Monday, May 20, 2013

Nano scale structure contributes to Gaboon viper camouflage

Bitis rhinoceros, West African Gaboon viper (a) The snake partly on white
background and (b) partly on leafy substrate similar to the natural habitat.
The West African Gaboon viper is a highly effective ambush predator that becomes invisible in leaf litter due to the empty black patches of its skin that are virtually indistinguishable from shadows on the forest floor. In a new paper Spinner and colleagues (2013) examine the micro-ornamentation from shed skins from two Gaboon vipers, Bitis rhinoceros, and find its excellent camouflage is due not only to its overall coloration and pattern but to the microstructure of the scales. The viper's skin is geometrically patterned and features velvet black spots that have an exceptional spatial depth due to their velvety surface texture. The authors found a unique hierarchical pattern of leaf-like microstructures striated with nanoridges on the snake scales that coincides with the distribution of the black coloration. Velvet black areas have four times less reflectance and higher absorbance than other scales in the ultraviolet to near infra-red spectral range.

The authors suggest that the microornamentation in velvet black regions of the Gaboon viper skin is unique in snakes. Leaf-like microstructures with both nanoridges and hair-like nanoprotuberances that coincide with black skin coloration have not been previously described. Other members of the genus Bitis have less complex dorsal patterns of lower micro-scaled elevation with pits, a structure similar to that of the pale regions of Gaboon viper skin. When the research team coated the scales from the pale regions of skin with gold-palladium they took on a metallic appearance. But when the scales over the black patches were coated the color contrast remained because coated black areas remain black. Thus, the surface structures of the black scales was responsible for the velvet black appearance.

The entire article can be found on-line.

Spinner, Kovalev, Gorb & Westhoff. 2013. Snake velvet black: Hierarchical micro and nanostructure enhances dark colouration in Bitis rhinoceros. Scientific Reports. http://dx.doi.org/10.1038/srep01846

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