Novel implications on the genetic structure of representative populations of Saccharina japonica (Phaeophyceae) in the Northwest Pacific as revealed by highly polymorphic microsatellite markers

Although the original Saccharina japonica populations in China are assumed to have been accidentally introduced from Japan in 1920s, few investigations have been performed to prove it. Genetic structure analysis is expected to shed light on this question. In the present study, 11 highly polymorphic microsatellite markers were employed to analyze the genetic structure of representative populations of S. japonica in the Northwest Pacific, including the four varieties from Japan. Populations from China had a much lower level of genetic diversity than the ones from Japan in terms of the number of alleles, private alleles and locally common alleles, and the values of heterozygosity, suggestive of the founder effect in the introduced populations. Both the Bayesian model-based and genetic distance-based analyses revealed three major clusters: (1) S. japonica var. japonica, var. religiosa, and var. ochotensis from Hokkaido, as well as the populations from Korea and Russia; (2) populations from China; and (3) var. diabolica. Saccharina japonica var. diabolica harbored the highest number of private alleles, with three of them having a frequency of 1.00 at three loci, which have the potential to be used as specific markers to distinguish this variety from others. Significant genetic differentiation was found between almost all the populations except for a few cultivated populations from China. Populations from China were most closely related to S. japonica var. japonica, which was in turn most close to var. religiosa and the Korean population. The microsatellite markers used in this study were shown to be polymorphic enough to decipher the subtle genetic structure of S. japonica, including the different varieties.