Freeze Tolerance and Postfreeze Recovery in the Frog Pseudacris crucifer
This study characterizes freeze tolerance and postfreeze recovery in the frog Pseudacris crucifer. We collected frogs from Pennsylvania during the autumns of 1994 and 1995. All experiments occurred in the laboratory and employed a freezing temperature of -1.5 C. This treatment froze 45% of the body water in these frogs, and they were clearly tolerant of internal freezing. However, their survival was inversely proportional to freeze duration (3 day = 85.0%, 7 day = 52.6%, and 28 day = 0%). Cutaneous blood flow, breathing, hind-leg retraction, righting reflex, and jumping ability returned to surviving frogs within 24-48 h following the conclusion of a 3-day freeze. Complex behavioral responses (e.g., jumping) required more time to return than did basic physiological functions (e.g., cutaneous blood flow). Interestingly, rates of oxygen consumption were not altered during the recovery period with respect to the prefreeze value. This study indicates that the freezing survival of P crucifer is markedly influenced by the duration of the freeze episode, which may be an important ecological limitation during winters having few intervening thaws. Recovering frogs require 1-2 days to fully regain complex motor responses; whereas vital functions are restored quickly, and oxygen consumption is not measurably altered during this period.