在永昼与极夜间，斯瓦尔巴驯鹿如何重新定义生物钟的法则
High in the Svalbard archipelago, where the sun neither sets for four months nor rises for another four, a quiet biological riddle shuffles across the tundra. The local reindeer (Rangifer tarandus platyrhynchus) endure one of Earth’s most extreme photic regimes, yet they remain metabolically active through light and dark alike. Most scientists had assumed that all mammals lean on a master circadian clock—an oscillating feedback loop of gene expression in the suprachiasmatic nucleus, synchronized by retinal light signals—to govern feeding, sleep, and hormonal tides. However, field observations in the stark valleys of Nordenskiöld Land have long hinted that these compact herbivores might operate differently, grazing in short, arrhythmic bouts irrespective of the sun’s geometry.
Recent telemetry studies, deploying finely calibrated GPS collars and body-temperature loggers on 60 adult females, have mapped this decoupling in unprecedented detail. Across 18 consecutive months, the animals exhibited no stable 24‑hour activity pattern during the midnight‑sun summer; instead, they cycled through burst‑like feeding and resting at intervals of two to four hours, a cadence known as ultradian rhythmicity. In winter, the pattern subtly shifted—heart rate and rumen fermentation rates dipped during the prolonged twilight, yet the ultradian structure persisted, defying the notion that environmental lighting merely resets a canonical clock. Transcriptomic analyses of hypothalamic tissue, conducted on opportunistically collected samples from road‑killed individuals, revealed that key clock‑gene transcripts (such as Per2 and Bmal1) were expressed at constitutively low levels, with markedly damped amplitude compared to rodents or even to migratory caribou.
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