caa a22 4500 605514291 CHVBK 20210128100704.0 cr unu---uuuuu 210128e20150501xx s 000 0 eng 10.1007/s00360-015-0891-y doi (NATIONALLICENCE)springer-10.1007/s00360-015-0891-y Thermoregulation and energetics in hibernating black bears: metabolic rate and the mystery of multi-day body temperature cycles [Elektronische Daten] [Øivind Tøien, John Blake, Brian Barnes] Black bears overwintering in outdoor hibernacula in Alaska decrease metabolism to as low as 25% basal rates, while core body temperature (T b) decreases from 37 to 38°C to a mid-hibernation average of 33°C. T b develops cycles of 1.6-7.3days length within a 30-36°C range, with no circadian component. We do not know the mechanism or function underlying behind the T b cycles, although bears avoid T b of <30°C and shorter cycles are predicted from higher rates of heat loss in colder conditions. To test this we manipulated den temperatures (T den) of 12 hibernating bears with body mass (BM) from 35.5 to 116.5kg while recording T b, metabolic rate (M), and shivering. T b cycle length (0.8-11.2days) shortened as T den decreased (partial R 2=0.490, p<0.001). Large bears with low thermal conductance (TC) showed more variation in T b cycle length with changes in T den than did smaller bears with high TC. Minimum T b across cycles was not consistent. At low T den bears shivered both during rising and decreasing phases of T b cycles, with minimum shivering during the fastest drop in T b. At higher T den the T b pattern was more irregular. Mean M through T b cycles was negatively correlated to T den below lower critical temperatures (1.4-10.4°C). Minimum M (0.3509W/kg±0.0121 SE) during mid-hibernation scaled to BM [M (W)=1.217×BM (kg)0.6979, R 2=0.855, p<0.001]. Hibernating thermal conductance (TC) was negatively correlated to BM (R 2=0.721, p<0.001); bears with high TC had the same T b cycle length as bears with low TC except at high T den, thus not supporting the hypothesis that cooling rate alone determines T b cycle length. We conclude that T b cycling is effected by control of thermoregulatory heat production, and T b cycling may not be present when hibernating bears use passive thermoregulation. More intense shivering in the rising phase of cycles may contribute to the prevention of muscle disuse atrophy. Bears hibernating in cold conditions use more energy during hibernation than in warmer conditions. At T den below lower critical temperature, no extra energy expenditure results from T b cycling compared to keeping a stable T b. Springer-Verlag Berlin Heidelberg, 2015 Hibernation nationallicence Bears nationallicence Thermoregulation nationallicence Shivering nationallicence Metabolic rate nationallicence Total body thermal conductance nationallicence T b : Core body temperature nationallicence T den : Den temperature nationallicence T outside : Outside temperature nationallicence BM : Body mass nationallicence M : Metabolic rate nationallicence EMG : Electromyogram nationallicence LCT : Lower critical temperature nationallicence TC : Total body thermal conductance nationallicence Tøien Øivind Institute of Arctic Biology, University of Alaska Fairbanks, 99775-7000, Fairbanks, AK, USA aut Blake John Veterinary Services, University of Alaska Fairbanks, 99775-6980, Fairbanks, AK, USA aut Barnes Brian Institute of Arctic Biology, University of Alaska Fairbanks, 99775-7000, Fairbanks, AK, USA aut Journal of Comparative Physiology B Springer Berlin Heidelberg 185/4(2015-05-01), 447-461 0174-1578 185:4<447 2015 185 360 https://doi.org/10.1007/s00360-015-0891-y text/html Onlinezugriff via DOI BK010053 XK010053 XK010000 Metadata rights reserved Springer special CC-BY-NC licence nationallicence 1 research-article jats NATIONALLICENCE NATIONALLICENCE NL-springer NATIONALLICENCE 856 40 https://doi.org/10.1007/s00360-015-0891-y text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Tøien Øivind Institute of Arctic Biology, University of Alaska Fairbanks, 99775-7000, Fairbanks, AK, USA aut NATIONALLICENCE 700 1- Blake John Veterinary Services, University of Alaska Fairbanks, 99775-6980, Fairbanks, AK, USA aut NATIONALLICENCE 700 1- Barnes Brian Institute of Arctic Biology, University of Alaska Fairbanks, 99775-7000, Fairbanks, AK, USA aut NATIONALLICENCE 773 0- Journal of Comparative Physiology B Springer Berlin Heidelberg 185/4(2015-05-01), 447-461 0174-1578 185:4<447 2015 185 360