PACKARD, M.J.; PACKARD, G.C.; Colorado State Univ.: Cold acclimation and cutaneous resistance to freezing in hatchling painted turtles, Chrysemys picta

Neonatal painted turtles overwinter in the natal nest and may be exposed to prolonged periods of ice and cold. Hatchlings survive by supercooling, a capability that depends on their ability to resist the inoculative freezing that attends penetration of ice into the body from frozen soil. Resisting inoculation requires changes in the integument before the onset of winter because the skin of newly-hatched turtles seemingly has little resistance to the penetration of ice. We assessed changes in the cutaneous barrier to inoculation using newly-hatched animals as well as turtles that had been acclimated for 5 wk to 24 or 3 C. Our goal was to confirm that cutaneous resistance to inoculation increases over time and to determine whether this change requires exposure to cold. Hatchlings were placed individually in artificial nests of wet soil and exposed to a nominal temperature of -2 C for 11 d. Body temperature was recorded every 10 min. All temperature records were examined for exotherms to determine who froze and who did not. Hatchlings acclimated to low temperature produced many fewer freezing exotherms than did unacclimated turtles or those acclimated to high temperature. Unacclimated animals and those acclimated to high temperature froze at about the same rate. Thus, animals acclimated to low temperature resist inoculative freezing (and survive) whereas those in the other treatments generally do not resist inoculation (and do not survive). Our results indicate that cold tolerance in general and resistance to inoculative freezing in particular develop fully only after acclimation to low temperatures and that hatchlings in natural nests are unlikely to use freeze tolerance as a strategy to survive the high subzero temperatures that may characterize early winter. Supported by NSF (IBN-0112283).