Oxygen consumption, thermal conductance, and torpor in the California pocket mouse <i>Perognathus californicus</i>

Abstract

Abstract Non‐torpid P. californicus have body temperatures which increase slightly as ambient temperature increases from 5° to 35°C. Their minimum oxygen consumption fits Newton's law of cooling, since minimum thermal conductance below thermal neutrality is virtually constant at 0.19 ml O 2 (gm hr °C) −1 . There is a thermal neutral point at 32.5° rather than a thermal neutral zone. Oxygen consumption at the thermal neutral point is 0.97 ml O 2 (gm hr) −1 . Maximum thermal conductance, measured at 35°, is 0.37 ml O 2 (gm hr °C) −1 . Evaporative water loss accounts for 5 and 15% of the value of minimum and maximum thermal conductance, respectively. Minimum oxygen consumption of mice in torpor is continuously dependent on body temperature from thermal neutrality to deep torpor. Q 10 values are between 1.6 and 3.2. The thermal conductance of torpid mice at ambient temperature below 30° is 0.19 ml O 2 (gm hr °C) −1 which is identical to the minimum thermal conductance of non‐torpid mice. Torpid mice at an ambient temperature of 30° have thermal conductance values between 0.23 and 0.40 ml O 2 (gm hr °C) −1 depending on their posture. Maximum oxygen consumption is linearly related to body temperature. At a normal body temperature of 38°, it is 11.6 ml O 2 (gm hr) −1 which is no greater than that of similar sized mammals which do not enter torpor. Although P. californicus consistently enters into and arouses from torpor at ambient temperatures of 15° to 30°, the torpor cycle is severely disturbed at temperatures between 10° and 12°. At these temperatures mice show irregular temporal patterns of torpor, do not enter torpor completely, and cannot arouse from torpor if body temperature falls below 15°. Observations on the behavior of torpid and non‐torpid P. californicus at various ambient temperatures are included in this report.