Miami researchers study frogs that freeze, then thaw back to life

Miami University researchers are uncovering the secrets to how tiny wood frogs survive sub-zero winters in Alaska.

The species rana sylvatica is also found in southern Ohio. During their hibernation, the frogs' bodies are completely frozen and then thaw back to life, according to Jon Costanzo, a senior research scholar at Miami University. Three graduate students recently made several trips to Alaska to collect the wood frogs for study.

“The frog doesn’t dig or try to get deep into the ground to avoid frost. It goes under a leaf litter or a piece of bark, maybe a stone,” said Costanzo.

The average temperature in January in some parts of Alaska is -32 C (-25 F), but the air temperature is much colder than where the frog hibernates.

Researchers said the frogs stop feeding and moving once winter hits and their organs, including the heart, shut down.

“After the heart stops, there’s no oxygen being delivered to the cells, and no carbon dioxide being removed from the cells and the body. They’re in a precarious state, all the cells in the body have to survive without oxygen,” said Costanzo.

Another amazing trick the frog can do is eliminate water from its organs.

“After they begin freezing, the water in their organs leaves the organs and forms ice outside the organ itself,” said Costanzo. He believes big ice crystals are formed inside the frog’s belly cavity.

According to researchers the wood frogs, which are about two to three inches in length, go through multiple freeze-thaw episodes throughout the winter.

Scientists don’t completely understand the entire process, but they do know that when the frog begins to freeze, chemicals such as glucose and urea accumulate in their bodies.

“They literally help tissue and cells survive the freezing and thawing,” said Costanzo.

Costanzo said the frogs only needed two days of thawing to resume normal movements. Once the frogs come back to life they immediately look not for food, but for a mate.

“This frog is the earliest breeding frog of all frogs in North America. It breeds in February,” said Costanzo.

Being frozen alive is not exclusive to the wood frog. Eastern box turtles, some lizards and snakes can also come back to life, according to Costanzo.

The National Science Foundation paid $368,458 for the three-year research that was recently extended for a fourth year. Costanzo’s findings were reported in the recent issue of the Journal of Experimental Biology.

To watch a time-lapse video of a thawing frog, click here.