, Volume 179, Issue 6, pp 691-700
Date: 11 Mar 2009

Energetics of arousal episodes in hibernating arctic ground squirrels

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Arctic ground squirrels overwintering in northern Alaska experience average soil temperature of −10°C. To examine energetic costs of arousing from hibernation under arctic compared to temperate conditions, captive ground squirrels were maintained in ambient temperatures (T a) of 2, −5 and −12°C. Rates of oxygen consumption and carbon dioxide production were used to estimate metabolic rate and fuel use during the three phases of arousal episodes: rewarming, euthermia, and recooling. Respiratory quotient comparisons suggest exclusive use of lipid during rewarming and mixed fuel use during euthermia. Animals rewarming from torpor at T a −12°C took longer, consumed more oxygen, and attained higher peak rates of oxygen consumption when compared to 2°C. T a had no significant effect on cost or duration of the euthermic phase. Animals recooled faster at −12°C than at 2°C, but total oxygen consumption was not different. T a had no significant effect on the total cost of arousal episodes when all three phases are included. Arousal episodes account for 86% of estimated costs of a complete hibernation cycle including torpor when at 2°C and only 23% at −12°C. Thus, due to the higher costs of steady-state metabolism during torpor, proportional metabolic costs of arousal episodes at T a characteristic of the Arctic are diminished compared to relative costs of arousals in more temperate conditions.

Communicated by H. V. Carey.