Abstract: Two hypotheses may explain the lack of metabolic depression at low temperature in hibernating reptiles from warm but not cool climates. (1) Physiological ability; reptiles from cool climates have resting metabolic rates elevated at low temperatures and so have greater potential for metabolic depression. (2) Energy benefit; hibernation is generally short in warm climates, so the energy saving possible at low temperature is small. These hypotheses can be separated in a warm-climate reptile that hibernates for a long period, such as the African tortoise Kinixys spekii, which is dormant for 7-8 months a year in winter and in the following hot dry season. Dormant tortoises had a reduced rate of oxygen consumption (VO₂) between 10 and 25^oC compared with resting VO₂ measured at the same temperatures in the active season, and at 10-15^oC compared with the resting VO₂ of controls kept active in winter. These data are consistent with hypothesis 2 but not hypothesis 1. The metabolic rate during dormancy was on average 59% of resting VO ₂, with minimum rates of 47-48% at 10 and 25^oC, similar to the minimum rates of about 50% of resting VO₂ in other hibernating reptiles. Aestivating ectotherms achieve greater metabolic depression, to about 25% of resting VO₂, possibly as a result of reduced gas exchange.

Can. J. Zool. 75: 1328-1335 (1997)