Regional and individual variation in body growth in winter of bank voles Clethrionomys glareolus

Abstract

Small rodent body growth usually stagnates or is negativeduring winter but large individuals in dense populationsexhibit pronounced winter growth. Growth of firstgeneration laboratory bank voles Clethrionomys glareolus(Schreber, 1780) from cyclic and noncyclic populations,born in late summer-early autumn and bred under constantconditions, was examined up to 4 months of age. Weightincrease between 2 and 4 months, corresponding to earlywinter growth, occurred only in one-fifth of the animals inmost groups but in considerably more than half of the malesfrom a cyclic population. Juvenile weights differed betweenpopulations in the same way as adult weights. Weights at 2and 4 months as well as maximum weights were positivelyrelated to weaning weights. Winter growth correlatedinsignificantly or negatively with weaning weight innoncyclic animals and positively with weaning weights incyclic animals. Individual differences were evidentlygenetically based as both parents and young were kept underidentical conditions. Population differences appear to beadaptations to nutritional rather than social conditions.