Spontaneous torpor was examined in 36 Pouched mice Soccosiomi/s campestris Peters, 1846 from 6 localities in southern Africa. Fifteen .individuals displayed characteristic bouts of torpor in which oxygen consumption (VO2) fell below 50% of the resting levels of non-torpid pouched mice for more than 2 hr during the early morning. These bouts ended in an abrupt increase in VO2 which oversfhot resting levels during arousal to normothermia. Minimum oxygen consumption (V02min) was not correlated with the energy saved during torpor, but there was a significant positive correlation between V02min and the duration of torpor (DO and also between Dt and energy saved. In contrast, there was a negative correlation between the cost of arousal and energy saved which suggests that the cost of regaining homeothermy can limit the energetic efficiency of short bouts of torpor. Pouched mice from all 6 localities had the capacity to enter torpor and there were no significant geographical differences in the incidence of torpor. However, there were substantial differences in the expression of torpor, and Pouched mice from localities experiencing more variable temperatures underwent significantly longer bouts of torpor which suggests that selection for torpor had been greater in more energetically unpredictable environments.
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