Molecular phylogenetic, population genetic and demographic studies of Nodularia douglasiae and Nodularia breviconcha based on CO1 and 16S rRNA

Complete mitochondrial genome of the worm snail Thylacodes adamsii (Littorinimorpha: Vermetidae) from South Korea

The worm snail Thylacodes adamsii (Mörch, 1859) (Littorinimorpha: Vermetidae) is a sessile gastropod that mainly inhabits rocky shores along the warm temperate to tropical ocean. Herein, the complete mitochondrial genome (mitogenome) of T. adamsii from South Korea was characterized. The genome is 14,913 bp in length and contains 13 protein-coding genes (PCGs), 22 tRNA genes, and 2 rRNA genes. The genome organization and base composition of T. adamsii are similar to those of other vermetids. A phylogenetic tree was reconstructed using maximum likelihood based on the nucleotide sequences of the 13 PCGs; this tree supported the monophyly of Vermetidae. The complete mitogenome of T. adamsii can assist with molecular species identification and vermetid phylogenetic research in the future.

Demographic and ecological niche dynamics of the Vietnam warty newt, Paramesotriton deloustali: Historical climate influences

Quaternary climatic cycles strongly affected the genetic diversification and ranges of organisms, shaping current genetic structures and distribution patterns. Urodeles provide ideal examples for exploring these dynamics over time and across space. In this study, we integrated a phylogeographic approach and ensemble species distribution modeling (eSDM) to infer the historical demography and distribution patterns of the Vietnam warty newt, Paramesotriton deloustali. Mitochondrial data revealed two groups, West and East, which diverged approximately 1.92 million years ago (Mya). Diversification was likely driven by change in the climate during early stages of the Pleistocene, with increasing monsoon and drought intensities. Biogeographic analysis indicated that the newt's current distribution formed as a result of vicariance events. In addition, the two groups occupy distinct ecological niches. Demographic reconstruction showed signs of expansion in the effective population sizes of the two major groups beginning around 0.11 and 0.15 Mya, respectively. However, eSDM showed fluctuating predicted distributions during the last interglacial, last glacial maximum, mid-Holocene, and present. Mountain systems in northern Vietnam are likely to have served as climatic refuges and to have played a crucial role in safeguarding species from the effects of climate change.

Possible species discrimination of a blotched nerite Nerita albicilla with their distribution pattern and demographic history in the Indo-Pacific

The blotched nerite Nerita albicilla (Linnaeus 1758) is distributed in intertidal areas of the Indo-Pacific. In South Korea, it has been found only in the southernmost region of Jeju Island so far. Owing to its limited distribution, it can be a promising intertidal species helpful for monitoring global climate change effects in the Korean Peninsula. We performed population genetic analyses based on 393 COI haplotypes from 697 N. albicilla, including 167 from this study and 530 from public databases. The results showed that there are two distinct genetic lineages in N. albicilla: PAIO (Palearctic, Australasia, Indo-Malay, and Oceania) and Afrotropic lineages. DNA barcoding gap analyses indicated that the two lineages could be differentiated into two different species: N. albicilla (PAIO) and N. originalis sp. nov. (Afrotropic) (3.96%). Additionally, it was revealed that their divergence time was ca. 5.96 Ma and dramatic diversification of COI haplotypes occurred during the late Pliocene and Pleistocene. The results of MDA, BSP, and neutrality test implied recent population size expansion, which was estimated to be ca. 250 Ka. Finally, we discussed whether the observation of N. originalis sp. nov. in South Korea is due to the northward migration through ocean currents caused by global warming or due to artificial activity through marine transportation.

Population Genetic Structures of the Jellyfish Aurelia coerulea Polyps along Korean Coasts and Implications as Revealed by Mitochondrial COI

The moon jellyfish, Aurelia coerulea, is is globally distributed, and its blooms have been responsible for severe environmental impacts. Benthic polyp populations are important for forming and maintaining medusa populations; however, their genetic structures are mostly unknown. Here, we analysed the genetic structure and phylogeographic pattern of A. coerulea polyps using the mitochondrial COI of 229 specimens collected from four different coastal regions of Korea. Molecular discrimination by COI assigned all polyps to A. coruelea. Population genetics revealed 53 haplotypes with high diversity and significant genetic structure, distinguishing two haplogroups (A and B) that coexist in all regions. Haplogroup A exhibited a star-like haplotype network pattern, while haplogroup B demonstrated a branched haplotype network pattern. Our results suggest that, the two haplogroups detected have existed in sympatry along Korean coasts. However, haplogroup A may have been established by a recent population expansion, while haplogroup B may have been established a long time ago. The strong genetic structure found within the polyp population of A. coerulea may have an effect on the moon jellyfish blooms on Korean coasts.

First Immunodetection of Sensory and Nervous Systems of Parasitic Larvae (Glochidia) of Freshwater Bivalve Nodularia douglasiae

Most freshwater mussels have an unusual life cycle that requires host fish species for larval (glochidia) development and dispersal. Glochidia have a unique morphological structure that adapts to parasitic lifestyles and survival. The morphology of the glochidial shells of most Unionoidea, a group of freshwater bivalve mollusks, has been studied in detail using light and scanning electron microscopy. This study summarizes our data on the glochidia shell morphology of the Asian mussel Nodularia douglasiae from two localities in the Primorsky Territory, the Russian Far East. In contrast to the shell morphology of glochidia, little is known about the neurodevelopment of the Unionoidea. Herein, we first demonstrate that the structures of the sensory, muscle, and nervous systems of the glochidia larvae of N. douglasiae differ dramatically from those of the comparable larval systems of marine bivalve species, as revealed through alpha-acetylated tubulin, serotonin (5-HT), and FMRFamide antibodies as well as phalloidin for detection of F-actin and whole-mount confocal microscopy. We found that the glochidia sensory system included four pairs of tubulin-lir multicilia hair cells. Non-ciliar tubulin-lir cells synthesize the neuropeptide FMRFamide and are identified as afferent neurons collecting information from peripheral tubulin-lir hair sensory cells to nervous regulators. The glochidia’s muscular system was represented by a smooth adductor, retractors, and minor muscle bundles associated with the shell and visceral organs. The 5-HT-lir larval system is arranged most simply and consists of two immunopositive neurons innervating the adductor. The FMRFamide-lir system is more complicated and consists of several neuronal centers comprising neuronal bodies and their neurites in different areas of the larva. The FMRFamide-lir neurons are closely associated with sensory hair cells, and others, together with 5-HT-lir neurons, may be involved in the anlagen of adult ganglia. Thus, the nervous system of N. douglasiae glochidia is drastically different from other mollusks and lophotrochozoans because of the absence of an apical organ and the location and composition of FMRFamide and 5-HT cells. Morphological, molecular, and behavioral investigations of Unionoidea taxa need to be further conducted to investigate the parasite-host relationship, nerve-dependent regulation of parasite behavior, and evolution of mollusks.

Liolophura species discrimination with geographical distribution patterns and their divergence and expansion history on the northwestern Pacific coast

The chiton Liolophura japonica (Lischke 1873) is distributed in intertidal areas of the northwestern Pacific. Using COI and 16S rRNA, we found three genetic lineages, suggesting separation into three different species. Population genetic analyses, the two distinct COI barcoding gaps albeit one barcoding gap in the 16S rRNA, and phylogenetic relationships with a congeneric species supported this finding. We described L. koreana, sp. nov. over ca. 33°24′ N (JJ), and L. sinensis, sp. nov. around ca. 27°02′–28°00′ N (ZJ). We confirmed that these can be morphologically distinguished by lateral and dorsal black spots on the tegmentum and the shape of spicules on the perinotum. We also discuss species divergence during the Plio-Pleistocene, demographic expansions following the last interglacial age in the Pleistocene, and augmentation of COI haplotype diversity during the Pleistocene. Our study sheds light on the potential for COI in examining marine invertebrate species discrimination and distribution in the northwestern Pacific.