Centre for Biological Rhythm Research, Ahmednagar College, Ahmednagar, Maharashtra State, India.
Chronobiol Int. 2012 Mar;29(2):157-65. doi: 10.3109/07420528.2011.644875.
Synergic contribution of light and temperature is known to cause a paradoxical masking effect (inhibition of activity by bright light and high temperature) on various rhythms of animals. The present study reports the paradoxical masking effects of 1000-lux photophase at 25°C on the locomotor activity rhythm of Drosophila malerkotliana. Flies were subjected to light (L)-dark (D) 12:12 cycles wherein the photophase was varied from 10 to 1000 lux, whereas the scotophase was set to 0 lux in these and subsequent LD cycles. At 10, 100, and 500 lux, the flies were diurnal; however, at 1000 lux they were nocturnal. Transfer from LD 12:12 cycles to continuous darkness (DD) initiated free-running rhythmicity in all flies. Free-running rhythms of the flies switched from the 10-lux to the 500-lux groups started from the last activity-onset phase of the rhythm following 3-5 transient cycles, suggesting involvement of the circadian pacemaker. In contrast, the free-running rhythm of the flies of the 1000-lux group began abruptly from the last lights-on phase of the LD cycle, indicating noninvolvement of the pacemaker. Furthermore, all flies showed nocturnal activity in the two types of LD 12:12 cycles when the photophase was 1000 lux. The first type of LD cycles had three succeeding photophases of 100, 1000, and again 100 lux, whereas the second type of LD cycles had only one photophase of 1000 lux, but the LD 12:12 cycles were reversed to DL 12:12 cycles. Apparently, the combined effects of light and temperature caused such paradoxical masking effects. This hypothesis was tested by repeating the above experiments at 20°C. Flies in all experiments exhibited a diurnal activity pattern, even when the photophase was 1000 lux. Thus, the present study demonstrates that the paradoxical masking effect in D. malerkotliana was caused by the additive influence of light intensity and temperature. This strategy appears to have physiological significance, i.e., to shun and thus protect against the bright photophase at high temperature in the field.
光和温度的协同作用已知会对动物的各种节律产生反常掩蔽效应（强光和高温抑制活动）。本研究报告了 1000 勒克斯光相在 25°C 下对果蝇 malerkotliana 运动活动节律的反常掩蔽效应。苍蝇被置于光（L）-暗（D）12:12 周期中，其中光相从 10 到 1000 勒克斯不等，而在这些和随后的 LD 周期中，暗相设置为 0 勒克斯。在 10、100 和 500 勒克斯时，苍蝇是昼行性的；然而，在 1000 勒克斯时，它们是夜行性的。从 LD 12:12 周期转移到连续黑暗（DD）中，所有苍蝇都启动了自由运行的节奏。苍蝇的自由运行节奏从 10 勒克斯组到 500 勒克斯组的转换始于节律最后一次活动开始相位之后的 3-5 个瞬态周期，表明涉及到生物钟起搏器。相比之下，1000 勒克斯组苍蝇的自由运行节奏从 LD 周期的最后一次光照开始相位突然开始，表明起搏器未参与。此外，当光相为 1000 勒克斯时，所有苍蝇在两种类型的 LD 12:12 周期中都表现出夜间活动。第一种类型的 LD 周期有三个连续的光相，分别为 100、1000 和 100 勒克斯，而第二种类型的 LD 周期只有一个 1000 勒克斯的光相，但 LD 12:12 周期被颠倒为 DL 12:12 周期。显然，光和温度的综合效应导致了这种反常掩蔽效应。通过在 20°C 下重复上述实验来检验这一假设。在所有实验中，苍蝇都表现出昼行性活动模式，即使光相为 1000 勒克斯。因此，本研究表明，果蝇 malerkotliana 中的反常掩蔽效应是由光强度和温度的附加影响引起的。这种策略似乎具有生理意义，即在野外躲避并因此保护免受高温下强光的影响。
