A new study published today suggests that a group of Antarctic fish that have evolved a set of “antifreeze proteins” to survive in extremely cold water are unlikely to be able to adapt to warmer waters because of these proteins. This finding is of particular concern given these Antarctic notothenioid fishes represent close to 90% of the total biomass of the region.
Antifreeze proteins: Explanation from Dr Clive Evans
“What we have found is that antifreeze proteins not only stop ice from growing inside Antarctic fishes, but they also stop it from melting,” Dr Clive Evans, of the School of Biological Sciences, explained on Tuesday in a statement.
“The ice inside the fish is actually ‘superheated’; that is, it remains stable above its expected melting point, and this is a direct consequence of the binding of antifreeze proteins to the ice crystal surface,” said Evans.
“This is the first demonstration of the existence of ‘ superheated ice’ inside living organisms, he continued, “but it presents a significant problem for the fishes since the only known way for them to melt internal ice is through warming of the freezing seawater they inhabit.”
Evans explains the problem is the fish simply can’t survive in warmer waters due to the evolution of these antifreeze proteins. “Internal ice, protected by antifreeze proteins, seems a permanent burden for most fish in this area and is likely to prove lethal.”
He elaborates on the problem. “What we have here is an evolutionary paradox. The adaptive evolution of fish antifreeze proteins has enabled Antarctic fishes to survive in freezing seawater by stopping internal ice from growing, but at they same time by inducing a superheating capacity these proteins have reduced the opportunity for melting the ice burden, thus increasing the risk of dying.”
More details from researchers
The exact consequences of superheated ice are not known, but researchers believe that accumulation of ice inside the fishes is likely to have adverse physiological consequences.
If the fish end up carrying ice crystals around all their lives, researcher Chi-Hing Cheng said, it is possible that ice particles could obstruct small capillaries or cause dangerous inflammatory responses.
Researcher Paul Cziko compares the unmelted ice cystlas to dangers posed by asbestos particles in the lungs or blood clots in the brain. “Since much of the ice accumulates in the fishes’ spleens, we think there may be a mechanism to clear the ice from the circulation,” he said.
“This is just one more piece in the puzzle of how notothenioids came to dominate the ocean around Antarctica,” he said. “It also tells us something about evolution. That is, adaptation is a story of trade-offs and compromise. Every good evolutionary innovation probably comes with some bad, unintended effects.”