The impossible predicament of the death newts

Summary

So a few days ago I posted about newts, and I mentioned that there was an American newt that was ridiculously toxic. But then (I said) there wasn’t space or time to go into why. And of course I was immediately bombarded by many* comments and e-mails asking why. *threeWell, fine. The world’s most toxic newt is Taricha granulosa, the Rough-Skinned Newt, a modest little amphibian native to the North American Pacific Northwest, west of the Cascades from around Santa Cruz, CA up to the Alaska Panhandle. It’s so toxic that the poison from a single newt can easily kill several adult humans. You could literally die from licking this newt, just once.(But note that the newt is toxic, not venomous. It doesn’t bite or sting. You could handle one safely, as long as you washed your hands thoroughly afterwards. Very, very thoroughly.)Okay, but… why? Lots of newts are mildly toxic. Why is this particularly newt so extremely toxic? Turns out this is a fairly deep rabbit hole! I’ll try to teal deer it. The simple version: the newt is in an arms race with the common garter snake, Thamnophis sirtalis. The garter snake is a small-to-medium sized snake that is common all over North America. It’s a slim, elegant little creature that is usually found in or near water. And while it will eat pretty much anything it can catch, the garter snake particularly likes amphibians: small frogs, salamanders and newts. And in the Pacific Northwest, it really likes snacking on the Rough-Skinned Newt. So the garter snakes of the Pacific Northwest have been evolving resistance to tetrodotoxin. (As you may recall, tetrodotoxin is the stuff that makes the blue-ringed octopus so deadly. It’s produced by symbiotic bacteria that live in the newt’s body, mostly on its skin.) And as the garter snakes evolve resistance, the newts have to evolve ever greater toxicity. And as the newts get more toxic… right. Feedback loop! That’s the simple version. Except this is biology, so of course it’s not that simple. One thi...