Out in the cold: how do lizards survive extremely low temperatures in Patagonia, Argentina?

CECCHETTO, NICOLÁS; MEDINA, MARLIN; IBARGÜENGOYTÍA, NORA RUTH

Congreso; 8th World Congress of Herpetology; 2016

Sub-zero temperatures are a dangerous challenge for most animals, even more so for ectotherms. Few reptile species can endure the harsh conditions of high latitudes and altitudes, where the landscape is covered by snow and daylight is scarce in the coldest months of the year. Physiologically, reptiles can adopt two strategies: freeze tolerance or freeze avoiding (by supercooling). Herein we explore how lizards in the mountains of Patagonia are adapted to survive the extreme cold, whether they show acclimation and if they use supercooling or freeze avoiding mechanisms to survive the winter. During mid-summer (January-February 2015; N = 10) and autumn (April 2016; N = 18), individuals of L. pictus were captured in the ski center of La Hoya, Esquel, Argentina (42° 49´ S, 71° 15´ W; 1400 masl). For the cooling experiments, a group of experimental lizards were placed individually in dry plastic containers immersed in ice and salt, while a control group was in the same conditions, kept at room temperature (24°C). The lizards were connected to a data logger?s thermometer by ultrathin thermocouples inserted in the cloaca to monitor body temperature. Individuals reached temperatures as low as -5 °C without freezing for long periods (3.5 to 25 hours). Individuals were sacrificed by decapitation and samples of liver and heart were obtained. All samples were then tested for albumin, total proteins, glucose, cholesterol, triglycerides, LDL, HDL, Calcium, Magnesium and Urea. Lizards showed an increase in autumn (compared with summer) in total proteins, albumin and urea, suggesting an acclimation response, while triglycerides and glucose decreased. In autumn, there was an increase in blood glucose for experimental individuals in comparison with the control group, suggesting that lizards use glucose in a freeze avoidance mechanism combined with appropriate shelter selection, allowing them to survive in the inhospitable conditions of Patagonian Mountains.