Seasonal change in the capacity for supercooling by neonatal painted turtles

Hatchlings of the North American painted turtle (Chrysemys picta) typically spend their first winter of life inside the shallow, subterranean nest whe re they completed incubation the preceding summer. This facet of their natu ral history commonly causes neonates in northerly populations to be exposed in mid-winter to ice and cold, which many animals survive by remaining unf rozen and supercooled. We measured the limit of supercooling in samples of turtles taken shortly after hatching and in other samples after 2 months of acclimation (or acclimatization) to a reduced temperature in the laborator y or field. Animals initially had only a limited capacity for supercooling, but they acquired an ability to undergo deeper supercooling during the cou rse of acclimation. The gut of most turtles was packed with particles of so il and eggshell shortly after hatching, but not after acclimation. Thus, th e relatively high limit of supercooling for turtles in the days immediately after hatching may have resulted from the ingestion of soil land associate d nucleating agents) by the animals as they were freeing themselves from th eir eggshell, whereas the relatively low limit of supercooling attained by acclimated turtles may have resulted from their purging their gut of its co ntents. Parallels mag, therefore, exist between the natural-history strateg y expressed by hatchling painted turtles and that expressed by numerous ter restrial arthropods that withstand the cold of winter by sustaining a state of supercooling.