Molecular evidence reveals a closer relationship between Japanese and mainland subtropical specimens of a widespread tree species, Acer mono

Clarifying the evolutionary relationship between island organisms and those of the adjacent mainland is critical in understanding the dispersal and evolution of species. Considerable research has been conducted on the relationship between plants of the East Asian mainland and the Japanese archipelago as well as the roles of the East China Sea and the Korea (Tsushima) Strait in plant evolution. However, most previously studied species have limited range distributions, which may preclude a comprehensive understanding. Acer mono is a widespread deciduous tree in East Asia. By integrating chloroplast DNA sequences and nuclear microsatellite data, we identified a close genetic relationship between Japanese and subtropical mainland populations. However, different details are revealed by chloroplast DNA sequences and nuclear microsatellite data. The chloroplasts from the northwestern part of the eastern subtropical populations were more closely related to the archipelago populations (CP2 clade), but no shared haplotypes were found, which may indicate an ancestral connectivity. Contrarily, plants from the eastern part of the eastern subtropics and the archipelago populations were assigned into the same gene pool based on nuclear microsatellite data (K = 6), which probably reflects a recent glaciation connection via pollen dispersal. Our study implies that the Korea (Tsushima) Strait may have been a long-term barrier for A. mono, while the East China Sea may have served as a corridor for pollen dispersal.