April 2, 2009--Many animals are colorful to demonstrate fitness and health to one another—the robin's red breast is a sterling example. But pigment, like everything else in the body, comes at an energy cost.

For animals that live in the dark, such an expense is unnecessary, so most are pale and colorless. Yet caecilians, amphibians with earthworm-like bodies that spend most of their lives underground, are bafflingly colorful.

Combining information about caecilian behavior and evolutionary history, researchers Katharina Wollenberg at the Technical University of Braunschweig in Germany and John Measey at the South African National Biodiversity Institute suggest that just a little bit of light exposure was all it took for color to evolve in these animals.

Above, the caecilian Boulengerula boulengeri, found in the cloud forests of Tanzania, is blue—and blind. Since its bright colors are not demonstrating fitness to blind kin, researchers think color might have evolved when its distant ancestors spent time on the surface.

The research will appear in an upcoming issue of the Journal of Evolutionary Biology.

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