Genetic diversity in the threatened insular endemic plant Aster asa-grayi (Asteraceae)

Genetic diversity in an insular endemic plant Aster asa-grayi was examined using enzyme electrophoresis. Distribution of A. asa-grayi is restricted to only four subtropical islands of Japan, and this species is listed as 'vulnerable to extinction' in the Red Data Book of Japanese wild plants. A total of 161 individuals were sampled from five populations on four islands. Genetic diversity values at the population level were very low, compared to other plant species with a similar life history. Genetic variability at the species level is comparable to the mean value of endemic species. Genetic differentiation among populations is extremely high (G(ST) = 0.71), indicating that the gene flow among populations is highly impeded, and pollen and seed dispersal is limited due to the pollinators and the seed morphology. This is because the four islands are geographically isolated. Fixation indices suggested that most populations do not randomly cross. To conserve the genetic diversity of the species, artificial crossings among different island populations are necessary.