The Ecological Physiology of a Supercooled Vertebrate

Colorado State University, Fort Collins CO

Investigators

Abstract

This is a proposal to investigate the ecological physiology of overwintering hatchlings of the North American painted turtle (Chrysemys picta). This widely-distributed and abundant species has become a model organism for studies on the ecology and evolution of freshwater chelonians. The natural history of painted turtles differs from that of most other species in an important respect, however. Whereas neonates of other aquatic turtles usually emerge from their nest in late summer or autumn and move to a nearby marsh, lake, or stream to spend their first winter, hatchling painted turtles typically remain inside their shallow, subterranean nest throughout their first winter and do not come above ground until the following spring. This behavior commonly causes neonatal painted turtles at northern localities to be exposed during winter to ice and cold with temperatures in some nests going below -10oC. Many hatchlings withstand such exposure and emerge from their nest when the ground finally thaws in the spring. Hatchlings tolerate the cold of mid-winter by becoming supercooled (i.e., they remain unfrozen at temperatures below the equilibrium freezing point for their bodily fluids). Although this "adaptive strategy" has many benefits for neonatal turtles, the strategy also has important consequences one of the more important of which is a shutdown of the circulation at temperatures near -10oC. The proposed investigation will focus on the use of energy reserves by liver, heart, and brain in animals subjected to the stagnant anoxia that results from shutdown of the circulation, and on the patterns of accumulation by different organs of the lactic acid that is produced in anaerobic respiration. The work will yield important new insights concerning the physiology of neonatal turtles and also may identify new methods for storing transplantable organs for use in human and/or veterinary medicine.