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Natural freeze-tolerance in hatchling painted turtles?
Gary C Packard1, Mary J Packard
1Department of Biology, Colorado State University, 80523-1878, Fort Collins, CO, USA. packard@lamar.colostate.edu
Summary
North American painted turtle hatchlings survive cold winters by preventing freezing through integument resistance and ice-nucleating agent removal, not by tolerating ice formation. This supercooling ability may predate their adaptation to winter conditions.
Area of Science:
- Herpetology
- Environmental Physiology
- Evolutionary Biology
Background:
- North American painted turtle (Chrysemys picta) hatchlings overwinter in nests facing freezing conditions.
- A common belief suggests hatchlings tolerate freezing, but evidence points to freeze avoidance as their primary survival strategy.
Purpose of the Study:
- To investigate the mechanisms by which painted turtle hatchlings survive sub-zero temperatures during overwintering.
- To determine if hatchlings possess antifreeze properties or rely on other physiological adaptations.
Main Methods:
- Analysis of integumental resistance to ice penetration.
- Measurement of ice-nucleating agent concentrations in hatchling tissues.
- Assessment of physiological responses, including cardiac function and metabolic pathways, at sub-zero temperatures.
Main Results:
- Hatchling integument becomes resistant to ice penetration before winter.
- Turtles reduce ice-nucleating agents, facilitating supercooling.
- Sub-zero temperatures impair cardiac function and increase reliance on anaerobic metabolism, potentially leading to acidosis.
Conclusions:
- Painted turtle hatchlings primarily survive winter by supercooling, avoiding freezing through physiological and integumentary changes.
- The observed adaptations for cold tolerance may have evolved prior to the species' northward expansion, suggesting they are not solely winter-specific adaptations.