Evolutionary effects of geographic and climatic isolation between Rhododendron tsusiophyllum populations on the Izu Islands and mainland Honshu of Japan

Geographic and environmental isolations of islands and the mainland offer excellent opportunity to investigate colonization and survival dynamics of island populations. We inferred and compared evolutionary processes and the demographic history of Rhododendron tsusiophyllum, in the Izu Islands and the much larger island Honshu, treated here as the mainland, using thousands of nuclear SNPs obtained by ddRAD-seq from eight populations of R. tsusiophyllum and three populations of R. tschonoskii as an outgroup. Phylogenetic relationships and their habitats suggest that R. tsusiophyllum had evolved and migrated from cold north to warm south regions. We detected clear genetic divergence among populations in three regions of Honshu and the Izu Islands, suggesting restricted migration between them due to isolated habitats on mountains even in the mainland. The three regions have different changes in effective population size, especially, genetic diversity and population size of the Izu Islands ...

岛屿与大陆的地理及环境隔离为探究岛屿种群的殖民化与生存动态提供了绝佳契机。我们利用ddRAD-seq技术从8个钝叶杜鹃（Rhododendron tsusiophyllum）种群及3个椿年杜鹃（R. tschonoskii）种群（作为外类群）获得的数千个核单核苷酸多态性（nuclear SNPs），推断并比较了伊豆群岛及被视为大陆的较大岛屿本州岛上钝叶杜鹃的演化过程与种群历史。系统发育关系及其生境表明，钝叶杜鹃由寒冷的北方地区演化并迁移至温暖的南方地区。我们检测到本州岛三个区域及伊豆群岛的种群间存在显著遗传分化，这表明即使在大陆，山脉隔离的生境也导致了种群间迁移受限。这三个区域的有效种群大小变化存在差异，尤其是伊豆群岛的遗传多样性与种群规模……