Département de Biologie and Institut de Biologie Intégrative et des Systèmes (IBIS), Université Laval, Québec, QC G1V 0A6, Canada.
J Exp Biol. 2021 Dec 15;224(24). doi: 10.1242/jeb.242970. Epub 2021 Dec 17.
The circadian clock is an internal timekeeping system shared by most organisms, and knowledge about its functional importance and evolution in natural environments is still needed. Here, we investigated the circadian clock of wild-caught threespine sticklebacks (Gasterosteus aculeatus) at the behavioural and molecular levels. Although their behaviour, ecology and evolution are well studied, information on their circadian rhythms are scarce. We quantified the daily locomotor activity rhythm under a light:dark cycle (LD) and under constant darkness (DD). Under LD, all fish exhibited significant daily rhythmicity, while under DD, only 18% of individuals remained rhythmic. This interindividual variation suggests that the circadian clock controls activity only in certain individuals. Moreover, under LD, some fish were almost exclusively nocturnal, while others were active around the clock. Furthermore, the most nocturnal fish were also the least active. These results suggest that light masks activity (i.e. suppresses activity without entraining the internal clock) more strongly in some individuals than others. Finally, we quantified the expression of five clock genes in the brain of sticklebacks under DD using qPCR. We did not detect circadian rhythmicity, which could indicate either that the clock molecular oscillator is highly light-dependent, or that there was an oscillation but that we were unable to detect it. Overall, our study suggests that a strong circadian control on behavioural rhythms may not necessarily be advantageous in a natural population of sticklebacks and that the daily phase of activity varies greatly between individuals because of a differential masking effect of light.
生物钟是大多数生物共有的内部计时系统，但其在自然环境中的功能重要性和进化仍有待研究。在这里，我们从行为学和分子水平上研究了野生三刺鱼（Gasterosteus aculeatus）的生物钟。尽管它们的行为、生态学和进化已得到广泛研究，但关于其昼夜节律的信息却很少。我们在光照-黑暗循环（LD）和持续黑暗（DD）条件下量化了它们的每日活动节律。在 LD 条件下，所有鱼都表现出明显的昼夜节律，而在 DD 条件下，只有 18%的个体保持节律。这种个体间的差异表明生物钟仅在某些个体中控制活动。此外，在 LD 条件下，一些鱼几乎完全是夜行性的，而另一些鱼则全天都很活跃。此外，最夜行性的鱼也是最不活跃的。这些结果表明，在某些个体中，光对活动的抑制（即抑制活动而不使内部时钟同步）比其他个体更强。最后，我们使用 qPCR 在 DD 条件下测定了鱼脑中 5 种时钟基因的表达。我们没有检测到昼夜节律性，这可能表明时钟分子振荡器高度依赖于光，或者存在振荡，但我们无法检测到。总的来说，我们的研究表明，强烈的行为节律生物钟控制在自然种群的三刺鱼中不一定是有利的，而且由于光的掩蔽效应不同，个体之间的活动日相差异很大。
