Garter Snakes and House Mice: Freezing Their Little Tails Off

Karly Black, Patrick Fenlon, Elizabeth Forst and Lisa Kuithy

CU Boulder, Fall 2002

We compared the effects of cold temperature on respiration rates in an ectotherm, western terrestrial garter snakes (<I>Thamnophis elegans</I>), and an endotherm, domestic mice (<I>Mus musculus</I>). Ectotherms have enzymes that have evolved to function in a wide range of temperatures (DiDomenico and Moreno, 2002), while endotherms regulate temperature metabolically and possess enzymes that are more sensitive to changes in temperature. We hypothesized that these inherent physiological differences in enzyme function between ectotherms and endotherms would result in different responses in respiratory rate between garter snakes and domestic mice at cooler temperature. We predicted that cooler temperatures would cause a greater increase in rate of CO2 production in the endothermic mice relative to the ectothermic snakes.

We used four baby garter snakes and three adult house mice as test subjects. We placed the subjects into a container covered with aluminum foil in order to eliminate visual cues during testing. We attached a CO2 probe and measured respiratory rates of snakes and mice separately, for six minutes at room temperature (24°C) and at "cold" temperature (15°C). The snakes had low rates of CO2 production at both temperatures and showed a small increase in respiratory rate at the cooler temperature (2.62 ppm/min/g room and 7.00 ppm/min/g cold). The mice had an initial rate of 127.7 ppm/min/g at room temperature and a rate of 175.4 ppm/min/g at the cold temperature. Our results were consistent with predictions based on our hypothesis. The change in respiratory rate for mice at the cold temperature was 10 times that seen in the snakes. In addition, the mice were seen huddling together, panting, and shivering which indicates a physiological response to regulate temperature. The snakes also huddled together but we did not observe a shivering response. In conclusion, our results provide preliminary support for our hypothesis. The endothermic mice were more responsive to the decrease in temperature and showed several physiological responses associated with temperature regulation. If endotherms fail to regulate internal core temperatures, enzymatically controlled reactions could not occur at a rate sufficient to sustain life.