Ice-age endurance: DNA evidence of a white spruce refugium in Alaska

Abstract

Paleorecords offer key information for evaluating model simulations of species migration in response to forecast climatic change. However, their utility can be greatly compromised by the existence of glacial refugia that are undetectable in fossil records (cryptic refugia). Despite several decades of investigation, it remains controversial whether Beringia, the largely unglaciated area extending from northeastern Siberia to the Yukon Territory, harbored small populations of certain boreal tree species during the last glaciation. Here, we present genetic evidence for the existence of a glacial refuge in Alaska that helps to resolve this long-standing controversy. We sequenced chloroplast DNA (cpDNA) of white spruce (Picea glauca), a dominant boreal tree species, in 24 forest stands across northwestern North America. The majority of cpDNA haplotypes are unique, and haplotype diversity is relatively high in Alaska, arguing against the possibility that this species migrated into the region from areas south of the Laurentide Ice Sheet after the end of the last glaciation. Thus, white spruce apparently survived long glacial episodes under climatic extremes in a heterogeneous landscape matrix. These results suggest that estimated rates of tree migration from fossil records may be too high and that the ability of trees to track anthropogenic warming may be more limited than previously thought.Beringia ͉ Picea glauca ͉ refugia ͉ chloroplast ͉ climate change

Chloroplast DNA variation of Betula humilis Schrk. in Poland and Belarus

“…The most common birch haplotypes should be considered ancestral because they are centrally located in the minimum spanning tree and occur at high frequencies (Avise 2000). Polymorphisms involving more than one base substitution are likely to pre-date the LGM (Anderson et al 2006), and hence, birch haplotypes I and II probably diverged before the last glaciation because they differ from one another by three mutations. In contrast, most of the locally occurring and rare haplotypes differ by single mutations from their ancestors, and thus, we believe that these haplotypes are the result of recent mutation events.…”

Evolution and diversification within the intertidal brown macroalgae Fucus spiralis/F. vesiculosus species complex in the North Atlantic

“…The separation between northern and southern entities almost certainly predates the LGM because it is unlikely that so many steps could have evolved in just 20,000 yrs, although divergence may be much higher in a selfing species characterized by smaller population size. One-step mutations based on modeling predictions for mitochondrial DNA suggest 50,000 yrs is minimal (Wares, 2002) and chloroplast DNA (both genes and introns) have an even slower mutation rate (Anderson et al, 2006).…”

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.…”