Colour predicts toxicity poison frog

Animals have smart strategies to defend themselves against predators. Poison frogs are good examples: with bright colours they warn predators that they are distasteful. But why are some poison frogs blue, and others red or yellow?  Research by Martine Maan (University of Groningen, the Netherlands) and Molly Cummings (University of Texas at Austin, USA) provides an answer to this question: colours can predict very accurately how toxic a poison frog is.

Funded by the Netherlands Organisation for Scientific Research (NWO-Rubicon), Martine Maan and Molly Cummings investigated Dendrobates (Oophaga) pumilio, a Panamanian poison frog with extremely diverse coloration. In some areas, these frogs are yellow with black spots, in other places they are bright orange or dark blue.

Birds

Maan and Cummings discovered that this colour variation coincides with an extreme diversity in toxicity. Among the ten investigated colour morphs, there was a 40-fold difference in toxicity. The biologists subsequently calculated how the frog colours would be perceived by birds, probably important natural enemies of these frogs. They found that the most conspicuously coloured frogs – as seen through bird eyes – were also the most toxic. Thus, birds can predict the toxicity of the frogs by looking at their colours.

Less accurate

The study also shows how important it is to know the intended audience of a colour signal. Different animal species have different visual systems, and as a result they see things differently. The researchers also estimated how colours would be seen by crabs and snakes, but for those animals the conspiciousness of the frogs was a much less accurate indicator of toxicity.

Differences in toxicity

It is not yet known how the differences in toxicity arise. The frogs obtain toxic compounds from a specialised diet of ants, mites and other small arthropods. Possibly, these prey creatures are more abundant in some places than others, leading to differences in toxicity between frogs that inhabit different areas.

NWO-Rubicon

The Rubicon program of the Netherlands Organisation for Scientific Research (NWO) provides young researchers the opportunity to conduct postdoctoral research abroad. Martine Maan used this grant to work with Molly Cummings at the University of Texas at Austin. Currently, Martine Maan is based at the University of Groningen in the Netherlands.

More information:

-  Martine Maan; tel.  (+31) (0)50 363 2196; m.e.maan rug.nl
- The paper “Poison frog colors are honest signals of toxicity, particularly for bird predators” by Martine Maan & Molly Cummings appeared in Januar 2012 as an open-access article in The American Naturalist.

-  The American Society of Naturalists has published a version for laymen of the article.