Data from: Freezer on, lights off! Environmental effects on activity rhythms of fish in the Arctic

Polar regions are characterised by acute seasonal changes in environment, with organisms inhabiting these regions lacking diel photoperiodic information for parts of the year. We present the first high-resolution analysis of diel and seasonal activity of free-living fishes in polar waters (74°N), subject to extreme variation in photoperiod, temperature and food availability. Using biotelemetry, we tracked two sympatric ecomorphs of lake-dwelling Arctic charr (Salvelinus alpinus n=23) over an annual cycle. Charr activity rhythms reflected the above-surface photoperiod (including under ice), with diel rhythms of activity observed. During the dark winter solstice period, charr activity became arrhythmic and much reduced, even though estimated light levels were within those at which charr can feed. When twilight resumed charr activity ensued as diel vertical migration, which continued throughout spring and increasing day-length, despite stable water temperatures. Diel activity rhythms ceased during polar day, with a sharp increase in arrhythmic fish activity occurring at ice-break. Despite contrasting resource use, circannual rhythms were mirrored in the two ecomorphs, although individual variability in activity rhythms was evident. Our data support conclusions of functionally adaptive periods of arrhythmicity in polar animals, suggesting maintenance of a circannual oscillator for scheduling seasonal behavioural and developmental processes.极地生境以剧烈的季节性环境变化为典型特征，栖息于此的生物在一年中的部分时段缺乏昼夜光周期（diel photoperiod）相关信息。本研究首次对北纬74°极区水域内的野生鱼类开展昼夜与季节活动模式的高分辨率分析，该水域的光周期、水温及食物可获得性均存在极端波动。 我们通过生物遥测（biotelemetry）技术，在完整年度周期内追踪了湖栖北极红点鲑（Salvelinus alpinus）的两个同域共存生态型，共计23尾个体。红点鲑的活动节律与地表光周期变化（包括冰下环境）高度契合，且可观测到明确的昼夜活动节律。在黑暗的冬至期（winter solstice），红点鲑的活动转变为无节律状态且大幅减弱，即便此时的估算光照水平仍处于红点鲑可摄食的范围之内。 当暮光重现时，红点鲑的活动以昼夜垂直迁移（diel vertical migration）形式恢复，并贯穿整个春季与昼长递增的时段，即便水温保持稳定。极昼（polar day）期间，昼夜活动节律完全消失；融冰（ice-break）期时，无节律活动的个体数量急剧攀升。 尽管两种生态型的资源利用模式存在显著差异，但二者的年节律特征保持一致，不过个体间的活动节律仍存在明显差异。 本研究数据支持极地动物存在功能性适应性无节律时段的结论，表明极地动物维持着一套年节律振荡器（circannual oscillator），用于调控季节性行为与发育进程。