Potential effects of glacial history on allozyme variation in Tofieldia pusilla (Michaux)Persoon (Liliaceae)

Allozyme diversity in the subarctic-boreal plant species Tofieldia pusilla (Michaux)Persoon (Liliaceae) was analyzed in populations across northern Canada to determine whether the present-day geographical distribution of this diversity could be explained by glacial history. Only five of the fourteen loci surveyed were polymorphic (0.95 criterion) at more than one population. Relative to other monocots, members of the Liliaceae and its close relative Triantha racemosa, T. pusilla exhibited low allozyme variation across all populations (Ht=0.109). Weak trends show populations from southwest Yukon (a potential contact zone between multiple refugia and southern populations) were the most variable. Only one genotype was detected in each of three disjunct populations at Lake Superior suggesting that each population may consist of a single clone. High genetic identity values were detected amongst all populations and a UPGMA phenogram and MDS analyses showed poor geographic structuring. Allozyme data provided limited support for elements of both the Tabula Rasa (periglacial populations in the east) and Glacial Refugium (Beringia, Cordilleran nunataks and a potential northeastern arctic refugium) hypotheses to explain glacial survival and recolonization in Tofieldia pusilla. There was weak evidence, based on genetic identity values, to suggest that populations from Lake Superior and eastern Canada shared a common ancestry prior to the Wisconsinan, likely in southern periglacial populations. The presence of shared rare alleles in western populations lent some support to the hypothesis that dispersal from western refugia (i.e. Beringia and potentially Cordilleran nunataks) played an important role in the recolonization of this species. The overall trends in the data could imply that a bottleneck event reduced the diversity in this species before the Wisconsinan and that occasional long-distance dispersal may have occurred across much of Canada.