Thermoregulation in pronghorn antelope (Antilocapra americana,Ord) in winter

Abstract

SUMMARY Conservation of energy is a prerequisite thermoregulatory strategy for survival in northern hemisphere winters. We have used thermistor/data logger assemblies to measure temperatures in the brain, carotid artery, jugular vein and abdominal cavity, in pronghorn antelope to determine their winter body temperature and to investigate whether the carotid rete has a survival role. Over the study period mean black globe and air temperature were–0.5±3.2°C and –2.0±3.4°C, respectively, and mean daytime solar radiation was ∼186 W m–2. Brain temperature (Tbrain, 39.3±0.3°C) was higher than carotid blood temperature (Tcarotid,38.5±0.4°C), and higher than jugular temperature(Tjugular, 37.9±0.7°C). Minimum Tbrain (38.5±0.4°C) and Tcarotid (37.8±0.2°C) in winter were higher than the minimum Tbrain (37.7±0.5°C) and Tcarotid (36.4±0.8°C) in summer that we have reported previously. Compared with summer, winter body temperature patterns were characterized by an absence of selective brain cooling (SBC), a higher range of Tbrain, a range of Tcarotidthat was significantly narrower (1.8°C) than in summer (3.1°C), and changes in Tcarotid and Tbrain that were more highly correlated (r=0.99 in winter vs r=0.83 in summer). These findings suggest that in winter the effects of the carotid rete are reduced, which eliminates SBC and prevents independent regulation of Tbrain, thus coupling Tbrain to Tcarotid. The net effect is that Tcarotid varies little. A possible consequence is depression of metabolism, with the survival advantage of conservation of energy. These findings also suggest that the carotid rete has wider thermoregulatory effects than its traditional SBC function.