Parasitism, life history traits and immune defence in cyprinid fish from Central Europe

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Pathogen-mediated selection for MHC variability in wild zebrafish

ABSTRACT Hypothesis: Genes of the major histocompatibility complex (MHC) show high variability, which is believed to arise through pathogen-mediated selection. Organism: Zebrafish (Danio rerio) from seven independent natural populations. Location: Bangladesh: two sites in Khulna District in the River Ganges drainage, and five sites in Mymensingh District in the River Brahmaputra drainage. Methods: We investigated the relationship of parasite abundance and diversity with allelic variability of the MHC class II B gene in natural populations of zebrafish. A sample of 120 zebrafish was screened for metazoan parasites, and a subsample of 77 was assessed for immunogenetic variation. In total, 2475 metazoan parasites from 23 taxa were identified and 13 unique MHC class IIB alleles were isolated. Conclusion: We found no evidence for a heterozygote advantage, and overall there was lower than expected heterozygosity of MHC alleles. We identified lower parasite abundance and diversity with specific MHC alleles, and this pattern varied between geographic regions. Results suggest that MHC variability in zebrafish is maintained by frequency-dependent and fluctuating selection

Parasite communities and genetic structure of non-native pumpkinseed, Lepomis gibbosus, in different Black Sea drainages of Ukraine

In recent years, pumpkinseed Lepomis gibbosus (Actinopterygii: Centrarchidae) have spread intensively to many parts of Europe, including Ukraine. In this study, we (1) assess intra-population genetic variability in five widely-spaced Ukrainian pumpkinseed populations and compare their population genetic structure with other European populations and (2) provide a comprehensive survey of pumpkinseed parasites across the region. Discriminant analysis of principal components and FST analyses based on microsatellites indicated that all five populations formed discrete clusters. Within Europe, Ukrainian populations were most closely associated with populations from the River Danube, suggesting that the Danube is the main source of all Ukrainian pumpkinseed populations. The parasite fauna comprised 15 taxa, most of which (92%) were native to North America (monogenea Onchocleidus similis and O. dispar; myxozoan Myxobolus dechtiari). Parasites acquired in the species' new range occurred accidentally, with only Trichodina ciliates found relatively frequently and the eye flukes Diplostomum pseudospathaceum and Tylodelphys clavata occurring at higher prevalence. Absence of specific monogeneans in pumpkinseed from estuaries (Khadzhibey and Sukhyi Lymans) indicates low tolerance of Onchocleidus species to salinity

Trematode Diplostomum pseudospathaceum inducing differential immune gene expression in sexual and gynogenetic gibel carp (Carassius gibelio): parasites facilitating the coexistence of two reproductive forms of the invasive species

IntroductionParasite-mediated selection is considered one of the potential mechanisms contributing to the coexistence of asexual-sexual complexes. Gibel carp (Carassius gibelio), an invasive fish species in Europe, often forms populations composed of gynogenetic and sexual specimens.MethodsThe experimental infection was induced in gynogenetic and sexual gibel carp using eye-fluke Diplostomum pseudospathaceum (Trematoda), and the transcriptome profile of the spleen as a major immune organ in fish was analyzed to reveal the differentially expressed immunity-associated genes related to D. pseudospathaceum infection differing between gynogenetic and sexual gibel carp.ResultsHigh parasite infection was found in gynogenetic fish when compared to genetically diverse sexuals. Although metacercariae of D. pseudospathaceum are situated in an immune-privileged organ, our results show that eye trematodes may induce a host immune response. We found differential gene expression induced by eye-fluke infection, with various impacts on gynogenetic and sexual hosts, documenting for the majority of DEGs upregulation in sexuals, and downregulation in asexuals. Differences in gene regulation between gynogenetic and sexual gibel carp were evidenced in many immunity-associated genes. GO analyses revealed the importance of genes assigned to the GO terms: immune function, the Notch signaling pathway, MAP kinase tyrosine/threonine/phosphatase activity, and chemokine receptor activity. KEGG analyses revealed the importance of the genes involved in 12 immunity-associated pathways – specifically, FoxO signaling, adipocytokine signaling, TGF-beta signaling, apoptosis, Notch signaling, C-type lectin receptor signaling, efferocytosis, intestinal immune network for IgA production, insulin signaling, virion - human immunodeficiency virus, Toll-like receptor signaling, and phosphatidylinositol signaling system.DiscussionOur study indicates the limited potential of asexual fish to cope with higher parasite infection (likely a loss of capacity to induce an effective immune response) and highlights the important role of molecular mechanisms associated with immunity for the coexistence of gynogenetic and sexual gibel carp, potentially contributing to its invasiveness

The effect of posthodiplostomosis on the cyprinid fish fry

Posthodiplostomosis, called also black-spot disease, is caused by metacercariae of Posthodiplostomum cuticola (Trematoda, Diplostomatidae). These parasites were studied on the cyprinid fish in floodplain area of the River Dyje in South Moravia. Twelve species from 16 totally explored Cyprinids were infected by metacercariae of P. cuticola during 1998, 1999 and 2001. Roach (Rutilus rutilus), rudd (S. erythrophthalmus), silver bream (B. bjoerkna), common bream (A. brama), bitterling (R. sericeus) and Prussian carp (C. auratus gibelio) were infected in all followed seasons. These species were histologicaly examined. During the cyst development the progressive maturation of connective tissue in outer layer of the cyst and infiltration of pigment cells were observed. Production of black pigment around the parasite cyst was chacteristic host reaction. Mainly melanocytes and in a small measure iridocytes took part in the pigmentation. The metacercariae of P. cuticola caused in the juvenile fish spine and body deformation. By high invasion the tissue dystrophy was observed

Data from: Metazoan parasites of African annual killifish (Nothobranchiidae): abundance, diversity, and their environmental correlates

Estimates of biodiversity and its global patterns are affected by parasite richness and specificity. Despite this, parasite communities are largely neglected in biodiversity estimates, especially in the tropics. We studied the parasites of annual killifish of the genus Nothobranchius that inhabit annually desiccating pools across the African savannah and survive the dry period as developmentally arrested embryos. Their discontinuous, non-overlapping generations make them a unique organism in which to study natural parasite fauna. We investigated the relationship between global (climate and altitude) and local (pool size, vegetation, host density and diversity, and diversity of potential intermediate hosts) environmental factors and the community structure of killifish parasites. We examined metazoan parasites from 21 populations of four host species (Nothobranchius orthonotus, N. furzeri, N. kadleci, and N. pienaari) across a gradient of aridity in Mozambique. Seventeen parasite taxa were recorded, with trematode larval stages (metacercariae) being the most abundant taxa. The parasites recorded were both allogenic (life cycle includes non-aquatic host; predominantly trematodes) and autogenic (cycling only in aquatic hosts; nematodes). The parasite abundance was highest in climatic regions with intermediate aridity, while parasite diversity was associated with local environmental characteristics and positively correlated with fish species diversity and the amount of aquatic vegetation. Our results suggest that parasite communities of sympatric Nothobranchius species are similar and dominated by the larval stages of generalist parasites. Therefore, Nothobranchius serve as important intermediate or paratenic hosts of parasites, with piscivorous birds and predatory fish being their most likely definitive hosts

Trichodinid Ectoparasites (Ciliophora: Peritrichia) of Non-native Pumpkinseed (Lepomis gibbosus) in Europe

Three species of trichodinid ciliates, common parasites or symbionts of aquatic invertebrates and vertebrates, have been reported from pumpkinseed (Lepomis gibbosus, Centrarchidae) in both their native (Trichodina fultoni, T. tumefaciens) and introduced (T. fultoni, Trichodinella epizootica) ranges. In this study, we report five additional trichodinid taxa collected from invasive L. gibbosus in France and two regions of the Czech Republic. We describe a new species, Trichodina lepomi sp. n., recorded in L. gibbosus from both countries. The new species differs from T. nigra by absence of posterior projection of blade, absence of notch/ indentation opposing ray apophysis, absence of ray apophysis and the blade not being displaced anteriorly relative to ray as significantly as in T. nigra. Two widely distributed species, identified as Trichodina acuta and T. cf. heterodentata, were observed on juvenile fish in the Dyje river basin (Czech Republic). Finally, two undescribed species f Trichodina sp. and Tripartiella sp. are reported. Detailed description of the new species and comparison with other congeneric species are presented

Trichodinid Ectoparasites (Ciliophora: Peritrichia) of Non-native Pumpkinseed (Lepomis gibbosus) in Europe

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The parasite community of round goby

Round goby, Neogobius melanostomus (Pallas, 1814), an invasive Ponto-Caspian fish species, were registered in the upper Elbe for the first time in 2015, near the City of Ústí-nad-Labem (Czech Republic), apparently introduced by shipping. We sampled 53 individuals from this newly introduced population on May 18 (spring) and October 21 (autumn) 2016 in order to assess parasite load. Seven taxa were recorded, comprising two ciliates, one digenean (metacercariae), one acanthocephalan (cystacanth), two nematodes (larvae) and mollusc glochidia. No specific parasites were registered. Only the acanthocephalan Pomphorhynchus tereticollis was found in high numbers and occurred in both seasons, all other parasites occurring sporadically. Such a low parasite load is typical for Ponto-Caspian gobiids introduced far from their host range, and complies with the predictions of the ‘enemy release hypothesis’. All parasite species were probably acquired in the upper Elbe itself. According to the ‘parasite spillback’ concept, round goby could potentially play an important role in P. tereticollis distribution in the Elbe