Freeze Avoidance in a Mammal: Body Temperatures Below 0°C in an Arctic Hibernator

Abstract

Hibernating arctic ground squirrels, Spermophilus parryii, were able to adopt and spontaneously arouse from core body temperatures as low as -2.9 degrees C without freezing. Abdominal body temperatures of ground squirrels hibernating in outdoor burrows were recorded with temperature-sensitive radiotransmitter implants. Body temperatures and soil temperatures at hibernaculum depth reached average minima during February of -1.9 degrees and -6 degrees C, respectively. Laboratory-housed ground squirrels hibernating in ambient temperatures of -4.3 degrees C maintained above 0 degree C thoracic temperatures but decreased colonic temperatures to as low as -1.3 degrees C. Plasma sampled from animals with below 0 degree C body temperatures had normal solute concentrations and showed no evidence of containing antifreeze molecules.

Mammal survival at the Cretaceous–Palaeogene boundary: metabolic homeostasis in prolonged tropical hibernation in tenrecs

“…These hypothermic influences do not occur in hibernators. In the most extreme case, Arctic ground squirrels (Urocitellus parryii) maintain T b at 228C to 238C during three-week hibernation bouts [44]. There is much debate surrounding the fitness benefits of IBAs in temperate hibernators given the very high energetic costs that are involved in arousals [40,41,45].…”

Adenosine receptors mediate the hypoxic ventilatory response but not the hypoxic metabolic response in the naked mole rat during acute hypoxia

“…Typically, these animals are most hypoxia-tolerant while over-wintering. During this period, they exhibit metabolic rate depression mediated in part by a profound decrease in body temperature (T b ) and entry into a torpor-like state [5]. These responses drastically reduce systemic energy demands and extend survival time in hypoxia.…”

Metabolic cycles in a circannual hibernator

“…Hibernation, characterized by months of fasting and dramatic oscillations between states of cold and warm body temperature (T b ), ensues only after adequate fat stores are deposited (7). Most of the fall and winter months are spent in a state of deep torpor in which metabolic, heart, and respiratory rates are reduced to Ͻ5% of their summer equivalents, and body temperature declines to as low as 0°C, or even below (5). However, all hibernating mammals spontaneously reverse torpor at regular intervals by elevating metabolic rate and employing strictly endogenous mechanisms of heat production including shivering and nonshivering thermogenesis.…”