Persistence of Freeze Tolerance in Terrestrially Hibernating Frogs after Spring Emergence

Abstract

Freeze tolerance is an adaptation for winter survival in various species of terrestrially-hibernating frogs. We assessed the persistence of freeze tolerance in four species collected at breeding ponds after the spring emergence from hibernation. Rana sylvatica, Hyla versicolor, H. crucifer, and Pseudacris triseriata were as tolerant of whole body freezing in early spring as they were in autumn or winter, based on survival at -2.5 C for periods ranging up to 8 d. In later spring, after animals had begun to feed, tolerance to freezing declined sharply. Whole animal supercooling points (-1.2--2.5 C) were the same in spring as in autumn but the capacity for producing cryoprotectants in response to the initiation of freezing was generally reduced in spring animals. Levels of glucose or glycerol produced in spring animals during freezing were often at least 10 fold lower than amounts which typically accumulate in animals in autumn or winter under equivalent freezing exposures. This reduced capacity for cryopro