Seasonal variations in the polysomnographic sleep/wake cycle and activity/rest pattern in the dromedary camel...

Seasonal variations influence environmental factors such as ambient temperature, sunlight duration and the availability of food resources, leading many species to develop behavioral and physiological adaptations. The present study explores the effect of seasonality on locomotor activity, rest and sleep patterns in captive dromedaries. Six adult female dromedaries were studied during the four seasons. Non-invasive PSG recordings (EEG, EOG, EMG) and behavioral observations were made over 72-h periods per season for each animal. The photoperiod varied seasonally from approximately 12.4 h in spring, 14.2 h in the summer, 12.4 h in autumn and 10.1 h in winter. The results reveal a robust diurnal activity pattern in dromedaries, with activity mainly concentrated during the day and rest dominating at night. The duration of motor activity shortened between summer and winter (17.1 h vs. 11.6 h). Seasonal differences were observed in vigilance states. In winter, the percentage of wakefulness was lower (52. 9%) than in summer (59. 8%), while drowsiness was higher in winter (10.1%) than in summer (6.8%). During the day, rumination was observed to be higher in summer (14.4%) than in winter (8.6%). Furthermore, total sleep time (TST), defined as the sum of drowsiness, NREM sleep and REM sleep, was significantly higher in winter (4.8 h) than in summer (3.6 h). This study demonstrates that the duration of activity, rest and sleep in dromedaries varies according to the season in outdoor captivity. The longer winter dark phase (~ 14 h) was accompanied by an increase in total sleep duration compared to the shorter summer dark phase (~ 10 h). These findings underscore the pivotal role of photoperiodic changes in regulating the locomotor activity/rest and sleep/wake cycles of desert species.