Freeze Tolerance and Cryoprotectant Synthesis of the Pacific Tree Frog Hyla regilla
Freeze tolerance and cryoprotectant synthesis was examined in Hyla regilla, collected from Northern California in the spring and fall. Specimens frozen at 2 C for six and 12 hours had a survival rate of 10% and 80%, respectively, in both seasons. This is the first report of freeze tolerance for H. regilla. Freezing caused a fivefold increase in plasma glucose levels in the spring and a 14-fold increase in the fall. Ice formation induced a rise in liver glucose and glycerol production in both seasons with concentrations of liver glucose being greater in the fall than in the spring. The increase in glucose was accompanied by a significant decline in liver glycogen. Seasonal differences in muscle glycogen levels in response to freezing were not shown, suggesting that the liver is the organ responsible for cryoprotectant synthesis. The rise in plasma glucose, along with increased levels of liver glucose and glycerol in response to freezing, suggests that these compounds are being used as cryoprotectants, with glucose being the primary component.Abstract
Effect of freezing exposure on metabolite levels in liver of Hyla regilla Examined in the spring and fall of 1996. Values are means ± SEM. Units expressed in µmol/g wet weight with glycogen expressed in glucose units. * Significantly different from corresponding control value by the Student's t-test, P ≤ 0.05. Error bars represent a 95% confidence interval
Effect of freezing exposure on the metabolite levels in muscle of Hyla regilla examined in the spring and fall of 1996. Values are means ± SEM. Units expressed in µmol/g wet weight with glycogen expressed in glucose units. Significantly different from corresponding control value by the Student's t-test, P ≤ 0.05. Error bars represent a 95% confidence interval