Freeze tolerance and the dynamics of ice formation in wood frogs (Rana sylvatica) from southern Ohio

Abstract

Freeze tolerance and ice formation were examined in a population of Rana sylvatica from southern Ohio following their emergence in February. Frogs were tolerant of freezing at −2.5 °C but did not survive freezing at −5.5 °C. The level of glucose in the blood of frogs frozen for 48 h at −2.5 °C was fivefold higher than in unfrozen frogs. Both interpopulational and seasonal factors appeared to modify freeze tolerance and ice accumulation in Rana sylvatica when compared with previous studies. The directly determined time course of ice formation roughly paralleled the duration of the exotherm in this species. Ice content of frogs was determined using calorimetry and integrated to the specific heat of wet and dry masses. The equilibrium ice content represented nearly two-thirds of the total water content of these frogs. Freezing beyond this level proved lethal to frogs.