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Saline Pond, Death Valley, California
Credit & Copyright: Dr. Bruce G.
Explanation: No, it's not Mars. But it is a land of extremes. Nearly 280 feet (85 meters) below sea level, today the temperature here has reached over 120F (49C). Thirsty? Don't drink this water. It is highly saline -- a shallow salt pond that grows and shrinks with the seasons and the rare rainfalls.
But here is an amazing phenomenon ... life. Tiny fish the size of my little finger. The Death Valley pupfish. Cyprinodon salinus salinus can survive in water nearly as hot as this stifling air and 2 to 3 times more salty than ocean water. These are indeed extremophiles -- life forms that exist on the boundary of tolerance of temperature and haline (salt) conditions.
Death Valley pupfish populations are highly diverse genetically. Studies by Duvernell and Turner suggest that they all had a common ancestor and that the populations diversified mostly by what is called "genetic drift" or random loss of genes that occurs in small, isolated populations.
Genetic drift can increase the differences in gene pools between populations, but it can also severely decrease the genetic variation within populations ... so much so that the fitness -- reproductive capability -- of individuals within populations can greatly decline. Perhaps genetic drift and the resulting loss of genetic diversity within each population accounts for the fact that the pupfish have been disappearing.
Valley pupfish -- amazing but imperiled extremophiles in
a harsh land!
Next week's picture: The Burning Mountains of Swaziland
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