Wolf body mass cline across Minnesota related to taxonomy?

Recent genetic studies suggest that in northern Minnesota two species of wolves (Canis lupus L., 1758 or western wolf and Canis lycaon Schreber, 1775 (= Canis rufus Audubon and Bachman, 1851) or eastern wolf) meet and hybridize. However, little morphological information is available about these two types of wolves in Minnesota. We analyzed the mass of 950 female wolves and 1006 males older than 1 year from across northern Minnesota and found that it increased from 26.30 ± 0.56 kg (mean ± SE) for females and 30.60 ± 0.72 kg for males in northeastern Minnesota to 30.01 ± 0.43 kg for females and 35.94 ± 0.45 kg for males in northwestern Minnesota (females: r2= 0.79, P < 0.02; males: r2= 0.63, P = 0.06). These mass differences add morphological information to the identities of eastern and western wolves and support the view that ranges of the two species meet in Minnesota.