Responses to freezing exposure by hatchling turtles Trachemys scripta elegans: factors influencing the development of freeze tolerance by reptiles

from a Louisiana population display a significant ability to withstand the freezing of extracellular body fluids. All animals survived at least 2 h of freezing at-2.5 or —4°C. At-2.5°C, survival declined to 50 % after 6h of freezing and no animals recovered after 24 h or longer, when mean ice content reached 54.7 ± 1.4 % of total body water. At-4°C, all turtles recovered from 4h of freezing exposure with a mean ice content of 49.6±2.4 %, but survival dropped sharply thereafter with no animals recovering after 8h, when ice content had reached 64.5±0.7 %. Survival times were substantially shorter and percentage ice values greater than compar-able values for hatchling painted turtles (Chrysemys picta (Schneider)) from northern populations subjected to identical freezing exposures. The ability to synthesize cryoprotectants in response to freezing was poorly developed in T. s. elegans; maximal accumulation of glucose was only 3.2 jimolg"1 wet mass in liver. Lactate content increased two- to threefold in oxygen-sensitive organs (heart and brain) during freezing, but levels of lactate and other putative cryoprotectants were unchanged in other organs. Total free amino acid content rose significantly in liver, muscle and blood during freezing; increased taurine concentration was primarily responsible for the changes in liver and blood. The capacity for freezing survival by T. s. elegans hatchlings from southern populations would be of limited use for hibernation in a cold climate, but the metabolic responses to freezing displayed by these animals might be enhanced by northern populations to increase their freeze tolerance