Kohji Uchida

GENETIC DIVERSITY IN FAGUS CRENATA (JAPANESE BEECH) : INFLUENCE OF THE DISTRIBUTIONAL SHIFT DURING THE LATE-QUATERNARY

Genetic diversity at 11 loci encoding nine enzymes was studied in 23 populations of Japanese beech Fagus crenata Blume distributed throughout the range of the species. Levels of genetic diversity were high for both within species (expected mean heterozygosity: 0.194) and within populations (expected mean heterozygosity: 0.187), whereas the level of genetic diversity among populations was low (GST = 0.038), as observed in various long-lived, woody plants. Despite the low differentiation among populations, geographical patterning of the variation was observed. Populations in south-western Japan tended to have greater within-population variation and to be more highly differentiated when compared with those in north-eastern Japan. In addition, allele frequencies observed at eight loci were significantly related to latitudinal and/or longitudinal gradients and showed clinal variation across the range of the species. Principal components analysis revealed that the populations tended to cluster according to their geographical locations. The nonrandom patterns of variation were probably shaped by relatively recent historical events such as late-Quaternary migration and founding events.

Genetic diversity and the genetic structure of natural populations of Chamaecyparis obtusa : implications for management and conservation

We investigated 25 natural populations of Chamaecyparis obtusa using 51 cleaved amplified polymorphic sequence (CAPS) markers, which were developed using information on sequence-tagged sites (STS) in Cryptomeria japonica. Most CAPS markers have codominant expression patterns, and are suitable for population studies because of their robustness and convenience. We estimated various genetic diversity parameters, including average heterozygosity (He) and allelic richness and found that the more peripheral populations tended to have lower genetic diversity than central populations, in agreement with a previous theoretical study. The overall genetic differentiation between populations was low, but statistically significant (GST=0.039), and similar to the level reported in a previous allozyme study. We attempted to detect non-neutral loci associated with local adaptation to clarify the relationship between the fixation index (FST) and He values for each locus and found seven candidates non-neutral loci. Phylogenetic tree analysis of the populations and Bayesian clustering analysis revealed a pattern of gradually increasing isolation of populations with increasing geographical distance. Three populations had a high degree of linkage disequilibrium, which we attribute to severe bottlenecks due to human disturbance or competition with other species during their migration from refugia after the most recent glaciation. We concluded that the small populations in western Japan and in Kanto district are more important, from a conservation perspective, than the populations in central Japan, due to their genetic divergence, relatively small sizes and restricted areas.

Mitochondrial DNA variation in natural populations of Japanese larch (Larix kaempferi).

Abstract Levels of genetic variation within and among natural populations of Japanese larch [Larix kaempferi (Lamb.) Carrière] were evaluated by Restriction Fragment Length Polymorphism (RFLP) analysis of mitochondrial DNA (mtDNA) obtained from 209 individuals representing 14 natural populations distributed across most of the species’ natural range in central Japan. Polymorphisms were screened by two RFLP techniques: Southern hybridization of mitochondrial gene probes and Polymerase Chain Reaction (PCR)-RFLP analysis of sequence-tagged sites. However, obvious polymorphism was only detected around the coxIII gene, following digestion with the EcoRI restriction enzyme, in the Southern hybridization analysis. Five haplotypes were identified across the 14 populations, with 11 populations exhibiting little or no genetic variation. Within-population genetic variation was low (HS = 0.158), while population differentiation was substantial (a standardized genetic differentiation measure, G’ST = 0.581). The northernmost, marginal population on Mt. Manokamidake made a significant contribution to the total detected genetic variation. The mtDNA variation displayed geographic structure despite the restricted natural distribution of Japanese larch. Results of this study should be useful for establishing criteria for the genetic conservation and management of natural populations of the species.