A Toxic Relationship

"When I was an undergraduate student, my professor told me a story about three hunters, out here in the coast range, being found dead, and there was a newt boiled in their coffee pot."

- Edmund Brody Junior

Brody's professor suggested that he do a project to determine if the newt was toxic. He did, and it was. Brody learned that "This (newt) is probably the most poisonous animal in the world, with enough skin-toxin to kill tens of thousands of mice or perhaps a hundred people." Newts of the genus Taricha contain varying amounts of tetrodotoxin (TTX for short), which interferes with neural connections to muscles, by clogging a sodium channel, leading to paralysis and death. The rough-skinned newts (Taricha granulosa) that Brody was studying in Oregon bear the highest amount of TTX.

Some other organisms including pufferfish, octopuses, and various shellfish species contain tetrodotoxin. Most often the animals that bear TTX get it through their diet. Newts don't appear to receive TTX from their food so there must be some internal mechanism the newt uses to synthesize the poison. No one has yet to determine how newts do this.

After discovering just how preposterously toxic the newts were, Brody wondered why they would contain so much TTX that they could kill potential predators many times over. As it turns out, there is one predator that can survive eating a rough-skinned newt - the common garter snake (Thamnophis sirtalis). The two species are clinched in a coevolutionary arms race. Toxicity and resistance, respectively, are the weapons of the newt and the snake. As the snakes become more resistant to TTX, the newts develop the ability to produce more poison.

A friend of mine commented, after reading my last blog about the outrageously poisonous newts, "This little guy’s defense mechanism seems more like a revenge mechanism if he has to be eaten for it to work?" Scientists observed a newt crawling out of a bullfrog's mouth, unharmed, 15 minutes after being swallowed. Other newts survived ingestion by common garter snakes for up to 85 minutes. One would think that if all snakes that eat poisonous newts die there would be no possibility to evolve resistance to the poison.

As it turns out, the snakes resist the effects of TTX to varying degrees, and the newts produce toxin ranging from little or none to absurdly huge quantities. A few snakes reject newts that may taste more toxic than the snake can resist. The snakes are not immune to TTX though. Resistance does come at a price. Snakes invariably move slower after exposure. Highly resistant snakes move more slowly all the time, whether they have eaten a newt or not. Some snakes become fully paralyzed for a while after eating a poisonous newt. Slow moving or weakened snakes are easy prey for their predators. Some suggest that resistance is futile.

Newts that are highly toxic live to reproduce passing on their stronger ability to produce the neurotoxin, and snakes that survive eating poisonous newts pass on their genes for being resistant. On and on it goes, but where does it stop? Some say it has already ended. In areas where newts possess the most toxicity, even the least resistant snakes can survive eating the most toxic newts. Apparently, resistance is NOT futile.