Out of the ancient lake: Multiple riverine colonizations and diversification of the freshwater snails in the genus Semisulcospira around Lake Biwa.

Ancient lakes are a hotspot of biodiversity. Freshwater species often experience spectacular species radiation after colonizing lakes from riverine habitats. Therefore, the relationship between the fauna of the ancient lakes and the surrounding riverine system has a special significance in understanding their origin and evolutionary history. The study of ancient lake species often focused on the lake colonization of riverine species. In contrast, far less attention has been placed on the reverse direction: the riverine colonization of the lake species, despite its importance in disentangling their complex evolutionary history. The freshwater snails in the genus Semisulcospira involve endemic groups that radiated in the ancient Lake Biwa. Using genetics and fossil records, we inferred that the ancestors of these lake-endemic Semisulcospira snails historically colonized the riverine habitats at least three times during the Middle Pleistocene. Each colonization resulted in the formation of a new lineage that was genetically and morphologically distinct from other lineages. Further, one of these colonizations was followed by hybridization with a cosmopolitan riverine species, which potentially facilitated the population persistence of the colonizers in the new environment. Despite their complex histories, all these colonizers were currently grouped within a single species, Semisulcospira kurodai, suggesting cryptic diversity in this species. This study highlights the significance of the riverine colonizations of the lake species to fully understand the diversification history of freshwater fauna in and around the ancient lakes.

Chromosome-Scale Genome Assembly of the Freshwater Snail Semisulcospira habei from the Lake Biwa Drainage System.

Semisulcospira habei is a freshwater snail species endemic to the Lake Biwa drainage and belongs to a species group radiated within the lake system. We report the chromosome-scale genome assembly of S. habei, including eight megascaffolds larger than 150 Mb. The genome assembly size is about 2.0 Gb with an N50 of 237 Mb. There are 41,547 protein-coding genes modeled by ab initio gene prediction based on the transcriptome data set, and the BUSCO completeness of the annotated genes was 92.2%. The repeat elements comprise approximately 76% of the genome assembly. The Hi-C contact map showed seven well-resolved scaffolds that correspond to the basic haploid chromosome number of S. habei inferred from the preceding karyotypic study, while it also exhibited one scaffold with a complicated mosaic pattern that is likely to represent the complex of multiple supernumerary chromosomes. The genome assembly reported here represents a high-quality genome resource in disentangling the genomic background of the adaptive radiation of Semisulcospira and also facilitates evolutionary studies in the superfamily Cerithioidea.

Role of Semisulcospira gottschei extract as medicinal food on reflux esophagitis in rats.

Gastroesophageal reflux disease (GERD) is a globally prevalent disease and results from a reflux of gastric contents into the esophagus. Existing synthetic drug-based treatments for GERD have various drawbacks including refractory symptoms, relapse, or resistance due to long-term use or may result in mucosal degeneration, polyps, and osteoporosis. Semisulcospira gottschei (SE), a freshwater snail, has been generally consumed as a food source due to its excellent flavor and nutritional value in Korea and considered to have therapeutic properties for various diseases including dyspepsia, stomachache, and hepatic diseases. The present study aims to investigate whether Semisulcospira gottschei extract (SGE) has a protective effect on reflux esophagitis-induced rat models. The anti-inflammatory effects of SGE were evaluated via NO production in LPS-induced Raw 264.7 macrophage. And the protection effects of SGE were analyzed by assessing the amelioration of mucosal damage and expression of inflammation-associated proteins in reflux esophagitis (RE) rats. Our results indicate that SGE significantly suppressed NO production in LPS-induced raw 264.7 cells without any cytotoxicity. We observed mucosal lesions and histological changes in the esophagus of RE control rats. However, SGE treatment markedly ameliorated mucosal lesion ratio indicated through histological changes. SGE administration suppressed the expression of proteins related to inflammation, such as p-NF-κB, p-IκBα, COX-2, and TNF-α, in esophageal tissue. Moreover, SGE elevated the expression of claudin-5, which is a tight junction protein, involved in barrier function of epithelium and endothelium. The results suggest that SGE is useful as a medicinal food in esophagitis and may be helpful in developing effective treatment protocols for GERD.

Trematode diversity in freshwater snails from a stopover point for migratory waterfowls in Hokkaido, Japan: An assessment by molecular phylogenetic and population genetic analyses.

The cryptic diversity of trematodes was evaluated in the Nagayama-Shinkawa River, an artificial canal of the Ishikari River System of Hokkaido, Japan. Numerous migratory waterfowls use the canal as a stopover point in every spring season. The lymnaeid snail, Radix auricularia, and the semisulcospirid snail, Semisulcospira libertina, colonize the static and flowing water areas, respectively. The trematode fauna of the two snails was assessed by molecular phylogenetic and population genetic analyses. Each of distinctive clades in mitochondrial DNA trees was arbitrarily set as a species. In total, 14 species of the families Diplostomidae, Echinostomatidae, Notocotylidae, Plagiorchiidae, and Strigeidae occurred in R. auricularia, wherease S. libertina harbored 10 species of the families Echinochasmidae, Heterophyidae, Notocotylidae, and Lecithodendridae and Cercaria creta, an unclassified species whose adult stage is still unknown. The species diversity of the larval trematodes could be recognized as a "hot spot", suggesting that the seasonal visit of waterfowls is very important to spread trematodes and to keep their diversity. A high intraspecific genetic diversity was observed in the echinostomatid, notocotylid, echinochasmid, and heterophyid species, whose definitive hosts include birds. It seems likely that each of the parasite populations is always disturbed by repeated visits of waterfowls.

Population genetic structure of Semisulcospira gottschei: simultaneous examination of mtDNA and microsatellite markers.

Semisulcospira gottschei is an Asian endemic species inhabiting Korea and China. However, genetic structure analysis of the resource management of this species has not been performed. To investigate the genetic diversity among populations, microsatellites can be used to determine the geographic origins of marine and freshwater species. This study investigated the genetic structures of the Korean and Chinese populations of S. gottschei based on mitochondrial DNA (mtDNA) Cytochrome oxidase subunit I (COI) and polymorphic microsatellite loci developed from Semisulcospira coreana. Analysis of the mtDNA COI sequence revealed 43 haplotypes, which indicated no gene flow between the Korean and Chinese populations. To further elucidate the genetic structures of the Korean and Chinese populations, the population genetics of S. gottschei were analyzed using nine microsatellite markers. The genetic diversity analysis showed an average of 5.25 alleles per locus, with an average allelic richness of 4.02. Excessive homozygosity was found at all loci, which was expected to be due to the presence of null alleles at all loci. Populations of S. gottschei formed two separate clusters according to pairwise FST and AMOVA. Also, the UPGMA tree, PCA, STRUCTURE, and GeneClass indicated separation of the 11 populations into two clusters: Korea and China. These results have potential use in the management, restoration, and distinction of the origin country of populations.

Ancient drainage networks mediated a large-scale genetic introgression in the East Asian freshwater snails.

Biogeography and genetic variation of freshwater organisms are influenced not only by current freshwater connections but also by past drainage networks. The Seto Inland Sea is a shallow enclosed sea in Japan, but geological evidence showed that a large freshwater drainage had intermittently appeared in this area between the late Pliocene and Pleistocene. Here, we demonstrated that this paleodrainage greatly affected the genetic variation of the East Asian freshwater snails, Semisulcospira spp. We found that the mtDNA haplotypes originated in the Lake Biwa endemic Semisulcospira species at the upstream side of the paleodrainage were frequently observed in the riverine Semisulcospira species at its downstream side. The genome-wide DNA and morphological analyses consistently showed that there was no clear evidence of nuclear introgression between the Lake Biwa endemics and riverine species. These results suggest that the large paleodrainage had facilitated mitochondrial introgression and had broadly spread the introgressed mtDNA haplotypes to its downstream region around the Seto Inland Sea. Our study highlights the role of paleodrainages in shaping the genetic variation of freshwater organisms.

Systematic relationships of Chinese freshwater semisulcospirids (Gastropoda, Cerithioidea) revealed by mitochondrial sequences.

The systematics of Semisulcospiridae in China is revised here based on morphological characters and mitochondrial phylogenetics. Phylogenetic relationships within the Chinese semisulcospirids were assessed via DNA sequences from mitochondrial analysis (cytochrome c oxidase I and 16S rRNA). This research contains most morphospecies of semisulcospirids previously recorded in China. Based on these results, the family of Chinese Semisulcospiridae is represented by three genera: i.e., viviparous Semisulcospira Böttger, 1886, oviparous Hua Chen, 1943 and Koreoleptoxis Burch and Jung, 1988. These genera can be distinguished from each other by reproductive anatomy, reproductive mode, and radula features. Species of Hua are mainly distributed in southwest China and Guangxi, whereas Koreoleptoxis and Semisulcospira are mainly distributed in south and northeast China.

Comparative analysis of complete mitochondrial genomes with Cerithioidea and molecular phylogeny of the freshwater snail, Semisulcospira gottschei (Caenogastropoda, Cerithioidea).

In this study, we determined the complete mitochondrial genome (mt genome) of Semisulcospira gottschei for the first time and then compared it with the mt genome of species belonging to Cerithioidea. The mt genome consists of 13 protein-coding genes (PCGs), 2 ribosomal RNAs (rRNAs), 22 transfer RNAs (tRNAs) and non-coding region with a total length of 16,101 bp. The type of constitutive genes and the direction of the coding strand which appeared in the mt genome were the same as the ones observed in Cerithioidea except for the tRNA-Q and tRNA-R positions. The S. gottschei mt genome had a non-coding region with an AT-rich loop between tRNA-F and tRNA-C regions. In regard to molecular phylogeny, two types of analysis were performed to confirm the introgressive hybridization of S. gottschei and to identify the phylogenetic location among the species in Caenogastropoda. As a result, S. gottschei used in this study belonged to the same clade as other non-introgressed S. gottschei. As for the molecular phylogenic analysis of species belonging to Caenogastropoda, S. gottschei was found to be the closest to S. coreana taxonomically and to be included in Cerithioidea.

The complete mitochondrial genome of freshwater snail, Semisulcospira coreana (Pleuroceridae: Semisulcospiridae).

We have determined the mitochondrial DNA of Semisulcospira coreana. The complete mitogenome was 15,398 bp in length, encoding 13 protein-coding genes, 22 transfer RNA genes, and 2 ribosomal RNA genes. Phylogenetic analysis showed that the mitochondrial DNA of S. coreana was much closely related to other Semisulcospira species. This mitogenome could be helpful information for a variety of biodiversity researches in Korean freshwater snail.

Origins of Semisulcospira libertina (gastropoda: semisulcospiridae) in Taiwan.

The most accepted hypothesis has suggested that the fauna in Taiwan Island originated from South China, but some studies supported the Japan, Ryukyu Archipelago, and Taiwan Islands as a unique biogeographical district. This study examines whether the populations of freshwater snail Semisulcospira libertina in Taiwan are closer to those in Japan based on the mitochondrial cytochrome c oxidase subunit I (COI) gene sequences. Our study shows the populations in North Taiwan originated from Japan and the cyclic glacial caused the migrations among islands and continent repeatedly; the populations in South Taiwan might originate from South China or South Asia. Our results will not only affect the conclusions in phylogeography of freshwater species in Taiwan but also change the sampling plans in the future studies about evolutionary of freshwater species in East Asia.

[Investigation on epidemic foci of paragonimiasis in eastern part of Zhenghe County, Fujian Province].

OBJECTIVE: To investigate the species and hosts of Paragonimus and its infection rate in eastern part of Zhenghe County, Fujian Province, so as to determine the local foci of Paragonimus. METHODS: The snails, crabs and stools of wild cats were collected for the examinations of cercariae, metacercariae and eggs of Paragonimus. The geographical and environmental conditions of the areas were also investigated. RESULTS: A total of 4 890 Pseudobythinella jianouensis snails and 1 035 Semisulcospira liberlina snails were examined, and the cercariae of Paragonimus were only found in P. jianouensis, with an infection rate of 0.10% (5/4 890). Bottapotamon zhengheensis sp. nov. as the second intermediate host of P. skrjabini, were examined, and the infection rate was 85.29% (29/34) and the average numbers of metacercariae per crab and per gram of crab tissues were 3.85 and 0.62, respectively. Thirty-six Sinopotamun fujianensis crabs, as the second intermediate host of P. westermani, were examined, and the infection rate was 38.89% (14/36) and the average numbers of metacercariae per crab and per gram of crab tissues were 6.43 and 0.03, respectively. The eggs of Paragonimus were detected in 1 of 2 muck specimens of wild cats. CONCLUSIONS: The data suggest that there is a focus of middle-to-high level of infection caused by P. westermani and P. skrjabini in the eastern part of Zhenghe County.

Investigation on epidemic foci of paragonimiasis in eastern part of Zhenghe County,Fujian Province / 中国血吸虫病防治杂志

Objective To investigate the species and hosts of Paragonimus and its infection rate in eastern part of Zhenghe County,Fujian Province,so as to determine the local foci of Paragonimus. Methods The snails,crabs and stools of wild cats were collected for the examinations of cercariae,metacercariae and eggs of Paragonimus. The geographical and environmental conditions of the areas were also investigated. Results A total of 4 890 Pseudobythinella jianouensis snails and 1 035 Semisul?cospira liberlina snails were examined,and the cercariae of Paragonimus were only found in P. jianouensis,with an infection rate of 0.10%(5/4 890). Bottapotamon zhengheensis sp. nov. as the second intermediate host of P. skrjabini,were examined, and the infection rate was 85.29%(29/34)and the average numbers of metacercariae per crab and per gram of crab tissues were 3.85 and 0.62,respectively. Thirty?six Sinopotamun fujianensis crabs,as the second intermediate host of P. westermani,were examined,and the infection rate was 38.89%(14/36)and the average numbers of metacercariae per crab and per gram of crab tissues were 6.43 and 0.03,respectively. The eggs of Paragonimus were detected in 1 of 2 muck specimens of wild cats. Conclu?sion The data suggest that there is a focus of middle?to?high level of infection caused by P. westermani and P. skrjabini in the eastern part of Zhenghe County.

Complete mitochondrial genome of a freshwater snail, Semisulcospira libertina (Cerithioidea: Semisulcospiridae).

The first complete mitochondrial genome (mitogenome) of Cerithioidea (Gastropoda: Caenogastropoda) was determined using a freshwater snail Semisulcospira libertina (Cerithioidea: Semisulcospiridae) as a representative species of the superfamily. The mitogenome was 15,432 bp in length, including 13 typical invertebrate protein-coding genes, 22 transfer RNA genes and 2 ribosomal RNA genes. The overall base composition was 31.4% for A, 17.8% for C, 34.8% for T and 16.0% for G with a A+T bias. The mitogenome of S. libertina displayed novel gene order arrangement compared with published Caenogastropoda mitogenomes to date. This mitogenome contributed in resolving phylogenetic position and interrelationships of Cerithioidea.

SDS-PAGE for foot proteins of Semisulcospira in Zhejiang Province / 中国血吸虫病防治杂志

Objective To understand the biochemical characters of the intra-species of Semisulcospira and importance of paragonimiasis transmission. Methods The foot proteins of six species of Semisulcospira in Zhejiang Province were studied and compared by SDS-PAGE. Results 17-20 protein bands were found with molecular weight 27-162 kDa. Two strong bands,93 kDa and 52 kDa, were the same among the six species of Semisulcospira. The similitude coefficient was 0.74-0.85. Conclusion Two strong bands,93 kDa and 52 kDa, would be the protein markers of Semisulcospira, which may be related to the transmission of paragonimiasis.[