Metabolic physiology of euthermic and torpid lesser long-eared bats, Nyctophilus geoffroyi (Chiroptera: Vespertilionidae)

Abstract

Thermal and metabolic physiology of the Australian lesser long-eared bat, Nyctophilus geoffroyi, a small (ca. 8 g) gleaning insectivore, was studied using flow-through respirometry. Basal metabolic rate of N. geoffroyi (1.42 ml O2 g-1 h-1) was 70% of that predicted for an 8-g mammal but fell within the range for vespertilionid bats. N. geoffroyi was thermally labile, like other vespertilionid bats from the temperate zone, with clear patterns of euthermy (body temperature >32°C) and torpor. It was torpid at temperatures ≤25°C, and spontaneously aroused from torpor at ambient temperatures ≥5°C. Torpor provided significant savings of energy and water, with substantially reduced rates of oxygen consumption and evaporative water loss. Minimum wet conductance (0.39 ml O2 g-1 h-1 °C-1) of euthermic bats was 108% of predicted, and euthermic dry conductance was 7.2 J g-1 h-1 °C-1 from 5-25°C. Minimum wet and dry conductances of bats that were torpid at an ambient temperature of 15-20°C (0.06 ml O2 g-1 h-1 °C-1 and 0.60 J g-1 h-1 °C-1) were substantially less than euthermic values, but conductance of some torpid bats increased at lower ambient temperatures and approached values for euthermic bats. Metabolic rates of bats torpid at ambient temperatures >10°C and bats euthermic in the thermoneutral zone indicated a metabolic Q10 of 3.9. That high Q10 suggested that there may have been an intrinsic reduction in metabolic rate during torpor, in addition to down-regulation of thermoregulation (which accounted for most of the reduction in metabolic rate) and the normal Q10 effect.