Morphological and molecular analysis of the tropical hermit crab Calcinus vachoni (Decapoda, Diogenidae) and its potential association with colonial anemone.

Calcinus is the colorful hermit crab genus belonging to the family Diogenidae and is often found in coral reefs of the tropical Indo-West Pacific region, including southern Honshu, Japan, which is the northern limit of their occurrence. In the present study, we found C. vachoni for the first time in the intertidal zone of Jeju Island-the southernmost island of South Korea. We examined their morphology and provided a diagnosis of their morphological details with illustrations. In addition, the Korean Calcinus population was genetically characterized using mtDNA cox1 sequences and by placing them into three previously reported regional haplogroups. The phylogenetic tree from maximum likelihood analysis revealed that Korean C. vachoni is assigned to the C. vachoni haplogroups exclusively, one of the three well-supported mitochondrial haplogroups with distinct geographic ranges (i.e., C. vachoni, C. aff. vachoni Cooks, and C. aff. vachoni Mascarenes). This result provides new information on the species distribution of C.vachoni, extending their geographic range further north into the southern coast of Korea. In this study, we also first report the potential association of C. vachoni with their co-occurring colonial anemone species Palythoa aff. mutuki and dead coral head of Pocillopora species based on our on-site observation and a public coral collection database of Calcinus species. However, their ecological association with co-occurring coral species is putatively assumed for now and therefore has to be validated by compelling evidence from further field observation and experimental studies (i.e., whether the presence/absence of colonial anemones affects the behavior and survival of the hermit crabs).

Cryptic diversity and population genetic structure of the mantis shrimp Oratosquilla oratoria in South Korea.

BACKGROUND: The Japanese mantis shrimp Oratosquilla oratoria has two genetic lineages in its Chinese and Japanese populations, which are considered cryptic species. However, the Korean O. oratoria populations have only been studied morphologically, and their genetic diversity pattern remains unknown. OBJECTIVE: To examine the genetic diversity of the Korean O. oratoria populations to explore its cryptic diversity and underlying processes. METHODS: We sequenced the mitochondrial cytochrome c oxidase I gene of 107 O. oratoria individuals from 8 sampling sites in South Korea. Their genetic diversity and haplotype data were compared to previously reported data from 16 Chinese and 6 Japanese populations. RESULTS: The haplotype network, analysis of molecular variance, FST values, and Bayesian skyline plot of the Korean O. oratoria populations confirmed that they were divided into two genetic lineages corresponding to the two previously identified cryptic species, which might be correlated to ocean currents and water temperature. In addition, the population genetic analysis indicated that both lineages had high genetic diversity. Although the Geoje region belongs to the southern group, it only contained lineage N, which could be related to the specific environmental characteristics of Geoje or the hybridization of the two lineages of O. oratoria. CONCLUSION: Korean O. oratoria populations have enough cryptic diversity to be described as cryptic species and are correlated with ocean currents and water temperatures. Lineage N dominance in Geoje might be related to environmental characteristics or hybridization.

Population genetic analysis reveals secondary contact between Eriocheir sinensis and E. japonica in South Korea.

BACKGROUND: The Chinese mitten crab (Eriocheir sinensis) and the Japanese mitten crab (E. japonica) of the family Varunidae, which are also critical fishery species in their native habitats, including China, Japan, and South Korea, exhibit a rare migration life history for the decapod life cycle. Eriocheir sinensis and E. japonica in South Korea may have originated from speciation or secondary contact in South Korea after speciation of these two species; however, the genetic relationship between these South Korean populations remains unclear, and need to be clarified. OBJECTIVE: This study examined the population genetic properties of E. sinensis and E. japonica in South Korea to reveal the origin of their co-existence. METHODS: Mitochondrial DNA cytochrome c oxidase I sequences of 120 E. sinensis and E. japonica from 6 sampling sites in South Korea were sequenced. Their genetic diversity and haplotype data were compared to previously reported data from the Chinese mainland, Taiwan, Japan, and Russia. RESULTS: The haplotype network, analysis of molecular variance, FST values, Mantel test, and Bayesian skyline plot results of South Korean E. sinensis and E. japonica demonstrated that E. sinensis and E. japonica were isolated from their central populations, Chinese and Japanese populations, by the distance due to the temperature, salinity, ocean current flow, or a geohistorical event. In addition, genetic analysis indicated that the South Korean populations of the two species were marginal populations, exhibiting low genetic diversity, significant negative neutrality values, and radial haplotype networks. The current results also suggest that the Geum River is an overlapping habitat for the natural populations of E. sinensis and E. japonica in South Korea. Further research is required to examine the geohistorical and evolutionary event between E. sinensis and E. japonica in South Korea. CONCLUSIONS: The co-existence of E. sinensis and E. japonica in South Korea may have originated from secondary contact after their speciation.

Morphological and molecular analyses of parasitic barnacles (Crustacea: Cirripedia: Rhizocephala) in Korea: preliminary data for the taxonomy and host ranges of Korean species.

Morphological and molecular analyses of Korean rhizocephalan barnacle species were performed to examine their host ranges and taxonomy. Morphological examination and molecular analysis of mtDNA cox1, 16S, and nuclear 18S rRNA sequences revealed nine rhizocephalan species from three genera of the two families, Sacculinidae and Polyascidae. Phylogenetic analysis of molecular sequences revealed two new species candidates in the genus Parasacculina, and three Sacculina species (S. pilosella, S. pinnotherae, and S. imberbis) were transferred to the genus Parasacculina. Examination of host ranges revealed higher host specificity and lower infestation rates in Korean rhizocephalan species than rhizocephalans from other geographic regions. This is the first report of the taxonomy, species diversity, and host ranges of Korean parasitic rhizocephalan barnacles based on their morphological and molecular analyses. More information from extensive sampling of parasitic barnacles from a wide range of crustacean host species is necessary to fully understand their taxonomy, prevalence on decapod hosts, and phylogenetic relationships among major rhizocephalan taxa.

Comparative study of the hemolymph microbiome between live and recently dead American lobsters Homarus americanus.

Lobsters and other crustaceans do not have sterile hemolymph. Despite this, little is known about the microbiome in the hemolymph of the lobster Homarus americanus. The purpose of this study was to characterize the hemolymph microbiome in lobsters. The lobsters were part of a larger study on the effect of temperature on epizootic shell disease, and several died during the course of the study, providing an opportunity to examine differences in the microbiomes between live and recently dead (1-24 h) animals. The hemolymph microbiomes of live lobsters was different from those in dead animals and both were different from the tank microbiome in which the animals had been held. The microbiomes of live lobsters were more diverse and had a different suite of bacteria than those from dead animals. The dominant taxa in live lobsters belonged to Flavobacteriaceae and Rhodobacteraceae, whereas Vibrionaceae and Enterobacteriaceae were predominant in the dead lobsters. Although aquarium microbiomes overlapped with the hemolymph microbiomes, there was less overlap and lower abundance of taxa in comparison with hemolymph from live lobsters. Previous studies reporting bacteria in the digestive tract of lobsters suggested that Vibrionaceae and Enterobacteriaceae had invaded the hemolymph via the gut. Our study suggests that hemolymph bacteria abundant in live lobsters do not originate from the tank milieu and comprise a rich, natural, or native background of bacterial constituents.

Phylogeographic studies on two shore crab species from East Asia: similar but different stories.

BACKGROUND: The genetic structure of marine organisms in the East Asian region has long been a subject of interest. Two grapsid crab species, Hemigrapsus penicillatus (De Haan, 1835) and Hemigrapsus sanguineus (De Haan, 1835), are commonly found in the rocky intertidal zones around this region. They are known to spread via larval migration, which makes them an appropriate model species for observing the genetic structure of East Asian intertidal invertebrate animals. OBJECTIVE: We investigated the genetic structure of the East Asian crabs H. penicillatus and H. sanguineus. METHODS: We collected specimens of H. penicillatus from seven locations (42 individuals) and of H. sanguineus from ten locations (58 individuals) in Korea, Japan, and Taiwan. We investigated and compared the genetic diversity and structure of populations of these species using mitochondrial cytochrome oxidase subunit I (COI) sequences. RESULTS: Our results show that both species are genetically structured between South Korea and Japan, and that the Taiwan population forms a cluster that is separate from those of the other countries. Populations of H. penicillatus contain less genetic diversity than those of H. sanguineus. CONCLUSION: These results suggest that there is a genetic structure between the two species at present in East Asia.

Diversity of Parasitic Peltogastrid Barnacles (Crustacea: Cirripedia: Rhizocephala) on Hermit Crabs in Korea.

We performed a diversity study on parasitic barnacles (Crustacea: Cirripedia: Rhizocephala: Peltogastridae) that parasitize hermit crabs in Korea. Their morphological, ecological, molecular (cytochrome c oxidase subunit I, 16S rRNA), and biogeographical characteristics were examined. Three species were identified based on GenBank sequences and the external morphology of the externa. In addition, this study proposes four new candidate species. This is the first report on the family Peltogastridae from Korea. Six hermit crab species were found to be new hosts to peltogastrids. Korean peltogastrids are less prevalent on their host hermit crabs than those from Japan are, especially in the west coast of Korea. Peltogasterella gracilis is widely distributed throughout Korea, Peltogaster lineata is located on the east coast, and Peltogaster postica is only located on Jeju Island.

Subdividing the Common Intertidal Hermit Crab Pagurus minutus Hess, 1865 (Decapoda: Anomura: Paguridae) Based on Molecular, Morphological and Coloration Analyses.

Jibom Jung, Jongwoo Jung, and Won Kim (2018) A phylogenetic study was conducted to investigate whether distinct genetic groups are present within the East Asian Pagurus minutus. In this study, 167 individuals of P. minutus were collected along the coasts of South Korea, east coast of Honshu, west coast of Kyushu, Okinawa Islands of Japan, and Taiwan. The collection of P. minutus was divided into three groups based on the differences in cytochrome c oxidase subunit I (COI) sequences and morphological and color characters: Major Group (MAG), Minor Group (MIG), and Taiwan-Okinawa Group (TOG). MAG commonly inhabits the entire coast of South Korea (except for the northeast coast), east coast of Honshu, and west coast of Kyushu in Japan. MIG predominantly inhabits the northeast coast of South Korea, while a small proportion inhabits the west coast of South Korea and west coast of Kyushu in Japan. TOG is restricted to Taiwan and the Okinawa Islands of Japan. The COI divergence among MAG, MIG, and TOG was larger than the minimum interspecific divergence of the other Pagurus species. Little ingroup COI divergences exist in the MAG and MIG, but distinct ingroup COI divergence is present between the two subgroups of TOG inhabiting Taiwan and Okinawa Islands. MAG, MIG, and TOG show minor differences among morphological characters. Each specimen of these three groups has distinguishing color patterns. These differences in molecular, morphological and color characters suggest that P. minutus are separated into three groups at the species level, and this subdivision of P. minutus shows that additional phylogenetic studies of other hermit crabs and common marine decapod species in East Asia are needed.