Abstract:Nutritional effects on growth and reproduction of bank volesClethrionomys glareolus(Schreber) were established by laboratory breeding of wild-caught and laboratory-born animals from two Swedish locations. The animals were kept on either a standardized folivore or a standardized granivore diet,C. glareolusbeing intermediate in natural food habits. South SwedishC. glareolusare less cyclic (with fairly stable populations) and more granivorous than northern conspecifics. The body growth of wild-caught animals was favoured by the granivore diet for southern and by a folivore diet for northern animals. South Swedish animals demonstrated greater reproductive output with a granivore diet than with a folivore diet. Young of laboratory-born southern animals became larger when the mothers were given a granivore diet. Instead, young females of wild-caught mothers were mature at weaning to a larger extent if provided with a folivore diet. These differences are interpreted to reflect digestive adaptation just after weaning, with post-weaning diets on roughage (folivore diet or a field diet) favouring animals being kept on rabbit pellets and with cereal diets after weaning still more favouring animals kept on granivore diets. Differences in reactions to food types between origins and generations can be explained by an evidently common inter-generational effect on maturation and breeding.