Fig. 1.

Frequency of haplotypes from the western clade (white, red, green, and yellow) and the eastern clades (blue) in each sampling site (same as Fig. 4). The black shading indicates the location of the driftless region during the Illinoian glacial maximum. The dashed line indicates the extent of the Laurentide ice sheet during the Wisconsin glaciation. Haplotypes from the eastern clades are restricted to southern and eastern sites with a sharp increase in frequency in the three easternmost sites. Ancestral western clade haplotypes IL-NW and WI-NW (yellow) are found only in northwestern sites. All western clade haplotypes found in southernmost populations (red) are derived from haplotype IL-C (green) that was derived from the ancestral haplotypes.