Piccolin Fabio, Suberg Lavinia, King Robert, Kawaguchi So, Meyer Bettina, Teschke Mathias
Section Polar Biological Oceanography, Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Bremerhaven, Germany.
Institute for Chemistry and Biology of the Marine Environment, Carl von Ossietzky University of Oldenburg, Oldenburg, Germany.
Front Physiol. 2018 Dec 20;9:1715. doi: 10.3389/fphys.2018.01715. eCollection 2018.
Antarctic krill (), a key species in the Southern Ocean, reduce their metabolism as an energy saving mechanism in response to the harsh environmental conditions during the Antarctic winter. Although the adaptive significance of this seasonal metabolic shift seems obvious, the driving factors are still unclear. In particular, it is debated whether the seasonal metabolic cycle is driven by changes in food availability, or if an endogenous timing system entrained by photoperiod might be involved. In this study, we used different long-term photoperiodic simulations to examine the influence of light regime and endogenous rhythmicity on the regulation of krill seasonal metabolic cycle. Krill showed a seasonal cycle of growth characterized by null-to-negative growth rates during autumn-winter and positive growth rates during spring-summer, which was manifested also in constant darkness, indicating strong endogenous regulation. Similar endogenous cycles were observed for the activity of the key-metabolic enzyme malate dehydrogenase (MDH) and for the expression levels of a selection of metabolic-related genes, with higher values in spring-summer and lower values in autumn-winter. On the other side, a seasonal cycle of oxygen consumption was observed only when krill were exposed to simulated seasonal changes in photoperiod, indicating that light-related cues might play a major role in the regulation of krill oxygen consumption. The influence of light-regime on oxygen consumption was minimal during winter, when light-phase duration was below 8 h, and it was maximal during summer, when light-phase duration was above 16 h. Significant upregulation of the krill clock genes , 2, and 1, as well as of the circadian-related opsins 1a and , was observed after light-phase duration had started to decrease in early autumn, suggesting the presence of a signaling cascade linking specific seasonal changes in the Antarctic light regime with clock gene activity and the regulation of krill metabolic dormancy over the winter.
南极磷虾是南大洋的关键物种，在南极冬季，它们会降低新陈代谢，作为一种节能机制以应对恶劣的环境条件。尽管这种季节性代谢转变的适应性意义似乎很明显，但其驱动因素仍不清楚。特别是，关于季节性代谢周期是由食物可获得性的变化驱动，还是涉及由光周期夹带的内源性计时系统，存在争议。在本研究中，我们使用不同的长期光周期模拟来研究光照模式和内源性节律对磷虾季节性代谢周期调节的影响。磷虾表现出季节性生长周期，其特征是秋冬季节生长速率为零至负增长，春夏季节为正增长，这在持续黑暗中也有体现，表明存在强大的内源性调节。关键代谢酶苹果酸脱氢酶（MDH）的活性以及一系列与代谢相关基因的表达水平也观察到类似的内源性周期，春夏季节值较高，秋冬季节值较低。另一方面，仅当磷虾暴露于模拟的光周期季节性变化时，才观察到耗氧量的季节性周期，这表明与光相关的线索可能在磷虾耗氧量的调节中起主要作用。冬季光照阶段持续时间低于8小时时，光照模式对耗氧量的影响最小，夏季光照阶段持续时间高于16小时时，影响最大。在初秋光照阶段持续时间开始减少后，观察到磷虾生物钟基因、2和1以及与昼夜节律相关的视蛋白1a和的显著上调，这表明存在一个信号级联，将南极光照模式的特定季节性变化与生物钟基因活性以及冬季磷虾代谢休眠的调节联系起来。
