drool over Antarctica. Its an ideal place to study evolution,
they say. This is partly because the continents harsh
environment has contributed to the evolution of an abundance
of elegant biological adaptations. Life forms running the
gamutfrom bacteria and fish to plants and birdshave
figured out ingenious ways to survive the continents
frigid, dry climate and relentless winds.
the Notothenioids, a group of more than 120 marine fish species,
most of which are native to Antarctic waters. Antarctic Notothenioids
have remarkable proteins in their bloodstream that prevent
them from freezing. These "antifreeze proteins",
as they are commonly known, bind to tiny ice crystals in their
bodies, inhibiting further growth.
cod (Boreogadus saida)
for a larger image)
Dr. Christopher Zimmerman, ISH
survive the frigid waters of the Arctic Ocean, the Arctic
coda genetically unrelated fish to the Notothenioidsdeveloped
an antifreeze protein nearly identical to the Notothenioid
one. This independent development of the same adaptation
in response to similar environmental conditions is known
as convergent evolution.
marine fish from temperate and tropical regions dont
have antifreeze proteins, and would freeze to death in the
frigid Antarctic waters. Thats because the water temperature
(28°F or 1.9°C) is below the freezing point
of their blood. (While pure water freezes at 0°C, the
salt in sea water lowers the freezing point to about 2°C.)
Notothenioids dominate all of Antarcticas marine habitats.
Not only do they comprise about half of Antarctic marine fish
species, they account for 95 percent of all fish biomass in
the region. As a result,
theres not much of a variety of marine fish species
outside the Notothenioids. In contrast, temperate and tropical
regions, such as coral reefs, have much higher fish diversity,
with ample distribution of species among many species groups.