Neurobiology and Genetics, Theodor Boveri Institute, Biocentre, University of Würzburg, 97074 Würzburg, Germany.
Faculty of Science, Biology Centre of the Czech Academy of Sciences, Institute of Entomology and University of South Bohemia, 37005 Ceske Budejovice, Czech Republic.
Curr Biol. 2019 Nov 18;29(22):3928-3936.e3. doi: 10.1016/j.cub.2019.09.032. Epub 2019 Oct 31.
Nearly all organisms evolved endogenous self-sustained timekeeping mechanisms to track and anticipate cyclic changes in the environment. Circadian clocks, with a periodicity of about 24 h, allow animals to adapt to day-night cycles. Biological clocks are highly adaptive, but strong behavioral rhythms might be a disadvantage for adaptation to weakly rhythmic environments such as polar areas [1, 2]. Several high-latitude species, including Drosophila species, were found to be highly arrhythmic under constant conditions [3-6]. Furthermore, Drosophila species from subarctic regions can extend evening activity until dusk under long days. These traits depend on the clock network neurochemistry, and we previously proposed that high-latitude Drosophila species evolved specific clock adaptations to colonize polar regions [5, 7, 8]. We broadened our analysis to 3 species of the Chymomyza genus, which diverged circa 5 million years before the Drosophila radiation [9] and colonized both low and high latitudes [10, 11]. C. costata, pararufithorax, and procnemis, independently of their latitude of origin, possess the clock neuronal network of low-latitude Drosophila species, and their locomotor activity does not track dusk under long photoperiods. Nevertheless, the high-latitude C. costata becomes arrhythmic under constant darkness (DD), whereas the two low-latitude species remain rhythmic. Different mechanisms are behind the arrhythmicity in DD of C. costata and the high-latitude Drosophila ezoana, suggesting that the ability to maintain behavioral rhythms has been lost more than once during drosophilids' evolution and that it might indeed be an evolutionary adaptation for life at high latitudes.
几乎所有的生物体都进化出了内源性的自我维持的计时机制，以跟踪和预测环境中的周期性变化。昼夜节律钟，其周期约为 24 小时，使动物能够适应昼夜节律。生物钟具有高度适应性，但强烈的行为节律可能不利于适应弱节律环境，如极地[1,2]。几项研究发现，包括果蝇在内的一些高纬度物种在恒常条件下表现出高度无节律性[3-6]。此外，来自亚北极地区的果蝇物种在长日照下可以将傍晚的活动延长到黄昏。这些特征取决于生物钟网络的神经化学，我们之前提出，高纬度果蝇物种进化出了特定的生物钟适应性，以殖民极地[5,7,8]。我们将分析范围扩大到了 Chymomyza 属的 3 个物种，它们在果蝇辐射之前大约 500 万年就已经分化[9]，并在低纬度和高纬度都有分布[10,11]。C. costata、pararufithorax 和 procnemis 这 3 个物种，无论其起源纬度如何，都具有低纬度果蝇物种的生物钟神经元网络，并且它们的活动不会在长光照期跟踪黄昏。然而，高纬度的 C. costata 在持续黑暗（DD）下变得无节律，而两种低纬度物种仍然保持节律性。C. costata 在 DD 下的无节律性和高纬度 Drosophila ezoana 的无节律性背后有不同的机制，这表明在果蝇的进化过程中，维持行为节律的能力已经不止一次丧失，而且它可能确实是适应高纬度生活的一种进化适应性。
