Circadian Organization in Reindeer

Nature. 2005 Dec 22;438(7071):1095-6. doi: 10.1038/4381095a.


The light/dark cycle of day and night synchronizes an internal 'biological clock' that governs daily rhythms in behaviour, but this form of regulation is denied to polar animals for most of the year. Here we demonstrate that the continuous lighting conditions of summer and of winter at high latitudes cause a loss in daily rhythmic activity in reindeer living far above the Arctic Circle. This seasonal absence of circadian rhythmicity may be a ubiquitous trait among resident polar vertebrates.

MeSH terms

  • Animals
  • Arctic Regions
  • Behavior, Animal / physiology
  • Behavior, Animal / radiation effects
  • Biological Clocks / physiology
  • Circadian Rhythm / physiology*
  • Circadian Rhythm / radiation effects*
  • Darkness*
  • Environment
  • Reindeer / classification
  • Reindeer / physiology*
  • Seasons*
  • Sunlight*
  • Time Factors