One Species, Ten Patterns? Why Poison Dart Frogs Dress Differently

By Veronique Greenwood | November 8, 2011 12:22 pm

Above, the real deal; below, the clay models used to test predators’ reactions to local and foreign frog markings.

Sometimes, you have to make a thousand frogs from modelling clay to make your point.

A single species of poison dart frog sports ten completely different coloration patterns, depending on where they live. Are these color divisions being encouraged by the birds that prey on them?, wondered evolutionary biologist Mathieu Chouteau from the University of Montreal. To find out, he set out 1800 clay frogs, made by himself and his (saintly!) girlfriend, in the Peruvian forest.

Since each coloration pattern lives in a different area, in each spot he put out a frog with the local pattern, a frog with a foreign pattern, and a frog with no pattern at all, and looked at how predatory birds reacted to them. He found that indeed, birds knew that their local pattern meant a poisonous meal, and they were more likely to avoid those frogs while preying heavily on the foreigners. The birds’ apparent knowledge of their local pattern could indeed be keeping the different populations of frogs from mixing.

But why do the frogs, which are all of one species, have such a variety of patterns? It could be that their specific habitats have different requirements when it comes to camouflage, but this could also be one of those situations that illustrates how random evolution can be: genetic drift, in which a pattern or trait of no particular prominence is cemented into place by pressures from the surrounding environment—in this case, predators who’ve gotten used to one pattern—could also be in play. Once a certain pattern is established, it may be selected for for no reason other than that it’s already present.

[via ScienceNOW]

Image courtesy of M. Chouteau and The American Naturalist

  • Victoria Kostadinova

    Amazing! But we can’t help thinking–what happened to all those little clay frogs, the birds that tired to eat them?

  • Veronique Greenwood

    Good question! Most of the clay frogs were not actually eaten by the attacking birds. The researcher went around at 24-hr intervals to look for marks of predation–signs that birds had attacked the models, like gouges on either side where talons struck the earth. While about 14% of the models were missing or eaten by ants or roaches (apparently there are some giant roaches in the Peruvian rain forest!), the rest were still where the researcher had left them, but with marks from talons on them or around them. It was by counting those marks that he came up with his numbers about predation on the various types. When the experiment was done, the models were gathered up and removed from the forest.

  • Iain

    in which a pattern or trait of no particular prominence is cemented into place by pressures from the surrounding environment

    This got me to thinking about human beauty and conformity and how we are far more comfortable with ‘similar’ than odd or bizarre. Just look at how skateboarders, punks, goths, emo’s are automatically judged to be undesirables.
    Maybe our brains are wired to accept the normal and reject or marginalize the abnormal.
    Something we share with the frogs and perhaps all species.
    So the outies have to mate among themselves causing subspecisation.


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