Statistics summarizing the data.

We estimated different summary statistics for the two genes separately and for the combined region. The number of segregating sites directly reflects the genetic variability and therefore the effective population size. Additionally we provided frequency based statistics such as average pairwise sequence difference. Interestingly we found higher variation in cytochrome b gene than in the control region, which is consistent with observations in modern collared lemmings [31] but in contrast to mtDNA variation in other rodents [33]. (Seg.Sites…segregating sites, Haplotypes…number of haplotypes, Pairw. Diff…average pairwise sequence difference, Nucleo. Div…nucleotide diversity, Hapl.Div…haplotype diversity).