Reptiles at Risk

Freezing Solid...Taking Winter to the Extreme!

Posted by Jeff Hathaway on November 4, 2009 at 2:03 PM

Winter obviously means colder weather. Air temperatures in Ontario often fluctuate between +10 Celsius and -40 Celsius (depending where you are). There are two problems with winter temperatures. The first is that fluctuation. It is very hard for animals to live when the temperature changes drastically. We survive this by insulating with warm winter clothes. Reptiles find suitable hibernacula (overwintering sites) that remain stable...usually underground. We will talk more about hibernacula next week. The second problem with our winters is how cold it actually gets! Remember that reptiles are the same temperature as what is around them (ectotherms). Winter temperatures mean that reptiles are cold! While some reptiles retreat further underground to places that don't freeze (look forward to the next segment on hibernacula), some stay where temperatures drop below freezing.

The classic example of this is hatchling Painted Turtles. Mother Painted Turtles lay their eggs in June and July. The eggs incubate during the warm summer months, and the babies hatch usually in August and September. Some of these hatchlings dig their way out of the nest, and make the journey to a safe wetland that fall. Oddly though, some hatchlings stay in the nest over the entire winter and will dig their way out the next spring. Often, the temperatures in these shallow (~15cm) nests dips below zero. The hatchlings survive this cold temperatures by allowing parts of their body to naturally freeze. Painted Turtles are special in this category as the only reptiles to show this adaptation to cold weather. A great deal of research has been done on this amazing ability to freeze solid and thaw out naturally. It seems futuristic, but people always seem to be interested in cryobiology (freezing) and using it to live into the future! Dr. Costanzo at Miami University in Ohio has done a much of the work. For those interested in a more in depth look at the freeze tolerance in hatchling Painted Turtles, check out http://www.units.muohio.edu/cryolab/projects/hatchlingturtle.htm. There are also videos of Painted Turtle hatchlings thawing out!

Painted Turtles are joined with four species of frogs that are able to survive cold temperatures. Most of these species need to be able to survive cold weather because they usually spend the winter in forests under the layer of leaves on the ground. One of these frogs is our own Wood Frog. Check out this link for more information about Wood Frog freezing, as well as videos showing an individual thawing after being completely frozen http://www.units.muohio.edu/cryolab/projects/woodfrogfreezing.htm

So next week we will introduce you to underground hibernacula and how they influence the behaviours of reptiles in Ontario.

M.