University of Konstanz, Limnological Institute, Mainaustr. 252, 78464 Konstanz, Germany.
University of Konstanz, Limnological Institute, Mainaustr. 252, 78464 Konstanz, Germany.
Zoology (Jena). 2021 Feb;144:125856. doi: 10.1016/j.zool.2020.125856. Epub 2020 Oct 19.
Nearly all organisms show daily and seasonal physiological and behavioural responses that are necessary for their survival. Often these responses are controlled by the rhythmic activity of an endogenous clock that perceives day length. Day length differs not only between seasons but also along latitudes, with different seasonal day lengths between the north and the south. Both seasonal and latitudinal differences in day length are discussed to be perceived/processed by the endogenous clock. Some species are distributed over a wide range of latitudes; it should be highly adaptive for these species to be able to time physiological responses (e.g. migration behaviour and diapause) according to the organisms' respective photoperiod, i.e. their respective seasonal and latitudinal day length. The mediator of day length is the indoleamine hormone melatonin which is synthesized by melatonin-producing enzymes (AANAT and HIOMT). These enzymes are in turn controlled by an endogenous clock. The ubiquitous aquatic keystone organism Daphnia possess clock and melatonin synthesis genes that are rhythmically expressed over 24hours. We were able to show that the 24-h rhythm of D. magna's clock persists in constant darkness and is thus truly circadian. In one particular photoperiod, all D. magna clones produced a similar melatonin concentration due to a fixed AANAT activity. However, we have demonstrated that clones originating from different latitudes are adapted to their respective photoperiod by showing a geographic cline in clock and downstream melatonin synthesis gene expression. These findings hint at the problem locally adapted organisms face when they are forced to leave their respective photoperiod, e.g. because of climate change-driven range-expansion. If such a species is incapable of adjusting its endogenous clock to an unknown photoperiod, it will likely become extinct.
几乎所有生物体都表现出日常和季节性的生理和行为反应，这些反应是它们生存所必需的。这些反应通常由感知日长的内源性时钟的节律活动控制。日长不仅在季节之间有所不同，而且在纬度上也有所不同，南北之间的季节性日长也有所不同。内源性时钟被认为可以感知/处理季节性和纬度差异的日长。有些物种分布在很宽的纬度范围内；对于这些物种来说，能够根据生物体各自的光周期（即各自的季节性和纬度日长）来调整生理反应（例如迁徙行为和休眠），这应该是高度适应的。中介物是褪黑素，它是由褪黑素产生酶（AANAT 和 HIOMT）合成的。这些酶反过来又受到内源性时钟的控制。普遍存在的水生关键生物溞类拥有时钟和褪黑素合成基因，这些基因在 24 小时内呈节律性表达。我们能够证明，大溞的时钟 24 小时节律在持续黑暗中持续存在，因此是真正的昼夜节律。在一个特定的光周期中，由于 AANAT 活性固定，所有大溞的克隆都会产生相似的褪黑素浓度。然而，我们已经证明，来自不同纬度的克隆通过显示时钟和下游褪黑素合成基因表达的地理渐变来适应各自的光周期。这些发现暗示了当地适应的生物体在被迫离开各自的光周期时所面临的问题，例如由于气候变化导致的范围扩大。如果这样的物种无法将其内源性时钟调整到未知的光周期，它很可能会灭绝。
