Origins ANTARCTICA, Scientific Journeys from McMurdo to the Pole
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Fish: Fresh, Not Frozen

Map of Gondwanaland
  © NSF
  Gondwanaland, around 150 million years ago, before the land mass that is now Antarctica separated from the land mass that is now South America.
   

Mutating Genes and Shifting Continents
Notothenioids did not attain their regal status in the Antarctic marine ecosystem by chomping other species to oblivion. Rather, scientists believe that the dominance of the Notothenioids is a product of genetic and geological history.

Up until about 30 million years ago, researchers say, the waters around Antarctica were warmer than they are today. That’s because South America was connected to Antarctica (see map at right), allowing warm air from the north to flow into Antarctic waters.

Fossil evidence indicates that the warmer waters permitted a greater diversity of marine fish species than there is today; many different groups of fish species thrived. The 90 or so Notothenioid species that inhabit Antarctica today did not exist—only a single ancestral Notothenioid species.

But sometime between 5 and 14 million years ago, the confluence of two changes—one genetic and one geological—radically changed this species distribution.

The genetic event was a tiny change, or mutation, in the DNA of an ancestral Notothenioid. The mutation created a DNA segment in the fish that coded for an antifreeze protein.

But the ocean was warmer at the time, so the Notothenioids didn’t need the protein. As a result, the mutation neither helped nor hurt survival chances—and had no significant impact on the population of antifreeze-protein carriers.

Around the same time, a shift in the earth’s continental plates changed the shape of the Earth's land masses, ripping off the tail end of South America from what is today Antarctica. The resulting unbroken band of seas around Antarctica created a powerful water current encircling the continent, preventing Antarctic waters from mixing with warmer seas. Over time, the Antarctic seas grew much colder.

Map of circumantarctic currents

The current patterns around Antarctica today.

 

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