Genetic structure of Vaccinium vitis-idaea in lowland cool spot and alpine populations : microrefugia of alpine plants in the midlatitudes

Local cool spots (wind-holes) in lowland areas of midlatitudes may act as microrefugia for cold-adapted species outside of their typical alpine habitats. We examined the genetic structure of Vaccinium vitis-idaea, a common alpine species in Japan, in eight lowland wind-hole and five surrounding alpine populations. We collected leaf samples and genotyped seven microsatellite loci. Clonal patches (genets) were common in almost all populations. An analysis of annual shoot growth suggested that individuals in the wind-hole populations were long-lived (> 500 years old). Genetic diversity (allelic richness) and differentiation (F (ST)) of the wind-hole populations were lower and higher than those of the alpine populations, respectively. No significant isolation-by-distance trend in the genetic structure was detected for the wind-hole or alpine populations. All wind-hole populations had negative inbreeding coefficients (F (IS)), suggesting no tendency toward homozygosity due to inbreeding, regardless of the small populations geographically isolated from the large alpine populations. Therefore, wind-holes may harbor genetically isolated but stable populations due to clonal growth, limited gene flow, and abortion of selfed seeds by early acting inbreeding depression. Analysis of molecular variance demonstrated that genetic variations among and within populations contributed more to regional genetic diversity than those between wind-hole and alpine populations, suggesting that the wind-hole and alpine populations are important for maintaining the genetic diversity of midlatitude V. vitis-idaea populations. On the other hand, Bayesian clustering showed that some wind-hole populations geographically close to the alpine populations had mixed genetic compositions of the alpine and wind-hole populations