Abstract
Organisms use circadian rhythms to anticipate and exploit daily environmental oscillations. While circadian rhythms are of clear importance for inhabitants of tropic and temperate latitudes, its role for permanent residents of the polar regions is less well understood. The high Arctic Svalbard ptarmigan shows behavioral rhythmicity in presence of light-dark cycles but is arrhythmic during the polar day and polar night. This has been suggested to be an adaptation to the unique light environment of the Arctic. In this study, we examined regulatory aspects of the circadian control system in the Svalbard ptarmigan by recording core body temperature (Tb) alongside locomotor activity in captive birds under different photoperiods. We show that Tb and activity are rhythmic with a 24-h period under short (SP; L:D 6:18) and long photoperiod (LP; L:D 16:8). Under constant light and constant darkness, rhythmicity in Tb attenuates and activity shows signs of ultradian rhythmicity. Birds under SP also showed a rise in Tb preceding the light-on signal and any rise in activity, which proves that the light-on signal can be anticipated, most likely by a circadian system.
Highlights
The Earth’s rotation around its own axis causes daily oscillations in environmental factors such as light and ambient temperature
We explored the implication of Arctic life on the circadian control of core body temperature (Tb)
Svalbard ptarmigan held under short photoperiod (SP) and long photoperiod (LP) displayed clear daily rhythms in Tb with a 24-h period (p < 0.05 by χ2periodogram), while birds under LL and DD showed no significant rhythmicity in Tb for a chosen 10-day period (p > 0.05 for all periods by χ2-periodogram; Figures 2A–C)
Summary
The Earth’s rotation around its own axis causes daily oscillations in environmental factors such as light and ambient temperature. Biological Rhythms in Svalbard ptarmigan master clock (the suprachiasmatic nucleus in mammals) or a network of clocks (in the pineal gland, eyes and the hypothalamus of bird and reptiles; Menaker et al, 1997) These master clocks entrain to the environmental cycle primarily through the lightdark signal (Pittendrigh, 1960) and impose rhythmicity onto peripheral tissue, e.g., by circulating hormones such as melatonin produced in the pineal gland (Pevet and Challet, 2011). This leads to rhythmic physiology and behavior
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