，我们提出了一个关于窄型与 M. toyamai 同物异名的假设。
发现如果窄型与 M. toyamai 是同一种，那么窄型的 SSU rDNA 序列与 M. paratoyamai（99.3%）、Myxobolus acinosus Nie 和 Li，1973（98.6%）和 Myxobolus longisporus Nie 和 Li，1992（98.7%）的相似性比与 M. toyamai（97.6%）更高，这将是自相矛盾的。根据上述假设分析的结果，窄型和 M. toyamai 被认为是不同的物种。总之，目前的双形态型物种被估计与 M. paratoyamai Kato、Kasai、Tomochi、Li 和 Sato，2017 是同一种。考虑到这个种名已经被 Myxobolus paratoyamai Nie 和 Li，1992 抢先使用，因此提出了替代名 Myxobolus pseudoacinosus nom. nov.。
本研究解决了多态性粘孢子虫的分类困境，并证明了 M. pseudoacinosus 是一个具有两种形态型的独特物种。本研究可以为今后遇到类似分类复杂性的研究提供一个基线。
