Population genetic structure of the acanthocephalan Acanthosentis cheni in anadromous, freshwater, and landlocked stocks of its fish host, Coilia nasus

Parasites of Moroccan desert Coptodon guineensis (Pisces, Cichlidae): transition and resilience in a simplified hypersaline ecosystem

Sebkha Imlili (Atlantic Sahara) is a salt flat with over 160 permanent holes of hypersaline water generated in the Holocene and inhabited by euryhaline organisms that are considered to be relics of the past, including the cichlid fish Coptodon guineensis. We surveyed the fish parasites four times over one year, to i) identify the parasites, and ii) determine possible seasonality in infection patterns. Over 60% of the fish were infected by one to three helminths: an acanthocephalan in the intestine and two digenean metacercariae in the kidney, spleen, liver, muscle, and mesenteries. The acanthocephalan Acanthogyrus (Acanthosentis) cf. tilapiae was identified morphologically and molecularly; only one digenean (the heterophyid Pygidiopsis genata) could be identified molecularly. Both identified parasites were present throughout the sampling periods; the unidentified metacercariae were present only in summer and fall. Mean intensities, but not prevalence of infection by the acanthocephalan, reflected a biannual pattern of transmission. Infection accrued with fish size, possibly due to cannibalism. Because the water holes include only a few invertebrates, the intermediate hosts of these parasites can be inferred to be the gastropod Ecrobia ventrosa for the digeneans and either the copepod Cletocamtpus retrogressus or the ostracod Cyprideis torosa for the acanthocephalan. This ecosystem appears stable and provides a window into the past, as the acanthocephalan likely switched from freshwater tilapia to C. guineensis when the Sebkha formed. However, this is a vulnerable environment where the survival of these parasites depends on interactions maintained among only very few hosts.

Phenotypic plasticity, genetic structure, and systematic position of Neoechinorhynchus emyditoides Fisher, 1960 (Acanthocephala: Neoechinorhynchidae) a parasite of emydid turtles from the Nearctic and Neotropical regions

The taxonomy of the 10 recognized Neoechinorhynchus species associated with emydid turtles is complex due to the morphological conservatism. In the present study, specimens of N. emyditoides from northern and southeastern Mexico exhibit great phenotypic plasticity on its diagnostic characteristics. We sequenced three molecular markers: the internal transcribed spacers ITS1, ITS2 and 5.8S gene, the D2 + D3 domains of the large subunit from nuclear DNA and cytochrome c oxidase subunit I (cox1 ) from mitochondrial DNA. Sequences of the nuclear molecular markers were aligned and compared with other congeneric species associated with emydids available in GenBank. Phylogenetic analyses supported the polyphyly of Neoechinorhynchus . The species from emydids formed a clade, which was subdivided into five subclades that correspond with each species analysed (N. pseudemydis , N. chrysemydis , N. emydis , N. schmidti and N. emyditoides ). To understand better the genetic structure of N. emyditoides a haplotype network was inferred with 29 cox1 sequences, revealing the presence of 13 haplotypes, two of which were shared and 11 were unique. The high values of fixation index, F st (0.4227–0.8925) detected between the two populations from southeastern and the two from northern Mexico indicated low genetic flow among the populations. Our data suggest that the Neoechinorhynchus species associated with emydid turtles diversified in the eastern USA and that of N. emyditoides expanded its distribution range reached southeastern Mexico.

Variations and Potential Factors of Gut Prokaryotic Microbiome During Spawning Migration in Coilia nasus

Coilia nasus is influenced by various external pressures during spawning migration and these anadromous transitions can lead to specific gut microbiome characteristics that affecting the host biological process. Therefore, the purpose of this study was to determine the variations of components and functions in the gut prokaryotic microbiome during spawning migration as well as the key factors that triggered the changes. The gut microbiome in C. nasus was mainly consisted of Proteobacteria, Bacteroidetes, Firmicutes, Deinococcus-Thermus and Fusobacteria via 16S rRNA Gene Amplicon Sequencing. The relative abundance of Acinetobacter and Clostridium increased, while Corynebacterium, Actinomyces, Bacillus, Klebsiella and Ochrobactrum decreased after entering freshwater, indicated the preference of C. nasus gut microbial members transferred from seawater to freshwater. Additionally, the proportion of Firmicutes significantly decreased and then increased, as well as the arise of some soil bacteria in gut, corresponding to the phenomenon that C. nasus are fasting during the upstream process and refeeding after entering the spawning grounds. The function prediction of gut microbiome was also consistent with the above results. The present study generally demonstrated the gut microbiome dynamics and the significant correlation between the gut microbiome and salinity and feeding behavior in the spawning migration of C. nasus.

Metabolic mechanisms of Coilia nasus in the natural food intake state during migration

As a prominent member of freshwater and coastal fish faunas, Coilia nasus migrates annually from the sea up the Yangtze River in China to spawn. It is traditionally believed that C. nasus generally do not feed during their spawning migration. However, we recently documented the occurrence of food intake phenomenon in C. nasus following voluntary fasting. The purpose of the current study is to explore the metabolic mechanisms on C. nasus in response to food intake during migration. A total of 23,159 differentially expressed mRNA molecules and 204 metabolites were identified in transcriptome and metabolome analyses. Our results provide insights into the activation of energy consumption and reinforcement of energy storage during migration, and also identify key genes involved in food intake regulation. Our findings will be useful for future research on population recruitment and energy utilization in wild C. nasus.

Transcriptome and metabolome analyses of Coilia nasus in response to Anisakidae parasite infection

Parasites from the family Anisakidae are capable of infecting a range of marine fish species worldwide. Coilia nasus, which usually feeds and overwinters in coastal waters and spawns in freshwater, is highly susceptible to infection by Anisakidae. In this study, we used scanning electron microscopes to show that C. nasus infected by Anisakidae exhibited damage and fibrosis of the liver tissue. To better understand host immune reaction and metabolic changes to Anisakidae infection, we used a combination of transcriptomic and metabolomic method to characterize the key genes and metabolites, and the signaling pathway regulation of C. nasus infected by Anisakidae. We generated 62,604 unigenes from liver tissue and identified 391 compounds from serum. Of these, Anisakidae infection resulted in significant up-regulation of 545 genes and 28 metabolites, and significant down-regulation of 416 genes and 37 metabolites. Seventy-four of the 961 differentially expressed genes were linked to immune response, and 1, 2-Diacylglycerol, an important immune-related metabolite, was significantly up-regulated after infection. Our results show activation of antigen processing and presentation, initiation of the T cell receptor signaling pathway, disruption of the TCA cycle, and changes to the amino acid and Glycerolipid metabolisms, which indicate perturbations to the host immune system and metabolism following infection. This is the first study describing the immune responses and metabolic changes in C. nasus to Anisakidae infection, and thus improves our understanding of the interaction mechanisms between C. nasus and Anisakidae. Our findings will be useful for future research on the population ecology of C. nasus.

Molecular characterization ofNeoechinorhynchus cylindratusVan Cleave, 1913 (Acanthocephala: Neoechinorhynchidae), a parasite of the largemouth bass (Micropterus salmoides) in northern Mexico

Members of the genusNeoechinorhynchusStiles & Hassall, 1905 are endoparasites of freshwater fishes, brackish water fishes, and freshwater turtles distributed worldwide. In North America, 33 species have been described. One of the most widely distributed species in the eastern United States and Canada isNeoechinorhynchus (Neoechinorhynchus) cylindratus,a common acanthocephalan that infects centrarchid fishes. In the current study, adult specimens ofN. (N) cylindratuswere collected from largemouth bass (Micropterus salmoides) from the Purificación River in northern Mexico. In the same freshwater system, two additional congeneric species (Neoechinorhynchus (Neoechinorhynchus) emyditoidesandNeoechinorhynchus (Neoechinorhynchus) panucensis) were collected and analysed. Sequences of the large subunit, internal transcribed spacers ITS1 and ITS2, 5.8S from nuclear DNA, and sequences of the cytochromecoxidase subunit I (cox1) from mitochondrial DNA were generated and aligned with other sequences obtained from GenBank. Maximum likelihood and Bayesian inference analyses inferred for each dataset showed thatN. (N) panucensis,N. (N) emyditoidesandN. (N) cylindratuswere nested within several clades, indicating that these species do not share a common ancestor. Our phylogenies also revealed that the genusNeoechinorhynchusis paraphyletic, requiring further taxonomic revision using phylogenetic systematics and re-examination of morphological and ecological data. The presence of severalN. (N) cylindratusadults in northern Mexico allowed us to typify this species for the first time using a combination of morphological and molecular characteristics. The current record shows a wide distribution range ofN. (N) cylindratusacross Canada, the United States and Mexico in the Nearctic region.

Mayarhynchus karlae n. g., n. sp. (Acanthocephala: Neoechinorhynchidae), a parasite of cichlids (Perciformes: Cichlidae) in southeastern Mexico, with comments on the paraphyly of Neoechinorhynchus Stiles & Hassall, 1905

Mayarhynchus n. g. (Acanthocephala: Neoechinorhynchidae) is erected for Mayarhynchus karlae n. g, n. sp. described from the intestine of four species of cichlid fishes distributed from southeastern Mexico. The new genus placed in the family Neoechinorhynchidae (Ward, 1917) Van Cleave, 1928, is readily distinguished from the other 17 genera in the family by having a small proboscis armed with 45-46 relatively weak rooted hooks arranged in nine longitudinal rows of five hooks each. In addition, Mayarhynchus n. g., n. sp. is diagnosed by the presence of a short trunk, body wall with five dorsal and one ventral giant hypodermal nuclei, proboscis receptacle nearly cylindrical with single layered wall, lemnisci broad and flat with large nuclei, testes in tandem, cement gland with eight large nuclei, and eggs elongate to oval. Partial sequences of the cytochrome c oxidase subunit 1 (cox1), internal transcribed spacers (ITS1 + 5.8S + ITS2), and the D2-D3 domains of the large subunit rRNA gene (28S) were obtained for five specimens of the new species and other species belonging to the Neoechinorhynchidae. Phylogenetic analyses confirmed that the new genus belongs to the Neoechynorhynchidae and indicated that the genus Neoechynorhynchus Stiles & Hassall, 1905 is not monophyletic. Comparison between three populations of the new species yielded nine variable sites for cox1, 11 for ITS and four for 28S.

Changes of gonadotropin-releasing hormone receptor 2 during the anadromous spawning migration in Coilia nasus

Background

An increase in the activity of the pituitary-gonad axis (PG-axis) and gonad development are essential for the onset of spawning migration in teleosts. In the fish Coilia nasus, gonad development and spawning migration up the Yangtze River occurs by the end of each summer. We hypothesized that gonadotropin releasing hormones receptor 2 (GnRH-R2), which together produce a signal that interacts with the PG-axis, may help to regulate spawning migration processes.

Results

In this regard, we (1) characterized the gonadosomatic index (GSI) in the anadromous fish C. nasus; (2) analyzed the GnRH-R2 mRNA expression levels in ovary and brain, and concentrations in the serum; and (3) identified the GnRH-R2 protein distribution in the brain and ovaries. We found strong relationships between all of these indices.

Conclusions

The results indicate that GnRH-R2 could act together to promote spawning during the anadromous migration. There is some evidence that the GnRH-R2 gene expression levels and protein distributions change in association with the migratory behavior.

The complete mitochondrial genome of Acanthosentis cheni (Acanthocephala: Quadrigyridae)

Acanthosentis cheni is a marine or brackish acanthocephalan found in fish. The complete mitochondrial genome of A. cheni (Acanthocephala: Quadrigyridae) is first sequenced. It is a circular molecule of 13,695 bp in size and consists of 12 protein-coding genes (PCGs), 20 transfer RNA (tRNA) genes, 2 ribosomal RNA (rRNA) genes. Except tRNA-Gln, all other mitochondrial genes were encoded on the heavy strand. The gene order and orientation of A. cheni mitogenome are basically identical to that of other acanthocephala. This study will facilitate the further research of the population genetics of this species and systematic analyses of the acanthocephala.