Abstract
The winter-resident Korean bats, Murina leucogaster ognevi, show a circadian cycle of thermoregulation and locomotion in summer, as do other bat species in temperate regions. They are most active between dusk and dawn with body temperature (Tb) of 35-4OC, and are usually torpid in their roost sites for the rest of day with their Tb close to ambient temperature (Ta) of around 15C. The present study was conducted to determine thermogenic and thermolabile properties of the heterothermic bats that would influence their daily feeding activities and ultimately, their energy conservation strategy. Testing on active male Murina, resting metabolic rate (RMR, gauged by oxygen consumption rate) at the lower limit of thermoneutral zone (31C) was 2.0 L kq-1 h-1. The regression slope of RMR below the thermoneutral zone (an index of metabolic thermal sensitivity) was -0.38 L $kg^{-l} h^{-1} C^{-1}$. The metabolic rate at the roost Ta (15C) was 4.5 times the lowest RMR in the active state but becomes nearly zero in the torpid state. This implies that by being torpid during daytime (between dawn and dusk), the individual bats would save about 4.7 kcal each day in mid-summer. Interspecific comparisons of thermal metabolic response over a mass scale suggest that the smaller bats show a relatively higher metabolic rate in thermoneutral zone and a greater thermal sensitivity of metabolism, which follows the general principle seen in homeothermic metabolism. Thermolabile features in metabolic responses seem to be fairly common for these bats in conditions other than a fully active state. Types of thermolabile responses and their energetic significance are discussed.
