Surviving the cold

Gray tree frog Credit: StingrayPhil

Gray tree frog

Credit: StingrayPhil

We had our first snow of the season the day before Thanksgiving, and that got me to thinking about one of my favorite ecological challenges:  how animals survive the winter. 

Bigger animals have it relatively easy:  they hunker down for a long winter’s nap or fly to warmer climes (though the latter is actually fraught with peril).  But what do smaller, less mobile animals do?

Like everything in nature, the solutions are wonderful and diverse.  And tree frogs have my favorite solution.  They freeze.

When our skin freezes, ice forms with all its crystalline points which puncture and kill cells.  We call this frost bite.

Tree frogs (and a few other land frogs like spring peepers and wood frogs) have evolved mechanisms that allow ice to grow inside them.  They proactively trigger ice growth so it forms in smooth, flat sheets (rather than sharp spikes) between their skin and muscles, in their abdomens, and even in their eyes.  And they fill their cells with natural anti-freeze (usually as glucose, a sugar) that keeps ice out and helps them endure dehydration.

This adaptation has a couple of advantages.  First, it allows the frogs to survive the winter beneath the leaf litter, since they can’t burrow into soil deep below the frost line like toads or sit on the unfrozen bottom of ponds like bullfrogs.  Second, when spring comes, they’re out in the sun singing and eating while bullfrogs and American toads are still trapped.

The sound of singing tree frogs is a harbinger of spring and a wonderful element of Northeastern nights.  But for me, the real magic of these little frogs is the ingenious solution they’ve found to winter’s greatest challenge.