Frozen Frogs: How Amphibians Survive the Harsh Alaskan Winters

As winter approaches, many of us hunker down and virtually “hibernate” for the season. Classic hibernation in the wild conjures images of furry bears, but other animals are not so lucky to have immense fat stores or fur to protect them from the elements. Frogs that live at northern latitudes have neither of these, but must find ways to survive the harsh winter season. Their solution? Freezing…but not to death.

Wood frogs (Lithobates sylvaticus) freeze upwards of 60% of their bodies during the winter months. “For all intents and purposes, they are dead,” said Don Larson, a Ph.D. student at Fairbanks who is interested in how frogs in some of the harshest conditions of Alaska alter their physiology to survive the long and extremely cold winters. Unlike previous studies, Larson used standard lab-based experiments, but also included measurements to track a population in the wild.

Beginning in October, Larson tracked frogs throughout the harsh winter season. Prior to freezing for the entire season, he observed that frogs underwent 10-15 cycles of freezing and then thawing. Thinking that such freeze/thaw cycles may be the key to the frogs’ survival through the winter season, Larson wanted to mimic these natural conditions back in the lab. To do this, he conducted a lab experiment where frogs were left unfrozen, frozen directly, or frozen through a freeze/thaw cycle.

In the wild, all frogs survived throughout the long winter where temperatures ranged from -9°C to -18°C, a longer and colder period than previously observed with wood frogs. How did they avoid becoming frog-flavored popsicles? One clue was the amount of glucose in the frog’s tissues, one of the primary agents that “protect” the frogs while they freeze. In both field and lab settings where the freeze/thaw cycles occurred, glucose concentrations increased between 2 and 10-fold, levels that have never been previously observed.

Glucose production occurs as frogs begin to freeze. Thus, Larson thinks that the high number of freeze/thaw cycles allows for a greater increase in glucose production. This process is akin to the deliberate hyperventilation of divers prior to submerging, which serves to increase the volume of air that their lungs can consume. The frogs’ version of hyperventilation — the freeze/thaw cycles — increases their glucose levels to allow them to survive longer and colder conditions.

Read the full story here.

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About jensera

Jennifer Harrington is a Toronto-based illustrator, writer and graphic designer. She illustrated the best-selling children’s book series 'A Moose in a Maple Tree,' which includes the titles 'A Moose in a Maple Tree,' 'The Night Before a Canadian Christmas' and 'Canadian Jingle Bells.' She is also the owner of JSH Graphics, a boutique graphic design agency that specializes in print and web advertising. With her latest project, Eco Books 4 Kids, Jennifer has partnered with illustrator Michael Arnott to create a series of ecologically-themed ebooks for children. Her next book, 'Spirit Bear,' is due for release in the Summer of 2013. Jennifer offers two different school presentations for her 'Moose in a Maple Tree' collection, an illustration demonstration and a Christmas concert series, which can be booked at www.amooseinamapletree.com. She will be taking bookings for school readings of 'Spirit Bear' beginning in October 2013.

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  1. Frog conservation in Madagascar | Dear Kitty. Some blog - January 17, 2014

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