Mimicry in (Non)-Toxic Frogs

I heard a very interesting story on the Nature Podcast (2006/3/8) about mimicry in Poisonous Frogs in Ecuador. It concerned a situation in which there were two species of poisonous frogs in the same area, one more toxic than the other. The surprising result was that a non-poisonous frog imitated the colouring of the less toxic of the two frogs.

The explanation for this given by the letter's co-author, Catherine Darst, was as follows. Predators that try eating the more toxic frog develop an aversion to a broad spectrum of similar frogs, including the less toxic variety. In contrast, creatures that eat the less toxic frog develop a more specific aversion to frogs with its colouring only. The counterintuitive result is that imitating the less toxic of the two poisonous species affords the imitator protection from predators who have sampled either species of toxic frog, while imitators of the more toxic frog are protected only from animals that have tried this more toxic species. Darst supported this idea with experiments involving chicks as predators.

This is a subtle argument, so let's draw it out a little more, and make it concrete by making the toxic frogs red (for the more poisonous) and blue.

Cast of Characters

Frog	Toxicity	Chicks eating this eat / avoid
	Highly Toxic
	Somewhat Toxic
	Non Toxic (red frog imitator)
	Non Toxic (blue frog imitator)

Protection

So who is protected from whom?

Imitator	Predators that have tried red frogs	Predators that have tried blue frogs
	Won't eat red imitators	Will eat red imitators
	Won't eat blue imitators	Won't eat blue imitators

So...

So the blues have it: by imitating the less poisonous frog, the non-toxic frog indeed gets protection from predators that have tried either toxic frog species.

Reference

Predator learning favours mimicry of a less-toxic model in poison frogs Catherine R. Darst, Molly E. Cummings Nature 440, 208-211 (09 Mar 2006) Letters to Editor.