Snakes Get Out of the Game

Last week, I told the story of the rough-skinned newts with the toxic skin and the garter snakes that eat them. I talked about the Red Queen Hypothesis and the evolutionary arms race, and all sorts of fun science-y terms that make basic interactions seem really, really impressive and cool. Today, I finish the story.

The two big names in this research are Edmund Brodie, Jr. and Edmund “Butch” Brodie, III. The research being described here is coming out of their labs. So, scientists have been looking at how resistant snakes are to the toxin (TTX) found on the skin of those newts. If the snakes have absolutely no resistance to the toxin, then the newt just waits for the snake to die and literally crawls out of the snake’s mouth. If the snakes are completely resistant, then they eat the newt and that’s that for the newt. The expectation is that often times the snakes are somewhere in the middle ““ resistant to some newts, not resistant to others, based on how much toxin the newts are packing.

To test the resistance, the researchers would run a snake down a chute, then inject some toxin into the snake and then have the snake run down the chute again. Depending on the resistance of the snake, the toxin would either have no effect or would slow the snake down. The researchers were using only sub-lethal concentrations of the toxin because it is bad research form to just kill animals without solid justification. If there was no difference between the snake’s first run and their toxin-run, then they were marked as resistant to that level of toxin. The researchers kept increasing the level of toxin until the snake showed a decrease in their run time down the chute.

But, and here’s where things get sassy, some of the snakes never showed a decrease in their run time down the chute.  Well, to be fair, there might have been some level of toxin that made the snakes move more slowly, but the researchers could not afford to purchase it ““ that’s how resistant those snakes are.

You might remember from last week that the toxin works by affecting the sodium channels, which in turn affects how cells communicate. By preventing the sodium channels from working correctly, the toxin can lead to paralysis and death. Sodium channels are very important, but they can be altered by relatively simple changes in the genome.

When researchers looked at the genome of the super-resistant snake, they found several changes in the genome that altered the snake’s sodium channels and thus made them resistant to the toxin. These resistant snakes can eat any newt ““ they are no longer part of the arms race. They have, in effect, won.

So what comes next? Is this just another phase in the Red Queen interaction, or is this really the end of the game? Will these snakes always be resistant to the newts? Will this resistance spread throughout the entire snake population? Sure, some questions have been answered about this system, but now there are many, many more. And that’s what makes science so exciting.