In studying the toxicity and abundance of all three species, Darst found that the harmless frog mimics either toxic frog where they live separately. In the north, the mimic looks like the less toxic species; in the south, it looks like the more toxic species.
Where all three live together, she unexpectedly found that the mimic looks like the less toxic, less abundant species.
"That is totally bizarre," says Darst. "The whole point of mimicry is to gain protection from predation."
Darst performed predator experiments using domestic chicks she collected from villages outside of Quito, Ecuador. The chicks quickly learned to avoid the highly toxic frogs during training sessions and subsequently avoided all other similar frogs, even those that weren't exact mimics.
The birds' learned avoidance and generalization helps explain how the harmless mimic frog can be more abundant than its model. (It's generally believed that if a mimic outnumbers its model, the system would break down because predators would stop associating color patterns with toxicity.)
If the mimics looked like the more toxic species, they might fall prey to predators who learned on the less toxic frog. By mimicking the less toxic frog, the mimic covers its bases. It gains protection from predators that have tasted both the more and less toxic frogs in the area.
When predators learn to generalize based on the most toxic species, Cummings says that mimics can actually be freed to evolve new color patterns and that this could also explain why poison frogs are so diverse.
"When predators generalize, it actually allows mimics to avoid the penalty of novelty," says Cummings. "This could be allowing diversity to take hold."
The frogs Darst and Cummings studied happen to live in the same forest basin where the famous naturalist Henry Bates first described mimicry in butterflies over 100 years ago. His the
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Source:University of Texas at Austin