Painted turtles, and other creatures that must endure freezing, face similar dangers. Their breathing stops and circulation is halted, but then these functions must resume when the animal defrosts.

The scientists found three categories of genes that encode for enzymes involved in this antioxidant defense. Some cause iron to bind up into proteins so that it is not floating freely in their bodies, a good thing since free iron promotes the creation of dangerous ROS. Other enzymes help the turtles cope with oxygen level extremes.

Freeze tolerance is especially important for painted turtles in northern regions because low food availability, predation threats and other risks keep hatchlings in their nests throughout the winter.

"Freezing survival by hatchling turtles in northern populations is basically a necessary response to circumstances they can't avoid — that is, they are stuck in a nest and the temperature of the ground around them drops well below 0° Celsius in midwinter — so survival requires that either freeze tolerance or supercooling be perfected!" said Storey.

She explained that supercooling is when an animal tries to avoid freezing in the first place, usually by releasing special "antifreeze" substances.

In a second study, published in the same journal, another team of scientists determined that European common lizards, Lacerta vivipara, possess a similar antioxidant system, but that it is triggered when the lizards are supercooling and not frozen.

Lead author Yann Voituron, a biologist at the Université Paul Sabatier de Toulouse in France, and his colleagues believe the antioxidants "may be in anticipation of the overgeneration of oxyradicals (ROS) when the temperature increases while thawing or at the end of supercooling."

Storey said that scientists have "only scratched the surface in understanding the coordinated changes in gene expression that go into freezing survival."

---

Name: Painted Turtle (Chrysemys picta)
Primary Classification: Testudines (Tortoises and Turtles)
Location: Southern Canada, northern Mexico and the continental United States.
Habitat: Marshes, ponds, lakes and creeks with soft, muddy bottoms.
Diet: Aquatic plants, algae, insects, crayfish, tadpoles, snails, slugs, small fish and carrion.
Size: Averages 4-10 inches in length.
Description: Green to black carapace (shell); yellow and red plastron (belly); reddish-brownish figure on plastron; black to olive skin with red and yellow stripes on head, neck, legs and tail; smooth, flattened, oval-shaped carapace.
Cool Facts: As many as 50 turtles will bask on a single log, often stacked on top of one another. It is mainly carnivorous when young, but prefers plants as it gets older.
Conservation Status: Common

Get More News: