Influence of acclimation and incubation medium on supercooling by hatchling painted turtles, Chrysemys picta

Summary 1Baby Painted Turtles, Chrysemys picta (Schneider 1783), ingest soil and fragments of eggshell as they are hatching from their eggs. The ingested soil typically contains bacterial nucleating agents that can cause water in the gut to freeze at high subzero temperatures. If ice forms in the gut, however, the crystals penetrate the wall of that organ and cause water in body compartments to freeze. Thus, newly hatched turtles freeze spontaneously at high subzero temperatures owing to the nucleation of ice by bacteria in the gut. 2Painted Turtles purge their gut of soil in the weeks after hatching, but removing particulate material from the GI tract does not, by itself, result in elimination of the bacterial nucleating agents. The purging of nucleating agents requires that hatchlings also be exposed to low (but non-freezing) temperatures. The response to low temperature is completed in little more than 1 month; a longer exposure does not elicit a demonstrable improvement in the capacity for supercooling. 3The limit of supercooling does not vary significantly among turtles hatching on different kinds of soil, despite the fact that different soils typically harbour different concentrations of nucleating agents. Thus, the risk of heterogeneous nucleation probably does not vary appreciably among turtles hatching and overwintering in different kinds of soil in the field. 4Hatchling Painted Turtles that have become acclimatized to low temperatures in the field presumably have acquired a high resistance to freezing by inoculation (as shown by prior study) and an enhanced capacity for supercooling (current study), thereby enabling many animals to withstand exposure to ice and cold during winter by remaining unfrozen and supercooled.