FREEZE TOLERANCE AND POSTFREEZE RECOVERY IN THE FROG PSEUDACRIS CRUCIFER

This study characterizes freeze tolerance and postfreeze recovery in t he frog Pseudacris crucifer. We collected frogs from Pennsylvania duri ng the autumns of 1994 and 1995. All experiments occurred in the labor atory and employed a freezing temperature of -1.5 C. This treatment fr oze 45% of the body water in these frogs, and they were clearly tolera nt of internal freezing. However, their survival was inversely proport ional to freeze duration (3 day = 85.0%, 7 day = 52.6%, and 28 day = 0 %). Cutaneous blood flow, breathing; hind-leg retraction, righting ref lex, and jumping ability returned to surviving frogs within 24-48 h fo llowing the conclusion of a 3-day freeze, Complex behavioral responses (e.g., jumping) required more time to return than did basic physiolog ical functions (e.g., cutaneous blood flow). Interestingly, rates of o xygen consumption were not altered during the recovery period with res pect to the prefreeze value. This study indicates that the freezing su rvival of P. crucifer is markedly influenced by the duration of the fr eeze episode, which may be an important ecological limitation during w inters 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 dur ing this period.