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

Thermal and metabolic physiology of the Australian lesser long-eared bat, N yctophilus geoffroyi, a small (ca. 8 g) gleaning insectivore, was studied u sing how-through respirometry. Basal metabolic rate of N. geoffroyi (1.42 m l O-2 g(-1) h(-1)) was 70% of that predicted for an 8-g mammal but fell wit hin the range for vespertilionid bats. N. geoffroyi was thermally labile, L ike other vespertilionid bats from the temperate zone, with clear patterns of euthermy (body temperature >32 degrees C) and torpor. It was torpid at t emperatures less than or equal to 25 degrees C, and spontaneously aroused f rom torpor at ambient temperatures greater than or equal to 5 degrees C. To rpor provided significant savings of energy and water, with substantially r educed rates of oxygen consumption and evaporative water loss. Minimum wet conductance (0.39 ml O-2 g(-1) h(-1 degrees)C(-1)) of euthermic bats was 10 8% of predicted, and euthermic dry conductance was 7.2 J g(-1) h(-1) degree s C-1 from 5-25 degrees C. Minimum wet and dry conductances of bats that we re torpid at an ambient temperature of 15-20 degrees C (0.06 ml O-2 g(-1) h (-1) degrees C-1 and 0.60 J g(-1) h(-1) C-1) were substantially less than e uthermic values, but conductance of some torpid bats increased at lower amb ient temperatures and approached values for euthermic bats. Metabolic rates of bats torpid at ambient temperatures >10 degrees C and bats euthermic in the thermoneutral zone indicated a metabolic Q(10) of 3.9. That high Q(10) suggested that there may have been an intrinsic reduction in metabolic rat e during torpor, in addition to down-regulation of thermoregulation (which accounted for most of the reduction in metabolic rate) and the normal Q(10) effect.