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Radical evolutionary change could happen in a few generations


In this story:

November 26, 1998
Web posted at: 12:05 a.m. EST (0505 GMT)

(AP) -- If the world suddenly gets hotter, you might survive better with a new skin color, or you might sprout a tail to maneuver in the dense tropical forest that spreads around the globe.

And, if scientists are correct, you might already be carrying the genes for these radical traits, and more.

Scientists working with fruit flies believe they have unlocked a vault of last-ditch genetic variations that kick in to help organisms survive in a much altered form that defies the neatly predictable, incremental pace of evolution.

Researchers at the University of Chicago and the Howard Hughes Medical Institute report in Thursday's issue of the journal Nature that the fruit flies expressed these prefabricated variations -- from weird limbs to different wings -- when scientists fooled the insects into thinking their climate was changing.

The physical changes erupted in the span of a few generations in the face of supposedly new and dire living conditions. In doing so, they radically changed the appearance and behavior of a creature that had looked and lived the same for eons.

Doomsday genes well hidden

Researchers caution this cache of doomsday genes has been unlocked only in controlled experiments.

Such emergency countermeasures are kept under tight molecular wraps in normal circumstances, they said. Nor has it been determined if these genes actually work this way in nature.

"This sounds like a very bad thing, and no doubt it is for most of the individuals," said study co-author Susan Lindquist of the University of Chicago. "But for some, the changes might be beneficial for adapting to a new environment. Genetic changes exposed in this way become the fodder for evolution."

In the 19th century, Charles Darwin described evolution as a gradual, orderly march by a species toward self-improvement.

In the fossil record, most evolutionary changes are seen to have unfolded over millions of years.

But not always.

Punctuated equilibrium theory

The theory of punctuated equilibrium championed by paleontologist Stephen Jay Gould and others suggests that evolution is a messy business driven by random disasters that force survivors to adapt hurriedly to new environmental conditions.

For example, mammals and other life forms flourished after an asteroid or comet hit Earth 65 million years ago, but dinosaurs perished.

"Evolution is often thought of as incremental," said biologist Andrew Cossins of the University of Liverpool in England. "But the fossil record contains many examples of apparently rapid changes in body form. This mechanism provides, for the first time, a means by which changes in body form can be substantial and stepwise rather than progressive."

Other scientists want to see whether such drastic variations can occur quickly outside the laboratory.

"In real life, are there organisms that change this way? Are there examples in nature that are going begging for an explanation like this?" said Aaron Bauer, a lizard geneticist at Villanova University.

Bauer studies a group of geckos native to the deserts of southwest Africa. He said one type of lizard could be a candidate for study because it looks and acts differently, yet its genome is nearly identical to other lizards in the area.

"If this molecular mechanism could be shown to be generally applicable among different organisms, it would be an important advance," Bauer said.

Key player: Hsp90

In the fruit fly experiments, the Chicago researchers determined that the genetic variations held in reserve depended on a protein called Heat shock protein 90.

Hsp90 is known as a chaperone protein. As temperatures rise, it prevents other proteins from going awry and disrupting normal cell functions and growth, and also prevents degenerative diseases.

However, Hsp90 gets spread too thin when conditions continue to deteriorate. With the chaperone distracted, many different proteins begin to misfire in cells. Genetic variations that were held in reserve begin to trigger.

In the experiments, the researchers deliberately reduced the levels of Hsp90 in fruit flies to simulate the biological response in fruit flies to climate change.

As many as 90 percent of the flies' offspring emerged with oddly shaped wings, strange bristle configurations and limb deformities. The eventual evolutionary benefits of these genetic changes were unknown, the researchers said.

The abnormalities persisted even when Hsp90 levels were returned to normal in later generations, suggesting the changes had become permanent in the fruit flies' genetic code, Lindquist said.

Copyright 1998   The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten, or redistributed.

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