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My research focuses on the late-Quaternary migration history of spruce, a taxon that dominates the modern boreal forests. Two alternative hypotheses have been proposed to explain the postglacial expansion of spruce in Alaska following the end of the last glaciation. The first suggests spruce expansion to be part of the rapid postglacial migration from refuge populations in southeastern North America. The second hypothesis involves the existence of refugia in unglaciated areas of Beringia and possibly Canada during the last glacial maxima (LGM), which expanded in size and geographic extent during the Holocene.
Inherent limitations of conventional techniques (pollen and macrofossil analysis) have made it impossible to resolve this controversy. I am using a new approach to test these hypotheses through molecular analysis of modern and fossil plant tissues (specifically needles). Results thus far using sequence data from two chloroplast introns and a pseudogene reveal the presence of haplotypes unique to Beringia, indicating a potential refuge during the LGM. Additional analysis currently underway includes the incorporation ancient DNA from lakebed microfossils along the inferred migration route, as well as the incorporation of black spruce to differentiate the migration history of the two species.
Understanding the Quaternary history of spruce is important in the context of biotic response to climatic change. The existence of spruce refugia in Beringia would imply that some spruce genotypes are resilient to extreme climatic variations. Alternatively, if spruce populations spread in one continuous northwestward wave, the remarkably fast migration rates documented by pollen records would suggest that spruce is capable of responding rapidly to climatic change. By combining molecular biology and paleoecology, this project has the potential to resolve these controversial issues and offer unique insights into ecosystem response to climatic forcing.
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