"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."

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E-mail: bau@desnews.com