Role of Photoperiod During Seasonal Acclimation in Winter-Active Small Mammals

  • Gerhard Heldmaier
  • Martin Klingenspor


Small mammals living in moderate or arctic climatic zones regularly experience seasonal changes in temperature and food availability. Ambient temperatures during winter are well below the thermoneutral zone of small mammals (15–30°C), and food is available only as a fraction of food availability during summer. Despite such unfavorable conditions, small mammals exploit habitats close to or even beyond the arctic circle [18, 51, 55]. Winter can be considered as a seasonal bottleneck for small mammals, causing pressure for the evolution of seasonal acclimation. An entire scope of behavioral and physiological adjustments is used for seasonal acclimation, which may include cessation of reproduction, reduction of body mass, improvements of fur insulation, and the occurrence of daily torpor or hibernation in the winter season. These measures can be used to reduce individual energy requirements during winter [32, 108]. On the other hand, the low ambient temperature in winter also demands improvements in cold tolerance in small mammals when they remain active during winter. This can be achieved by better insulation of winter fur as well as improvements in their capacity for thermoregulatory heat production. Thermal insulation of fur largely depends of the thickness of the air layer trapped in the fur. Small mammals have only a small capacity to increase the thickness of their fur and therefore have only a very limited possibility of seasonal improvement of thermal insulation [29, 43]. They have to rely on their capacity for heat production in order to maintain a high body temperature. Seasonal acclimation therefore appears a difficult task where small mammals have to solve a rather paradoxical situation, they have to exploit measures for reduction of their individual energy expenses, and at the same time to create a greater potential of energy dissipation for thermoregulation.


Small Mammal Brown Adipose Tissue Cold Acclimation Cold Exposure Short Photoperiod 
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© Springer-Verlag Berlin Heidelberg 2003

Authors and Affiliations

  • Gerhard Heldmaier
    • 1
  • Martin Klingenspor
    • 1
  1. 1.Gerhard Heldmaier and Martin Klingenspor Department of BiologyPhilipps-UniversityMarburgGermany

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