Population genetic structure and phylogeography of the ascidian, Halocynthia roretzi, along the coasts of Korea and Japan, inferred from mitochondrial DNA sequence analysis

Abstract

Abstract The genetic structure and phylogeography of the solitary ascidian Halocynthia roretzi (sea pineapple) in Korea and Japan were studied based on mitochondrial DNA cytochrome oxidase subunit I ( COI ) gene nucleotide variations. The COI haplotypes found were divided into two clades in a statistical parsimony network. From the extensive haplotype diversity, limited nucleotide diversity, neutrality test, and mismatch distribution analysis, the species appears to have undergone rapid population expansion from an ancestral population with a small effective population size due to glacial bottlenecking in the late Pleistocene. Pairwise population F ST estimates inferred distinct genetic differentiation between the population from the northernmost east coast of Korea and the remaining pooled coastal water populations, while other populations generally exhibited low levels of differentiation. Analysis of molecular variance showed a weak but significant differentiation among three geographic population groups. Overall, the moderate population structure of H. roretzi may have been influenced by high levels of gene flow caused by hydrographic conditions such as sea currents.