Photoperiod is a major factor regulating biological rhythms in animals and plants. At low latitudes, annual variation in daylength is low and species are expected to strongly rely on photic cues to reset their circadian clocks. A corollary is that individuals should be strongly affected by sudden changes in the photic regime as those generated by artificial light at night (ALAN). We tested this hypothesis in an anuran in Costa Rica (10°N). Using an outdoor experimental design, we exposed adult cane toads Rhinella marina, a broadly distributed tropical anuran species to two ALAN intensities (0.04 and 5 lx). Locomotor activity was reduced at the lowest intensity, and the activity pattern shifted from crepuscular to nocturnal. Contrary to humans and mice in which ALAN favor obesity, toads from the two exposed groups did not gain mass whereas controls did. Corticosterone was reduced at the highest intensity, a possible consequence of the reduced activity of toads or the altered regulation of their circadian pattern. Thus, the behavioral and physiological disruption that we observed supports the hypothesis of the strong reliance on photic cues to regulate circadian rhythms and control homeostasis in this intertropical anuran. Furthermore, our results suggest that the negative effects of ALAN on physiology, in particular body mass regulation, may differ between vertebrate groups, thus preventing anticipated generalization before more comparative studies have been carried out. We stress the importance of considering the impact of the changing nocturnal environment in the intertropical zone which host the largest fraction of biodiversity.

中文翻译：

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夜间人造光会改变热带无尾鹦鹉的活动、体重和皮质酮水平

光周期是调节动植物生物节律的主要因素。在低纬度地区，日长的年度变化很小，预计物种将强烈依赖光信号来重置其生物钟。一个推论是，个体应该受到夜间人造光（ALAN）产生的光状态突然变化的强烈影响。我们在哥斯达黎加（10°N）的一只无尾龙中检验了这一假设。使用户外实验设计，我们将成年甘蔗蟾蜍 Rhinella marina（一种广泛分布的热带无尾类动物）暴露在两种 ALAN 强度（0.04 和 5 lx）下。运动活动在最低强度时降低，活动模式从黄昏转向夜间。与 ALAN 偏爱肥胖的人类和小鼠相反，来自两个暴露组的蟾蜍没有增加体重，而对照组有。皮质酮在最高强度下降低，这可能是蟾蜍活动减少或昼夜节律模式改变的结果。因此，我们观察到的行为和生理破坏支持了强烈依赖光信号来调节昼夜节律和控制这种热带无尾类动物体内平衡的假设。此外，我们的研究结果表明，ALAN 对生理学的负面影响，特别是体重调节，可能在脊椎动物群体之间有所不同，因此在进行更多比较研究之前阻止了预期的泛化。