Mike Hague from the Brodie Lab published a new paper in Evolution Letters suggesting that reciprocal coevolution between newts and snakes does not explain local trait matching. Instead, predators seems to be evolving resistance to prey toxicity, but variation in prey defense correlates to neutral genetic structure.
You can read the paper here: https://onlinelibrary.wiley.com/doi/epdf/10.1002/evl3.184