If asked to name the most poisonous thing on Earth, few would have the tiny, rough-skinned newts (taricha granulosa) of Oregon on their list. However, this animal produces large amounts of a very deadly toxin, tetrodotoxin or TTX, through glands in its skin.
The amount produced varies from one newt to the next, but many produce enough toxin to kill predators many thousand times their size. Why would a tiny newt living in ponds around Oregon contain enough toxin to kill an elephant?
TTX is a pretty common toxin in nature and is deployed by more species than this tiny newt. TTX acts by blocking voltage-gated sodium channels on nerves and muscles. These microscopic protein channels line the nerves and muscles of all animal species and are responsible for electrical signaling. A toxin that can stop them from working would paralyze the nerves and muscles, and this is what TTX does.
It would seem that even a tiny amount would deter a predator from taking on this newt, but many species of birds, snakes, fish, dogs, and yes, even humans have died while ingesting this newt. The amount of toxin they possess is like using a sidewinder missile to shoot the spider in your house, so what gives?
Well, there is one predator out there who can eat this newt, and it is driving the increased toxicity in the newts. This predator benefits by having a personal food supply that hardly anything else on Earth can eat. The harmless garter snake (thamnophis sirtalis) that lives in the same range of these newts has evolved immunity to TTX.
The immunity varies from one snake to the next, just as the amount of poison does in the newts. In areas where you have super toxic newts, you find super resistant snakes. Snakes of the same species that do not live around the newts have no resistance to TTX at all.
These two species are locked in an arms race with each other, both evolving to win the race. This type of race leads to some extremes in nature, like a cat that can hit 70 mph or a tiny newt toxic enough to kill almost anything.
This is the game nature plays, and the cards it plays with are the genes of the species. Mutated sodium-channels in the snakes do not allow the TTX to bind to them very well, and thus the paralytic function is greatly reduced or absent. This mutated gene has been favored in the game of natural selection.
The story of the newt and the snake was happened upon by biologist Edmund Brodie Jr. and his son Edmund Brodie III. Many others have published on this topic also, and the full details of how the newt makes TTX is still being investigated. Searching “thamnophis sirtalis arms race” in Google Scholar will start you down the rabbit hole of the details of this story. To meet the newt and the Brodies, I recommend this short video, Toxic Newts/PBS LearningMedia, www.pbslearningmedia.org/resource/tdc02.sci.life.evo.toxicnewts/toxic-newts/.