Content area
Full text
Bears from the family Ursidae are the only terrestrial mammals that go through gestation, parturition, and lactation during hibernation. This is the 1st study to examine the influence of reproductive status (i.e., nonpregnant, pseudopregnant, or pregnant) on body temperature and blood biochemical profiles in hibernating black bears. Pregnant bears appeared to have higher and more stable body temperatures (37-38°C) than nonpregnant ones (34-36°C) during pregnancy, which was followed by a rapid drop to levels comparable to those of nonpregnant individuals after parturition. In midpregnancy (i.e., January), pregnant bears had higher blood glucose and lower triglyceride concentrations than did nonpregnant ones, whereas blood concentrations of free fatty acids, glycerol, and ketone bodies did not differ significantly. Plasma urea, creatinine, and urea/creatinine levels were significantly lower in pregnant bears than in nonpregnant ones. Pseudopregnant bears showed similar changes in body temperature and blood profiles to pregnant ones, but blood glucose levels in January were significantly lower than those in pregnant bears. These results suggest that pregnant bears maintain homeothermic conditions and supply nutrients to the fetus by stimulating thermogenesis, gluconeogenesis, and urea recycling during hibernation. In addition, these physiological changes appear to be mainly caused by corpus luteum-derived factors (e.g., progesterone) but also were facilitated by placental factors.
Key words: bears, body temperature, gestation, hibernation, metabolism, pregnancy, Ursus
© 2013 American Society of Mammalogists
DOI: 10.1644/12-MAMM-A-246.1
Mammalian hibernation is an adaptive strategy to survive during a food-scarce season by reducing energy consumption. Hibernation is characterized by inactivity, lower body temperature, reductions in breathing and heart rate, and metabolic suppression. Hibernation has been documented in 8 different groups of mammals (Carey et al. 2003), suggesting that hibernation may not have evolved within specific species but may be an ancestral trait that is shared by many species belonging to different orders. Among mammalian hibernators, bears, including the Japanese black bear (Ursus thibetanus japonicus), have a unique hibernation physiology, surviving for up to 6 months without eating, drinking, urinating, or defecating (Nelson 1973). Small hibernators, such as hamsters, woodchucks, and ground squirrels, enter torpor with a low body temperature (0-10°C) and exhibit periodic arousal by rewarming to euthermic levels (35-37°C [Wollnik and Schmidt 1995; Zervanos et al. 2010; Healy et al. 2012]). In contrast, bears do not exhibit such...