Patterns of geographic variation in the skull of Nearctic Ermine (Mustela erminea)

Abstract

A. H. Macpherson suggested that much of the current geographic diversity in species and species groups of arctic mammals resulted from isolation in glacial refugia during the Wisconsin glacial stage. The present study evaluates this refugium hypothesis using a statistical assessment of geographic variation in 13 craniometric characters of Nearctic Mustela erminea. There is significant geographic variation among samples of North American ermine. Most of the skull character variance in this species reflects differences in size and is clinal. Variation in skull size is better explained by temperature and precipitation variables than by geographic distance, suggesting that environmentally ordered selection for size has been superimposed on any size differentiation that occurred during isolation in refugia. Variation in skull shape shows a relatively low correlation with climatic variables, and partitioning tests on shape variation reveal discontinuities consistent with the refugium hypothesis. Distinctive groups of samples reflect possible refugial populations in Eastern Beringia, in periglacial refugia south of the Wisconsin ice in eastern North America, and in one or more western North American refugia.