Molecular Species Delimitation of the Genus Reishia (Mollusca: Gastropoda) along the Coasts of China and Korea.

Species of the predatory gastropod genus Reishia Kuroda and Habe, 1971 (Muricidae) inhabit intertidal rocky shores in East Asia. Due to their highly variable external shell morphology, the taxonomy of this genus at species-level is still in need of re-evaluation. Using DNA-based delimitation methods, we aimed to ascertain the number of species of Reishia along the coasts of China and adjacent Asian areas. Also, we looked for diagnostic traits using morphology-based statistical approaches. Our genetic data suggest that the studied individuals comprised two separate species of a Reishia complex in this region, in contrast to the previously proposed four or more taxa. This conclusion is further supported by statistical analyses of shell morphological characteristics. The morphospecies R. bronni (Dunker, 1860), R. jubilaea (Tan and Sigurdsson, 1990), and R. luteostoma (Holten, 1803) were assigned to a single taxon, indicating that they might be synonyms of the same species. The morphospecies R. clavigera (Küster, 1860) singly formed one group, suggesting that it is likely a valid name. The estimated divergence time of the two identified taxa indicates that speciation might have been associated with the sea level and temperature fluctuations during the Plio-Pleistocene period. Our study on Reishia species provides crucial information for further research on the ecology, evolutionary biology, and conservation of this genus.

Phylogeography of the Rock Shell Thais clavigera (Mollusca): Evidence for Long-Distance Dispersal in the Northwestern Pacific.

The present-day genetic structure of a species reflects both historical demography and patterns of contemporary gene flow among populations. To precisely understand how these factors shape current population structure of the northwestern (NW) Pacific marine gastropod, Thais clavigera, we determined the partial nucleotide sequences of the mitochondrial COI gene for 602 individuals sampled from 29 localities spanning almost the whole distribution of T. clavigera in the NW Pacific Ocean (~3,700 km). Results from population genetic and demographic analyses (AMOVA, ΦST-statistics, haplotype networks, Tajima's D, Fu's FS, mismatch distribution, and Bayesian skyline plots) revealed a lack of genealogical branches or geographical clusters, and a high level of genetic (haplotype) diversity within each of studied population. Nevertheless, low but significant genetic structuring was detected among some geographical populations separated by the Changjiang River, suggesting the presence of geographical barriers to larval dispersal around this region. Several lines of evidence including significant negative Tajima's D and Fu's FS statistics values, the unimodally shaped mismatch distribution, and Bayesian skyline plots suggest a population expansion at marine isotope stage 11 (MIS 11; 400 ka), the longest and warmest interglacial interval during the Pleistocene epoch. The lack of genetic structure among the great majority of the NW Pacific T. clavigera populations may be attributable to high gene flow by current-driven long-distance dispersal of prolonged planktonic larval phase of this species.

[COI-based DNA barcoding in Tapetinae species (Mollusca, Bivalvia, Veneridae) along the coast of CHINA].

DNA barcoding has exhibited charming effectiveness in species diagnosis, but some studies suggested the proportion of taxa that cannot be barcode-distinguished was still high. In the present study, the efficiency of the DNA barcoding for delimiting species of subfamily Tapetinae along the coast of China was tested. Fifty one original COI sequences of 11 species in five genera were analyzed. Among these sequences, 43 haplotypes were identified. Saturation plots generated for DNA barcode revealed that transitions became saturated after 10% to 15% sequence divergence. However, transversions were not saturated. Excluding Ruditapes variegata haplotype Hap33 that might be the result of a hybridization event, our finding showed that K2P-distances between conspecific sequences varied from 0% to 2.02% (0.46% on average), distances between congeneric sequences were from 17.21% to 32.24% (24.96% on average), and all conspecifics clustered together in the phylogentic trees. The proportion of individuals that can be distinguished by DNA barcoding was approximately 98% among 51 individuals analyzed in this study. Thus, the results evidenced that subfamily Tapetinae species can be efficiently identified through the use of DNA barcoding.