Journal of Comparative Physiology B

, Volume 165, Issue 4, pp 291–297

Reduction of metabolic rate and thermoregulation during daily torpor

  • X. Song
  • G. Körtner
  • F. Geiser
Original Paper

DOI: 10.1007/BF00367312

Cite this article as:
Song, X., Körtner, G. & Geiser, F. J Comp Physiol B (1995) 165: 291. doi:10.1007/BF00367312

Abstract

Physiological mechanisms causing reduction of metabolic rate during torpor in heterothermic endotherms are controversial. The original view that metabolic rate is reduced below the basal metabolic rate because the lowered body temperature reduces tissue metabolism has been challenged by a recent hypothesis which claims that metabolic rate during torpor is actively downregulated and is a function of the differential between body temperature and ambient temperature, rather than body temperature per se. In the present study, both the steady-state metabolic rate and body temperature of torpid stripe-faced dunnarts, Sminthopsis macroura (Dasyuridae: Marsupialia), showed two clearly different phases in response to change of air temperature. At air temperatures between 14 and 30°C, metabolic rate and body temperature decreased with air temperature, and metabolic rate showed an exponential relationship with body temperature (r2=0.74). The Q10 for metabolic rate was between 2 and 3 over the body temperature range of 16 to 32°C. The difference between body temperature and air temperature over this temperature range did not change significantly, and the metabolic rate was not related to the difference between body temperature and air temperature (P=0.35). However, the apparent conductance decreased with air temperature. At air temperatures below 14°C, metabolic rate increased linearly with the decrease of air temperature (r2=0.58) and body temperature was maintained above 16°C, largely independent of air temperature. Over this air temperature range, metabolic rate was positively correlated with the difference between body temperature and air temperature (r2=0.61). Nevertheless, the Q10 for metabolic rate between normothermic and torpid thermoregulating animals at the same air temperature was also in the range of 2–3. These results suggest that over the air temperature range in which body temperature of S. macroura was not metabolically defended, metabolic rate during daily torpor was largely a function of body temperature. At air temperatures below 14°C, at which the torpid animals showed an increase of metabolic rate to regulate body temperature, the negative relationship between metabolic rate and air temperature was a function of the differential between body temperature and air temperature as during normothermia. However, even in thermoregulating animals, the reduction of metabolic rate from normothermia to torpor at a given air temperature can also be explained by temperature effects.

Key words

Daily torpor Metabolic rate reduction Temperature Thermoregulation Marsupial, Sminthopsis macroura 

Abbreviations

BM

body mass

BMR

basal metabolic rate

C

apparent conductance

MR

metabolic rate

RMR

resting metabolic rate

RQ

respiratory quotient

Ta

air temperature

Tb

body temperature

Tlc

lower critical temperature

Ttc

critical air temperature during torpor

TMR

metabolic rate during torpor

TNZ

thermoneutral zone

αT

difference between body temperature and air temperature

VO2

rate of oxygen consumption

Copyright information

© Springer-Verlag 1995

Authors and Affiliations

  • X. Song
    • 1
  • G. Körtner
    • 1
  • F. Geiser
    • 1
  1. 1.Department of ZoologyUniversity of New EnglandArmidaleAustralia

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