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 'vul nerable to extinction' in the Red Data Book of Japanese wild plants. A tota l of 161 individuals were sampled from five populations on four islands. Ge netic diversity values at the population level were very low, compared to o ther plant species with a similar life history. Genetic variability at the species level is comparable to the mean value of endemic species. Genetic d ifferentiation among populations is extremely high (G(ST) = 0.71), indicati ng that the gene flow among populations is highly impeded, and pollen and s eed dispersal is limited due to the pollinators and the seed morphology. Th is is because the four islands are geographically isolated. Fixation indice s suggested that most populations do not randomly cross. To conserve the ge netic diversity of the species, artificial crossings among different island populations are necessary.