Genetic structure of Saccharina japonica in Japan and finding of a potential mitochondrial region for identification of geographic origin

Abstract

Essential information for the conservation unit is still unclear in commercially important kelp Saccharina japonica. Previous analyses of population genetic structure have yielded inconsistent results regarding the number of clusters, especially in Japan. Thus, the genetic structure of S. japonica in Japan was studied using the mitochondrial nad3-16S rDNA region. We detected 88 haplotypes in the 483 individuals collected from 46 localities. Unique haplotypes and one or a few shared haplotypes at a local scale were found in most localities. The observed genetic structure revealed cryptic invasions of S. japonica within Japan and the potential for the nad3-16S rDNA region to identify the geographic origin. Bayesian Analysis of Population Structure analysis and F_ST suggested genetic distinctiveness in southwestern Hokkaido. The haplotype network showed a more detailed starburst pattern compared with the results of previous studies based on mitochondrial COI and trnW-trnI. Accordingly, S. japonica in Japan may represent one genetic group that experienced a recent expansion. Unique or locally shared haplotypes and similarity in haplotype diversity on various coasts of Hokkaido could be explained by the refugia of S. japonica during the Last Glacial Maximum on various coasts. Furthermore, the present study also recognized inconsistencies in the genetic structure and distribution of S. japonica varieties. Therefore, further investigations focused on the taxonomic validation of varieties are needed.