title: Circadian organization in reindeer.
abstract: 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.
authors.affiliation: Department of Arctic Biology and Institute of Medical Biology, University of Tromsø, 9037 Tromsø, Norway.
authors.forename: Bob E H
authors.initials: BE
authors.lastname: van Oort
authors.forename: Nicholas J C
authors.initials: NJ
authors.lastname: Tyler
authors.forename: Menno P
authors.initials: MP
authors.lastname: Gerkema
authors.forename: Lars
authors.initials: L
authors.lastname: Folkow
authors.forename: Arnoldus Schytte
authors.initials: AS
authors.lastname: Blix
authors.forename: Karl-Arne
authors.initials: KA
authors.lastname: Stokkan
mesh_terms: D000818:Animals; D001110:Arctic Regions; D001522:Behavior, Animal / Q000502:physiology / Q000528:radiation effects; D001683:Biological Clocks / Q000502:physiology; D002940:Circadian Rhythm / Q000502:physiology* / Q000528:radiation effects*; D003624:Darkness; D004777:Environment; D012053:Reindeer / Q000145:classification / Q000502:physiology*; D012621:Seasons; D013472:Sunlight; D013997:Time Factors