Kaladchibachi Sevag, Negelspach David C, Zeitzer Jamie M, Fernandez Fabian-Xosé
Department of Psychology, University of Arizona, Tucson, AZ, USA.
Department of Psychiatry and Behavioral Sciences and Stanford Center for Sleep Sciences and Medicine, Stanford University, Stanford, CA, USA.
J Comp Physiol A Neuroethol Sens Neural Behav Physiol. 2025 Aug 6. doi: 10.1007/s00359-025-01754-5.
Light-mediated circadian entrainment is a fundamental sensory process across taxa, yet the contribution of ultraviolet-A (UVA; 315-400 nm) wavelengths remains poorly understood. Here, we characterize the phase-shifting effects of brief UVA light flashes in Drosophila ananassae, a species with known sensitivity to short-wavelength light via ocular and extraocular photoreceptors. Using a parametric array of 62 UVA LED protocols varying in flash duration (8, 16, 120 ms), frequency (0.13-1.0 Hz), and irradiance, we quantified circadian phase shifts in the locomotor activity rhythm under constant darkness following stimulation in either the delay (ZT13) or advance (ZT23) zones. Young flies (2-3 days old) exhibited robust phase delays and advances that scaled with flash luminance and frequency. Dose-response modeling revealed increased phase-shifting efficiency and lower energy thresholds with decreasing flash duration, especially at ZT23. By contrast, aged flies (40-45 days) showed significantly attenuated responses, particularly to 8 ms pulses, indicating an age-related decline in UVA sensitivity. These findings suggest that the insect circadian system is finely tuned to the temporal structure of UVA input, with optimal entrainment possibly occurring in response to brief, intermittent stimulation. The marked reduction in responsiveness with age highlights a potential erosion of fast-acting photoreceptive pathways. Given the conservation of UVA-sensitive photopigments across animals, these results offer comparative insights into how temporal light encoding influences circadian regulation across life stages and taxa.
光介导的昼夜节律同步是跨物种的一种基本感官过程，然而，紫外线A（UVA；315 - 400纳米）波长的贡献仍知之甚少。在这里，我们描述了在短管果蝇中短暂UVA闪光的相移效应，短管果蝇是一种通过眼内和眼外光感受器对短波长光具有已知敏感性的物种。我们使用了一个由62种UVA发光二极管协议组成的参数阵列，这些协议在闪光持续时间（8、16、120毫秒）、频率（0.13 - 1.0赫兹）和辐照度方面有所不同，我们在延迟（ZT13）或提前（ZT23）区域进行刺激后，在持续黑暗条件下量化了运动活动节律中的昼夜节律相移。年轻果蝇（2 - 3天大）表现出强烈的相位延迟和提前，其与闪光亮度和频率成比例。剂量反应模型显示，随着闪光持续时间的缩短，相移效率提高，能量阈值降低，尤其是在ZT23时。相比之下，老年果蝇（40 - 45天）的反应明显减弱，特别是对8毫秒脉冲的反应，这表明UVA敏感性存在与年龄相关的下降。这些发现表明，昆虫的昼夜节律系统对UVA输入的时间结构进行了精细调整，最佳同步可能是对短暂、间歇性刺激的反应。随着年龄增长反应性的显著降低突出了快速作用光感受途径的潜在衰退。鉴于动物中UVA敏感光色素的保守性，这些结果为时间光编码如何影响不同生命阶段和物种的昼夜节律调节提供了比较性见解。
