A Comparative Study of the Environmental Physiology of an East African Antelope, the Eland, and the Hereford Steer

SUMMARY To test the idea that large, free-living, desert ungulates use heterothermy to reduce water loss, we measured core body temperature(Tb) of six free-ranging, adult Arabian oryx (Oryx leucoryx) during 2 years in the arid desert of west-central Saudi Arabia. We report the first case of heterothermy in a free-living ruminant in a desert environment: Tb varied by 4.1±1.7°C day–1 during summer (June to September) and by 1.5±0.6°C day –1 during winter (November to March). Over both seasons, mean Tb was 38.4±1.3°C. During the day in both summer and winter, Tb increased continually, suggesting that oryx store heat instead of dissipating it by evaporation, whereas at night Tb decreased. The minimum Tb was lower in summer (36.5±1.16°C) than in winter (37.5±0.51°C)despite the fact that the temperature gradient between Tband air temperature (Ta) was larger and solar radiation was lower in winter. Throughout the year, daily variation in Tb appeared to reflect thermal load(Ta,max–Ta,min) rather than an endogenous rhythm. Behavioural thermoregulation was used by oryx to cope with thermal stress during summer: animals lay down in shade in the morning shortly before Ta exceeded Tb and remained there until evening when Tb–Tabecame positive. The use of heterothermy by oryx resulted in storage ofandwould672.4 kJ day–1 animal–1258.6 kJ day–1 animal–1in winter, if heat storage is based on calculations involving mean Tb. Todissipaterequirethisheatin summerby evaporation0.28 litres H2O day–1 animal–1and0.11 litres H2O day–1 animal–1 in summer and winter,respectively. Without heat storage in summer, we estimated that oryx would have to increase their water intake by 19%, a requirement that would be difficult to meet in their desert environment. If heat storage was calculated based on the daily change in Tb rather than on heat storage above mean Tb then we estimated that oryx saved 0.538 litres H2O day–1 animal–1during summer.

Section: Discussionmentioning

confidence: 88%

Section: Discussionmentioning

confidence: 99%

Section: Heterothermy and The Water Economy Of Free-living Arabian Ormentioning

confidence: 99%

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Heterothermy and the water economy of free-living Arabian oryx (Oryx leucoryx)

Ostrowski¹,

Williams

Ismael³

2003

“…Our data on variation in T b of gazelles provide an example of a small desert ungulate employing heterothermy to reduce evaporative water loss that would otherwise be required to maintain normothermic T b . their rectal T b by 4°C during the day, saving approximately 0.5·l of evaporative water (Taylor and Lyman, 1967;Taylor, 1969).…”

Section: Introductionmentioning

confidence: 99%

Heterothermy of free-living Arabian sand gazelles (Gazella subgutturosa marica) in a desert environment

Ostrowski¹,

Williams

2006

SUMMARY To test whether free-living desert ungulates employ heterothermy to reduce water loss, we measured core body temperature (Tb) of six free-living Arabian sand gazelles (Gazella subgutturosa marica), a small desert antelope (12–20 kg) that lives in the deserts of Saudi Arabia, where air temperature (Ta) often exceeds 40°C. We found that the mean daily Tb varied by 2.6±0.8°C during summer (June–July) and 1.7±0.3°C during winter (January–February); over both seasons, mean Tb was 39.5±0.2°C. During the day, in summer, Tb increased by more than 2°C when Ta>Tb and declined at night when Ta<Tb, suggesting that gazelles stored heat during day and dissipated it by non evaporative means during night. The minimum Tb was lower in summer(38.2±0.5°C) than in winter (38.6±0.3°C) despite the fact that the gradient between Tb and Ta was larger and solar radiation was lower in winter. Correlation between daily variation of Tb and mean,maximal Tas were significant in summer, but not in winter. To dissipate the amount of heat stored by gazelles would require an evaporative water loss of 33.5 ml H2O day–1 in summer and 23.2 ml H2O day–1 in winter. We tested whether the amplitude of daily variation in Tb was influenced by the level of water provided to six captive sand gazelles maintained under controlled conditions in summer. The daily amplitude of Tb was increased by 1.4°C when gazelles were denied drinking water but supplied with pre-formed water in food, and by 1.1°C when they were denied both water and food. Gazelles denied only drinking water increased the amplitude of variation in Tb, whereas when denied both food and water, they seemed to undergo a dehydration-hyperthermia, with increased mean and maximal Tb values but no decrease of minimal Tb. Free-ranging and captive gazelles surviving on pre-formed water in natural food used heterothermy during summer with no elevation of plasma osmolality,indicating that they were not in a state of dehydration. Our data on variation in Tb of gazelles provide an example of a small desert ungulate employing heterothermy to reduce evaporative water loss that would otherwise be required to maintain normothermic Tb.

“…This adaptation, known as adaptive heterothermy, is thus characterised by an increased amplitude of the nychthemeral body temperature rhythm (reportedly as much as 7°C) with a diurnal peak in body temperature near the end of the peak ambient heat load followed by an unusually low body temperature at night (Louw and Seely, 1982). Adaptive heterothermy has been reported in eland Tragelaphus oryx (Taylor, 1969;Taylor and Lyman, 1967), water-deprived camels Camelus dromedarius (Schmidt-Nielsen et al, 1957), oryx Oryx beisa (Taylor, 1969;Taylor, 1970), giraffe Giraffa camelopardalis (Langman and Maloiy, 1989) and, despite their smaller size, gazelles (Gazella granti and Gazella thompsonii; Taylor, 1970). At the time these studies were carried out, however, technical limitations precluded the continuous measurement of core body temperature in unrestrained animals exposed to natural environmental stressors.…”

mentioning

confidence: 99%

A year in the thermal life of a free-ranging herd of springbokAntidorcas marsupialis

Fuller

Kamerman

Maloney

et al. 2005

We used miniature data loggers implanted in the abdominal cavity to measure core body temperatures at 30·min intervals in eight (three males, five females) adult free-ranging springbok Antidorcas marsupialis in their natural habitat, over a period of 11-13 months. The animals were subjected to a nychthemeral range of air temperature that often exceeded 20°C, with an absolute minimum temperature of -6°C and a maximum of 34°C. Abdominal temperature exhibited a low amplitude (~1.2°C) nychthemeral rhythm, with a temperature peak near sunset and a trough shortly after sunrise. The amplitude of the nychthemeral rhythm of body temperature was not correlated with the 24·h range of air temperature. Although mean 24·h body temperatures were positively correlated with corresponding air temperatures, mean daily body temperature increased, on average, by only 0.02°C per 1°C increase in air temperature, so that it was only ~0.3°C higher in summer than in winter. Mean monthly body temperatures were strongly positively correlated with photoperiod and, in parallel with changes in the time of sunrise, the times at which the minimum and maximum body temperatures occurred were shifted ~1.2·h earlier in summer than in winter. Annual and daily variations in body temperature of springbok, like those of other free-living African ungulates, therefore appear to reflect an endogenous rhythm, entrained by the light:dark cycle, but largely independent of fluctuations in the environmental thermal load. Springbok exhibit remarkable homeothermy and do not employ adaptive heterothermy to survive in their natural environment.