Arctic Seasonal Timekeeping Initiative (ASTI), Department of Arctic and Marine Biology, UiT - The Arctic University of Norway, Framstredet 42, 9019 Tromsø, Norway.
Arctic Seasonal Timekeeping Initiative (ASTI), Department of Arctic and Marine Biology, UiT - The Arctic University of Norway, Framstredet 42, 9019 Tromsø, Norway; Divisjon for skog og utmark, NIBIO, Holtveien 66, 9016 Tromsø, Norway.
Curr Biol. 2021 Jun 21;31(12):2720-2727.e5. doi: 10.1016/j.cub.2021.04.009. Epub 2021 Apr 29.
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.
斯瓦尔巴群岛（北纬 74°-81°）位于高北极地区，在夏季有长时间的连续白昼，在冬季有长时间的连续黑夜，这显然使昼夜节律进化的主要驱动力得到放松。斯瓦尔巴特群岛松鸡（Lagopus muta hyperborea）是高北极地区特有的唯一一种常年居住的陆地鸟类，它对环境条件的极端年际变化具有显著的适应性。在这里，我们证明，尽管行为的昼夜节律控制在转移到持续光照条件下迅速消失，这与在极地夏季和极夜期间观察到的日常活动模式的丧失一致，但斯瓦尔巴特群岛松鸡仍然采用基于昼夜节律的机制来计时光周期。首先，我们显示在中脑基底部和垂体柄的恒定光下，节律钟基因表达的持续存在，这是季节性神经内分泌级联反应的关键组织。然后，我们采用“滑动骨骼光周期”方案，揭示了斯瓦尔巴特群岛松鸡季节性生物学的驱动力是对光的节律敏感性，这一特征取决于一个正常运作的昼夜节律。因此，高北极地区特殊的选择性压力有利于将昼夜节律与日常活动模式的组织分离开来，同时保持其对季节性同步的重要性。
