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

Abstract

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.

Physiological and life history strategies of a fossil large mammal in a resource-limited environment

“…Nevertheless, evidence is accumulating that certain ungulates significantly reduce endogenous heat production to cope with energetically challenging situations (food shortage, harsh climatic conditions) (32). Thus, seasonal fluctuations in metabolic rate and in body temperature (heterothermy) have been described for ungulates with a winter nadir in northern species (32)(33)(34) and with a summer nadir in desert species (35,36). Taking into account these recent advances in ungulate physiology, the zonal bone of Myotragus quite likely reflects seasonal fluctuations in metabolic rate and/or body temperature over an extended juvenile period in response to fluctuating resource conditions on the island.…”

Towards a mechanistic understanding of the responses of large terrestrial mammals to heat and aridity associated with climate change

“…A reduction in body core temperature also was evident in Arabian oryx (Fig. 3, [120]) and Arabian sand gazelles in summer [96,143], when environmental heat load was high but food was scarce. Similarly, free-living western grey kangaroos had lower 24 h minimum body core temperatures in summer, a dry season in their Australian habitat with reduced plant growth, than in winter [144].…”

Minimum daily core body temperature in western grey kangaroos decreases as summer advances: a seasonal pattern, or a direct response to water, heat or energy supply?

“…The period of most rapid rise in T c , which contributed the majority of the increase in daily T c amplitude in summer, occurred between 17:00 and 19:00h, a time when heat load was quite low compared with that during the hottest time of day, with solar radiation decreasing to zero just after 18:00h. That the rate of heat storage was five times higher near sunset than in the heat of the day [our calculation from data presented in fig.2 of Ostrowski and Williams (Ostrowski and Williams, 2006)] implies that it was not environmental heat load driving the T c patterns in sand gazelle.…”

“…In one of the few field studies that have presented evidence for the water-saving potential of heterothermy, Arabian sand gazelles exhibited an increased daily amplitude of T c in summer compared with winter, with a calculated water saving of 34mlday -1 (Ostrowski and Williams, 2006). But, contrary to the theoretical expectations, the gazelles stored heat at a slower rate during the hottest part of the day in summer than they did at the same time of day in winter, despite heat load being higher in summer [fig.2 in Ostrowski and Williams (Ostrowski and Williams, 2006)].…”

“…Two recent studies, conducted in the Saudi Arabian desert, have shown that the amplitude of T c in the Arabian oryx and the Arabian sand gazelle is related to the amplitude of environmental temperature and that heterothermy may be important for water saving in that arid environment (Ostrowski and Williams, 2006;Ostrowski et al, 2003). More recently, Hetem et al showed that the degree of heterothermy for a given environmental temperature varied with season in the Arabian oryx, with the animals maintaining homeothermy in a season in which some rain fell but exhibiting heterothermy on days with similar ambient temperature in the dry season (Hetem et al, 2010).…”