MUIR, T.J.*; COSTANZO, J.P.; LEE JR, R.E.; Miami University; Miami University; Miami University: Brief Cold Conditioning Improves Freeze Tolerance and Chill Tolerance in Hatchling Painted Turtles

Strategies for winter survival in hatchling turtles living in temperate climes involve avoidance of sub-freezing temperatures or an ability to survive them. Hatchling painted turtles (Chrysemys picta) employ the latter strategy and can survive a moderate degree of both freezing and supercooling during the winter, which they spend inside their natal nest. In the months between hatching and the onset of winter, painted turtles undergo physiological changes that increase their supercooling capacity, their ability to resist inoculative freezing, and their freeze tolerance. However, in addition to these seasonal changes, responses to relatively brief chilling episodes during winter may also improve their cold hardiness. We exposed winter-acclimated hatchling painted turtles to a non-lethal chilling bout (2 d at -7°C) before testing their cold hardiness. Cold conditioning had no effect on supercooling capacity or inoculation resistance. However, compared to control animals, these cold-conditioned turtles had higher plasma levels of the putative cryoprotectants glucose and lactate, and had higher survival and more rapid recovery following freeze-tolerance or supercooling trials. Therefore, brief cold conditioning conferred protection against subsequent low temperature stresses whose mechanisms of injury are likely different. Preliminary results suggest that the protective mechanism against chilling injury may be manifested in the central nervous system. Short-term cold conditioning likely increases the survival of hatchlings overwintering in a thermally-variable nest environment, and also may be used as a tool to elucidate the mechanisms of chilling injury.