High selfing and skewed reproductive success in the northernmost, extremely small and remote population of <i>Pinus parviflora</i> var. <i>pentaphylla</i>

Abstract In 1958, the northernmost population of Pinus parviflora var. pentaphylla , a temperate conifer species, was newly identified in central Hokkaido. It grows in an area of 0.5 ha at a distance of 40 km from the known distributional margin of the species. The population is particularly small, consisting of three reproductive trees and 110 vegetative individuals. For this population, four nuclear microsatellite loci were employed to investigate the reproductive pattern, fine‐scale spatial genetic structure (FSGS), and level of inbreeding, as well as infer the genotypes of two deceased reproductive individuals. The estimated reproductive pattern showed no gene flow, a high selfing rate, and highly skewed reproductive success, all of which can lead to a loss of population genetic diversity in subsequent generations. There was a significant and strong ( S p = 0.140) FSGS among understory individuals, and the mean kinship coefficients for short distance classes were higher than expected for full‐sibs. The strong FSGS reflects the aggregation of full‐sibs caused by the high selfing rate and uneven reproductive success, and may increase inbreeding in subsequent generations. The mean inbreeding coefficient of the understory individuals from the self‐fertilization of a single individual was significantly lower than expected from selfing with random sampling of genes, indicating inbreeding depression. The observed inbreeding depression is expected to hinder the regeneration of this population. Therefore, complete isolation and the limited number of reproductive individuals in the northernmost population unfavorably affect the reproductive process and may result in the loss of population genetic diversity and regeneration potential.