Brain, abdominal and arterial blood temperatures of free-ranging eland in their natural habitat

Abstract

Using implanted miniature data loggers we measured brain, arterial blood and abdominal temperatures at 5-min intervals in two free-ranging eland (Tragelaphus oryx) in their natural habitat. The animals were subjected to a nychthemeral range of globe temperature which exceeded 40 degrees C. Arterial blood exhibited a moderate amplitude (2.3 degrees C) nychthemeral rhythm, with a temperature peak at 1600-1800 hours, and a trough in the early morning at 0600-0800 hours. Mean abdominal temperature was 0.2-0.3 degrees C lower than the corresponding blood temperature, and had a peak-to-trough amplitude of 2.6 degrees C. Brain temperature closely paralleled changes in blood temperature but usually exceeded blood temperature by about 0.5 degrees C. Sporadic episodes of selective brain cooling occurred in one animal, but the duration and magnitude of such cooling was small (less than 0.4 degrees C), and took place only well above the mode of blood temperature. Our results do not support the concept that eland routinely employ adaptive heterothermy and selective brain cooling to survive in their natural environment.

Brain and arterial blood temperatures of free-ranging oryx (Oryx gazella)

“…However, we found no evidence that the use of SBC was enhanced in the arid-adapted oryx compared to other artiodactyls studied to date, namely the black wildebeest [11], goats [10], springbok [17], or eland [6]. In fact the calculated threshold for SBC in oryx of over 39.5°C is somewhat higher than that observed in other artiodactyl species [16].…”

“…3). The magnitude of the nychthemeral range in oryx body temperature was similar to that observed in zebras at the same location [7], and in eland exposed to similar conditions [6], but greater than that measured in freeranging black wildebeest [11], springbok [17], or goats living outdoors unrestrained [10]. Thus an intuitive supposition that larger mammals have smaller nychthemeral rhythms because of thermal inertia does not hold for the species studied to date.…”

“…In all free-ranging artiodactyls studied to date, the slope of the line relating T hyp to T car has been less than one and so, overall, the range of T hyp is smaller than T car [6,10,11,17]. However, the gross conclusions drawn from regression analyses obscure subtleties in control mechanisms, because the variation of each of the temperatures differed at different time scales.…”

“…These responses were assigned adaptive significance in that storage of heat reduces the demand for evaporative cooling and creates a temperature gradient for dry heat exchange to the environment [25]. However, free-ranging eland [6] exposed to similar fluctuations in ambient conditions as captive eland [25] exhibit much smaller nychthemeral body temperature ranges, an outcome which Fuller et al [6] ascribe to the inhibition of behavioural strategies in captive animals, especially interactions with conspecifics. A similar situation may exist with the oryx, since we found that ambient conditions spanning globe temperature ranges from 15 to 35°C had no effect on the body temperature range of free-ranging oryx (Fig.…”

“…The greatest hyperthermia experienced by free-ranging animals occurs when they are chased, and when they are chased they do not use SBC [6,11,17]. An alternative role for SBC in mammalian thermoregulation is that it modifies an animal's effector response to a thermal load by adjusting input from hypothalamic neurones in thermoregulatory pathways [9].…”