The curious thing Larson discovered is that when wood frogs are outside in their natural environment they accumulate much higher concentrations of glucose in their tissues than do frogs frozen in the lab.
Glucose concentrations in the outside frogs were 13-fold higher in muscle tissue, 10-fold higher in heart tissue and 3.3-fold higher in liver tissue compared to lab-frozen frogs, as described in their paper published in the Journal of Experimental Biology.
This extra protection enabled frogs to survive colder temperatures for a longer time than scientists previously thought, but Larson and Barnes wondered how they accumulated so much glucose?
Larson thinks the process that creates freezer burn on a frozen steak gives frogs the ability to survive being frozen at minimum temperatures below zero (minus 18 Celsius) for up to 218 days with 100 percent survival.
Frogs collected from sites in the Eastern U.S. and Canada have previously been shown to only survive being frozen for a few weeks and to no lower than about 19 degrees (minus 7.2 Celsius).
"In the field in early Autumn it's freezing during the night, thawing slightly during the day, and these repeated freezing episodes stimulate the frogs to release more and more glucose," Larson said. "It's not warm enough for long enough for the frog to reclaim much of that glucose and over time it accumulates giving the frog more protection against cell damage."
Lab-frozen frogs are held at a constant temperature and without the freeze-thaw cycles Larson observed in the wild and so the frogs made glucose only when they initially froze and that was that.
"Whether the extremes in freezing tolerance in Alaska frogs as compared to more southern populations are due to patterns of temperature change during freezing or are due to genetic differences
|Contact: Marie Thoms|
University of Alaska Fairbanks