Geographic isolation and colonization events have been considered complimentary historical processes in shaping the contemporary structure of regional biotas and taxonomic diversity. Accordingly, insight regarding vicariance and geodispersal might be gained by the analysis of phylogenetic pattern of related but geographically isolated taxa. Here, we examined endangered Rhodeus pseudosericeus in the Korean Peninsula based on mitochondrial cytochrome b sequences to provide information regarding the evolutionary origin of Amur-European bitterlings, Rhodeus sericeus and Rhodeus amarus. Our data and the contemporary distribution of R. pseudosericeus indicate that founding individuals have colonized the western coast of the Korean Peninsula via the paleo-Huang He River and since been subdivided into populations isolated by drainage formation. Our phylogenetic analyses indicated that it was likely R. pseudosericeus had a sister relationship to the R. sericeus-amarus complex, indicating that the R. sericeus-amarus clade originated from the dispersal of either R. pseudosericeus or its ancestral lineage. The geodispersal scenario based on our phylogenetic analyses supports the previous hypothesis that the Amur River likely created confluences with some tributaries of the paleo-Huang He River. Overall, the present study offers new insight into the taxonomic entity of R. pseudosericeus and a more comprehensive understanding of the phylogeographic history of R. sericeus and European bitterling lineages.

Gobiids are hyperdiverse compared with other teleost groups, with about 2,000 species occurring in marine, freshwater, and blackish habitats, and they show a remarkable variety of morphologies and ecology. Testing the effectiveness of DNA barcodes on species that have emerged as a result of radiation remains a major challenge in evolutionary biology. Here, we used the cytochrome c oxidase subunit 1 (COI) sequences from 144 species of gobies and related species to evaluate the performance of distance-based DNA barcoding and to conduct a phylogenetic analysis. The average intra-genus genetic distance was considerably higher than that obtained in previous studies. Additionally, the interspecific divergence at higher taxonomic levels was not significantly different from that at the intragenus level, suggesting that congeneric gobies possess substantial interspecific sequence divergence in their COI gene. However, levels of intragenus divergence varied greatly among genera, and we do not provide sufficient evidence for using COI for cryptic species delimitation. Significantly more nucleotide changes were observed at the third codon position than that at the first and the second codons, revealing that extensive variation in COI reflects synonymous changes and little protein level variation. Despite clear signatures in several genera, the COI sequences did resolve genealogical relationships in the phylogenetic analysis well. Our results support the validity of COI barcoding for gobiid species identification, but the utilization of more gene regions will assist to offer a more robust gobiid species phylogeny

Summary Since November 2017, mass mortalities of larvae of bay scallop (Argopecten irradians) were reported in hatcheries located at the southern area of Republic of Korea. Over 90% of larvae aged 5–10 days sank to the bottom of the tank and died. The hatcheries could not produce spat, and thus artificial seed production industry incurred huge losses. We identified Ostreid Herpesvirus‐1 μVar (OsHV‐1 μVar) associated with mass mortality by PCR, sequencing and transmission electron microscopy (TEM). All the samples were positive for OsHV‐1 μVar with 99% sequence identity to previously reported OsHV‐1 μVar sequences. Partial sequence of ORF‐4 of OsHV‐1 detected in this study was more closely related to sequences isolated from Europe. This is the first report to confirm the mortality caused by an OsHV‐1 infection in the bay scallop.

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Rhodeus notatus is a small freshwater bitterling species (Acheilognathidae; Cyprinoidea) native to China and the Korean Peninsula 15,20. Before Kim revised the taxonomy of Rhodeus 15 , R. notatus of the Korean Peninsula was called R. atremius or R. suigensis in Japan or treated as a subspecies of R. atremius (i.e., R. a. atremius and R. a. suigensis) 21. In fact, R. notatus has often been recognized as a member of the species complex including these two Japanese (sub)species and R. fangi in China, because these species share both the same number of chromosomes (i.e., 2n = 46), which is one pair less than other congeners, and other morphological features 22-24. The Korean species was eventually synonymized with R. notatus after it was demonstrated that it had more morphological traits in common with Chinese R. notatus than other species within this species complex 15. On the Korean Peninsula, R. notatus inhabits rivers flowing into the west and south coasts 25. The distribution of this species preserves the historical imprints of migration through the paleo-Yellow River and the process of spreading to the freshwater system on the Korean Peninsula. The species could have migrated between rivers by sharing estuaries on the west coastal continental shelf 11. Given that the continental shelf is not well-developed around the south coastal region, however, estuary coalescence might not be a major way to colonize the rivers flowing into the south coast, but instead it is more likely that gene flow occurred through the sharing of spatially proximal watersheds due to topographical erosion 13. If so, large-scale population migration could not have been possible. In this study, six mitochondrial and eight microsatellite loci were analyzed to estimate the level of intrapopulation genetic diversity, genetic structure among all major populations found on the Korean Peninsula and phylogenetic placement of R. notatus (Fig. 1). The results of these analyses were used to test four specific hypotheses about the geological and biogeographical history of freshwater ecosystem formation on the Korean Peninsula: i) R. notatus on the Korean Peninsula has originated from the paleo-Yellow River system, ii) the populations located in the rivers flowing into the west coast have genetic and phylogenetic signatures of estuary coalescence, iii) the populations of rivers flowing into the south coast where the continental shelf is not well-developed have signatures of history isolated from the western populations, and iv) the populations of the rivers flowing to the south coast, which probably formed through small-scale migration, have signatures of historical genetic drift.