The physiology of torpor in Perognathus hispidus
Wang, Lawrence Chia-Huang
Hudson, Jack W.
Master of Arts
Perognathus hispidus can thermoregulate and remain homeothermic between ambient temperatures of 5.0 to 34.0 °C.. Above 34 °C., animal became hyperthermic and death occured at Ta of 37 °C.. In the normothermic animal, the minimum oxygen consumption follows Newton's law of cooling, the thermal conductance is 0.201 cc 02/gm/hr/°C.. The thermoneutral zone extends from Ta of 30.5 to 33.5 °C. and oxygen consumption within the thermoneutral zone is 1.25 cc 02/gm/hr. Heart rate and respiratory rate increased with the decrease of ambient temperature below Ta of 30 °C.. Shivering was not observed until Ta was below 20 °C.. Occasional spontaneous torpors with food and water present were observed through out the year in the laboratory. However, the typical response is normothermia under the pre-sence of food and water over a range of ambient temperatures from 5-24 °C.. When food supply was withheld or restricted, P. hispidus invariable became torpid within 24 hours at Ta between 4 and 24 °C.. During entrance into torpor, heart rate decreases prior to the decrease of oxygen consumption and body temperature. Skipped heart beats and irregular apnea are characteristics during the entry period. Intermittent shiverings were observed electrically during entrance. Cooling rate was slower in the normal entrance than the cooling of dead animal. During torpor, minimum heart rate was between 25-60 beats/Min and respiratory rate was irregular with prolonged apnea. Oxygen consumption decreased to 2-13% of the normothermic value. Body temperature was within 2 °C. of the ambient above Ta of 14 °C.; below 14 °C., delta T increases as Ta decreases. The length of torpor in a single bout was less than 24 hours and it decreases as Ta decreased from 17 to 1.5 °C.. During arousal, the maximum heart rate was between 420- 570 beats/Min and respiratory rate around 200 breathes/Min. Maximum oxygen consumption usually doubles the normothermic value and is characterized by an overshoot. Body temperature rewarmed to within normothermic range after arousal and moderate neck-abdomen temperature difference was found during arousal. The arousal rate was 0.51 °C./Min. Animal can reduce 2/3 of its energy requirement by using torpor than remain normothermic at Ta of 16 °C.. Field observations indicate torpor was occured in P. hispidus under natural conditions. It is concluded that daily torpor represents a physiological adaptation to the environment in P. hispidus.