Rapid evolution of Anguillicola crassus in Europe: species diagnostic traits are plastic and evolutionarily labile

Background Since its introduction from Taiwan to Europe around 1980, Anguillicola crassus, a natural parasite of the Japanese eel (Anguilla japonica), has acquired the European eel (Anguilla anguilla) as a novel definitive host. In this host the nematode differs noticeably in its body mass and reproductive capacity from its Asian conspecifics. We conducted a common garden experiment under a reciprocal transplant design to investigate whether differences in species-diagnostic morphological traits exist between two European and one Asian population of A. crassus and if yes whether these have a genetically fixed component. Results We found that worms from Germany, Poland and Taiwan differ in the size and shape of their body, oesophagus and buccal capsule. These changes are induced by both phenotypic plasticity and genetic divergence: in the European eel, nematodes from Europe as well as from Taiwan responded plastically with larger body and oesophagus dimensions compared to infections in the Japanese eel. Interestingly, the oesophagus simultaneously shows a high degree of genetically based changes being largest in the Polish strain kept in A. anguilla. In addition, the size and shape of the buccal capsule has undergone a rapid evolutionary change. Polish nematodes evolved a genetically fixed larger buccal capsule than the German and Taiwanese populations. The German strain had the smallest buccal capsule. Conclusions This study provides evidence for the genetic divergence of morphological traits in A. crassus which evolved over a timescale of about 30 years. Within Europe and in the European eel host these alternations affect characters used as diagnostic markers for species differentiation. Thus we provide an explanation of the discrepancy between morphological and molecular features reported for the parasitic nematode featured here, demanding general caution in morphological diagnosis of parasites discovered in new hosts

Pathological and ecological host consequences of infection by an introduced fish parasite

The infection consequences of the introduced cestode fish parasite Bothriocephalus acheilognathi were studied in a cohort of wild, young-of-the-year common carp Cyprinus carpio that lacked co-evolution with the parasite. Within the cohort, parasite prevalence was 42% and parasite burdens were up to 12% body weight. Pathological changes within the intestinal tract of parasitized carp included distension of the gut wall, epithelial compression and degeneration, pressure necrosis and varied inflammatory changes. These were most pronounced in regions containing the largest proportion of mature proglottids. Although the body lengths of parasitized and non-parasitized fish were not significantly different, parasitized fish were of lower body condition and reduced weight compared to non-parasitized conspecifics. Stable isotope analysis (δ15N and δ13C) revealed trophic impacts associated with infection, particularly for δ15N where values for parasitized fish were significantly reduced as their parasite burden increased. In a controlled aquarium environment where the fish were fed ad libitum on an identical food source, there was no significant difference in values of δ15N and δ13C between parasitized and non-parasitized fish. The growth consequences remained, however, with parasitized fish growing significantly slower than non-parasitized fish, with their feeding rate (items s−1) also significantly lower. Thus, infection by an introduced parasite had multiple pathological, ecological and trophic impacts on a host with no experience of the parasite

Molecular Phylogeny of the Acanthocephala (Class Palaeacanthocephala) with a Paraphyletic Assemblage of the Orders Polymorphida and Echinorhynchida

Acanthocephalans are attractive candidates as model organisms for studying the ecology and co-evolutionary history of parasitic life cycles in the marine ecosystem. Adding to earlier molecular analyses of this taxon, a total of 36 acanthocephalans belonging to the classes Archiacanthocephala (3 species), Eoacanthocephala (3 species), Palaeacanthocephala (29 species), Polyacanthocephala (1 species) and Rotifera as outgroup (3 species) were analyzed by using Bayesian Inference and Maximum Likelihood analyses of nuclear 18S rDNA sequence. This data set included three re-collected and six newly collected taxa, Bolbosoma vasculosum from Lepturacanthus savala, Filisoma rizalinum from Scatophagus argus, Rhadinorhynchus pristis from Gempylus serpens, R. lintoni from Selar crumenophthalmus, Serrasentis sagittifer from Johnius coitor, and Southwellina hispida from Epinephelus coioides, representing 5 new host and 3 new locality records. The resulting trees suggest a paraphyletic arrangement of the Echinorhynchida and Polymorphida inside the Palaeacanthocephala. This questions the placement of the genera Serrasentis and Gorgorhynchoides within the Echinorhynchida and not the Polymorphida, necessitating further insights into the systematic position of these taxa based on morphology

Parasites of non-native freshwater fishes introduced into england and wales suggest enemy release and parasite acquisition

When non-native species are introduced into a new range, their parasites can also be introduced, with these potentially spilling-over into native hosts. However, in general, evidence suggests that a high proportion of their native parasites are lost during introduction and infections by some new parasites from the native range might occur, potentially resulting in parasite spill-back to native species. These processes were investigated here using parasite surveys and literature review on seven non-native freshwater fishes introduced into England and Wales. Comparison of the mean numbers of parasite species and genera per population for each fish species England andWaleswith their native ranges revealed\9 % of the native parasite fauna were present in their populations in England and Wales. There was no evidence suggesting these introduced parasites had spilled over into sympatric native fishes. The non-native fishes did acquire parasites following their introduction, providing potential for parasite spill-back to sympatric fishes, and resulted in non-significant differences in overall mean numbers of parasites per populations between the two ranges. Through this acquisition, the non-native fishes also had mean numbers of parasite species and genera per population that were not significantly different to sympatric native fishes. Thus, the non-native fishes in England and Wales showed evidence of enemy release, acquired new parasites following introduction providing potential for spill-back, but showed no evidence of parasite spill-over

Description Of Subadult Pallisentis (Pallisentis) Rexus (Acanthocephala An Examination Of The Species Identity

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