World's only iridescent mammal is a shiny accident

Animals from butterflies to birds have iridescent colours to draw the eye. But why golden moles? They spend most of their lives in near-darkness - and they're blind.

Now a study of the structure of the hairs shows that they may be designed to streamline the moles or repel water, rather than attract a mate.

Matthew Shawkey of the University of Akron in Ohio took samples from four golden mole species, all with blue or green iridescence. Electron microscopes revealed that the hairs were flattened into paddle shapes, giving a greater surface area to reflect light.

Unusually, the scales on each hair contained alternating light and dark layers. Each layer bent the rays of light just like oil on water (Biology Letters, DOI: 10.1098/rsbl.2011.1168). Shawkey says this is the first example of a multilayer reflector in hair.

The iridescence is an evolutionary accident, he believes. The hairs' structure may make them more sturdy, repel water, or streamline the moles so they can move quickly through dirt and sand. "Penguin feathers are flattened like this," he points out.

Most iridescent animals probably evolved it for communication, but golden moles are a rare exception, says St?phanie Doucet of the University of Windsor in Ontario, Canada. Some burrowing snakes and beetles are also iridescent, probably for similar reasons, she adds.

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