Frozen frogs: How amphibians survive the harsh Alaskan winters

Jan 07, 2014 by Shane Hanlon

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 (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.

While previous research has shown that wood frogs can tolerate low temperatures for short periods of time, frogs in Larson's study survived longer, had a higher incidence of survival (100%), and survived at colder temperatures than ever previously recorded. Moreover, his work highlights glucose as an agent for the survival of in the harsh winter conditions. Now that Larson has a better understanding of how a frog's physiology changes in response to the winter season, his next step is to understand how things living inside them, such as parasites, will be affected. He hopes to use his current research to shape future studies that examine the role of the cold environment on host-parasite interactions in frogs.

Explore further: Alaskan wood frogs stock up on solutes to survive

add to favorites email to friend print save as pdf

Related Stories

Alaskan wood frogs stock up on solutes to survive

Aug 23, 2013

Outwardly, the tiny wood frog, Rana sylvatica, does not look like your regular arctic inhabitant. Yet despite their tiny stature, these little frogs are actually quite hardy and can tolerate freezing of up ...

Tree frogs chill out to collect precious water

Sep 29, 2011

Research published in the October issue of The American Naturalist shows that Australian green tree frogs survive the dry season with the help of the same phenomenon that fogs up eyeglasses in the winter.

The last croak for Darwin's frog

Nov 20, 2013

Deadly amphibian disease chytridiomycosis has caused the extinction of Darwin's frogs, believe scientists from the Zoological Society of London (ZSL) and Universidad Andrés Bello (UNAB), Chile.

Recommended for you

Chinese mosquitos on the Baltic Sea

1 hour ago

The analysis of the roughly 3,000 pieces is still in its infant stage. But it is already evident that the results will be of major significance. "Amazingly often, we are finding–in addition to Asian forms–the ...

Baby zebra is latest success in research partnership

2 hours ago

The recent birth of a female Grevy's zebra foal at the Saint Louis Zoo marks another milestone in a long-running Washington University in St. Louis research partnership that is making significant contributions ...

'Killer sperm' prevents mating between worm species

20 hours ago

The classic definition of a biological species is the ability to breed within its group, and the inability to breed outside it. For instance, breeding a horse and a donkey may result in a live mule offspring, ...

Rare Sri Lankan leopards born in French zoo

23 hours ago

Two rare Sri Lankan leopard cubs have been born in a zoo in northern France, a boost for a sub-species that numbers only about 700 in the wild, the head of the facility said Tuesday.

User comments : 0