Origin and Mechanism of Evolution of Antifreeze
Glycoproteins in Polar Fishes
Chi-Hing C. Cheng
Department of Molecular and Integrative Physiology, University of Illinois,
Urbana, IL 61801, USA
Introduction
The frigid waters of the polar oceans delimit the cold extreme for marine
life. This is particularly true in the case of the thermally isolated Antarctic
Ocean which is perpetually near or at freezing (-1.9 0c) due to the thermal
barrier imposed by the Antarctic Circumpolar Current [1]. The most
fundamental survival challenge faced by teleost fishes in these waters is a
physical one - the threat of being frozen. The body fluids of marine te1eosts
including polar species are hyposmotic to sea water, 300-600 mOsM [2,3]
versus 1000 mOsM, and thus have a higher colligative freezing point than
the latter, -0.56 °c to -1.1 °c versus -1.86 DC. By these simple physical
considerations alone, freezing death would be unavoidable especially in
the presence of ice. Unlike some reptiles and amphibians, fish cannot
survive even partial freezing of their body fluids. A number of polar and
subpolar fishes had overcome this environmental challenge with a
biological solution - they evolved ice-binding antifreeze proteins which
enabled them to successfully colonize icy habitats that were otherwise out
of their reach. The impact of the evolution of these unique anti freezing
proteins on organismal and ecological success is manifested most
strikingly in the case of the Antarctic notothenioid fishes - a single teleost
suborder (Notothenioidei) that has come to dominate today's Antarctic fish
fauna in terms of species number (-50%) and biomass (~90%) [2,4-6].
Although other forms of adaptations - biochemical, physiological,
anatomical, and behavioral (other papers, this Vol.) - have also evolved
and must have contributed in concert to the ecological success of the
notothenioids in their frigid environment, it is fair to say that since a frozen
fish could not evolve, the emergence of the antifreeze protein function to
assure survival in the first place was pivotal in allowing other adaptations
and organismal diversification to occur.
It is intuitively obvious that the driving force for the evolution of
antifreeze proteins was the cooling of the polar oceans to freezing
temperatures over geologic time. What is not obvious is where these novel
G. di Prisco. E. Pisano, A. Clarke (Eds)
Fishes of Antarctica. A biological overview
© Springer-Verlag Italia 1998
Glycoproteins in Polar Fishes
Chi-Hing C. Cheng
Department of Molecular and Integrative Physiology, University of Illinois,
Urbana, IL 61801, USA
Introduction
The frigid waters of the polar oceans delimit the cold extreme for marine
life. This is particularly true in the case of the thermally isolated Antarctic
Ocean which is perpetually near or at freezing (-1.9 0c) due to the thermal
barrier imposed by the Antarctic Circumpolar Current [1]. The most
fundamental survival challenge faced by teleost fishes in these waters is a
physical one - the threat of being frozen. The body fluids of marine te1eosts
including polar species are hyposmotic to sea water, 300-600 mOsM [2,3]
versus 1000 mOsM, and thus have a higher colligative freezing point than
the latter, -0.56 °c to -1.1 °c versus -1.86 DC. By these simple physical
considerations alone, freezing death would be unavoidable especially in
the presence of ice. Unlike some reptiles and amphibians, fish cannot
survive even partial freezing of their body fluids. A number of polar and
subpolar fishes had overcome this environmental challenge with a
biological solution - they evolved ice-binding antifreeze proteins which
enabled them to successfully colonize icy habitats that were otherwise out
of their reach. The impact of the evolution of these unique anti freezing
proteins on organismal and ecological success is manifested most
strikingly in the case of the Antarctic notothenioid fishes - a single teleost
suborder (Notothenioidei) that has come to dominate today's Antarctic fish
fauna in terms of species number (-50%) and biomass (~90%) [2,4-6].
Although other forms of adaptations - biochemical, physiological,
anatomical, and behavioral (other papers, this Vol.) - have also evolved
and must have contributed in concert to the ecological success of the
notothenioids in their frigid environment, it is fair to say that since a frozen
fish could not evolve, the emergence of the antifreeze protein function to
assure survival in the first place was pivotal in allowing other adaptations
and organismal diversification to occur.
It is intuitively obvious that the driving force for the evolution of
antifreeze proteins was the cooling of the polar oceans to freezing
temperatures over geologic time. What is not obvious is where these novel
G. di Prisco. E. Pisano, A. Clarke (Eds)
Fishes of Antarctica. A biological overview
© Springer-Verlag Italia 1998