Short photoperiods reduce winter energy requirements of the meadow vole, Microtus pennsylvanicus

Abstract

Adult male voles were maintained for 10 weeks in long or short photoperiods (14 or 10 hr light/day) at 23 degrees C and then for 6 days at 10 degrees C. Short photoperiod voles weighed approximately 20% less and consumed 36% and 42% fewer calories than did long-day animals at 23 degrees C and 10 degrees C, respectively. Relative energy intake (kcal/g body mass) was lower for short-than long-day voles at 10 degrees C. Short-day animals gathered more nesting material than their long-day counterparts at both ambient temperatures. Absolute as well as relative wet weights of interscapular brown adipose tissue were reduced in short-day voles and their testes were regressed. Two types of dorsal pelage hairs were longer in short- than in long-day voles; a dense undergrowth of light gray hairs, present in all short-day voles, was completely absent or only sparsely represented in the pelage of long-day animals. Photoperiod is a major proximate factor mediating winter adaptations of meadow voles: By decreasing body mass and reducing food requirements, short photoperiods presumably diminish winter foraging activity and energy devoted to thermoregulation. Increases in nest-building activity, growth of a winter pelage, and testicular regression are other changes induced by short daylengths that facilitate survival of over-wintering voles.