Amphibians cope with winter

#Middlebury #MLT

Illustration © Ross Wiley.

By JANINE SULLIVAN-WILEY

Deep winter in Middlebury brings sub-freezing temperatures for days and weeks on end, causing the ground to freeze hard as a brick. We humans can bundle up and turn on the heat in our homes; mammals have fur and can generate their own heat.

But what about moist-skinned, soft-bodied, cold-blooded creatures like amphibians? How do frogs, toads and salamanders survive when everything is frozen? Alice Hallaran, former biology teacher, enthusiastic naturalist and Middlebury Land Trust board member had the answer: antifreeze!

But let’s back up a bit. We never see frogs, toads or salamanders in the winter because they hibernate when the temperatures get too cold. Where they hibernate – in a place called a hibernaculum (you never know when that word will come in handy) – will vary by species.

Some salamanders and aquatic frogs like the American bullfrog (Rana catesbeiana) and leopard frog (Rana pipiens) typically hibernate underwater, lying just on top of the mud. They don’t tunnel into the mud like turtles do as they need to continue to get oxygen from the water, which they absorb through their skin. That means the pond must have adequate oxygen levels at the bottom or a frog or toad can die.

Interestingly, the water at the bottom of a pond is also the warmest, due to the unusual thermodynamic properties of water. A relatively warm day might even find the amphibians swimming around a bit, looking for a mid-winter snack.

Terrestrial frogs such as American toads (Bufo americanus) use another strategy. They are good enough at digging to burrow below the frost line and make it through the winter that way.

Terrestrial amphibians without those digging skills have yet another method of surviving through the frozen months. These tender creatures find a hibernaculum (see … useful word) deep in leaf litter or in crevices in logs or rocks, all locations much more susceptible to freezing, as are the frogs or salamanders tucked in there.

Those without digging skills include two of my favorite frogs, the wood frog (Rana sylvatica) and spring peeper (Hyla crucifer), and salamanders such as the dusky salamander (Desmognathus fuscus), red-backed salamander (Plethodon cinereus), and the terrestrial stage of the red-spotted newt or red eft (Notophthalmus v. viridescens). All live in this part of Connecticut.

This brings us back to the amazing fact that these amphibians produce their own antifreeze: a highly concentrated glucose that protects delicate tissues and organs from freezing. Ice crystals might still form in their body cavity or under the skin, but the antifreeze protects vital organs like heart and lungs. In this state, amphibians may appear dead: amphibian ice cubes, with no breathing or heartbeat.

These otherwise fragile little animals thereby pull off their winter to spring antifreeze survival strategy, hibernating in their icy state through the coldest weeks, enabling their miraculous thaw and slow return to life in the spring when they can again entertain us with their trilling and chirping.

You can contact this writer at jswspotlight@gmail.com; visit the Middlebury Land Trust on Facebook or the website at middleburylandtrust.org. Happy New Year!