[Genetic characterization of different populations of Rhopilema esculentum based on the mitochondrial COI sequence.]

To investigate the genetic characterization and population genetic structure of Rhopilema esculentum, we sequenced the mtDNA COI gene (624 bp) in 56 individuals collected from Liaodong Bay and the Ganghwado Island in the estuarine waters of the Han River. In addition, the homologous sequences of other 15 individuals which were sampled from the Bohai and Yellow seas and Sea of Japan were analyzed. A total of 28 polymorphic nucleotide sites were detected among the 71 individuals, which defined 32 haplotypes. Haplotype diversity levels were high (0.91±0.06-0.94±0.01) in R. esculentum populations, whereas those of nucleotide diversity were moderate to low [(0.60±0.34)%-(0.68±0.40)%]. Compared with several other giant jellyfish species, the variation level of R. esculentum was high. Phylogeographic analysis of the COI region revealed two lineages. The pairwise F_ST comparison and hierarchical molecular variance analysis (AMOVA) showed that significant population structure existed throughout the range of R. esculentum. The results of this study indicated that the life-cycle characteristics, together with possible anthropogenic introduction such as stock enhancement and the prevailing ocean currents in this region, were proposed as the main factors that determined the genetic patterns of R. esculentum.