Microstructure-mediated optical effects in southern African snakes

Optical effects are found to enhance the appearance of various botanical structures, insects, birds, and snakes. These effects are often due to structural colours which result from the manipulation of incident light by... [ view full abstract ]

Optical effects are found to enhance the appearance of various botanical structures, insects, birds, and snakes. These effects are often due to structural colours which result from the manipulation of incident light by micro-structures present on the surface.

The optical effects which result from microstructures on the snake epidermis may offer the animal ecological and physiological benefits. For example, Spinner et al. (2013) showed that Bitis rhinoceros (West African Gaboon Adder) has micro-structures with complex nanoscopic detail on dark scales that produces structural velvet blackness. As a result, black regions have a lower reflectance than pale regions when controlled for pigmentary effects.

Using electron microscopy, we examined two southern African species for microstructure-mediated optical effects. In Bitis arietans (Puff Adder) we found significant differences (U = 184.00; p <0.0001) in the height of microstructures between black (40 μm) and pale (17 μm) scale regions, but no differences (t8,0.8 = 0.26; p = 0.80) in the density of microstructures on each region. These results show that the colour of B. arietans scales is primarily a product of optical effects which result from the height of micro-structures. The optical effects likely improve the camouflage of B. arietans on which it relies extensively as an ambush forager.

Hemachatus haemachatus (Rinkhals) bears hierarchically arranged microscopic ridges across its scales in three distinct orders (figure 1): primary (30 um), secondary (5 um), and tertiary (0.4 um). The orders span both the visible and infra-red spectra of the electromagnetic range and may explain the species ability to thermoregulate successfully in even cold climates with a thermal uptake at almost 1 degree Celsius per minute during basking.

This is the first study to report microstructure-mediated optical effects in southern African snakes. Micro-optics may have far-reaching biological significance with respect to animal ecology and physiology. Further, the natural designs of such surfaces provide inspiration for man-made designs in bio-mechanics, hydrophobicity, camouflage, and thermal uptake.