FREEZING SURVIVAL OF THE GARTER SNAKE THAMNOPHIS-SIRTALIS-PARIETALIS

Cold hardiness was evaluated for the red-sided garter snake, Thamnophis sirtalis parietalis. Snakes collected in the autumn near communal den sites showed an ability to supercool (Supercooling point, SCP = -5.5-degrees-C). However, by midwinter, supercooling capacity was reduced and snakes cooled only to -0.8 to - 1.2-degrees-C before freezing. Survival of freezing and body ice contents were determined over a time course of freezing exposure at -2.5-degrees-C. Snakes recovered fully after freezing exposures of 3 h or less that produced ice contents of up to 40% of total body water. After longer periods and with ice contents of over 50%. survival was reduced. Only 50% of snakes survived 10 h of freezing and no snakes recovered after 24 or 48 h with a maximal ice content of 70% of body water. Putative cryoprotectants were assessed in seven organs (liver, kidney, muscle, intestine, brain, tung, heart) as well as the eggs after 5 h of freezing at -2.5-degrees-C. Glucose content increased 4-fold in liver, and lactate rose by 50% in heart, but levels of these and other possible cryoprotectants did not increase in other organs during freezing. However, a high free amino acid pool, including 14-24-mu-mol/g wet weight taurine, was present in the organs. The data suggest that long-term freezing survival is not part of the winter hibernation strategy of this species, but tolerance of brief freezing exposures may be adaptive in dealing with overnight frosts when the animals are active above ground.