Hau Michaela, Romero L Michael, Brawn Jeff D, Van't Hof Thomas J
Department of Ecology and Evolutionary Biology, Princeton University, Princeton, New Jersey 08544, USA.
Gen Comp Endocrinol. 2002 Mar;126(1):101-12. doi: 10.1006/gcen.2002.7776.
In polar habitats, continuous daylight (polar day) can prevail for many weeks or months around the summer solstice. In the laboratory, continuous light conditions impair or disrupt circadian rhythms in many animals. To determine whether circadian rhythms are disrupted under natural polar day conditions in a species that is only a summer resident in polar regions we analyzed diel rhythms in plasma concentrations of melatonin, testosterone (T), and 17-beta estradiol (E(2)) during the summer solstice in Arctic-breeding Lapland Longspurs (Calcarius lapponicus). We compared these profiles to those of conspecifics housed in outdoor aviaries at a mid-latitude site in Seattle, Washington, during spring, summer, fall, and winter. Under polar day conditions plasma melatonin concentrations of Lapland Longspurs were strongly suppressed, but still showed a significant diel rhythm. Likewise, plasma T in males, and E(2) in females, showed significant diel changes in Arctic birds. Lapland Longspurs housed at mid-latitude in Seattle showed high-amplitude melatonin cycles at all times of the year, and the duration of the nightly melatonin secretion was positively correlated with the duration of the dark phase. We found no diel changes in plasma T in Seattle males in May, but Seattle females showed significant day/night differences in plasma E(2) in May. The data suggest that even under polar day conditions diel rhythms can persist. The maintenance of hormone rhythms could provide a physiological basis to reports of rhythmic behavior in many birds during the Arctic summer.
在极地栖息地，夏至前后可能会持续数周或数月的极昼（极昼期）。在实验室中，持续光照条件会损害或扰乱许多动物的昼夜节律。为了确定在极地地区仅夏季栖息的物种在自然极昼条件下昼夜节律是否会被打乱，我们分析了北极繁殖的拉普兰铁爪鹀（Calcarius lapponicus）在夏至期间血浆中褪黑素、睾酮（T）和17-β雌二醇（E₂）浓度的昼夜节律。我们将这些数据与华盛顿州西雅图市中纬度地区室外鸟舍中饲养的同物种个体在春、夏、秋、冬四季的情况进行了比较。在极昼条件下，拉普兰铁爪鹀的血浆褪黑素浓度受到强烈抑制，但仍表现出显著的昼夜节律。同样，北极地区雄性的血浆T和雌性的E₂也表现出显著的昼夜变化。在西雅图中纬度地区饲养的拉普兰铁爪鹀一年中任何时候都表现出高振幅的褪黑素周期，夜间褪黑素分泌的持续时间与黑暗期的持续时间呈正相关。我们发现西雅图的雄性在5月份血浆T没有昼夜变化，但西雅图的雌性在5月份血浆E₂表现出显著的昼夜差异。数据表明，即使在极昼条件下，昼夜节律也可能持续存在。激素节律的维持可能为许多鸟类在北极夏季有节律行为的报道提供生理基础。
