Morphological polymorphism in tapeworms: redescription of Caryophyllaeus laticeps (Pallas, 1781) (Cestoda: Caryophyllidea) and characterisation of its morphotypes from different fish hosts

New cytogenetic data on Caryophyllaeus laticeps and Paracaryophyllaeus gotoi, parasites of evolutionary interest

Caryophyllideans are intestinal parasites of freshwater fishes, occupying a basal position among the ‘true’ tapeworms. We performed detailed cytogenetic analyses of the well-known caryophyllidean species Caryophyllaeus laticeps. For comparison, we also examined for the first time the chromosomes of Paracaryophyllaeus gotoi, a specific parasite of loaches in China. Both species showed a diploid chromosome number of 2n = 20, n = 10m. Chromomycin A3 (CMA3)/diamidino-2-phenylindole (DAPI) staining performed for the first time in the class Cestoda revealed CMA3+/DAPI− bands in the pericentromeric regions of the short arms of chromosome pair no. 7 in the karyotype of C. laticeps. Fluorescence in situ hybridization with the 18S rDNA probe confirmed the presence of a single cluster of major rDNA near the centromere on a pair of small chromosomes in both species. These findings support the hypothesis that the ancestral state in the family Caryophyllaeidae is a single interstitial cluster of major rDNA genes and thus one nucleolar organizer region per haploid genome. Our results, which we presented together with literature data plotted on a phylogenetic tree, show stability of caryophyllidean karyotypes at the genus level, but showed differences between genera without a clear phylogenetic signal. The data allowed us to at least formulate a hypothesis about the ancestral haploid chromosome number of n = 10 for the family Caryophyllaeidae and possibly for the sister family Capingentidae. In addition, we compared two populations of C. laticeps from water bodies with different levels of polychlorinated biphenyl contamination, showing a slightly increased incidence of chromosomal abnormalities at the contaminated site.

Somatic Dimorphism in Cercariae of a Bird Schistosome

Phenotypic polymorphism is a commonly observed phenomenon in nature, but extremely rare in free-living stages of parasites. We describe a unique case of somatic polymorphism in conspecific cercariae of the bird schistosome Trichobilharzia sp. “peregra”, in which two morphs, conspicuously different in their size, were released from a single Radix balthica snail. A detailed morphometric analysis that included multiple morphological parameters taken from 105 live and formalin-fixed cercariae isolated from several naturally infected snails provided reliable evidence for a division of all cercariae into two size groups that contained either large or small individuals. Large morph (total body length of 1368 and 1339 μm for live and formalin-fixed samples, respectively) differed significantly nearly in all morphological characteristics compared to small cercariae (total body length of 976 and 898 μm for live and formalin samples, respectively), regardless of the fixation method. Furthermore, we observed that small individuals represent the normal/commonly occurring phenotype in snail populations. The probable causes and consequences of generating an alternative, much larger phenotype in the parasite infrapopulation are discussed in the context of transmission ecology as possible benefits and disadvantages facilitating or preventing the successful completion of the life cycle.

Hazardous pollutants in the environment: Fish host-parasite interactions and bioaccumulation of polychlorinated biphenyls

The present paper reports on the interrelationships of fish, parasites and the bioaccumulation of hazardous organic compounds in the Zemplínska Šírava water reservoir in eastern Slovakia, which is heavily polluted with polychlorinated biphenyls (PCBs). The concentrations of these contaminants were measured in various fish matrices (dorsal and abdominal muscle tissues, hepatopancreas, intestine wall and adipose tissue) of the freshwater bream, Abramis brama (Cyprinidae), and in its intestinal parasite Caryophyllaeus laticeps (Cestoda), which was used for the first time as a model for a PCB bioaccumulation study. Regarding the fish, the highest concentrations of PCBs were found in the intestine, followed by hepatopancreas and muscle tissues. The amounts of PCBs were higher in abdominal muscles than in their dorsal parts. Concentrations of ∑PCBs above the limits set by European regulations were detected in both muscle parts in the fish, confirming the persistent unfavorable conditions in this locality and high risk for biota and humans. Based on bioconcentration factor values (BCFs), PCBs reached much higher levels in cestodes compared to bream matrices. Some significant differences in PCB amounts between infected and uninfected bream were determined. Fulton's condition factor (CF) significantly differed in infected and non-infected fish (p ˂ 0.05), with CF values surprisingly lower in fish free of parasites compared to parasitized fish, which suggests a "mutualistic" relationship between the parasite and its host.

Molecular evidence of three closely related species of Biacetabulum Hunter, 1927 (Cestoda: Caryophyllidea): a case of recent speciation in different fish hosts (Catostomidae)?

Monozoic tapeworms (Caryophyllidea) are dominant components of parasite communities of suckers (Catostomidae) in North America, with Biacetabulum Hunter, 1927 representing one of the more species-rich genera. Molecular (28S rDNA) and morphological (including scanning electron microscopy and histology) evaluation of newly collected tapeworms from different fish hosts revealed the existence of four similar (and three closely related) species of Biacetabulum. These four species differ from their congeners by having a long body (up to 48 mm long) with a very long, slender neck (its length represents ≥30% of total body length), a large, globular scolex with a prominent central acetabulum-like loculus on the dorsal and ventral sides, two pairs of shallow lateral loculi and a distinct, slightly convex apical disc, and a cirrus-sac that is situated between the anterior arms of the ovarian wings. Taken together, the morphological and molecular data and the host associations of these species provide evidence of their host specificity. Biacetabulum isaureae n. sp. occurs in notch clip redhorse, Moxostoma collapsum, in South Carolina (USA), B. longicollum n. sp. in silver redhorse, Moxostoma anisurum (type host), and golden redhorse, M. erythrurum, in Manitoba (Canada) and West Virginia (USA), B. overstreeti n. sp. in a spotted sucker, Minytrema melanops, in Mississippi, and B. hypentelii n. sp. in northern hogsucker, Hypentelium nigricans, in Tennessee (USA). The new species differ from each other in the number of postovarian vitelline follicles, the posterior extent of preovarian vitelline follicles and relative size of the cirrus sac.

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.

Morphological variation of Aplectana hylambatis (Nematoda: Cosmocercidae) from different anuran hosts and localities in Argentina

Aplectana hylambatis is a nematode with a wide geographic distribution and low host specificity. In spite of numerous reports, until this moment, the morphological variations between different hosts and localities have not been studied. We studied 401 specimens collected from five host species from seven localities in Argentina, and examined the following morphological characters: mamelon-like cuticular protuberances anterior to the vulva, structure of the gubernaculum and the spicules, number and arrangement of caudal papillae, and the measurements of twelve characters in females and eleven characters in males. The results showed that mamelon-like protuberances and caudal papillae varied in number and arrangement between different hosts and localities. The metrical study revealed that five characters in males and six in females contributed to variability; nine characters showed significant differences between host species and localities. Specimens of A. hylambatis collected from R. arenarum formed a group clearly differentiated from the rest of the specimens. The results from this study highlight the importance of examining as many specimens as possible from different host samples and from several localities to cover the intraspecific variations.

The occurrence of the common European fish cestode Caryophyllaeus laticeps (Pallas, 1781) in the River Irtysh, China: a morphological characterization and molecular data

The cestode Caryophyllaeus laticeps (Pallas, 1781) is a highly polymorphic species with several morphotypes, and belongs to the most widespread species of monozoic tapeworm (Cestoda: Caryophyllidea) found in the Palaearctic zoogeographic region with a wide range of cyprinid fish hosts. This paper provides the first reliable evidence about the occurrence of C. laticeps in northern China that is based on detailed morphological characteristics and mitochondrial cox1 sequences. C. laticeps was found in freshwater bream Abramis brama (L.), in the River Irtysh, with the prevalence of 40% and mean intensity of infection 8. The tapeworms were rather similar in their morphological characters to the morphotype 1 of C. laticeps which is typified by the possession of a slender body with a flabellate wide scolex, narrow neck, robust, long and clearly visible vas deferens, large, and almost spherical cirrus-sac containing well-developed internal seminal vesicle and the first vitelline follicles and first testes beginning far from anterior margin of the body. Subsequent molecular analysis confirmed the morphological identification of the species. Our results show that the studied specimens were firmly clustered into the C. laticeps clade and formed a monophyletic group with C. laticeps morphotype 1 and 2 from Europe and Russia. In China, C. laticeps is a non-indigenous fish parasite, which has the most probably been introduced into the Irtysh River basin with its typical host inhabiting Russia.

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.