Department of Zoology, Tel Aviv University , Tel Aviv , Israel.
Chronobiol Int. 2013 Nov;30(9):1123-34. doi: 10.3109/07420528.2013.805337. Epub 2013 Aug 8.
Daily rhythms are heavily influenced by light in two major ways. One is through photic entrainment of a circadian clock, and the other is through a more direct process, referred to as masking. Whereas entraining effects of photic stimuli are quite similar in nocturnal and diurnal species, masking is very different. Laboratory conditions differ greatly from what is experienced by individuals in their natural habitat, and several studies have shown that activity patterns can greatly differ between laboratory environment and natural condition. This is especially prevalent in diurnal rodents. We studied the daily rhythms and masking response in the fat sand rat (Psammomys obesus), a diurnal desert rodent, and activity rhythms of Tristram's jird (Meriones tristrami), a nocturnal member of the same subfamily (Gerbillinae). We found that most sand rats kept on a 12 h:12 h light-dark (LD) cycles at two light intensities (500 and 1000 lux) have a nocturnal phase preferences of general activity and higher body temperature during the dark phase. In most individuals, activity was not as stable that of the nocturnal Tritram's jirds, which showed a clear and stable nocturnal activity pattern under the same conditions. Sand rats responded to a 6-h phase advance and 6-h phase delay as expected, and, under constant conditions, all tested animals free ran. In contrast with the nocturnal phase preference, fat sand rats did not show a masking response to light pulses during the dark phase or to a dark pulse during the light phase. They did, however, have a significant preference to the light phase under a 3.5 h:3.5 h LD schedule. Currently, we could not identify the underlying mechanisms responsible for the temporal niche switch in this species. However, our results provide us with a valuable tool for further studies of the circadian system of diurnal species, and will hopefully lead us to understanding diurnality, its mechanisms, causes, and consequences.
昼夜节律主要通过两种主要方式受到光的影响。一种是通过光对生物钟的诱导，另一种是通过更直接的过程，称为掩蔽。虽然光刺激的诱导作用在夜间和日间物种中非常相似，但掩蔽作用却大不相同。实验室条件与个体在其自然栖息地中所经历的条件有很大的不同，几项研究表明，活动模式在实验室环境和自然条件之间可能有很大的差异。这在日间啮齿动物中尤为普遍。我们研究了昼间沙漠啮齿动物肥沙鼠（Psammomys obesus）的昼夜节律和掩蔽反应，以及同一亚科（Gerbillinae）的夜间成员特里斯特拉姆沙鼠（Meriones tristrami）的活动节律。我们发现，大多数在两种光照强度（500 和 1000 勒克斯）下保持 12：12 光暗（LD）循环的沙鼠在暗期表现出夜间活动相偏好和较高的体温。在大多数个体中，活动不如夜间特里斯特拉姆沙鼠稳定，后者在相同条件下表现出清晰而稳定的夜间活动模式。沙鼠如预期的那样对 6 小时的相位提前和 6 小时的相位延迟做出反应，并且在恒定条件下，所有测试的动物都自由运行。与夜间相偏好相反，肥沙鼠在暗期对光脉冲或光期对暗脉冲没有表现出掩蔽反应。然而，它们在 3.5：3.5 LD 方案下确实对光期有明显的偏好。目前，我们无法确定导致该物种时间生态位转换的潜在机制。然而，我们的结果为我们进一步研究昼间物种的生物钟系统提供了有价值的工具，并有望帮助我们理解昼间性及其机制、原因和后果。
