Molecular Paleoecology of Permafrost Mammals

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The Arctic is well known as a unique scientific resource for biologybecause it contains exceptional records of past climatic fluctuations andthe concomitant interactions between biota and an extreme environment.Preliminary research has shown that the bones from animals from thepermafrost contain a further important record of global change - a geneticrecord, detailing faunal evolution through the Late Pleistocene.Preliminary studies reveal that ancient DNA techniques and the polymerasechain reaction (PCR) can be used to recover, amplify, and sequencemitochondrial DNA (mtDNA) of up to 600 base pairs (bp) in length from avariety of permafrost specimens from extensive deposits near Dawson, YukonTerritories and Fairbanks, Alaska. These permafrost deposits date from 20to 50 thousand years ago and contain thousands of bones from previousinhabitants of the area, making this resource a national treasure,comprising the largest collection of Pleistocene genetic information in theworld. In addition to testing long-standing systematic issues, DNA fromthese bones can be used to examine the consequences of past environmentalchanges, such as the opening of the Bering land bridge, and climate andanthropogenic effects on population genetics.Permafrost DNA will be used to examine several questions concerning theeffects of Late Pleistocene ecology on the genetics of modern populations,and how the effects of current environmental change and biologicalintroductions compare with that of the recent past. Mitochondrial controlregion and cytochrome b DNA sequences of approximately 200-300 bp will besequenced from about 20 specimens each of wolf (Canis lupus), moose (Alcesgigas) and elk (Cervus elaphus) to examine how genetic diversity haschanged since the Late Pleistocene. All three taxa have fossil records ofmore than several thousand years in North America, yet the geneticdiversity of modern North American populations is sufficiently limited thatrecent bottlenecks appear to have occurred. These results will becontrasted with those from analyses of the caribou (Rangifer tarandus) andthe brown bear (Ursus arctos), which also have a long record in NorthAmerica but have moderate amounts of genetic diversity in modernpopulations, perhaps due to large population sizes throughout the LatePleistocene.As well as examining changes in genetic diversity through time, thepermafrost DNA will be used to assess the relationship of Late Pleistocenepopulations to their modern counterparts. We will distinguish among fourpossible alternatives: 1) extant populations have DNA sequences that arephylogenetically distinct from those in the Old World and are directlyrelated to those from Late Pleistocene North American predecessors. Thisresult implies genetic continuity and continental isolation throughout theLate Pleistocene and that modern populations survived recent glacialconditions and megafaunal extinction events in relative isolation; 2) DNAsequences of modern populations do not share a common ancestry with thosein the permafrost implying that North American lineages went extinctsometime in the past 18,000 years and were replaced by those of an OldWorld ancestry existing in Beringia; 3) modern populations have a mixtureof DNA haplotypes that are related to those from the Late Pleistocene ofNorth America and the Old World implying recent admixture between Old andNew World populations; and 4) both modern and permafrost populations have amixture of DNA haplotypes of Old and New World ancestry implying a historyof continental mixing over the Late Pleistocene.Ancient DNA research has promised to allow evolutionary change tobe observed through real time but has been constrained by the number ofsamples and time frame that it has been possible to analyse. This projectwill fulfil that potential since it permits genetic change to be recordedin two large, well sampled natural populations (Fairbanks and Dawson) overa time frame of tens of thousands of years. It will also lead to a betterunderstanding of the factors involved in molecular preservation underpermafrost conditions, and suitable storage and handling regimes forspecimens uncovered by current mining operations. No organized collectingprogram currently exists for this valuable resource, and each year hundredsof specimens from this genetic museum are simply washed away downstream