title: Variation in the daily rhythm of body temperature of free-living Arabian oryx (Oryx leucoryx): does water limitation drive heterothermy?
abstract: Heterothermy, a variability in body temperature beyond the limits of homeothermy, has been advanced as a key adaptation of Arabian oryx (Oryx leucoryx) to their arid-zone life. We measured body temperature using implanted data loggers, for a 1-year period, in five oryx free-living in the deserts of Saudi Arabia. As predicted for adaptive heterothermy, during hot months compared to cooler months, not only were maximum daily body temperatures higher (41.1 ± 0.3 vs. 39.7 ± 0.1°C, P = 0.0002) but minimum daily body temperatures also were lower (36.1 ± 0.3 vs. 36.8 ± 0.2°C, P = 0.04), resulting in a larger daily amplitude of the body temperature rhythm (5.0 ± 0.5 vs. 2.9 ± 0.2°C, P = 0.0007), while mean daily body temperature rose by only 0.4°C. The maximum daily amplitude of the body temperature rhythm reached 7.7°C for two of our oryx during the hot-dry period, the largest amplitude ever recorded for a large mammal. Body temperature variability was influenced not only by ambient temperature but also water availability, with oryx displaying larger daily amplitudes of the body temperature rhythm during warm-dry months compared to warm-wet months (3.6 ± 0.6 vs. 2.3 ± 0.3°C, P = 0.005), even though ambient temperatures were the same. Free-living Arabian oryx therefore employ heterothermy greater than that recorded in any other large mammal, but water limitation, rather than high ambient temperature, seems to be the primary driver of this heterothermy.
authors.affiliation: Brain Function Research Group, School of Physiology, Medical School, University of the Witwatersrand, 7 York Road, Parktown, Johannesburg 2193, South Africa. robyn.hetem@wits.ac.za
authors.forename: Robyn Sheila
authors.initials: RS
authors.lastname: Hetem
authors.forename: Willem Maartin
authors.initials: WM
authors.lastname: Strauss
authors.forename: Linda Gayle
authors.initials: LG
authors.lastname: Fick
authors.forename: Shane Kevin
authors.initials: SK
authors.lastname: Maloney
authors.forename: Leith Carl Rodney
authors.initials: LC
authors.lastname: Meyer
authors.forename: Mohammed
authors.initials: M
authors.lastname: Shobrak
authors.forename: Andrea
authors.initials: A
authors.lastname: Fuller
authors.forename: Duncan
authors.initials: D
authors.lastname: Mitchell
mesh_terms: D000064:Acclimatization; D000818:Animals; D000866:Antelopes / Q000502:physiology*; D001833:Body Temperature Regulation; D002940:Circadian Rhythm; D003681:Dehydration / Q000503:physiopathology; D003889:Desert Climate; D004326:Drinking; D005260:Female; D006358:Hot Temperature / Q000009:adverse effects; D008297:Male; D017440:Photoperiod; D012529:Saudi Arabia; D012621:Seasons