Strawberry poison frogs from neighbouring islands in the Bocas del Toro Archipelago in Panama, Central America, look strikingly different. Some are vivid blue, some blinding yellow, others lurid green or orange, even though they are all the same species.
Females were thought to rely on males’ courtship calls, which are identical from island to island, to find mates. Now, research by Kyle Summers from East Carolina University and colleagues has provided the first evidence that the frogs use colour to choose between males, helping to explain how the species has split into groups that sound the same but look so different.
The team allowed green frogs from Pope Island and orange frogs from Nancy Key to meet in carefully designed glass tanks. Females had a choice between two potential mates, one green and one orange. The glass prevented physical contact, and tape recordings of the same courtship call were played behind both frogs.
To find out if the females were making their decision based on colour, half the experiments were carried out under normal light, and half under pure blue light. In the same way that orange street lights can alter the colour of cars, the blue light made the green and orange frogs appear identical.
When no colour difference was visible, the females chose their mate seemingly at random. Under normal light, when the only difference was colour, the females chose mates that were the same colour as themselves.
(Proceedings of the Royal Society vol. 266, p2141-5)