Phylogeographic History of White Spruce During the Last Glacial Maximum: Uncovering Cryptic Refugia

Abstract

Although a recent study of white spruce using chloroplast DNA uncovered the presence of a glacial refuge in Alaska, chloroplast failed to provide information on the number or specific localities of refugia. Recent studies have demonstrated the utility of nuclear microsatellites to refine insights into postglacial histories. The greater relative rate of mutation may allow finer scale resolution of historic dynamics, including the number, location, and sizes of refugia. Genetic data were acquired from screening 6 microsatellite loci on approximately 14 trees from each of 22 populations located across the central and western boreal forests of Canada and Alaska. Our studies combining microsatellites with Bayesian analyses of population structure in white spruce support the phylogeographic patterns uncovered using chloroplast, separating Alaskan from non-Alaskan regions. Results also support the idea that north-central Alaska served as a glacial refugium during the last glacial maximum. Additionally, the relationship between the degree of genetic differentiation and geographic distance indicated that gene flow played a more important role in structuring non-Alaskan populations, whereas drift played a more important role in structuring Alaskan populations (R(ST)'s for non-Alaskan populations 0.029 ± 0.007 and 0.083 ± 0.012 for Alaskan populations). Microsatellites also substantiate the bidirectional patterns of gene flow previously uncovered using chloroplast DNA but indicate much greater movement and mixing. Results from our Bayesian analyses also suggest the existence of additional cryptic refugia. However, the locations have been obscured by high gene flow (R(ST) averaging 0.057 ± 0.004).

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

“…More favorable environmental conditions for sexual reproduction and successful trembling aspen seedling establishment in this area [57, 58] may have contributed to increase allelic richness through recombination in populations from the Albertan foothills of the Rocky Mountains. The existence of a refugium in Beringia during the LGM has been reported for P. glauca [9, 23] and was consistent with the model simulation of suitable refugial habitats for this species (performed with the Community Climate Model and the Geophysical Fluid Dynamics Laboratory Model) [8], which suggested the presence of P. glauca in Beringia during the LMG. Moreover, those simulations also suggested the presence of suitable habitats for P. contorta and P. tremuloides in Beringia [8].…”

“…Williams [7] and Roberts and Hamann [8] have reconstructed the evolution of land covered by several tree species in North America since the LGM, thereby allowing the identification of potential refugia for those species. Also, molecular studies have shown evidence of genetic structure for several North American plant species [9–14]. …”

Late Quaternary environmental and landscape dynamics revealed by a pingo sequence on the northern Seward Peninsula, Alaska

“…However, more recent work by Anderson et al (2006Anderson et al ( , 2011 report phylogeographic evidence of possible local Beringian spruce populations, which reintroduces the notion of a glacial refugium. Brubaker et al (2005) suggest that spruce pollen values during the LGM and Lateglacial, while low, may nevertheless indicate restricted spruce populations.…”

Extending glacial refugia for a European tree: genetic markers show that Iberian populations of white elm are native relicts and not introductions

“…For many widespread tree species, it is precisely the populations at the edge of the distribution range that accumulate most of the intraspecific genetic variation, either because they correspond to glacial (micro-) refugia (for example, Kelly et al, 2010;Anderson et al, 2011), or because they represent contact zones between migrants from such refugia (Hewitt, 2004;Magri et al, 2006). Conservation of natural marginal populations of species has therefore long been considered crucial for the preservation of genetic diversity and evolutionary potential (Newton et al, 1999;Moritz, 2002).…”