Population genetic structure and phylogenetic origin of Triops longicaudatus (Branchiopoda: Notostraca) on the Korean Peninsula

The small notostracan crustacean Triops longicaudatus (LeConte, 1846) is considered a living fossil, with a geological record that reaches back to the Carboniferous Period, and is widespread in North America. This species has been found since 1986 on the Korean Peninsula and was officially designated by the Korean government as an endangered species. No taxonomic survey has yet been performed for the samples of Triops found in Korea. Here, we examined the population genetic structure from 79 individuals of T. longicaudatus throughout the species' geographical range in Korea and to elucidate the phylogenetic relationships among T. longicaudatus-long, T. logicaudatus-short, and T. newberryi, using the nucleotide sequences of COI (643 bp) and ND1 (444 bp). A total of eight haplotypes in COI and nine haplotypes in NDI were found, and 15 haplotypes (HI-HI5) from the combined data of the two genes were also observed. The nested clade analysis and phylogenetic analyses unambiguously corroborate that the Korean populations are subdivided into three distinct genetic lineages. It is highly likely that the Korean populations of T. longicaudatus belong to T. longicaudatus-short. Additionally, T. longicaudatus-long and T. longicaudatus-short may be different, independent species, based on the present phylogeny, the number of legless abdominal rings (LAR), posterior marginal carapace teeth (PMCT), sexual mode, and egg colour. This work is the first comprehensive population genetic and phylogenetic approach for studying T. longicaudatus from East Asia.