Data from: Fine-scale assessment of genetic diversity of trembling aspen in northwestern North America

Background In North America, the last ice age is the most recent event
with severe consequences on boreal species’ ranges. Phylogeographic
patterns of range expansion in trembling aspen (Populus tremuloides)
suggested that Beringia is likely to be a refugium and the “ice-free
corridor” in Alberta may represent a region where small populations
persisted during the last glacial maximum (LGM). The purpose of this study
was to ascertain whether the origins of trembling aspen in western North
America are reflected in the patterns of neutral genetic diversity and
population structure. A total of 28 sites were sampled covering the
northwestern part of aspen’s distribution, from Saskatchewan to Alaska.
Twelve microsatellite markers were used to describe patterns of genetic
diversity. The genetic structure of trembling aspen populations was
assessed by using multivariate analyses, Mantel correlograms,
neighbor-joining trees and Bayesian analysis. Results Microsatellite
markers revealed little to no neutral genetic structure of P. tremuloides
populations in northwestern North America. Low differentiation among
populations and small isolation by distance (IBD) were observed. The most
probable number of clusters detected by STRUCTURE was K = 3 (∆K = 5.9).
The individuals in the populations of the 3 clusters share a common gene
pool and showed a high level of admixture. No evidence was found that
either Beringia or the “ice-free corridor” were refugia. Highest allelic
richness (AR) and lowest heterozygosity (Ho) were observed in Alberta
foothills of the Rocky Mountains. Conclusions Contrary to our hypothesis,
our results showed that microsatellite markers revealed little to no
genetic structure in P. tremuloides populations. Consequently, no
divergent populations were observed near supposed refugia. The lack of
detectable refugia in Beringia and in the “ice-free corridor” was due to
high levels of gene flow between trembling apsen populations. More
favorable environmental conditions for sexual reproduction and successful
trembling aspen seedling establishment may have contributed to increase
allelic richness through recombination in populations from the Albertan
foothills of the Rocky Mountains.