Panda’s Thumb

And so it is. Some of the most successful predators of small amphibians are another herpetological marvel, the garter snakes, Thamnophis. Unfortunately, if you feed ordinary garter snakes a diet of rough-skinned newts, they tend to move more and more slowly as the innervation of their skeletal muscles undergoes a toxin blockade, and if they eat enough, they die. This is not a good thing from the snake’s perspective, although the newts do get revenge and their relatives benefit from the subsequent reluctance of snakes to eat them. It also presents an evolutionary opportunity, in that resistance to TTX in snakes can be a real advantage, since they won’t die and they’ll be able to feast on squishy purplish-brown and orange tubes of meat.

This is happening right now. Populations of garter snakes, T. sirtalis, in California, Oregon, and Idaho are showing different degrees of resistance to TTX, and these differences are being traced right down to specific changes in the amino acid sequence of the snake sodium channel. It’s happening repeatedly, too, with different populations independently acquiring different variations that confer differing degrees of resistance.