Frogs Mimic Less-poisonous Neighbors

March 09, 2006

Many edible animals avoid ending up as something’s dinner by copying the appearance of poisonous animals—an effect called batesian mimicry. A new study in the 03 09 06 Nature describes a species of frog that maximizes its chances of survival by mimicking the less toxic of two local poisonous species—a seemingly counterintuitive tactic, but one that helps the frog to avoid the attentions of as many predators as possible.

Catherine Darst and Molly Cummings made their discovery in a group of frogs in the Ecuadorian Amazon. The non-poisonous frog, Allobates zaparo, shares territory with a very poisonous frog, Epipedobates parvulus, and another related but less noxious one, E. bilinguis, both of which have similar but distinct patterns of red warning spots. The authors found that where the three species overlap, A. zaparo tends to mimic E. bilinguis—the less poisonous of the two.

This seems confusing—instead, one might expect the mimic to display a pattern somewhere between the two, or for some mimics to copy one poison frog, while some mimic the other. But by studying the process by which chickens learn to avoid the poisonous frogs, Darst and Cummings show how the mimics get away with it. The more-poisonous frogs educate predators to avoid anything that looks remotely like the noxious animal. But with less-toxic frogs, the learning is much more specific. So by copying the less-poisonous species, A. zaparo remains unmolested by predators, regardless of which poison frogs they had previously encountered.

Abstract © 2006 Nature

“Predator learning favours mimicry of a less-toxic model in poison frogs,” Catherine R. Darst, Molly E. Cummings, Nature, March 09, 2006

Catherine Darst, University of Texas, Austin


Frog Figure

Allobates zaparo individuals in the Northern Ecuadorian Amazon resemble the poisonous Epipedobates bilinguis, which also occupies the northern range.

In the southern range, where only Epipedobates parvulus occurs, Allobates zaparo individuals resemble that species.

But where the two poisonous species coexist, Allobates zaparo individuals resemble Epipedobates bilinguis, the least poisonous and least common of the two poisonous species.