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Transient peripheral warming accompanies the hypoxic metabolic response in the golden-mantled ground squirrel

Glenn J. Tattersall^* and William K. Milsom

Department of Zoology, University of British Columbia, Vancouver, BC, Canada, V6T 1Z4

View larger version (46K): [in a new window]   Fig. 1. (A) Infrared thermogram of a golden-mantled ground squirrel. (B) Actual image of a squirrel (not taken simultaneously with A) to demonstrate the angle of the body (but not the head) at which the thermogram was taken. The squirrel was usually facing the camera and, hence, the head and front legs were clearly visible, with the cooler flank region dominating the rear part of the image.

View larger version (19K): [in a new window]   Fig. 2. Metabolic rates of oxygen consumption O2 (A) and CO2 production CO2 (B), and respiratory exchange ratio RER (C) during normoxia, 60 min of hypoxia (black bar) and 60 min of recovery in normoxia. Filled circles denote values at Ta=10°C, open circles at Ta=22°C, and filled squares at Ta=30°C. *Significant difference from normoxic control at 10°C; significant difference from normoxic control at 22°C; significant difference from normoxic control at 30°C (N=7).

View larger version (15K): [in a new window]   Fig. 3. Temperature differential between surface Ts and ambient temperature Ta (Ts—a) as a function of Ta for eyes (filled circles), nose (filled squares), ears (filled triangles), feet (filled diamonds) and flank (open circles) in normoxia (A) and after 15 min of hypoxia (B). A linear relationship between Ts—a and Ta implies minimal specific thermoregulatory adjustments in Ts, whereas a departure from linearity at a given Ta implies thermoregulatory adjustments at that surface to either increase or decrease heat loss.

View larger version (23K): [in a new window]   Fig. 4. Temperature differential between surface Ts and ambient temperature Ta (Ts—a) during normoxia, 60 min of hypoxia (black bar), and 60 min of recovery in normoxia on different body surfaces. Filled circles denote values at Ta=10°C, open circles at Ta=22°C, and filled squares at Ta=30°C. *Significant difference from normoxic control at 10°C; significant difference from normoxic control at 22°C; significant difference from normoxic control at 30°C (N=7).

View larger version (63K): [in a new window]   Fig. 5. Time series of infrared thermograms from one squirrel (Ta=22°C) during normoxia (30 min), hypoxia (60 min) and normoxic recovery (30 min). Images represent pictures taken at approximately 2 min intervals (eight images correspond to 30 min duration). Note the feet and ears warming up during the early period of hypoxic exposure, and the lack of peripheral warming during the recovery period of intense metabolic activity.

View larger version (25K): [in a new window]   Fig. 6. Change in surface temperature Ts during hypoxia (Ts) as a function of time and ambient temperature Ta on the different body surfaces. Colours indicate the Ts, as shown in the key.