SHE SAYS IT DOESN'T HURT: Ashley Wilkinson, a junior majoring in biology, prepares for a bite from a T. sirtalis. An experiment conducted by Wilkinson and fellow student Amanda Mortensen revealed a correlation between the aggression of garter snakes and their resistance to tetrodotoxin. / Photo by Jen Beasley

By Jen Beasley

January 22, 2007 | Amanda Mortensen and Ashley Wilkinson are snakebit. But the Utah State University juniors aren't down on their luck; they're just doing research.

While assisting in gathering garter snakes for a graduate student's research in Monterey County, Calif., the biology students observed that some of the captured snakes were quite aggressive. They began a project investigating whether there was a relationship between the snakes' resistance to tetrodotoxin -- a deadly neurotoxin found in the skin of the rough-skinned newt, a food source for some garter snakes -- and the aggression of the snake.

"We found this really, really amazing correlation between aggression and resistance," Mortensen said.

And how does one determine if a snake is aggressive? The old fashioned way: you stick your finger in front of it and see if it bites you.

"It doesn't hurt," Mortensen said. "It just feels like Velcro. Their teeth don't actually go through the skin."

The study, which was conducted using three species of neonate garter snakes, revealed that the more resistant a snake was to tetrodotoxin, the more aggressively it behaved. Snakes of the species T. elegans showed little resistance to the toxin, and generally fled when confronted. But individuals of the species T. atratus and T. sirtalis showed a greater resistance. In some 60-second trials the most resistant snakes struck as many as 70 times, Mortensen said.

The experiment was conducted in two stages. Because resistance to tetrodotoxin varies greatly between individuals and localities, each snake was put through a trial to determine its resistance. The women timed each snake in a trial crawl down a racetrack, and then injected it with a dose of the neurotoxin, and ran it through the course again to see how much it slowed down. They continued injecting the snake with the toxin until it was slowed down by 50 percent.

"Some of the sirtalis were super-resistant," Mortensen said. "In order to slow one down, they would have to eat enough tetrodotoxin to kill 900 people."

Once a snake's individual resistance was established, it was run through the 60-second bite trial. Mortensen used her fingers to gather the strikes, and Wilkinson used hers to write down the results. The different duties came down to scientific control.

"We had to have the same person do the same thing every time," Wilkinson said.

Though it remains unclear what causes the correlation between resistance and aggression, Edmund Brodie Jr., the biology professor who participated in the research, said resistance to the toxin has an obvious advantage for the snakes.

No creature besides the garter snakes can eat the rough-skinned newt, so there is no competition, and a newt can nourish a snake for about a week.

Wilkinson said they never killed a snake with the toxin, but they did occasionally give one so much that it couldn't crawl anymore. And one snake, known to the girls as "The Beast" because of its size, couldn't even be tested because the toxin required for its body weight would have been too expensive. One milligram of tetrodotoxin costs about $360. The study was funded by a grant from the National Science Foundation.

Tetrodotoxin is the same poison found in the Japanese puffer fish, which when improperly prepared has been known to kill adventurous diners. The neurotoxin affects the sodium channels in the body, which means it kills by debilitating the muscles and nervous system. There have been anecdotal cases of humans dying when the newts have gotten into campers' coffee pots and left enough toxin to kill, Mortensen said; however she didn't think their research could be used to create any kind of antivenin because the toxin is so fast acting.

Mortensen acknowledged that there may be no immediate medical use for their findings, but their findings are important to the scientific community.

"We gain a better understanding of the way genes work and the way genes are tied together, and how evolution itself works," she said.

Brodie Jr. said the study is significant because it clearly illustrates an example of co-evolution.

"We get evidence of snakes being more resistant, and evidence of newts being more toxic. So you have an arms race going on," he said. "This is so surprising that we have to go back and rethink the entire thing. I'm really pleased by the outcome of their results."

Brodie Jr. said the implications of the study are still unknown, but that they are potentially very significant.

"This will clearly lead to publication," he said. "This is one of the best systems for documenting co-evolution because we can see exactly where it's happening."

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