Statistical analysis of geographic variation in the skull of the arctic hare (Lepus arcticus)

Abstract

Morphometric variation in 21 characters of 470 skulls of Lepus arcticus from Canada and Greenland was analysed statistically. Geographic trends in variation were assessed separately in Canada and Greenland using composite samples derived from groupings of geographically contiguous localities. For most characters, univariate analyses revealed clines of decreasing size from the polar regions southwards, though jugal maxillary ridge width exhibited a reverse cline and maxilla orbital process width varied irregularly among samples. Discriminant analysis synthesized these trends such that the phenetic positions of the samples in discriminant space were approximately congruent with their geographic positions. The smoothness of the cline is interrupted between the Queen Elizabeth Islands and the islands of the lower Arctic Archipelago and is not paralleled by similar sharp environmental transitions. Gene flow across the water gap therefore seems to be very restricted. Discontinuities among the Greenland samples can be attributed partly to sampling or distributional hiatuses, but infraspecific differentiation appears to be occurring on either side of the Melville Bay glacial barrier. Statistically significant multiple regressions of factor scores of climatic variables on factor scores of skull morphology suggest thermoregulatory adaptation as a result of selection for increased skull size in colder climates, as is subsumed by Bergmann's rule.