Colour predicts toxicity

Researchers have discovered a correlation between the toxicity and colour of frogs. This relationship was the most visible to birds, the frog's most important natural enemy.
The study of the frog species Dendrobates (Oophaga) pumilio, conducted in Panama by a Groningen scientist and her colleague from the University of Texas, has been published in The American Naturalist. These frogs occur in a great variety of colours and colour combinations including yellow, green, blue, red and orange. The frogs are not all equally poisonous: some varieties are as much as forty times more poisonous than others.

The researchers discovered a direct correlation between colour and toxicity, with the most prominent frogs being the most poisonous. This relationship was the most perceptible for birds. For other animal species – such as crabs and snakes – that prey less on frogs, the link was not as obvious. Each of these animals has a different visual system with different colour perception. For the frogs’ natural enemies, birds, the relationship was measurable.

What isn’t clear to the researchers yet is how the differences in toxicity develop. One explanation could be found in the source of the poison. Frogs eat poisonous ants, mites and other small arthropods; the poisons are stored and the frogs become poisonous. It could be that this poisonous prey is not present everywhere to the same degree.