Biogeographic and evolutionary implications of size variation in North American least weasels (Mustela nivalis)

Geographic variation in the skulls of least weasels, Mustela nivalis, from North America, Central Europe and Siberia was investigated to determine the influence of environmental variation and recent biogeographic history. The clustering pattern of 16 populations, based on overall morphological similarity, revealed the existence of four large groups, which were assigned to the subspecies rixosa, eskimo, vulgaris, and subpalmata, each associated with a specific geographic area and showing a distinct degree of sexual dimorphism. Variation in size was not associated with these four groups. Variation in degree of sexual dimorphism was less within each of these groups than among them, despite considerable environmental changes, suggesting that ecological factors are not significant. Relative to M. erminea, which was used as the outgroup, M. subpalmata constitutes a very distinct taxon that deserves consideration as a separate species. The eskimo and rixosa groups, though differing in size, still show large differences in shape that cannot be explained by simple isometric or allometric size gradients of variation. Isolation of the North American fauna during the glaciations, rather than ecological factors, seems to be the key factor determining differences between the eskimo and rixosa populations. This suggests that M. rixosa should be considered a valid species. [References: 51] 51

Author S. Reig
Year 1997
Secondary title Canadian Journal of Zoology
Volume 75
Number 12
Pages 2036-2049