Molecular characterization of Atractolytocestus sagittatus (Cestoda: Caryophyllidea), monozoic parasite of common carp, and its differentiation from the invasive species Atractolytocestus huronensis

Molecular evidence of a putative new Atractolytocestus Anthony, 1958 (Cestoda: Caryophyllidea) species parasitic on common carp (Cyprinus carpio) in the People's Republic of China

Three tapeworm species belonging to the genus Atractolytocestus Anthony, 1958 (Cestoda: Caryophyllidea) were reported from the common carp, Cyprinus carpio L., 1758 in the People's Republic of China so far: Atractolytocestus sagittatus; Atractolytocestus tenuicollis; and Atractolytocestus huronensis. In this study, we identified a putatively new tapeworm species in common carp from the Danjiangkou Reservoir in Central China (Hubei Province). The species is morphologically similar to A. sagittatus, but it differed conspicuously in sequences of three molecular markers. Ribosomal internal transcribed spacers 2 sequence identity of the new species was 94.7–95.5%, 91.8–92.7% and 80.0–83.9% with A. huronensis, A. tenuicollis and A. sagittatus, respectively. cytochrome c oxidase and NADH dehydrogenase subunit 3 sequence identity with these three species was lower than 92%. We conclude that this is a new tapeworm species, and we named it after the locality: Atractolytocestus danjiangkouensis n. sp.

Comparative analysis of monozoic fish tapeworms Caryophyllaeus laticeps (Pallas, 1781) and recently described Caryophyllaeus chondrostomi Barčák, Oros, Hanzelová, Scholz, 2017, using microsatellite markers

The monozoic tapeworm Caryophyllaeus laticeps has been characterized by five markedly different morphotypes largely corresponding to different fish hosts. Recently, the most distinct morphotype 4 from the common nase Chondrostoma nasus was studied in more details resulting in description of a new species Caryophyllaeus chondrostomi. The molecular study based on mitochondrial cox1 and ribosomal lsrDNA did not reveal any interspecific differences between C. laticeps and C. chondrostomi and did not provide any molecular support for recognition of these two species. In the current study, six polymorphic microsatellite markers were applied in order to detect molecular differences between the two species and to provide molecular evidence of validity of C. chondrostomi. While all six microsatellite loci were amplified in different geographic populations of C. laticeps, only two of them provided the amplification product in C. chondrostomi. Results on the Bayesian analysis assigned C. chondrostomi and all geographic populations of C. laticeps to distinct clusters. Neither any close relationships among C. laticeps populations nor specific position of C. chondrostomi were revealed. Contrary, the results of the principal coordinate analysis revealed striking genetic separation of C. chondrostomi with no overlaps with any of the C. laticeps population or morphotype. Caryophyllaeus chondrostomi very probably underwent morphological divergence as a result of ongoing speciation, but this process has not yet been accompanied by sufficient genetic divergence. In this particular case, microsatellites were proved to be better molecular discriminative markers than rDNA and mtDNA.

How to become a successful invasive tapeworm: a case study of abandoned sexuality and exceptional chromosome diversification in the triploid carp parasite Atractolytocestus huronensis Anthony, 1958 (Caryophyllidea: Lytocestidae)

Background

A cytogenetic analysis of the new local triploid population of the caryophyllidean tapeworm Atractolytocestus huronensis, a unique parthenogenetic species with the ability to colonise new regions, was performed to understand the inner structure of its chromosome complement.

Methods

A karyotype analysis was carried out using classical Giemsa staining and C-banding combined with fluorescent DAPI staining. A hypothesis that triplets are composed from three homologue chromosomes of approximately the same length and same centromere position was tested statistically for multiple dependent variables using a non-parametric Friedman’s ANOVA. The chromosomal location of ribosomal DNA clusters within the nucleolar organization region (NORs) and telomeric (TTAGGG)_n sequences were detected by fluorescent in situ hybridization (FISH). Chromosomes were subjected to AgNO₃ staining in order to determine whether the rDNA sites represent active NORs.

Results

The cytogenetic analysis confirmed the karyotype composed from eight chromosome triplets (3n = 24) as well as the existence of a pair of NORs located on each chromosome of the second triplet. Six NORs varied their activity from cell to cell, and it was reflected in the numbers of nucleoli (from 1 to 5). A huge morphological diversification of homologue chromosomes was originally detected in six out of eight triplets; the homologue elements differed significantly either in length and/or morphology, and some of them carried discernible interstitial telomeric sequences (ITSs), while the end telomeres were minute. The heterochromatin bands with high AT content varied irregularly, and the course of aberrant spermatogenesis was evident.

Conclusions

Diversification of homologues is a unique phenomenon very likely caused by the long-term absence of a recombination and consequential accumulation of chromosome rearrangements in the genome of A. huronensis during species evolution. Unalterable asexual reproduction of the tapeworm, along with international trade in its host (carp), is facilitating its ongoing spread.

Tour around the globe: The case of invasive tapeworm Atractolytocestus huronensis (Cestoda: Caryophyllidea), a parasite of common carp

The monozoic tapeworm Atractolytocestus huronensis Anthony, 1958 (Cestoda: Caryophyllidea), an intestinal parasite of the common carp, is characterized by its invasive character and potential to colonize new territories. It was initially described from North America and has also been found in several European countries. The most recent findings of A. huronensis originated from China and South Africa; however, no data on genetic relationships of these populations were available. The current study provides the first molecular characterisation of A. huronensis from South Africa and China using a partial sequence of mitochondrial cytochrome c oxidase subunit 1 (cox1) and a complete ribosomal ITS2 spacer. Ribosomal and mitochondrial data were applied for phylogenetic analyses in order to assess the genetic interrelationships among global A. huronensis populations. Divergent intragenomic copies of ribosomal ITS2 were detected in all analysed specimens; the structure and frequency of the ITS2 variants of tapeworms from China and South Africa corresponded with the data on ITS2 paralogues observed previously in A. huronensis from Slovakia, the United States and the United Kingdom. The phylogenetic analysis of cox1 indicated that A. huronensis exist in two slightly differentiated clusters; one cluster was supported by all phylogenetic approaches (NJ, ML, BI) and was represented by samples from China, the USA and the UK. A second cluster was represented by tapeworms from continental Europe (Slovakia, Hungary, Romania, Croatia) and South Africa. Haplotype network analysis revealed that the highest population diversity occurs in China. The results provide useful pilot information about the interrelationships of A. huronensis on four continents and indicate that China, or the eastern Palaearctic, served as the original source population for the global expansion of this invasive tapeworm. Data on the origin and distribution of the common carp, the only specific host of A. huronensis, are also discussed.

Development of microsatellite markers in Caryophyllaeus laticeps (Cestoda: Caryophyllidea), monozoic fish tapeworm, using next-generation sequencing approach

Caryophyllaeus laticeps (Pallas 1781) (Cestoda: Caryophyllidea) is a monozoic tapeworm of cyprinid fishes with a distribution area that includes Europe, most of the Palaearctic Asia and northern Africa. Broad geographic distribution, wide range of definitive fish hosts and recently revealed high morphological plasticity of the parasite, which is not in an agreement with molecular findings, make this species to be an interesting model for population biology studies. Microsatellites (short tandem repeat (STR) markers), as predominant markers for population genetics, were designed for C. laticeps using a next-generation sequencing (NGS) approach. Out of 165 marker candidates, 61 yielded PCR products of the expected size and in 25 of the candidates a declared repetitive motif was confirmed by Sanger sequencing. After the fragment analysis, six loci were proved to be polymorphic and tested for heterozygosity, Hardy-Weinberg equilibrium and the presence of null alleles on 59 individuals coming from three geographically widely separated populations (Slovakia, Russia and UK). The number of alleles in particular loci and populations ranged from two to five. Significant deficit of heterozygotes and the presence of null alleles were found in one locus in all three populations. Other loci showed deviations from Hardy-Weinberg equilibrium and the presence of null alleles only in some populations. In spite of relatively low polymorphism and the potential presence of null alleles, newly developed microsatellites may be applied as suitable markers in population genetic studies of C. laticeps.

Parasites of commercially important fish from Lake Naivasha, Rift Valley, Kenya

In Lake Naivasha, the common carp Cyprinus carpio L. 1758 was accidentally introduced from fish farms adjacent to River Malewa in 1999 and now forms the bulk of the total fish caught. Since its introduction, no study has been made on its parasitic community nor are there any reports on ectoparasites from other fish species in this lake to the best of our knowledge. Therefore, the aim of this study was to describe the parasitic community of C. carpio and two other commercially important fish species: Oreochromis leucostictus and Tilapia zillii. Additionally, the abundant Barbus paludinosus was included in the study. A total of 286 fish (145C. carpio, 56 O. leucostictus, 18 T. zillii, and 67 B. paludinosus) were collected during the year 2011 and examined. Ten taxa of parasites were recovered from C. carpio dominated by the monogenean Dactylogyrus minutus, occurring with a prevalence (p) of 99.3%. Thirteen taxa of parasites were identified from O. leucostictus dominated by monogeneans Cichlidogyrus spp. (p = 91.1%). T. zillii harbored nine taxa of parasites with the digenean Tylodelphys sp. (p = 83.3%) being dominant and B. paludinosus harbored 11 taxa of parasites dominated by an unidentified monogenean of the genus Dactylogyrus (p = 83.6%). C. carpio had the lowest helminth species diversity and richness while monogenetic trematodes, which have never been reported from fish in Lake Naivasha, were the most prevalent parasites recovered.