Garter snakes, newts in genetic war
By Joe Bauman
Deseret Morning News
Monday, April 11, 2005
http://deseretnews.com/dn/view/0,1249,600125315,00.html
For years, scientists at Utah State University have been documenting a
"chemical arms race" between normally toxic newts and the garter snakes that eat
them. Now they have discovered the genetic changes that allow the snakes to
evolve molecular defenses against the poison.
The garter snake has evolved a resistance to the normally deadly toxins
carried by newts, making them its prey. Researchers say the newt carries enough
neurotoxins to kill 50,000 mice or 10 people.
In a 2002 study in the journal Science, Geffeney, the Brodies (father and son
professors) and Ruben showed that the newts and snakes were locked in the arms
race. What's new is that they now know the molecular basis for the snake's
defense.
The poison binds to a particular place on the protein molecule. In most
animals, these proteins are the same, and the poison bonds to an important part
of the molecule. From chickens to rats and humans, the sodium channels are
vulnerable to TTX. But not in the garter snake.
The snakes' genetic makeup mutated so that the protein was shaped
differently. The poison could not bind onto the new shape.
Snake muscles with the modified proteins were able to function even with
high doses of the poison, the researchers found.
"We made specific mutations and we showed that the specific mutations
altered the ability of the TTX to bind to the protein," she said.
"So we ended up learning more about the shape of the protein," Geffeney was
surprised to see changes in such an important part of the protein.
Another discovery was that separated populations of garter snakes differ in
their amino acid sequences. In their separate habitats, at least two populations of
garter snakes apparently evolved the defenses on their own.
One question the team would like to answer, she said, is "How many times has
this elevated level of resistance evolved?"
The elder Brodie, former chairman of USU's Biology Department, said the
study has extended the research into the fields of neurobiology and genomics.
"Shana set out to isolate the proteins that form the sodium channel, and could
sequence those and determine the mutations that had taken place in those
populations that were resistant," he said.
Possibly other populations of garter snakes would show additional changes,
he said. "We know that the changes have evolved at least twice independently."
So who's winning the chemical arms race?
"It seems to be sliding back and forth," Brodie said. "The snakes may be ahead
for the moment, but it's variable, area to area."
donald j haarmann
-------------------------------
The way to capture a [chemistry] student's attention is
with a demonstration where the is a possibility
the teacher may die.
Jearl Walker
Cleveland State University.
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