Blood and brain temperatures of free-ranging black wildebeest in their natural environment.
ABSTRACT Using miniature data loggers, we measured the temperatures of carotid blood and brain in four wildebeest (Connochaetes gnou) every 2 min for 3 wk and every 5 min, in two of the animals, for a further 6 wk. The animals ranged freely in their natural habitat, in which there was no shelter. They were subject to intense radiant heat (maximum approximately 1,000 W/m2) during the day. Arterial blood temperature showed a circadian rhythm with low amplitude (< 1 degree C) and peaked in early evening. Brain temperature was usually within 0.2 degrees C of arterial blood temperature. Above a threshold between 38.8 and 39.2 degrees C, brain temperature tended to plateau so that the animals exhibited selective brain cooling. However, selective brain cooling sometimes was absent even when blood temperature was high and present when it was low. During helicopter chases, selective brain cooling was absent, even though brain temperature was near 42 degrees C. We believe that selective brain cooling is controlled by brain temperature but is modulated by sympathetic nervous system status. In particular, selective brain cooling may be abolished by high sympathetic activity even at high brain temperatures.
Article: Body temperature daily rhythm adaptations in African savanna elephants (Loxodonta africana).[show abstract] [hide abstract]
ABSTRACT: The savanna elephant is the largest extant mammal and often inhabits hot and arid environments. Due to their large size, it might be expected that elephants have particular physiological adaptations, such as adjustments to the rhythms of their core body temperature (T(b)) to deal with environmental challenges. This study describes for the first time the T(b) daily rhythms in savanna elephants. Our results showed that elephants had lower mean T(b) values (36.2 +/- 0.49 degrees C) than smaller ungulates inhabiting similar environments but did not have larger or smaller amplitudes of T(b) variation (0.40 +/- 0.12 degrees C), as would be predicted by their exposure to large fluctuations in ambient temperature or their large size. No difference was found between the daily T(b) rhythms measured under different conditions of water stress. Peak T(b)'s occurred late in the evening (22:10) which is generally later than in other large mammals ranging in similar environmental conditions.Physiology & Behavior 12/2007; 92(4):560-5. · 2.87 Impact Factor
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ABSTRACT: Temperature profoundly influences physiological responses in animals, primarily due to the effects on biochemical reaction rates. Since physiological responses are often exemplified by their rate dependency (e.g., rate of blood flow, rate of metabolism, rate of heat production, and rate of ion pumping), the study of temperature adaptations has a long history in comparative and evolutionary physiology. Animals may either defend a fairly constant temperature by recruiting biochemical mechanisms of heat production and utilizing physiological responses geared toward modifying heat loss and heat gain from the environment, or utilize biochemical modifications to allow for physiological adjustments to temperature. Biochemical adaptations to temperature involve alterations in protein structure that compromise the effects of increased temperatures on improving catalytic enzyme function with the detrimental influences of higher temperature on protein stability. Temperature has acted to shape the responses of animal proteins in manners that generally preserve turnover rates at animals’ normal, or optimal, body temperatures. Physiological responses to cold and warmth differ depending on whether animals maintain elevated body temperatures (endothermic) or exhibit minimal internal heat production (ectothermic). In both cases, however, these mechanisms involve regulated neural and hormonal over heat flow to the body or heat flow within the body. Examples of biochemical responses to temperature in endotherms involve metabolic uncoupling mechanisms that decrease metabolic efficiency with the outcome of producing heat, whereas ectothermic adaptations to temperature are best exemplified by the numerous mechanisms that allow for the tolerance or avoidance of ice crystal formation at temperatures below 0◦C.Comprehensive Physiology. 01/2012; 2:2151-2202.
Wildlife Society Bulletin 01/2009; · 0.95 Impact Factor