Freezing survival, body ice content and blood composition of the freeze-tolerant European common lizard, Lacerta vivipara

Abstract.

To investigate the freeze tolerance of the European common lizard, Lacerta vivipara, we froze 17 individuals to body temperatures as low as –4 °C under controlled laboratory conditions. The data show that this species tolerates the freezing of 50% of total body water and can survive freezing exposures of at least 24-h duration. Currently, this represents the best known development of freeze tolerance among squamate reptiles. Freezing stimulated a significant increase in blood glucose levels (16.15±1.73 µmol.ml^–1 for controls versus 25.06±2.92 µmol.ml^–1 after thawing) but this increase had no significant effect on serum osmolality which was unchanged between control and freeze-exposed lizards (506.0±23.8 mosmol.l^–1 versus 501.0±25.3 mosmol.l^–1, respectively). Tests that assessed the possible presence of antifreeze proteins in lizard blood were negative. Recovery at 5 °C after freezing was assessed by measurements of the mean time for the return of breathing (5.9±0.5 h) and of the righting reflex (44.8±4.5 h). Because this species hibernates in wet substrates inoculative freezing may frequently occur in nature and the substantial freeze tolerance of this lizard should play a key role in its winter survival.