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.
Image courtesy of M. Chouteau and The American Naturalist