Hatchling painted turtles (Chrysemys picta) survive exposure to subzero temperatures during hibernation by avoiding freezing

Abstract

Hatchling painted turtles (Chrysemys picta) were placed individually into artificial nests constructed in jars of damp soil and then were cooled slowly to temperatures between-7.7 and-12.7 °C. Distinct exotherms were recorded in all jars when water in the soil began to freeze at temperatures between-0.9 and-2.4 °C. A second (animal) exotherm was subsequently detected in some of the jars when water in hatchlings also began to freeze. An animal exotherm occurred in the temperature records for all 23 hatchlings that died in tests terminating at temperatures between-7.7 and-10.8 °C, but no such exotherm was apparent in the temperature records for the 23 turtles that survived these treatments. Moreover, the 4 hatchlings that produced exotherms in tests terminating between-11.5 and-12.7 °C failed to survive, but 5 of 7 hatchlings that produced no exotherm in these tests also died. Thus, turtles that die at subzero temperatures above-11 °C apparently succumb to freezing when ice propagates across their integument from the frozen soil, but animals that die at temperatures below-11 °C generally perish from some other cause. These findings indicate that hatchling painted turtles overwintering inside their shallow, subterranean nests survive exposure to subzero temperatures by avoiding freezing instead of by tolerating freezing.