title: Basking hamsters reduce resting metabolism, body temperature and energy costs during rewarming from torpor.
abstract: Basking can substantially reduce thermoregulatory energy expenditure of mammals. We tested the hypothesis that the largely white winter fur of hamsters (Phodopus sungorus), originating from Asian steppes, may be related to camouflage to permit sun basking on or near snow. Winter-acclimated hamsters in our study were largely white and had a high proclivity to bask when resting and torpid. Resting hamsters reduced metabolic rate (MR) significantly (>30%) when basking at ambient temperatures (Ta) of ∼15 and 0°C. Interestingly, body temperature (Tb) also was significantly reduced from 34.7±0.6°C (Ta 15°C, not basking) to 30.4±2.0°C (Ta 0°C, basking), which resulted in an extremely low (<50% of predicted) apparent thermal conductance. Induced torpor (food withheld) during respirometry at Ta 15°C occurred on 83.3±36.0% of days and the minimum torpor MR was 36% of basal MR at an average Tb of 22.0±2.6°C; movement to the basking lamp occurred at Tb<20.0°C. Energy expenditure for rewarming was significantly reduced (by >50%) during radiant heat-assisted rewarming; however, radiant heat per se without an endogenous contribution by animals did not strongly affect metabolism and Tb during torpor. Our data show that basking substantially modifies thermal energetics in hamsters, with a drop of resting Tb and MR not previously observed and a reduction of rewarming costs. The energy savings afforded by basking in hamsters suggest that this behaviour is of energetic significance not only for mammals living in deserts, where basking is common, but also for P. sungorus and probably other cold-climate mammals.
authors.affiliation: Research Institute of Wildlife Ecology, Department of Integrative Biology and Evolution, University of Veterinary Medicine Vienna, Savoyenstrasse 1, Vienna 1160, Austria fgeiser@une.edu.au fgeiser@une.edu.au.
authors.forename: Fritz
authors.identifier: 0000-0001-7621-5049
authors.initials: F
authors.lastname: Geiser
authors.affiliation: Research Institute of Wildlife Ecology, Department of Integrative Biology and Evolution, University of Veterinary Medicine Vienna, Savoyenstrasse 1, Vienna 1160, Austria.
authors.forename: Kristina
authors.initials: K
authors.lastname: Gasch
authors.affiliation: Research Institute of Wildlife Ecology, Department of Integrative Biology and Evolution, University of Veterinary Medicine Vienna, Savoyenstrasse 1, Vienna 1160, Austria.
authors.forename: Claudia
authors.initials: C
authors.lastname: Bieber
authors.affiliation: Research Institute of Wildlife Ecology, Department of Integrative Biology and Evolution, University of Veterinary Medicine Vienna, Savoyenstrasse 1, Vienna 1160, Austria.
authors.forename: Gabrielle L
authors.initials: GL
authors.lastname: Stalder
authors.affiliation: Research Institute of Wildlife Ecology, Department of Integrative Biology and Evolution, University of Veterinary Medicine Vienna, Savoyenstrasse 1, Vienna 1160, Austria.
authors.forename: Hanno
authors.initials: H
authors.lastname: Gerritsmann
authors.affiliation: Research Institute of Wildlife Ecology, Department of Integrative Biology and Evolution, University of Veterinary Medicine Vienna, Savoyenstrasse 1, Vienna 1160, Austria.
authors.forename: Thomas
authors.initials: T
authors.lastname: Ruf
mesh_terms: D000818:Animals; D001481:Basal Metabolism / Q000502:physiology*; D001831:Body Temperature / Q000502:physiology*; D001833:Body Temperature Regulation / Q000502:physiology; D006224:Cricetinae; D004734:Energy Metabolism / Q000502:physiology*; D005260:Female; D008297:Male; D012146:Rest / Q000502:physiology*; D017694:Rewarming; D013814:Thermal Conductivity; D013997:Time Factors; D064348:Torpor / Q000502:physiology*
keywords: Energy conservation; Passive warming; Phodopus; Radiant heat; Thermoregulation