Restricted seed dispersal is one of the most prevalent determinants of spatial genetic structure (SGS) at a fine spatial scale within a plant population. Rhododendron kaempferi and R. semibarbatum are common and coexistent Ericaceous species in the shrub layer of secondary deciduous broad-leaved forests in the northern Kanto District, central Japan. The two species have entomophilous flowers and are thought to have similar pollination styles. However, R. kaempferi produces threefold heavier seeds than R. semibarbatum. Therefore, we tested the hypothesis that the intensity of SGS was stronger in R. kaempferi than in R. semibarbatum in a forest stand. We comparatively examined the SGS for 73 individuals of R. kaempferi and 36 individuals of R. semibarbatum by using highly variable nuclear microsatellite loci. The analysis revealed significant SGS in both species at the shortest distance (<3 m); a measure to quantify SGS showed a counterintuitive result: R. semibarbatum exhibited stronger SGS than R. kaempferi. This result might be explained by the ecological consequences of R. semibarbatum producing lighter seeds, which might have greater dispersal efficacy, but its safe sites could be more restricted than those of R. kaempferi; in contrast, R. kaempferi producing heavier seeds might have more limited seed dispersal, but its safe sites for seedling establishment could be more prevalent than those for R. semibarbatum. The different strategies for the trade-off between seed weight and site selection of the two Rhododendron species might be reflected in the difference in the intensity of SGS in this study plot.

Ohkubo 2016 Genetic Diversity and Mating System of Regionally Endangered Pinus parviflora var. parviflora Populations in the Kanto District, Japan. J Jpn For Soc 98: 65 73 Several Pinus parviflora var. parviflora populations in the Kanto district were thought to be regionally endangered and affected by decreased population size and habitat fragmentation. In order to develop conservation strategies, this study aimed to assess the genetic diversity and mating system of their populations, including three endangered Boso, Tanzawa, and Hanazono and one intact Koshinzan populations, using four nuclear microsatellite SSR loci. The level of genetic diversity of mature trees of the Boso and Tanzawa populations was similar to that of the intact population. Analysis of the mating system revealed that the proportion of selfed progeny of saplings in the endangered populations was higher than that in the intact population and that the endangered populations had a lower effective number of pollen donors compared to the intact population . Multilocus heterozygosity MLH analysis indicated that the frequency of low MLH was high in saplings less than years old. The mode of MLH increased with the life history process. These findings suggest that mature trees in the endangered populations mostly retain high levels of genetic diversity, but the decline in the number of mature trees has resulted in increased selfing and decreased selfed saplings possibly due to inbreeding depression.