Figure 20.20 Resistance to a Toxin Comes at a Cost (A) Garter snakes (Thamnophis sirtalis) prey on rough-skinned newts (Taricha granulosa). Rough-skinned newts defend themselves by sequestering a neurotoxin, TTX, in their skin. In turn, TTX-resistant sodium channels have evolved in some snake populations, allowing the snakes to eat toxic newts but resulting in slower movement by the snakes. (B) High TTX resistance in garter snakes is found only in regions where snake and newt populations overlap (tan area).