Myxozoan Hidden Diversity: the Case of Myxobolus Pseudodispar Gorbunova, 1936
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Institute of Parasitology, Biology Centre CAS Folia Parasitologica 2020, 67: 019 doi: 10.14411/fp.2020.019 http://folia.paru.cas.cz Research Article Myxozoan hidden diversity: the case of Myxobolus pseudodispar Gorbunova, 1936 Martina Lisnerová1,2, Petr Blabolil3, Astrid Holzer1, Pavel Jurajda4 and Ivan Fiala1,2 1Institute of Parasitology, Biology Centre of the Czech Academy of Sciences, České Budějovice, Czech Republic; 2Department of Parasitology, Faculty of Sciences, University of South Bohemia, České Budějovice, Czech Republic; 3Institute of Hydrobiology, Biology Centre of the Czech Academy of Sciences, České Budějovice, Czech Republic; 4Institute of Vertebrate Biology of the Czech Academy of Sciences, Brno, Czech Republic Abstract: Myxobolus pseudodispar Gorbunova, 1936 (Myxozoa) was originally described as a parasite of common roach, Rutilus rutilus (Linnaeus), with developing stages in muscles and spores disseminated in macrophage centres of different organs and tissues. Later, this parasite was described from several other cyprinids, but with relatively large intraspecific differences based on SSU rDNA gene sequences. Within our long-term study on myxozoan biodiversity, we performed a broad microscopic and molecular screening of various freshwater fish species (over 450 specimens, 36 species) from different localities. We investigated the cryptic species status of M. pseudodispar. Our analysis revealed four new unique SSU rDNA sequences of M. pseudodispar as well as an infection in new fish host species. Myxobolus pseudodispar sequence analysis showed clear phylogenetic grouping according to fish host criterion forming 13 well-recognised clades. Using 1% SSU rDNA-based genetic distance criterion, at least ten new species of Myxobolus Bütschli, 1882 may be recognised in the group of M. pseudodispar sequences. Our analysis showed the paraphyletic character of M. pseudodispar sequences and the statistical tests rejected hypothetical tree topology with the monophyletic status of the M. pseudodispar group. Myx- obolus pseudodispar represents a species complex and it is a typical example of myxozoan hidden diversity phenomenon confirming myxozoans as an evolutionary very successful group of parasites with a great ability to adapt to a new hosts with subsequent speciation events. Keywords: Myxozoa, phylogeny, PCR screening, cryptic species, host specificity. The Myxozoa is a diverse group of endoparasites with hosts (e.g., Liu et al. 2019, Rocha et al. 2019). The diver- a worldwide distribution numbering more than 2,600 de- sity success of the Myxobolus is assumed to be caused by scribed species, which represents approx. 20% of cnidari- the shape of spores with lateral flattening that enabled eas- ans (Okamura et al. 2015, 2018). However, much of myxo- ier invasion of tissues from precursors that lived in body zoan biodiversity appears to be hidden (Bartošová-Sojková liquids and cavities. Therefore, they could colonise many et al. 2014, Hartikainen et al. 2016). Their complex life types of tissues (Fiala et al. 2015). Species of Myxobolus cycle involves two hosts: invertebrates (Oligochaeta, constitute the largest clade in the phylogenetic tree branch- Polychaeta and Bryozoa) as a definitive host, and verte- ing within the oligochaete-infecting lineage of myxozoans brates (mainly fish, rarely amphibians, reptiles, birds or (Holzer et al. 2018). However, it is a paraphyletic taxon mammals) as an intermediate host (Okamura et al. 2015). with Henneguya Thélohan, 1892; Thelohanellus Kudo, Myxozoan infections in fish are frequently inconspicuous; 1933; Unicauda Davis, 1944; Cardimyxobolus Ma, Dong however, several myxozoans are highly pathogenic for et Wang, 1982 and species of Hennegoides Lom, Tonguthai their hosts causing whirling disease or proliferative kidney et Dyková, 1991 clustering with species of Myxobolus (see disease in salmonid fish (Hedrick et al. 1993, Gilbert and Fiala 2006, Liu et al. 2019). Granath 2003). The genus Myxobolus is morphologically characterised Myxobolus Bütschli, 1882 is the largest genus of the by ovoid or rounded spores with smooth shell valves and Myxozoa with more than 850 described species (Eiras et with two mostly pyriform, sometimes unequal polar cap- al. 2005, 2014). Species of Myxobolus have been reported sules (Lom and Dyková 2006). Myxospore valve projec- from fish worldwide (e.g., Carriero et al. 2013, Lövy et al. tions (appendages) typical for species of Henneguya, Uni- 2018, Folefack et al. 2019). They infect mostly freshwater cauda and Hennegoides appeared or have been lost several fish but they have been found also in brackish and marine times independently in myxobolid evolution (Liu et al. Address for correspondence: Ivan Fiala, Biology Centre of ASCR, Institute of Parasitology, and Faculty of Science, University of South Bohemia, Branišovská 31, České Budějovice, 37005, Czech Republic. Phone: +420387775450; Fax.: +420385310388; E-mail: [email protected] This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. doi: 10.14411/fp.2020.019 Lisnerová et al.: Hidden diversity of Myxobolus pseudodispar 2019) similarly as a loss of one of the polar capsules, the al. (2018) suggested that SSU rDNA difference as low as trait characteristic for species of the genus Thelohanellus 2.4% does not necessarily define conspecificity. (see Zhang et al. 2019). In the present study, we aimed to analyse data from It has been proved many times by phylogenetic analyses a large-scale screening of freshwater fishes to resolve the based on molecular data that molecular taxonomy of the ge- cryptic species status of M. pseudodispar. We assess the nus Myxobolus and other myxozoan genera does not entirely host specificity of each M. pseudodispar clade and trace reflect morphological similarities of myxozoan spores. Phy- the myxospore morphology of M. pseudodispar and relat- logenetic relationships rather correlate with host environ- ed species on the evolutionary tree. ment, host and host tissues preferences (Andree et al. 1999, Kent et al. 2001, Eszterbauer 2004, Fiala 2006, Fiala and MATERIALS AND METHODS Bartošová 2010, Holzer et al. 2018). Although a study by Salim and Desser (2000) demonstrated clustering of species Sample collection and light microscopy of Myxobolus according to the morphology of the spores, During our large-scale research on the biodiversity of myxo- analysis by Andree et al. (1999) and Eszterbauer (2004) re- zoan parasites of freshwater fish in Europe, overall, 452 fish (36 ported relationships based on the site of infection. Host-as- species from different fish orders) were collected in ponds, dams sociated phylogenetic pattern of Myxobolus spp. has been and rivers in the Czech Republic (408) and in the Danube River suggested by Carriero et al. (2013) as well as by Liu et al. (44) in Bulgaria during the years 2016–2018. Host species num- (2019), who made a comprehensive analysis of all available bers are summarised in Supplementary Table 1. sequences of SSU rDNA of Myxobolus spp. Fish from the Czech Republic were parasitologically exam- Myxobolus pseudodispar Gorbunova, 1936 was origi- ined using light microscopy (Olympus BX51 microscope) at nally described as a common myxozoan parasite of com- 400× magnification to detect the presence of spores, plasmodia mon roach (Rutilus rutilus [Linnaeus]) with developing or other development stages of Myxozoa in gills, kidney and gall stages in muscles and spores disseminated in macrophage bladder. Other host tissues were not included in the examination, centres of different organs and tissues. Since the original and therefore myxosporean plasmodia in muscles or skin could description, M. pseudodispar has been documented from not be formed. Digital photos of fresh spores were taken at 1000× different organs (gills, kidney, liver, muscle, skin and magnification using an Olympus DP70 camera. Spores were spleen) of many cyprinids e.g., Abramis brama (Linneaus); measured from digital images using ImageJ 1-48q (Wayne Ras- Alburnus alburnus (Linnaeus); Blicca bjoerkna (Lin- band, http://imagej.nih.gov/ij). Gills, kidneys and gall bladders naeus); Pseudochondrostoma polylepis (Steindachner); of fish from Bulgaria were fixed only for molecular processing. Squalius squalus (Bonaparte); Achondrostoma arcasii (Steindachner); Scardinius erythrophthalmus (Linnaeus) DNA isolation, PCR, cloning and sequencing (Gorbunova 1936, Gonzalez-Lanza and Alvarez-Pellitero All obtained fish tissue samples were kept in 400 μl of TNES 1985, Baska 1987, Eszterbauer et al. 2001, Székely et al. urea buffer (10 mM Tris-HCl with pH 8; 125 mM NaCl; 10 mM 2001, Molnár et al. 2002). EDTA; 0.5% SDS and 4 M urea). Genomic DNA extraction was Spores of M. pseudodispar are ovoid or rounded with an performed by standard phenol-chloroform extraction method irregular shape. Unequal polar capsules are located laterally with four-hour digestion with proteinase K (50 μg ml-1 180; Ser- from the longitudinal axis of the spore, which is the charac- va, Heidelberg, Germany) at 55 °C and final elution in 100 μl of ter distinguishing M. pseudodispar from morphologically DNAse-free water (Holzer et al. 2004). very similar Myxobolus dispar (Gorbunova 1936). Myxo- We screened all obtained DNA samples for myxozoan infec- bolus pseudodispar was considered as a junior synonym of tion