Thermoregulatory capabilities of the woodland dormouse, Graphiurus murinus

Abstract

The woodland dormouse, Graphiurus murinus, in common with many other small rodents, enters torpor under conditions of food deprivation and low temperatures. Its thermoregulatory capabilities under more favourable conditions, however, have not been investigated. We measured metabolism and thermoregulation in woodland dormice acclimated to long-day length, moderate temperature and abundant food over a temperature range (T_a) of approximately 5–37°C. The thermal neutral zone for this species lay between 29 and 35°C. Estimated resting metabolic rate (RMR) within this range averaged 21.10 ± 3.28 J g^-1 h^-1. Below 29°C energy expenditure increased with a decrease in T_a, with a maximum value of 90.76 J g^-1 h^-1 measured at 6°C. Both evaporative water loss (EWL) and thermal conductance (C) were minimal and independent of Tsub>a between 5 and 32°C but increased above the thermal neutral zone, maximum EWL and C being 6.7 mg g^-1 h^-1 (79% of metabolic heat production) and 19.74 J g^-1 h^-1 °C^-1 respectively, at 37.3°C. Thermal conductance and RMR of G. murinus were approximately 48% and 30% below predicted for rodents of equivalent mass, respectively. This pattern is consistent with that suggested for warm-temperate arboreal rodents. Although body temperature (T_b) was labile and was significantly related to T_a over the temperature range investigated, dormice maintained T_b s between 34 and 38°C using typical thermoregulatory responses that included increased activity at low Ta and postural adjustments and salivating at high T_a. While not as impressive as some rodent species, under favourable conditions G. murinus is a competent thermoregulator and torpor in the species is facultative.