title: Daily rhythms of physiological parameters in the dromedary camel under natural and laboratory conditions.
abstract: Camels are well adapted to hot arid environments and can contribute significantly to the economy of developing countries in arid regions of the world. Full understanding of the physiology of camels requires understanding of the internal temporal order of the body, as reflected in daily or circadian rhythms. In the current study, we investigated the daily rhythmicity of 20 physiological variables in camels exposed to natural oscillations of ambient temperature in a desert environment and compared the daily temporal courses of the variables. We also studied the rhythm of core body temperature under experimental conditions with constant ambient temperature in the presence and absence of a light-dark cycle. The obtained results indicated that different physiological variables exhibit different degrees of daily rhythmicity and reach their daily peaks at different times of the day, starting with plasma cholesterol, which peaks 24min after midnight, and ending with plasma calcium, which peaks 3h before midnight. Furthermore, the rhythm of core body temperature persisted in the absence of environmental rhythmicity, thus confirming its endogenous nature. The observed delay in the acrophase of core body temperature rhythm under constant conditions suggests that the circadian period is longer than 24h. Further studies with more refined experimental manipulation of different variables are needed to fully elucidate the causal network of circadian rhythms in dromedary camels.
authors.affiliation: Department of Animal Production, College of Food and Agricultural Sciences, King Saud University, Riyadh 11451, Saudi Arabia.
authors.forename: Ahmed A
authors.initials: AA
authors.lastname: Al-Haidary
authors.affiliation: Department of Animal Production, College of Food and Agricultural Sciences, King Saud University, Riyadh 11451, Saudi Arabia.
authors.forename: Khalid A
authors.initials: KA
authors.lastname: Abdoun
authors.affiliation: Department of Animal Production, College of Food and Agricultural Sciences, King Saud University, Riyadh 11451, Saudi Arabia.
authors.forename: Emad M
authors.initials: EM
authors.lastname: Samara
authors.affiliation: Department of Animal Production, College of Food and Agricultural Sciences, King Saud University, Riyadh 11451, Saudi Arabia.
authors.forename: Aly B
authors.initials: AB
authors.lastname: Okab
authors.affiliation: MRU Biomonitoring and Environmental Toxicology, Department of Biology, Faculty of Sciences and Techniques of Maradi, Maradi, Niger.
authors.forename: Mamane
authors.initials: M
authors.lastname: Sani
authors.affiliation: Circadian Rhythm Laboratory, Department of Psychology, Boise State University, Boise, ID 83725, USA. Electronic address: refinetti@circadian.org.
authors.forename: Roberto
authors.initials: R
authors.lastname: Refinetti
mesh_terms: D000818:Animals; D001522:Behavior, Animal / Q000502:physiology*; D001831:Body Temperature / Q000502:physiology; D002162:Camelus / Q000502:physiology*; D002940:Circadian Rhythm / Q000502:physiology*; D008297:Male; D017440:Photoperiod
keywords: Camelus dromedarius; Circadian rhythm; Core body temperature; Heat exposure; Nycthemeral rhythm; Rhythm robustness