Phylogeography of Japanese horse chestnut (<Emphasis Type="Italic">Aesculus turbinata</Emphasis>) in the Japanese Archipelago based on chloroplast DNA haplotypes

Japanese horse chestnut (Aesculus turbinata: Hippocastanaceae) is one of the typical woody plants that grow in temperate riparian forests in the Japanese Archipelago. To analyze the phylogeography of this plant in the Japanese Archipelago, we determined cpDNA haplotypes for 337 samples from 55 populations covering the entire distribution range. Based on 1,313 bp of two spacers, we determined ten haplotypes that are distinguished from adjacent haplotypes by one or two steps. Most of the populations had a single haplotype, suggesting low diversity. Spatial analysis of molecular variance suggested three obvious phylogeographic structures in western Japan, where Japanese horse chestnut is scattered and isolated in mountainous areas. Conversely, no clear phylogeographic structure was observed from the northern to the southern limit of this species, including eastern Japan, where this plant is more common. Rare and private haplotypes were also found in southwestern Japan, where Japanese horse chestnuts are distributed sparsely. These findings imply that western Japan might have maintained a relatively large habitat for A. turbinata during the Quaternary climatic oscillations, while northerly regions could not.     

Identification of 2chromosome region translocated onto the W chromosome by RFLP with EST-cDNA clones in the Gensei-kouken strains of the mulberry silkworm, Bombyx mori L

In silkworms, sex-limited strains are either obtained spontaneously or induced by X-rays or gamma rays. When a fragment of an autosome carrying a dominant allele of those genes responsible for certain characters is translocated onto a W chromosome, the female of the successive generations will express these phenotypic characters and sex discrimination can be facilitated. Gensei-kouken strains are sex-limited strains of silkworms developed by irradiating the pupae with gamma rays, by which a portion of the second chromosome is translocated onto the W chromosome. In these improved strains, the females are yellow-blooded and spin yellow cocoons. By using the EST-cDNA clones mapped on the Z chromosome, we identified the sex according to the polymorphic banding pattern or intensity of the signals. Furthermore, by using the clones on the second chromosome, the region of the second chromosome translocated onto the W chromosome was also defined. In both the A95 and A 96 strains selected for the present study, only the mid-portion of the second chromosome was translocated. The differences in length of the fragments translocated in these strains are discussed.     

Gene flow in an endangered willow <Emphasis Type="Italic">Salix hukaoana</Emphasis> (Salicaceae) in natural and fragmented riparian landscapes

Salix hukaoana is an endangered riparian pioneer tree that is distributed within a restricted area of Japan. Microsatellite genetic variations and genetic structures were investigated in 80 subpopulations patchily distributed within five river basins with varying degrees of habitat fragmentation. The correlation between geographic distance and genetic distance based on the Bayesian assignment test was significant across relatively intact riparian habitats, with steeper slopes of regression for more densely grouped subpopulations, suggesting restricted gene flow. However, the correlation became less apparent with increasing spacing of the habitat patches. These contradictory results are attributed to the increased chance of long-distance dispersal of sexual propagules among more isolated habitat patches. The observed accumulation of genetic diversity with increasing distance downstream along a few, but not all, of the rivers and the results of assignment tests suggested a downstream directionality of gene flow. The results of this study illustrate the patterns of genetic diversity and contemporary dispersal of S. hukaoana, and provide important insights into understanding the gene dispersal of riparian trees and into the conservation of genetic resources for this species.     

Analysis of topography and vegetation distribution using a digital elevation model: case study of a snowy mountain basin in northeastern Japan

This study examines the relations between the local variations in vegetation and topography using logistic regression (LR) and GIS in a snowy basin in the Ohu Mountains of northeastern Japan. The spatial distribution of seven vegetation classes interpreted from aerial photographs—(a) large-sparse crown beech forest, (b) middle-dense crown beech forest, (c) dwarf beech scrub, (d) dwarf bamboo thicket, (e) Japanese white pine forest, (f) snow-avalanche scrub or meadow, and (g) riparian forest—was analyzed with terrain parameters derived from a 10 m digital elevation model (10 m DEM) and parameters of landslide distribution and surface geology. While large-sparse crown beech forests dominate the slopes, smaller crown beech forests or scrubs are often found on the west-facing (i.e., windward side) upper parts of slopes and crests. On the contrary, snow-avalanche scrubs or meadows are found on the leeward side of steep slopes and concave plan curvatures. Dwarf bamboo thickets are often found on east-facing (i.e., leeward side) gently sloping crests, where the snow remains until summer. Japanese white pine forests respond positively to sharp ridges, whereas riparian forests show a positive response to the gently sloping lower parts of slopes and bottomlands at low elevation. The heterogeneous vegetation distribution in the basin indicates differences in site conditions (e.g., soil–water conditions), and the existence of various disturbance regimes induced by the strong winter monsoon with heavy snowfall, snow movements (e.g., avalanches), and temporal differences in snowmelt on different topographies. The estimated vegetation maps could be used for forest management and restoration.