Figure 5
The sensitivity of the heat production system is largely reduced during daily torpor while the reduction of set-point temperature was small.
(a) The relationship between the difference of TB from TA and VO2. Including the following panels, red and blue denote normal and torpid status, respectively. The slope of this relationship is the heat conductance, G. As in panel c, the dots represent the observed values, and the lines and shaded areas represent the means and the 89% HPDI intervals of the estimated values. (b) The posterior distribution of the estimated G. During torpor, G is smaller than during normal states. Decrease in G results in heat preservation. However, the TB decrease seen in daily torpor is indicating the decrease in G is overridden or induced by decrease of heat production. The bin size is 0.001 ml/g/hr/°C. As in panel d and e, the bold and thin lines denote the mean and the 89% HPDI intervals of the estimated values. (c) The relationship between minimum TB and VO2 seen during normal and torpid states among various TAs. The brightness of the dots is indicating the TA. The horizontal intercept of the line indicates the theoretical set-point of TB, which is TR (See Fig. 1a). During normal states, TB is kept relatively constant by employing oxygen and producing heat to fill the gap between TR and TA. On the other hand, during daily torpor, the sensitivity against TR - TB is weakened which is visualized by less steep slope, which is H, the open-loop negative feedback gain of the heat production loop (See Fig. 1a). (d) The posterior distribution of the estimated TR. During daily torpor, TR became smaller than normal states, although the mean difference was 3.79 °C. The bin size is 0.1 °C. (e) The posterior distribution of the estimated H. During daily torpor, H became dramatically smaller than normal states, which the mean difference reached to 4.70 ml/g/hr/°C. This is clearly showing that the open-loop gain of the heat production system reduced to 8.5% during daily torpor from the normal state. The bin size is 0.05 ml/g/hr/°C.
