Fine‐scale asexual and sexual reproduction in Quercus crispula var. horikawae, a stunted shrub oak, on a mountain with deep snow in central Japan

Abstract

Quercus crispula var. horikawae, a stunted shrub oak, occurs on mountains with deep snow on the Sea of Japan side of Japan. This oak generates patches of multiple creeping stems. It is unclear whether these patches are the result of asexual or sexual reproduction, or both. We therefore aimed to describe the clonal structure and gene flow in Q . crispula var. horikawae on Mount Nasu in central Japan by using nuclear microsatellites. Genotypes of 331 stems with no distinct connection with roots and creeping stems above the ground were determined using nine loci in two study plots, and 64 acorns from three mother genets in a plot were determined using eight loci. The results of the clonal identification indicated that the patches consisted of 51 genets; at least 85% of the stems may have been derived from asexual reproduction through sprouting and layering. The prominence of asexual reproduction may be a result of adaptation to the snowy environment. In contrast, 15% of the ramets in the study plots probably originate via sexual reproduction by seedling regeneration. Analyses of the spatial genetic structure and paternity showed that limited ability of the pollen and seeds to disperse might result in the spatial aggregations of closely related offspring at a relatively short distance (<10 m), and inbreeding, a factor that might reduce sexual reproduction, was not observed. Thus, sexual reproduction could be reduced by ecological rather than genetic factors, namely the hindrance of seedling regeneration by the dense coverage of dwarf bamboo (Sasa) on the forest floor.