around 150 million years ago, before the land mass that
is now Antarctica separated from the land mass that is
now South America.
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.
until about 30 million years ago, researchers say, the waters
around Antarctica were warmer than they are today. Thats
because South America was connected to Antarctica (see
map at right), allowing warm air from the north to flow
into Antarctic waters.
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 existonly
a single ancestral Notothenioid species.
sometime between 5 and 14 million years ago, the confluence
of two changesone genetic and one geologicalradically
changed this species distribution.
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.
the ocean was warmer at the time, so the Notothenioids didnt
need the protein. As a result, the mutation neither helped
nor hurt survival chancesand had no significant impact
on the population of antifreeze-protein carriers.
the same time, a shift in the earths 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.
current patterns around Antarctica today.