Genetic differentiation within and among island populations of the endangered plant Aster miyagii (Asteraceae), an endemic to the Ryukyu Islands

Genetic diversity was examined at 17 putative allozyme loci in 18 populations of the insular endemic plant Aster miyagii (Asteraceae). This species is geographically restricted to only three islands of the Ryukyu Islands and is on the federal list of threatened plants. Genetic differentiation within an island is small, suggesting that gene flow among populations on the same island is sufficiently large to prevent divergence. By contrast, genetic differentiation among islands is large, especially between Amamioshima Island and the other two islands, suggesting that gene flow between the islands is highly restricted. Two unique alleles are nearly fixed in populations on Amamioshima Island, which is the southernmost island of the three. Comparatively, genetic diversity is the smallest on Amamioshima Island. This genetic paucity on Amamioshima Island is probably a result of a population bottleneck at colonization or the small effective population size on this island. Genetic diversity at the species level of A. miyagii is larger than those of the species with a similar life history and of the congeneric widespread species, suggesting that the species has an old origin as an insular endemic species.