Masayuki Maki

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 distributed in only a few valleys within an approximately 10 km×6 km area on the Kyusyu Island of Japan, there are a relatively large number of individuals in this area. The percentage of polymorphic loci (P), the number of alleles per locus (A), the observed heterozygosity (HO) and the expected heterozygosity (HE) were 61.9, 1.93, 0.166 and 0.177, respectively, at the population level, and P, A and HE 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. The GST 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, Wrights fixation index and the intragametophytic selfing rate, indicate that the species is outcrossing. High genetic variability, in spite of narrowness of the distribution, may have resulted from a recent rapid decline in the population and/or the large effective population size resulting from the extensive gene flow among the populations.

The effect of geographic range and dichogamy on genetic variability and population genetic structure in Tricyrtis section Flavae (Liliaceae)

Populations of each of the four species of Tricyrtis sect. Flavae were sampled using enzyme electrophoresis to examine the effect of geographic range and dichogamy on the genetic diversity of the species. The most widespread species, T. nana, had the lowest level of genetic diversity at both the population and the species level. The depauperate genetic diversity at the population level of T. nana appears to result from the high self-fertilization of the species. The low genetic diversity at the species level of T. nana probably resulted from the bottleneck effect during the speciation process in which this species diverged from the progenitor species, T. flava. Genetic differentiation among populations was high in both adichogamous T. nana and protandrous T. flava. High self-fertilization in T. nana and the colonizing nature of T. flava are likely the main factors causing the differentiated population genetic structure. In contrast to a previous study on chloroplast DNA (cpDNA) variation in Tricyrtis sect. Flavae, T. nana was most closely related to T. flava, which corresponds to the morphological resemblance of both species.

Effects of Salinity and Temperature on Seed Germination in a Japanese Endangered Halophyte Triglochin maritimum (Juncaginaceae)

Triglochin maritimum (Juncaginaceae). Germination tests were carried out at three salinity levels (0,200,400 mM NaCl in which seeds were exposed to increasing- or decreasing temperatures. Effects of moist-chilling pretreatment (stratification) in 0,200 and 400 mM NaCl on seed germination at 0,200 and 400 mM NaCl, respectively, were also examined. Under the highest salinity condition (400 mM NaCl), no germination was observed. The seeds germinated very well (88%) in fresh-water after 5-month moist-chilling pretreatment. Longer moist-chilling pretreatment resulted in higher germination percentages. Moist chilling pretreatment in 0,200 and 400 mM NaCl for 5 month enhanced germination percentages to 10% (in 400 mM NaCl) –88% (in 0 mM NaCl).

GENETIC DIVERSITY IN ISLAND AND MAINLAND POPULATIONS OF ASTER SPATHULIFOLIUS (ASTERACEAE)

Using starch gel and polyacrylamide gel electrophoresis, we examined allozyme diversity in six island and seven mainland populations of Aster spathulifolius Maxim., a plant species occurring in the coastal regions of Korea and Japan. We estimated four parameters of genetic variability: percentage of polymorphic loci (P), mean number of alleles per locus (A), mean expected frequency of heterozygotes (he), and mean observed frequency of heterozygotes (ho). Genetic diversity within island populations (P = 35.6, A = 1.36, he = 0.103, and ho = 0.097) was not significantly less than within mainland populations (P = 37.1, A = 1 .37, he = 0.102, and ho = 0.092). The proportion of total genetic diversity found among the island populations (GST), among the mainland populations, and the total sample were 0.480, 0.427, and 0.491, respectively, indicating the number of migrants per generation (Nm) were 0.270, 0.335, and 0.259, respectively. This indicates that gene flow among the populations was highly restricted. Genetic diversity at the species level is fairly high for a species with a narrow distribution range. Genotypic frequencies did not deviate significantly from Hardy-Weinberg equilibria in most loci we examined, indicating that random mating occurs in the species.

Spatial Genetic Structure within Two Populations of a Self-Incompatible Perennial, Chionographis japonica var. japonica (Liliaceae)

Intrapopulational spatial genetic structure was examined in two populations ofChionographis japonica var.japonica, a self-incompatible perennial, by spatial autocorrelation analysis of enzyme polymorphism. Although most spatial autocorrelation indices (MoransI) in the shortes distance class were significantly positive, most in the other distance classes did not significantly deviate from the values expected from random distributions of genotypes in both populations. This contrasts with a spatial genetic pattern previously reported for a population of the predominantly selfing congener,C. japonica var.kurohimensis, indicating that pollen-mediated gene flow highly impedes genetic substructuring within populations of outcrossingC. japonica var.japonica. Genetic similarity in very proximate distance found in outcrossingC. japonica var.japonica is probably due to restricted dispersal of seeds.

Identification of conservation measures to protect the Japanese endangered plant species Aster kantoensis

To identify the factors responsible for degrading the habitat of the endangered plant species Aster kantoensis, as well as the vulnerable life stage where this occurs, we carried out sowing experiments. Two natural habitats were simulated, being situated along the floodplains of the Tama River in central Japan. Seeds collected from a natural habitat were sown in two apparently suitable locations (Tomoda and Ishida sites). Germination, survival, growth, and seed production were subsequently monitored from 1993 through to 1997. The Tomoda site was a gravel bar in floodplains formed by flooding in 1991, while the Ishida site (two plots) was one gravel bar where several plants were growing sparsely and another where a population had become extinct in 1992. Seed cohorts completed their life cycle within 3 years at the Ishida site and within 5 years at the Tomoda site. Monitored parameters at Ishida were substantially lower than those at Tomoda. In addition, estimates of population growth indicated an increase at Tomoda and a rapid decrease at Ishida. However, degradation of habitats seemed to occur at Tomoda over the monitored periods. In view of our results, we conclude that natural germination of about 0.13% is needed for increasing population size. The major factors for decreasing population size are believed to be the lack of safe sites for germination and seedling establishment in old habitats (>10years). Conservation measures are suggested based on these findings.