Arctic Science Journeys
Radio Script
1997

__________________

Antifreeze in Fish
__________________

STORY: Well, it should come as no surprise that the polar seas are cold. But it wasn't always this way. Millions of years ago it was very much different. Bruce Finney is a paleobiologist at the University of Alaska Fairbanks.

FINNEY: "There's evidence in the fossil record that there were many different types of plants and animals that would indicate a much warmer climate. There were trees such as Sequoias, a lot more deciduous trees, there were ferns, dinosaurs, and a lot of the marine fossils as well indicate much warmer temperatures. And then we've been on a cooling trend over the last 100 million years or so."

As the Arctic and Antarctic cooled, fish survived by evolving proteins that act as antifreeze in their blood. Chris DeVries is a biologist at the University of Illinois who studies these special proteins called glycoproteins.

DEVRIES: "What antifreeze does is absorb or bind to minute ice crystals that actually enter their system, and prevent them from growing any further. The amount of protection is sufficient that in conjunction with the salt in the body fluids to lower the freezing point of the blood to below the freezing point of seawater. And so basically they don't ever freeze up."

Knowing just when fish in the Arctic and Antarctic began producing antifreeze is important because it would help scientists understand how the global climate has changed. DeVries and fellow researchers traced the genetic origin of glycoproteins in a family of Antarctic fishes. They estimate the antifreeze gene first appeared there some five to 14 million years ago. This is about the same time experts believe Antarctica's Southern Ocean began to freeze.

DEVRIES: "Since these antifreeze proteins evolved for the primary function of surviving in freezing temperatures, it reflects on the marine environment that these fishes lived in. By figuring out when they evolved we can sort of give a independent biological indicator of when the Antarctic Ocean reached freezing temperatures."

Researchers say fish in the Antarctic and Arctic Oceans independently evolved nearly identical antifreeze proteins. But questions remain. For instance, did fish at opposite ends of the earth evolve similar genes at the same or different times? To find the answer, DeVries and her colleagues will trace the origins of the antifreeze gene in the Arctic cod. From that, they hope to learn when the big chill first came to the Arctic Ocean.

OUTRO: For Arctic Science Journeys, this is Debra Damron reporting from Fairbanks, Alaska.