CYCLIC VARIATION IN SKULL–BODY REGRESSIONS OF LEMMINGS

Abstract

A population cycle of brown and varying lemmings in the central Canadian arctic was accompanied by cyclic changes in the position of skull–body regressions. The regressions of log body weight and total length on condylobasal length, zygomatic breadth, and mastoid breadth showed highly significant changes in both slope and elevation, the shifts in elevation being more prominent. These changes appear in adult animals as well as in summer-born young. Whether these changes are phenotypic or genotypic is not known. They are not caused by seasonal changes in growth nor by changes in age structure of the population over the cycle. Nutritional effects cannot be ruled out but data available in the literature do not support a nutritional explanation. These changes could be genetic and involve a cyclic polymorphism.