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Abstract

Timing and quantity of sleep depend on a circadian (ca 24-h) rhythm and a specific sleep requirement. Sleep curtailment results in a homeostatic rebound of more and deeper sleep, the latter reflected in increased electroencephalographic (EEG) slow-wave activity (SWA) during non-rapid eye movement (NREM) sleep. Circadian rhythms are synchronized by the light-dark cycle but persist under constant conditions. Strikingly, arctic reindeer behavior is arrhythmic during the solstices. Moreover, the Arctic’s extreme seasonal environmental changes cause large variations in overall activity and food intake. We hypothesized that the maintenance of optimal functioning under these extremely fluctuating conditions would require adaptations not only in daily activity patterns but also in the homeostatic regulation of sleep. We studied sleep using non-invasive EEG in four Eurasian tundra reindeer (Rangifer tarandus tarandus) in Tromsø, Norway (69degreesN) during the fall equinox and both solstices. As expected, sleep-wake rhythms paralleled daily activity distribution, and sleep deprivation resulted in a homeostatic rebound in all seasons. Yet, these sleep rebounds were smaller in sum- mer and fall than in winter. Surprisingly, SWA decreased not only during NREM sleep but also during rumination. Quantitative modeling revealed that sleep pressure decayed at similar rates during the two behavioral states. Finally, reindeer spent less time in NREM sleep the more they ruminated. These results suggest that they can sleep during rumination. The ability to reduce sleep need during rumination—undisturbed phases for both sleep recovery and digestion—might allow for near-constant feeding in the arctic summer.

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Abstract

Reindeer in the Arctic seasonally suppress daily circadian patterns of behavior present in most animals. In humans and mice, even when all daily behavioral and environmental influences are artificially suppressed, robust endogenous rhythms of metabolism governed by the circadian clock persist and are essential to health. Disrupted rhythms foster metabolic disorders and weight gain. To understand circadian metabolic organization in reindeer, we performed behavioral measurements and untargeted metabolomics from blood plasma samples taken from Eurasian tundra reindeer (Rangifer tarandus tarandus) across 24 h at 2-h intervals in four seasons. Our study confirmed the absence of circadian rhythms of behavior under constant darkness in the Arctic winter and constant daylight in the Arctic summer, as reported by others.1 We detected and measured the intensity of 893 metabolic features in all plasma samples using untargeted ultra-high-performance liquid chromatography-mass spectrometry (UPLC-MS). A core group of metabolites (66/893 metabolic features) consistently displayed 24-h rhythmicity. Most metabolites displayed a robust 24-h rhythm in winter and spring but were arrhythmic in summer and fall. Half of all measured metabolites displayed ultradian sleep-wake dependence in summer. Irrespective of the arrhythmic behavior, metabolism is rhythmic (24 h) in seasons of low food availability, potentially favoring energy efficiency. In seasons of food abundance, 24-h rhythmicity in metabolism is drastically reduced, again irrespective of behavioral rhythms, potentially fostering weight gain.

Abstract

Join us on the dog sled! Immerse yourself in the beauty of Norwegian snow plains while you learn how to choose the right dog for the right task in the sled team and much more. The material was prepared for the project EDU-ARCTIC 2: from polar research to scientific passion – innovative nature education in Poland and Norway, which receives a grant of ca. 240 000 EUR received from Iceland, Liechtenstein and Norway under EEA funds. View with VR goggles or look around by moving your smartphone or by dragging the image left and right with the mouse.

Abstract

Sled dogs helped humans venture into the high North and settle in the Arctic. What makes these dogs so special? The material was prepared for the project EDU-ARCTIC 2: from polar research to scientific passion – innovative nature education in Poland and Norway, which receives a grant of ca. 240 000 EUR received from Iceland, Liechtenstein and Norway under EEA funds. View with VR goggles or look around by moving your smartphone or by dragging the image left and right with the mouse.

Abstract

Learn about the challenges and the beauty of farming on islands far off into the Norwegian sea. The material was prepared for the project EDU-ARCTIC 2: from polar research to scientific passion – innovative nature education in Poland and Norway, which receives a grant of ca. 240 000 EUR received from Iceland, Liechtenstein and Norway under EEA funds. View with VR goggles or look around by moving your smartphone or by dragging the image left and right with the mouse.

Abstract

Hundreds of years ago, indigenous people of the north domesticated wild reindeer and used them for food, clothing, housing and transport. See how Sami people of Norway still keep large herds of reindeer to produce meat for the market. The material was prepared for the project EDU-ARCTIC 2: from polar research to scientific passion – innovative nature education in Poland and Norway, which receives a grant of ca. 240 000 EUR received from Iceland, Liechtenstein and Norway under EEA funds. View with VR goggles or look around by moving your smartphone or by dragging the image left and right with the mouse.

Abstract

Did you know Santa’s reindeer are female (…or castrated males)? Watch our 360 video to learn why! The material was prepared for the project EDU-ARCTIC 2: from polar research to scientific passion – innovative nature education in Poland and Norway, which receives a grant of ca. 240 000 EUR received from Iceland, Liechtenstein and Norway under EEA funds. View with VR goggles or look around by moving your smartphone or by dragging the image left and right with the mouse.

To document

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.

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Abstract

The high Arctic archipelago of Svalbard (74°–81° north) experiences extended periods of uninterrupted daylight in summer and uninterrupted night in winter, apparently relaxing the major driver for the evolution of circadian rhythmicity. Svalbard ptarmigan (Lagopus muta hyperborea) is the only year-round resident terrestrial bird species endemic to the high Arctic and is remarkably adapted to the extreme annual variation in environmental conditions. Here, we demonstrate that, although circadian control of behavior disappears rapidly upon transfer to constant light conditions, consistent with the loss of daily activity patterns observed during the polar summer and polar night, Svalbard ptarmigans nonetheless employ a circadian-based mechanism for photoperiodic timekeeping. First, we show the persistence of rhythmic clock gene expression under constant light within the mediobasal hypothalamus and pars tuberalis, the key tissues in the seasonal neuroendocrine cascade. We then employ a “sliding skeleton photoperiod” protocol, revealing that the driving force behind seasonal biology of the Svalbard ptarmigan is rhythmic sensitivity to light, a feature that depends on a functioning circadian rhythm. Hence, the unusual selective pressures of life in the high Arctic have favored decoupling of the circadian clock from organization of daily activity patterns, while preserving its importance for seasonal synchronization.