Entraining to the polar day: circadian rhythms in arctic ground squirrels

Williams, Cory T.; Barnes, Brian M.; Yan, Lili; Buck, C. Loren

doi:10.1242/jeb.159889

Cited by 17 publications

(11 citation statements)

References 60 publications

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“…Overall, these results are similar to findings in brown bears (U. arctos), the polar bear's closest relative (Ware et al, 2012;Jansen et al, 2016), which are also capable of niche switching (Fortin et al, 2013). Polar bears are also similar to other Arctic dwellers, including arctic ground squirrels, bumble bees (Bombus terrestris and Bombus pascuorum), Arctic char (Salvelinus alpinus), red-backed voles (Clethrionomys rutilus), Lapland longspurs (Calcarius lapponicus), and Svalbard reindeer, which retain circadian rhythms even in the absence of light:dark cycles (Swade and Pittendrigh, 1967;Stelzer and Chittka, 2010;Williams et al, 2011;Ashley et al, 2012;Hawley et al, 2017;Williams et al, 2017;Arnold et al, 2018). What makes bears and some Arctic species distinct from those Arctic birds and insects that do not exhibit daily activity rhythms during these periods (Bloch et al, 2013;Steiger et al, 2013;Kobelkova et al, 2015) remains to be determined.…”

Section: Discussionmentioning

confidence: 99%

The Clock Keeps Ticking: Circadian Rhythms of Free-Ranging Polar Bears

et al. 2020

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Life in the Arctic presents organisms with multiple challenges, including extreme photic conditions, cold temperatures, and annual loss and daily movement of sea ice. Polar bears ( Ursus maritimus) evolved under these unique conditions, where they rely on ice to hunt their main prey, seals. However, very little is known about the dynamics of their daily and seasonal activity patterns. For many organisms, activity is synchronized (entrained) to the earth’s day/night cycle, in part via an endogenous (circadian) timekeeping mechanism. The present study used collar-mounted accelerometer and global positioning system data from 122 female polar bears in the Chukchi and Southern Beaufort Seas collected over an 8-year period to characterize activity patterns over the calendar year and to determine if circadian rhythms are expressed under the constant conditions found in the Arctic. We reveal that the majority of polar bears (80%) exhibited rhythmic activity for the duration of their recordings. Collectively within the rhythmic bear cohort, circadian rhythms were detected during periods of constant daylight (June-August; 24.40 ± 1.39 h, mean ± SD) and constant darkness (23.89 ± 1.72 h). Exclusive of denning periods (November-April), the time of peak activity remained relatively stable (acrophases: ~1200-1400 h) for most of the year, suggesting either entrainment or masking. However, activity patterns shifted during the spring feeding and seal pupping season, as evidenced by an acrophase inversion to ~2400 h in April, followed by highly variable timing of activity across bears in May. Intriguingly, despite the dynamic environmental photoperiodic conditions, unpredictable daily timing of prey availability, and high between-animal variability, the average duration of activity (alpha) remained stable (11.2 ± 2.9 h) for most of the year. Together, these results reveal a high degree of behavioral plasticity in polar bears while also retaining circadian rhythmicity. Whether this degree of plasticity will benefit polar bears faced with a loss of sea ice remains to be determined.

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Section: Discussionmentioning

confidence: 99%

The Clock Keeps Ticking: Circadian Rhythms of Free-Ranging Polar Bears

et al. 2020

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“…Surveys of diel organization across diverse Arctic species have revealed a diversity of behavioral patterns during the solsticial phases, with rhythmicity largely maintained in some species (e.g., arctic ground squirrel, polar bear, copepod, and several migrating birds) [31][32][33][34][35][36] but largely lost in others (e.g., Svalbard reindeer and Svalbard ptarmigan). 2,4,5,[37][38][39] This diversity indicates that the molding effect of Arctic life on the circadian network in relation to diel patterning is highly life history and ecotype dependent and therefore likely to resist a unifying rationale for involvement or exclusion.…”

Section: A Seasonal Imperative For Arctic Circadian Rhythmicitymentioning

confidence: 99%

Evidence for circadian-based photoperiodic timekeeping in Svalbard ptarmigan, the northernmost resident bird

et al. 2021

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“…The chronic absence of LD cycles is an abnormal condition for most organisms, except those living in extreme latitudes during winter such as the arctic ground squirrel ( 132 ) or the reindeer ( 133 ). Reindeers suppress their daily activity/rest pattern being active for most of the 24 h during the polar summer day in which constant lighting is present.…”

Section: Lighting Conditions and Their Impact On Metabolism And Weighmentioning

confidence: 99%

Circadian and Metabolic Effects of Light: Implications in Weight Homeostasis and Health

et al. 2017

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Daily interactions between the hypothalamic circadian clock at the suprachiasmatic nucleus (SCN) and peripheral circadian oscillators regulate physiology and metabolism to set temporal variations in homeostatic regulation. Phase coherence of these circadian oscillators is achieved by the entrainment of the SCN to the environmental 24-h light:dark (LD) cycle, coupled through downstream neural, neuroendocrine, and autonomic outputs. The SCN coordinate activity and feeding rhythms, thus setting the timing of food intake, energy expenditure, thermogenesis, and active and basal metabolism. In this work, we will discuss evidences exploring the impact of different photic entrainment conditions on energy metabolism. The steady-state interaction between the LD cycle and the SCN is essential for health and wellbeing, as its chronic misalignment disrupts the circadian organization at different levels. For instance, in nocturnal rodents, non-24 h protocols (i.e., LD cycles of different durations, or chronic jet-lag simulations) might generate forced desynchronization of oscillators from the behavioral to the metabolic level. Even seemingly subtle photic manipulations, as the exposure to a “dim light” scotophase, might lead to similar alterations. The daily amount of light integrated by the clock (i.e., the photophase duration) strongly regulates energy metabolism in photoperiodic species. Removing LD cycles under either constant light or darkness, which are routine protocols in chronobiology, can also affect metabolism, and the same happens with disrupted LD cycles (like shiftwork of jetlag) and artificial light at night in humans. A profound knowledge of the photic and metabolic inputs to the clock, as well as its endocrine and autonomic outputs to peripheral oscillators driving energy metabolism, will help us to understand and alleviate circadian health alterations including cardiometabolic diseases, diabetes, and obesity.

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Entraining to the polar day: circadian rhythms in arctic ground squirrels

Cited by 17 publications

References 60 publications

The Clock Keeps Ticking: Circadian Rhythms of Free-Ranging Polar Bears

The Clock Keeps Ticking: Circadian Rhythms of Free-Ranging Polar Bears

Evidence for circadian-based photoperiodic timekeeping in Svalbard ptarmigan, the northernmost resident bird

Circadian and Metabolic Effects of Light: Implications in Weight Homeostasis and Health

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