Comparison of fine-scale spatial genetic structure of two sympatricRhododendronshrub species in forest habitat having different seed weights: A case study

Abstract

AbstractRestricted seed dispersal is one of the most prevalent determinants of spatial genetic structure (SGS) at a fine spatial scale within a plant population.Rhododendron kaempferiandR. semibarbatumare 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. kaempferiproduces threefold heavier seeds thanR. semibarbatum. Therefore, we tested the hypothesis that the intensity of SGS was stronger inR. kaempferithan inR. semibarbatumin a forest stand. We comparatively examined the SGS for 73 individuals ofR. kaempferiand 36 individuals ofR. semibarbatumby 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. semibarbatumexhibited stronger SGS thanR. kaempferi. This result might be explained by the ecological consequences ofR. semibarbatumproducing lighter seeds, which might have greater dispersal efficacy, but its safe sites could be more restricted than those ofR. kaempferi; in contrast,R. kaempferiproducing heavier seeds might have more limited seed dispersal, but its safe sites for seedling establishment could be more prevalent than those forR. semibarbatum. The different strategies for the trade-off between seed weight and site selection of the twoRhododendronspecies might be reflected in the difference in the intensity of SGS in this study plot.