DINKELACKER, S.A.; COSTANZO, J.P.; LEE, R.E.; Miami University; Miami University; Miami University: Implications for the roles of anoxia tolerance and antioxidants in promoting freeze tolerance in hatchling turtles

The capacity for freeze tolerance varies among turtle species and is potentially limited by a functional anoxia that occurs during freezing, among other things. Because anoxia tolerance also varies among turtles species, we investigated whether anoxia tolerance is associated with freeze tolerance capacity by determining survival times and lactate concentrations during freezing/thawing and anoxia exposure. Also, to determine if oxidative stress is problematic during reoxygenation, we measured catalase activity in the liver following freezing and anoxia. Tolerance of freezing at -2.5�C varied among the species tested: Graptemys geographica, Chelydra serpentina, and Trachemys scripta survived less than 7 d of freezing whereas Emydoidea blandingii, Chrysemys picta, Terrapene ornata, and Malaclemys terrapin survived at least 7 d of freezing. Average times of survival in an N₂ atmosphere at 4�C ranged from 17 d in M. terrapin to 50 d in G. geographica. Plasma lactate concentrations increased significantly during anoxia (64 to 99 mmol L^-1) and freezing (17 to 28 mmol L^-1). However, longer survival times were not associated with lower lactate concentrations during freezing or anoxia. In most species, liver catalase activity in thawed and reoxygenated turtles was higher than in control turtles, suggesting that antioxidant activities are increased to cope with reactive oxygen species formation. We conclude that a measure of anoxia tolerance is found in freeze tolerant turtles, but anoxic stress is not limiting to freeze tolerance.