Redescription of Paradiplozoon hemiculteri (Monogenea, Diplozoidae) from the type host Hemiculter leucisculus, with neotype designation

Diversity, phylogeny and intraspecific variability of Paradiplozoon species (Monogenea: Diplozoidae) parasitizing endemic cyprinoids in the Middle East

Diplozoidae are common monogenean ectoparasites of cyprinoid fish, with the genus Paradiplozoon being the most diversified. Despite recent studies on Diplozoidae from Europe, Africa and Asia, the diversity, distribution and phylogeny of this parasite group appears to be still underestimated in the Middle East. The objective of this study was to investigate the diversity, endemism and host specificity of diplozoids parasitizing cyprinoid fish from the Middle East, considering this region as an important historical interchange of fish fauna, and to elucidate the phylogenetic position of Middle Eastern Paradiplozoon species within Diplozoidae. Four Paradiplozoon species were collected from 48 out of 94 investigated cyprinoid species. Three known species, Paradiplozoon homoion, Paradiplozoon bliccae and Paradiplozoon bingolensis, were recorded on new cyprinoid host species, and a new species, Paradiplozoon koubkovae n. sp., was recorded on Luciobarbus capito and Capoeta capoeta from the Caspian Sea basin in Iran and Turkey. Paradiplozoon bliccae, exhibiting a wide host range in the Middle East, expressed both morphological and genetic intraspecific variabilities. The four Paradiplozoon species collected in the Middle East were placed in divergent clades, showing the rich evolutionary history of diplozoid parasites in the Middle East. Our study also revealed that two lineages of African diplozoids have a Middle Eastern origin. We stress the importance of applying an integrative approach combining morphological, ecological and molecular methods to reveal the real diversity of diplozoids.

The complete mitochondrial genomes of Paradiplozoon yarkandense and Paradiplozoon homoion confirm that Diplozoidae evolve at an elevated rate

BACKGROUND

Diplozoidae are monogenean (Monogenea: Polyopisthocotylea) fish parasites characterised by a unique life history: two larvae permanently fuse into an X-shaped "Siamese" organism. Taxonomy and phylogeny of Diplozoidae and Polyopisthocotylea remain unresolved due to the unavailability of molecular markers with sufficiently high resolution. Mitogenomes may be a suitable candidate, but there are currently only 12 available for the Polyopisthocotylea (three for Diplozoidae). The only available study of diplozoid mitogenomes found unique base composition patterns and elevated evolution rates in comparison with other Monogenean mitogenomes.

METHODS

To further explore their evolution and generate molecular data for evolutionary studies, we sequenced the complete mitogenomes of two Diplozoidae species, Paradiplozoon homoion and Paradiplozoon yarkandense, and conducted a number of comparative mitogenomic analyses with other polyopisthocotyleans.

RESULTS

We found further evidence that mitogenomes of Diplozoidae evolve at a unique, elevated rate, which was reflected in their exceptionally long branches, large sizes, unique base composition, skews, and very low gene sequence similarity levels between the two newly sequenced species. They also exhibited remarkably large overlaps between some genes. Phylogenetic analysis of Polyopisthocotylea resolved all major taxa as monophyletic, and Mazocraeidea was split into two major clades: (Diplozoidae) + (all four remaining families: Diclidophoridae, Chauhaneidae, Mazocraeidae and Microcotylidae). It also provided further confirmation that the genus Paradiplozoon is paraphyletic and requires a taxonomic revision, so the two species may have to be renamed Indodiplozoon homoion and Diplozoon yarkandense comb. nov.

CONCLUSIONS

Although our findings indicate that mitogenomes may be a promising tool for resolving the phylogeny of Polyopisthocotylea, elevated evolutionary rates of Diplozoidae may cause phylogenetic artefacts, so future studies should pay caution to this problem. Furthermore, as the reason for their elevated evolution remains unknown, Diplozoidae are a remarkably interesting lineage for other types of evolutionary mitogenomic studies.

A New Species of Paradiplozoon (Monogenea: Diplozoidae), A Gill Parasite of the Schizothorax Fish (Cyprinidae: Schizothoracinae) from the Yarkand River, Xinjiang, China

INTRODUCTION

Monogeneans of the genus Paradiplozoon were found on the gills of specimens of five species of schizothoracid caught using fyke nets in the upper stream of the Yarkand River, Xinjiang, China in May-August 2019.

METHODS

The preserved parasite were stained with boric acid magenta and hematoxylin, respectively. Morphological observations, line drawings, photomicrographs and measurements were made in Nikon ECLIPSE E200 imaging optical microscope and digitally edited. The molecular analysis included the study of the sequence of the second internal transcribed spacer (ITS 2) of the ribosomal DNA region, calculation and analysis of genetic distance, with phylogenetic reconstructions based on the Bayesian inference and Maximum Likelihood analysis.

RESULTS

The natural infection rate of host fish was 10-88%. Morphological analysis indicated that the average length of the new species was 2.125 mm while the width was 0.69 mm. The anterior part was 1.387 mm in length and the average length of the posterior part was 0.545 mm. The vitellaria was well-developed and located in the front of the body. A single ovary (oval shaped) was located at the back end of the reproductive binding area. A testis (irregular mass) was located behind or parallelled to the ovary. The new species can be distinguished from all the recorded Paradiplozoon species in terms of morphological characteristics such as haptor, clamp and central hook morphology, intestine shape and body size. In addition, the second internal transcribed spacer (ITS 2) of the ribosomal DNA region of the diplozoid was compared with that of known diplozoids previously published. It indicated that there were significant differences between the new species and the published diplozoids.

CONCLUSION

Both morphological and molecular analysis support that the diplozoid is a new species. Based on the sampling location, the new species was named Paradiplozoon yarkandense n. sp.

Redescription of Paradiplozoon opsariichthydis (Jiang, Wu et Wang 1984) Jiang, Wu et Wang, 1989 (Monogenea, Diplozoidae)

Paradiplozoon opsariichthydis (Jiang, Wu et Wang, 1984) Jiang, Wu et Wang, 1989 (Platyhelminthes, Monogenea, Diplozoidae) is blood-feeding parasite from the gills of Asian cyprinid fish Opsariichthys bidens Günther, 1873. In this study, we present a morphological redescription of P. opsariichthydis neotype main morphological features e.g. size of body and clamps due to the fact that the type material is missing. We decided to supplement morphological descriptions by the relevant molecular data (internal transcribed spacer - ITS2) related to P. opsariichthydis adult worm isolates and other representatives of genus Paradiplozoon to cross verify our findings. In addition to that, this study also brings an attention to the host identification. Thus, parasite data were complemented by the determinant cytochrome oxidase b (cytb) sequences of its hosts. All novel sequences are deposited in GenBank. This combination of the morphological and molecular data related to both the parasite and its host seems to be the optimal approach to the general process of (re)description of highly host-specific parasitic organisms, which can then lead to a meaningful phylogenetic analysis.

Diversity and phylogeny of Paradiplozoon species (Monogenea: Diplozoidae) parasitising endemic cyprinoids in the peri-Mediterranean area, with a description of three new Paradiplozoon species

The Diplozoidae are monogenean parasites of mainly cyprinoid fishes with a unique life cycle, whereby two larvae undergo anastomosis and fuse into a single cross-shaped specimen. Paradiplozoon is the most species rich and widespread genus of the family, with a distribution range covering Eurasia and Africa; however, some areas remain underexplored and their diplozoid fauna is uncertain. In the present study, the Paradiplozoon diversity was investigated in the peri-Mediterranean region, which has the highest levels of cyprinoid diversity and endemism in Europe. A total of 36 endemic cyprinoid species were sampled from sites in north-west Africa and the southern European peninsulas and investigated for the presence of diplozoid parasites. Of five Paradiplozoon species collected, three were identified as new to science: Paradiplozoon moroccoensis n. sp. from the Moroccan endemic Luciobarbus lepineyi; Paradiplozoon ibericus n. sp. from Iberian endemic cyprinids and leuciscids and Paradiplozoon helleni n. sp. from the Greek endemic Scardinius acarnicus and Tropidophoxinellus hellenicus (descriptions provided herein). In addition, new host records for P. homoion and P. megan are presented, with the former being most prevalent in the investigated region. Phylogenetic analysis supported paraphyly of the genus Paradiplozoon, and suggests the need for a careful taxonomic re-evaluation of this genus. Furthermore, the results showed that endemic Paradiplozoon of the peri-Mediterranean do not form a monophyletic group, suggesting multiple origins of this parasite groups in different peri-Mediterranean regions.

Review on the molecular study of the Diplozoidae: analyses of currently available genetic data, what it tells us, and where to go from here

The use of molecular tools in the study of parasite taxonomy and systematics have become a substantial and crucial component of parasitology. Having genetic characterisation at the disposal of researchers has produced mostly useful, and arguably more objective conclusions. However, there are several groups for which limited genetic information is available and, coupled with the lack of standardised protocols, renders molecular study of these groups challenging. The Diplozoidae are fascinating and unique monogeneans parasitizing mainly freshwater cyprinid fishes in Europe, Asia and Africa. This group was studied from a molecular aspect since the turn of the century and as such, limitations and variability concerning the use of these techniques have not been clearly defined. In this review, all literature and molecular information, primarily from online databases such as GenBank, were compiled and scrupulously analysed for the Diplozoidae. This was done to review the information, detect possible pitfalls, and provide a "checkpoint" for future molecular studies of the family. Hindrances detected are the availability of sequence data for only a limited number of species, frequently limited to a single sequence per species, and the heavy reliance on one non-coding ribosomal marker (ITS2 rDNA) which is difficult to align objectively and displays massive divergences between taxa. Challenging species identification and limited understanding of diplozoid species diversity and plasticity are also likely restricting factors, all of which hamper the accurate taxonomic and phylogenetic study of this group. Thus, a more integrated taxonomic approach through the inclusion of additional markers, application of more rigorous morphological assessment, more structured barcoding techniques, alongside thorough capturing of species descriptions including genetypes, genophore vouchers and reference collections in open sources are encouraged. The pitfalls highlighted are not singular to the Diplozoidae, and the study of other groups may benefit from the points raised here as well.

Cytogenetics of Eudiplozoon nipponicum (Monogenea, Diplozoidae): Karyotype, spermatocyte division and 18S rDNA location

Ectoparasitic monogeneans of the family Diplozoidae have direct and monoxenous life cycle. The cytogenetics of monogeneans in general and diplozoids in particular, is a relatively underexplored area. This is why each new detailed description of a karyotype provides significant information about the evolution of monogenean chromosomes and contributes to a better understanding of phylogenetic relationships within this group. This study offers new data on the chromosomes of Eudiplozoon nipponicum, an invasive parasite of the common carp. This species' karyotype consists of seven pairs of telocentric chromosomes (2n = 14 t). After DAPI staining, we marked heterochromatin blocks on all chromosomes in the pericentromeric region. Silver staining (AgNO₃) and staining with fluorescent dye YOYO-1 revealed the presence of one large active nucleolus. Fluorescent in situ hybridization with an 18S rDNA probe revealed one cluster of ribosomal genes at the terminal part of the long arms of chromosome pair No. 7. We compared our results with studies on the phylogenetic relationships of diplozoids which applied a combination of molecular methods and classical morphological characterization and found that the results of our cytogenetic analysis are consistent with the hypothesis that E. nipponicum is more basal member of the family Diplozoidae.

Paradiplozoon yunnanensis n. sp. (Monogenea, Diplozoidae) from Sikukia gudgeri (Cyprinidae, Barbinae) in southwest China

Paradiplozoon yunnanensis n. sp. (Monogenea, Diplozoidae) is described from the gills of Sikukia gudgeri Smith, 1931 (Cyprinidae) collected from Jinghong Basin, a tributary of the international Lancang-Mekong River. This is the first diplozoid species from S. gudgeri and its description increases the number of Paradiplozoon species recorded in China to 25. The new species is distinguished from congeners by a combination of morphological and molecular features. The anterior end of the median plate is thickened in the marginal area and a narrow rectangular trapeze spur connects to the anterior jaw through two separate anterior joining sclerites. The posterior end of the median plate sclerite is invaginated with a smooth strip-shaped posterior joining sclerite. Comparison of a newly obtained sequence of rRNA ITS2 with 18 other congeneric sequences from GenBank provides support for separation of the new species.