HIGH GENETIC-VARIABILITY REVEALED BY ALLOZYMIC LOCI IN THE NARROW ENDEMIC FERN POLYSTICHUM-OTOMASUI (DRYOPTERIDACEAE)

Genetic variability was examined at 16 putative allozymic loci in the narrow endemic fern Polystichum otomasui. Although this species is dis tributed in only a few valleys within an approximately 10 km x 6 km ar ea on the Kyusyu Island of Japan, there are a relatively large number of individuals in this area. The percentage of polymorphic loci (P), t he number of alleles per locus (A), the observed heterozygosity (H-O) and the expected heterozygosity (H-E) were 61.9, 1.93, 0.166 and 0.177 , respectively, at the population level, and P, A and H-E were 81.3, 2 .69 and 0.199, respectively, at the species level, indicating that P. otomasui has extremely high allozymic variation for a fern species. Th e G(ST) value among the 10 populations examined within the range was 0 .108, suggesting that the interpopulation gene flow is high enough to impede genetic structuring. The mating system estimates, Wright's fixa tion index and the intragametophytic selfing rate, indicate that the s pecies is outcrossing. High genetic variability, in spite of narrownes s of the distribution, may have resulted from a recent rapid decline i n the population and/or the large effective population size resulting from the extensive gene flow among the populations.