Snakes around world evolve along similar path of poison resistance say biologists
Biologists at Utah State University have long been studying various species of North American snakes that have developed astonishing resistance to a deadly neurotoxin found in the seemingly harmless newts, one of the snakes' favourite foods.
Researchers have now discovered that different types of snakes in Central and South America and Asia have developed the same resistance in a surprisingly similar manner.
The findings of Chris Feldman, PhD '08, a former USU student now a professor at the University of Nevada at Reno, Edmund Brodie, Jr., USU professor of biology, Edmund Brodie III, Brodie's son, from the University of Virginia, and Mike Pfrender, former USU professor at the University of Notre Dame, appear in the March 5, 2012, online edition of the Proceedings of the National Academy of Sciences.
"We were able to break down the genetic basis of adaptations in each of these snakes," says Feldman, lead author and winner of the USU Robins Award as a 2006 graduate research assistant. "We found that each snake - from the neotropical earth snake of Central and South America to the East Asian tiger snake - evolved almost exactly the same way as garter snakes at the genetic level".
Each of the snakes feasts on amphibians that secrete tetrodotoxin or TTX, a poison far more deadly than cyanide. It's the same neurotoxin found in pufferfish that, prepared by rigorously trained chefs, offers sushi lovers an exhilarating, yet risky, culinary experience. Tetrodotoxin is also a suspected ingredient in zombie powder, an anesthetic-like concoction that makes humans appear dead at first and then return to a temporary semi-conscious state.
"Tetrodotoxin affects the proteins that control nerve impulses and the ability of muscles to pull," says Feldman. "At full strength, the poison instantly paralyzes nerve and muscle tissue in animals - including humans - resulting in rapid death."
The snakes in the team's study, however, have mutations that counteract the toxin at the protein level, preventing TTX from blocking the sodium channels in the muscles.
"This tells us two things: either these mutations are the perfect solution to avoid the poison, or they may be the only way around the problem," says Feldman.
What might limit the range of solutions, according to Brodie Jr. is the "cost" of the mutation.
"We know that mutation affects the speed of snakes," he says. "Mutant snakes are slower. A different mutation to block the toxin could have even more detrimental effects and this could explain why the current series of mutations is so similar in all species".
As part of an ongoing study, the team is studying caddis fly larvae, creatures very different from snakes, which appear to have developed a similar resistance to tetrodotoxin. In a naturally protective leaf, female newts lay eggs laced with - you guessed it - TTX. Most pond predators that ingest amphibian caviar do so at their own peril. The exception is caddisfly larvae.
"We're studying these larvae to see if they've adapted with snake-like mutations," says Brodie, Jr.
