Population Genetics And Phylogeography Of Saccharina Japonica In Northwestern Pacific Ocean

Saccharina japonica is a commercially and ecologically important brown seaweed and native to coast of Northwestern Pacific Ocean. To understand its origins, distribution and evolutionary history, we conducted population genetic and phylogeorgraphic analysis, which will be benefitial to the genetic breeding, conservation and utilization of the kelp. Followed results are obtained:(1) Based on the twomitochondrial markers(cox1 and trn W-L sequences), we investigated the genetic diversity, genetic structure and demographic history of the 26 S. japonica populations(612 individuals). It is showed that the kelp populations along the coast of Hokkaido in Japan exhibited the highest genetic diversity. Bayesian Analysis of Population Structure(BAPS) revealed four clusters in the kelp species(cluster 1: Hokkaido and South Korea; cluster 2: northwestern Hokkaido; cluster 3: Far Eastern Russia; cluster 4: China). The network inferred from concatenated data exhibited two shallow genealogies corresponding to two BAPS groups(cluster 2 and cluster 3). No direct gene flow between these two shal ow kelp genealogies, but the populations within genealogy exhibited the asymmetric gene exchange. Bayesian skyline plots(BSP) and neutrality tests implied that S. japonica populatio ns experienced postglacial expansion around 10.45 ka.(2) Two mitochondrial molecular markers(cox1 and trn W-L) and 24 microsatellite loci were used to study the origin, distribution and genetic patterns of the wild S. japonica populations. Compared with the other populations, those along the coast of Oshima in Hokkaido exhibited the highest genetic diversity, and with more private haplotypes and higher private al ele frequency. The most reasonable evolutio nar y scenario indicated that S. japonica originated from Oshima in southeastern Hokkaido, migrated into the western coast of Hokkaido and inched in the coast of Sakhalin in Russia. The kelp distribution process was presmuly driven by the Tsushima current; moreover the Limen current facilitated their distribution in the western coast of Japan Sea. The populations in the Far-eastern Russia coast formed into one genetic group, and those of Japanese and Korean formed the other genetic group, while populations in Sakhalin and northern coast of Hokkaido had genetic mixture. Due to the Limen current influences, the populations in western coast of Japan Sea exhibited significant genetic differentiation with the other kelp populations.(3) Nineteen microsatellite loci were used to explore the influence of domestication and breeding on the genetic patterns of S. japonica. It is showed that the wild kelp populations exhibited higher genetic diversity than the cultivated populatio ns. General y, consecutive selection, breeding and cultivation resulted in the decline of genetic diversity. Genetic structure of S. japonica populations could form into two major groups, the wild group(including the wild populations in Russia and Japan) and the domesticated group(including all populations in China except for DF3), which was confirmed by 30.49% of genetic variance between these two groups. Moderate genetic differentiation existed between the northern and southern cultivated kelp populatio ns, and it might be caused by the different breeding programme and seawater temperature influences. Referred from higher genetic similarities among the three wild populatio ns in Hokkaido and Honshu and Chinese populations, we proposed wild germplasm in Hokkaido and Honshu might be introduced to China for breeding and cultivation.