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Arb Notes for Jan. 18th - Frog Popsicles

January 24, 2013 at 9:39 am
By Anna Persmark '15

wood frog - Mich dept. of natural resources.jpg 

Biting Minnesota winds and below-freezing days are not always the most pleasant, but puffy jackets, mittens, scarves and hats keep the cold at bay. However, while we humans are able to bundle up or stay indoors to take advantage of central heating, most other species are not so lucky during the winter months.

            The Arboretum is home to eight species of frogs and toads, all of which must survive the brutal Minnesota winters. Have you ever wondered how? If not, you are likely not alone, but some of our amphibious neighbors have amazing survival techniques.

            Aquatic frogs, such as the Bullfrog and the Northern Leopard Frog, hibernate on the bottom of bodies of water, in shallow holes. Even during hibernation, aquatic frogs move a bit, though very slowly. It is crucial that the environment they are hibernating in does not become anoxic, because that would result in an untimely froggy demise.

            Terrestrial frogs have other winter survival mechanisms. The Wood Frog provides an example of one of the most interesting overwintering mechanisms; it can survive being frozen. Wood Frogs (Rana sylvatica) hibernate in burrows a few inches below leaf litter and debris, and if the temperature drops low enough, their body fluids freeze instantly. To promote instant freezing, these species use ice nucleating agents, which are present in their surroundings and can be ingested. They can tolerate up to 70 % of their body fluids freezing! Both Gray Tree Frogs and Cope’s Gray Tree Frog also possess the incredible ability of freeze tolerance.

So, next time you’re walking all the way from Goodhue to Sayles and feeling sorry for yourself as your snot freezes, just remember the frozen frogs that might be somewhere in the Arb.

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