Continental‐scale assessment of genetic diversity and population structure in quaking aspen (Populus tremuloides)

Abstract

Aim Quaking aspen (Populus tremuloides) has the largest natural distribution of any tree native to North America. The primary objectives of this study were to characterize range-wide genetic diversity and genetic structuring in quaking aspen, and to assess the influence of glacial history and rear-edge dynamics.Location North America.Methods Using a sample set representing the full longitudinal and latitudinal extent of the species' distribution, we examined geographical patterns of genetic diversity and structuring using 8 nuclear microsatellite loci in 794 individuals from 30 sampling sites.Results Two major genetic clusters were identified across the range: a southwestern cluster and a northern cluster. The south-western cluster, which included two subclusters, was bounded approximately by the Continental Divide to the east and the southern extent of the ice sheet at the Last Glacial Maximum to the north. Subclusters were not detected in the northern cluster, despite its continent-wide distribution. Genetic distance was significantly correlated with geographical distance in the south-western but not the northern cluster, and allelic richness was significantly lower in south-western sampling sites compared with northern sampling sites. Population structuring was low overall, but elevated in the south-western cluster.Main conclusions Aspen populations in the south-western portion of the range are consistent with expectations for a historically stable edge, with low within-population diversity, significant geographical population structuring, and little evidence of northward expansion. Structuring within the southwestern cluster may result from distinct gene pools separated during the Pleistocene and reunited following glacial retreat, similar to patterns found in other forest tree species in the western USA. In aspen, populations in the southwestern portion of the species range are thought to be at particularly high risk of mortality with climate change. Our findings suggest that these same populations may be disproportionately valuable in terms of both evolutionary potential and conservation value.

Assessing genetic diversity and population structure of <i>Salix viminalis</i> across Ergun and West Liao basin

“…AMOVA results also showed a moderate differentiation that 6.63% genetic variance was among populations, which was mainly due to the contrast between two basins (Table 3). Our result was consistent with previous studies that the differentiation was low to moderate for species of Saliaceae (Imbert and Lefèvre 2003;Smulders et al 2008;Lin et al 2009;Callahan et al 2013). However, the value of F ST in our study is higher than that for natural populations of S. viminalis in Czech Republic (F ST = 0.05) (Trybush et al 2012), which might be due to that the 12 populations in our study are distributed in two basins with long distance, and they are separated and isolated by Da Hinggan Mountains between them.…”

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

“…This set was subsequently reduced by Callahan [15] to 6 potential refugia for trembling aspen ( Populus tremuloides Michaux), including: Beringia, the Grand Banks, the northeastern United States, the “Driftless Area” of the mid-western United States, the “ice-free corridor” along the and eastern slopes of the Alberta Rocky Mountains, e.g., [16–18] and the Clearwater Refugium of northern Idaho, e.g., [19]. …”

“…For P. tremuloides , two models that were based on paleoecological data suggest the existence of refugial habitats in Beringia and was likely a true refugium for this species. Moreover, Callahan et al [27] have shown the existence of two distinct groups for trembling aspen, namely, one in southwestern USA, and the other in Canada and Alaska. Within the second group, the higher allelic richness that was detected in aspen populations located in Alaska and in Alberta suggests that Beringia was likely to be a true refugium and that the presence of an “ice-free corridor” in Alberta could have permitted to P. tremuloides to persist in this area during the LGM [15].…”

Imaging spectroscopy links aspen genotype with below-ground processes at landscape scales

“…Although microsatellites are generally considered to be neutral markers, differentiation based on microsatellite data can be indicative of genome-wide processes that also result in differentiation in loci coding for quantitative traits [119]. Genetic distance measures based on microsatellite data have been correlated with spatial distance in Western aspen [71], and have been shown to correlate with chemical distance in aspen systems at small spatial scales [59]. The ability of spectra to provide information regarding genetic variation within a species indicates the potential of imaging spectroscopy to assess landscapescale biodiversity in addition to characterizing traits related to chemistry and function.…”

“…Eight microsatellite loci were used to identify individual aspen genotypes: WPMS14, WPMS15, WPMS17, WPMS20 [69], PMGC486, PMGC510, PMGC2571 and PMGC2658 (http://www.ornl.gov/ sci/ipgc/ssr_resources.htm) [70]. Reactions were prepared following Mock et al [45] using primer-specific annealing temperatures provided in Callahan et al [71]. PCR products were analysed on ABI sequencers using and LIZ500 size standards, and scored using ABI GENEMAPPER v. 4 (Applied Biosystems, Rotkreuz, Switzerland).…”