In the Mar. 8 issue of Nature, Catherine Darst and Molly Cummings show that a harmless, colorful frog living in the Amazonian rainforest gets protected from predators not by mimicking its most poisonous neighbor, but by looking like a frog who's poison packs less punch.
The Texas biologists studied three species of poison dart frogs--one highly toxic species, one less toxic species and one harmless species. All live in the same area and are brightly colored, which warns predators that they may be poisonous.
In a series of predator learning experiments, the researchers found that the frogs' predators--in this case birds--learned to avoid anything remotely resembling the most toxic species.
"What we found is that predators are using stimulus generalization, which is a really old psychology theory," says Darst, graduate student in integrative biology. "When they learned on the more toxic frog, they generalized."
The harmless frogs can look like the less toxic poison frogs without losing any protection from predators.
The result is surprising, because mimicry theory predicts that when all three frogs occur in the same forest, the mimics would look like the more toxic frog species, the more abundant of the toxic frogs, or look like both the more and less toxic species.
"We've uncovered a new mechanism involved in mimicry processes," says Cummings, assistant professor of integrative biology. "A mimic species can actually become a different color pattern if it can enjoy the protection of the predator generalization brought on by more toxic species in the community."