Genetic structure in chloroplast and nuclear microsatellites in R osa rugosa around sea straits in northern J apan

Sea‐strait geological history and seawater dispersal patterns can affect the genetic structure of coastal plants. We investigated microsatellite (simple sequence repeat, SSR ) variations in chloroplast (cp) and nuclear (n) DNA of the coastal shrub R osa rugosa , native to northeastern A sia, and three species closely related to it. In northern J apan, we sampled R. rugosa along coasts around the S oya and T sugaru straits with different histories of the Q uaternary land formation as a result of different water depths. Both cp SSR and n SSR variations suggest rare hybridization between R . rugosa and the closely related species. Variations in one of two cp SSR s showed genetic differentiation between eastern and western H okkaido. This genetic structure may result from introgression from R. davurica in eastern H okkaido and/or isolation between the eastern and western coastlines of H okkaido as a result of the Q uaternary land formation in the S oya S trait. On the other hand, variations in 10 n SSR s were geographically homogeneous with weak isolation by distance along coastlines. These results suggest that extensive gene flow has been homogenizing the genetic structure of R . rugosa in northern J apan.