Biology
Predator-Prey Coevolution and the Arms Race in Toxic Newts and Garter Snakes
Quick fact
Rough-skinned newts (Taricha granulosa) produce enough tetrodotoxin to kill several humans, yet common garter snakes (Thamnophis sirtalis) have evolved resistance to this toxin, sometimes reaching levels 100-fold higher than other snake populations.
Why this is interesting
Imagine eating a newt that could kill you—yet some snakes do it and live. How do they survive?
Read the full explanation
Understanding Predator-Prey Coevolution and the Arms Race in Toxic Newts and Garter Snakes
Imagine a newt that packs a poison powerful enough to kill almost anything that tries to eat it. That’s the rough-skinned newt, which produces tetrodotoxin (TTX) in its skin. Now picture a snake, the common garter snake, that can eat that newt without keeling over. How? The snake has evolved a tiny change in its body—a mutation in the gene for a sodium channel, the very protein that TTX blocks. This mutation prevents TTX from binding, so the snake is resistant. But this resistance doesn’t come free: it makes the snake slower and less agile. So the newt becomes more toxic, the snake becomes more resistant, and they keep pushing each other in an evolutionary tug-of-war. This back-and-forth is called an arms race, and it’s a classic example of coevolution, where two species evolve in response to each other.
A deeper explanation
The arms race between newts and snakes is a vivid illustration of coevolution driven by reciprocal natural selection. Newts produce tetrodotoxin (TTX), a potent neurotoxin that binds to voltage-gated sodium channels in nerve and muscle cells, blocking nerve impulses and causing paralysis and death. Garter snakes, through mutations in the gene encoding the sodium channel, can alter the channel's structure so that TTX binds less effectively, conferring resistance. The degree of resistance varies among snake populations, and this variation correlates with the toxicity of local newts. This pattern is a geographic mosaic: in areas where newts are highly toxic, snakes have high resistance, and vice versa. The “arms race” escalates because snakes that are more resistant can eat toxic newts, gaining a food advantage, while newts that are more toxic are better protected. This reciprocal selection can lead to rapid evolutionary change, as seen in the genetic differences between snake populations. Understanding this system reveals how species interactions can shape evolutionary trajectories and biodiversity, and it underscores the dynamic, never-ending nature of adaptation.