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by
Michael Matz
Ecologists
drool over Antarctica. It’s an ideal place to study evolution,
they say. This is partly because the continent’s harsh
environment has contributed to the evolution of an abundance
of elegant biological adaptations. Life forms running the
gamut—from bacteria and fish to plants and birds—have
figured out ingenious ways to survive the continent’s
frigid, dry climate and relentless winds.
Meet
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.
Arctic
cod
(
Boreogadus saida
)
(
click
for a larger image)
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©
Dr. Christopher Zimmerman, ISH
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To
survive the frigid waters of the Arctic Ocean, the
Arctic
cod
—a genetically unrelated fish to the Notothenioids—developed
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
.
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Most
marine fish from temperate and tropical regions don’t
have antifreeze proteins, and would freeze to death in the
frigid Antarctic waters. That’s 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.)
The
Notothenioids dominate all of Antarctica’s 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,
there’s 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.
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