Thermoregulatory variations of high-altitude hibernators in relation to ambient temperature, season, and hibernation [Changements thermorégulateurs en relation avec la température ambiante, la saison et l'hibernation].

Résumé

The MR, Tb, RQ, and weight measurements were made on golden-mantled ground squirrels, Citellus lateralis, and yellowbelly marmots (Marmota flaviventris) eight times throughout l year. Time periods of study were 3-5 days in length, and occurred in August-September, mid-September, September-October, mid-December, mid-February, April-May, mid-July, and August-September. All studies were made at Rarcroft Laboratory of the White Mountain Research Station, located at 3,800 m. All animals were caught nearby. In active, nonhibernating animals, seasonal cycle of weight change (weights taken before MR study at Ta 30 C°) showed a large increase of weight in both species from A-S to S-O, a decrease to a yearly low in A-M, and a rapid increase through July to A-S. Body temperature also shows a seasonal cycle even in nonhibernating animals of these species, with decrease in Tb at the time hibernation normally begins, maintenance of a low temperature or even further decline in winter, and an increase to an annual high in summer. Metabolic rate of active animals also decreases at time of onset of hibernation to a seasonal low, followed by maintenance of low values through the normal period of hibernation, and an increase in summer. Metabolic rate at TA 30 C is not seasonally cyclic. The respiratory quotient is near unity in A-S, during the period of rapid fat deposition preceding onset of hibernation, with an abrupt decline after that time, and maintenance of low values or a further decline in winter, and a marked increase in summer. During hibernation, levels of all parameters tested were similar to those found previously for other species of hibernators. The MR averaged 0.030 ± 0.012 ml 02/g per hr for marmots and 0.066 ± 0.022 for ground squirrels at Ta 6 ± 2 C. The RQ was higher than expected during hibernation and reflected metabolism of some carbohydrate. It is concluded that hihernation in these high-altitlude species is not modified by their life under conditions of chronic hypoxia. The seasonal changes in thermoregulatory responses are caused by the demands of hibernation, even when the individuals studied do not hibernate, and appear not to be affected by chronic exposure to hypoxia.