Entrainment of circadian rhythms of locomotor activity by ambient temperature cycles in the dromedary camel

Abstract

In the dromedary camel, a well-adapted desert mammal, daily ambient temperature (Ta)-cycles have been shown to synchronize the central circadian clock. Such entrainment has been demonstrated by examining two circadian outputs, body temperature and melatonin rhythms. Locomotor activity (LA), another circadian output not yet investigated in the camel, may provide further information on such specific entrainment. To verify if daily LA is an endogenous rhythm and whether the desert Ta-cycle can entrain it, six dromedaries were first kept under total darkness and constant-Ta. Results showed that the LA rhythm free runs with a period of 24.8–24.9 h. After having verified that the light–dark cycle synchronizes LA, camels were subjected to a Ta-cycle with warmer temperatures during subjective days and cooler temperatures during subjective nights. Results showed that the free-running LA rhythm was entrained by the Ta-cycle with a period of exactly 24.0 h, while a 12 h Ta-cycle phase advance induced an inversion of the LA rhythm and advanced the acrophase by 9 h. Similarly, activity onset and offset were significantly advanced. All together, these results demonstrate that the Ta-cycle is a strong zeitgeber, able to entrain the camel LA rhythm, hence corroborating previous results concerning the Ta non-photic synchronization of the circadian master clock.

Seasonal variations in locomotor activity rhythm and diurnal activity in the dromedary camel (Camelus dromedarius) under mesic semi-natural conditions

“…Therefore, these insignificant changes in Ta do not explain why, at the transition from night to day, resting camels on sternal recumbency get up suddenly and start their daily activity and why, at the transition from day to night, the activity of the camels is unexpectedly interrupted, entering instantly into the nocturnal rest phase. In our previous studies (El Allali et al 2013;Farsi et al 2020), we have shown that, in the camel, the central circadian clock and its three outputs, the body temperature, locomotor activity and melatonin secretion rhythms, are entrained by Ta cycle. The no-involvement of Ta in the triggering of the activity onset and offset in the present study is not inconsistent with the previous demonstration of its entrainment of the circadian clock.…”

“…However, this study was formulated on a discontinuous ethogram and, furthermore, was limited to only two consecutive days of recording. Farsi et al (2018), Farsi et al (2020) provided the first demonstration of diurnal activity in dromedary camel. Recording of locomotory activity rhythm has been difficult due to several technical constraints meet in large mammals and particularly in this species (El Allali et al 2018).…”

“…For each enclosure, three cameras were positioned at a high of 2.5-3 m providing three viewpoints (frontal and two lateral views from the back, one from the right and the other from the left) covering the pen area to easily and clearly follow the camel's movements. The LA rhythms were recorded in each of individual camel using the validated video-locomotion scoring technique (Farsi et al 2020(Farsi et al , 2018. This technique uses six scores of activity with different amplitudes that are visualized throughout an analysis of recorded video sequences of each camel on a computer screen.…”

“…Much has been reported about the fascinating adaptive mechanisms displayed by the camel; however, its behavior and activity have not been fully studied to date. Recent data from our team (Farsi et al 2020(Farsi et al , 2018 revealed that, under natural conditions, camel exhibits a clear rhythm of activity corresponding to a pattern of diurnal activity. However, timing management of the daily activity pattern throughout the changing seasons is still not documented.…”

Role of Dorsomedial Hypothalamus GABAergic Neurons in Sleep–Wake States in Response to Changes in Ambient Temperature in Mice

“…The biological rhythm mainly controlled by the SCN is endogenous but it is also affected by the environmental cycles. There have been some studies that suggest that the circadian rhythm of locomotor activity in mice and dromedary camels is affected by the ambient temperature cycle [43,44]. Although, the effect of the ambient temperature cycle is weaker than the light/dark cycle [44], which are affected by the range, amplitude, and time of the ambient temperature cycle.…”