Morphological plasticity in Myxobolus Bütschli, 1882: a taxonomic dilemma case and renaming of a parasite species of the common carp

Abstract

BackgroundMyxozoans 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.ResultsIt 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.ConclusionsThis 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.Electronic supplementary materialThe online version of this article (10.1186/s13071-018-2943-0) contains supplementary material, which is available to authorized users.

Molecular Detection, Histopathology, and Scanning Electron Microscopy of Myxobolus koi Infecting Cyprinus carpio Koi

“…One of the symptoms of Myxobolus koi infections in Koi carp is the appearance of parasite cysts in the gills [32]. The fish were in fair physical condition, though the gills were characterized grossly by widespread, multifocal coalescence, with 2-3 mm nodular white foci [9, 33,34].…”

“…The gills function as a breathing apparatus, but also function to regulate the exchange of salt and water between the body and the environment and play a role in removing nitrogen-containing wastes [34,35,36]. Structural damage in the gills of fish very much influences the regulation of osmosis, disrupting breathing and osmoregulation processes of fish [37,38].…”

“…Molecular Detection, Histopathology and SEM of Myxobolus koi (Soelistyoadi, et al) several studies confirmed the importance of molecular features, and in some cases, they have been found to correlate with the results of molecular data based on the 18S rDNA sequence comparison [34,43]. PCR testing with specific primers in the DNA template amplification process will only display the appropriate band.…”

Myxozoan hidden diversity: the case of Myxobolus pseudodispar Gorbunova, 1936

“…The large diversity of species of Myxobolus together with a very simple myxospore morphology as the main taxonomic criterion is the cause of difficulties in the identification species of Myxobolus. Some myxosporeans may display a certain degree of myxospore polymorphism in the shape and size (Guo et al 2018), which makes the myxosporean taxonomy even more problematic.…”

“…Moreover, the study of Molnár et al (2002) indicated that morphologically similar species of Myxobolus from different fishes seem to be different species. In contrast, Guo et al (2018) suggested that SSU rDNA difference as low as 2.4% does not necessarily define conspecificity.…”