Shifting Crystals Change Chameleons’ Color

green, red, blue and brown chameleon on brown tree branch

Biological Strategy

Short-horned chameleon

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Image: Pierre Bamin / Unsplash / Public Domain - No restrictions

Modify Light/Color

Color in living systems comes from pigments and the interaction of light with surfaces. Color serves many purposes for living systems, such as attracting prey or mates, providing warnings, or protecting through camouflage. To create the effects needed for each purpose, living systems must control the expression or visibility of pigments and the interactions (such as reflectance and refraction) of light. To do so, they have strategies that modify color or light to increase or decrease the color’s position, intensity, opacity, and more. Male hummingbirds, for example, have brightly colored feather patches on their throats; the coloring comes from pigments, structures that refract light, or a combination of the two. When a male hummingbird hovers near a potential mate, it modifies the angle of these feathers to create a bright, colorful display. However, when it needs to mute the colors to reduce conspicuousness, such as to avoid a predator, it modifies the angle again.

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Reptiles

Class Reptilia (“creeping”): Lizards, crocodiles, turtles, snakes

Reptiles retain some of the key characteristics that first enabled vertebrates to live permanently on land. They have dry skin covered in scales made of keratin that help prevent water loss. (Amphibians still need to stick close to water to keep their skin moist.) Many reptiles reproduce by laying eggs that are watertight and have a yolk, so eggs can develop on land while staying moist and nourished. Reptiles are also ectotherms, meaning they don’t produce their own body heat. This means they burn through energy much more slowly than “warm blooded” creatures of the same size. It also means that they need to keep warm to keep active, which is why you might see them spending a seemingly inordinate amount of time simply basking in the sun.

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Pigments and nanoscale structures collaborate to help chameleon change its look.

The variety of colors that chameleons can display is produced through a combination of s and structural colors. Chameleon skin contains different types of chromatophore (color-bearing) cells organized in layers within the skin. The upper layer of skin contains cells with yellow and red pigments, while lower layers contain cells with dark melanin pigment, which appears black or brown. Just below the layer of yellow and red chromatophores is a layer of cells called iridophores (iridescent chromatophores) that produce structural color. Rather than containing pigment, iridophores contain an organized array of transparent, nano-sized crystals that reflect specific wavelengths of light. The reflected light is perceived as color.

The latest research on color-changing in chameleons reveals that they primarily change color by actively adjusting the spacing between these nanocrystals, which causes different wavelengths of light to be reflected. The crystal structures and pigments in chameleon skin both contribute to the overall color of the skin. For example, when blue light reflects off the crystal layer and travels through the yellow pigment above, the result humans see is the color green.

Researchers are still investigating the function of changing skin color in chameleons, but more recent research suggests that chameleons change color to communicate with one another during social interactions.

Check out this video by KQED Deep Look to learn more about how chameleons change color, and about how researchers are building synthetic chameleon skin that mimics these lizards’ color-changing mechanism.

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Image: Teyssier et al. 2015, doi:10.1038/ncomms7368 /

Image: Christopher Evans / Flickr /

Image: kuhnmi / Flickr /

Related Innovations

Innovation: Academia

Color-Changing Film Inspired by Chameleon Skin

Sichuan University

Bio-based film from Sichuan University is made of a combination of polymers and cellulose nanocrystals that makes it both color-changing and flexible.

Innovation: Academia

Colorful 3D Printing Inspired by Chameleons

University of Illinois Urbana-Champaign

3D printing process from University of Illinois, Urbana Champaign uses bottlebrush-shaped polymers to produce multiple colors from the same ink.

Last Updated March 1, 2017

References

Book

Historic and contemporary theories on chameleon color change

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Reference

Journal article

The discovery of the mechanism of colour-changes in the chameleon

Annals of Science | 08/06/2006 | A.E. Best

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Reference

Book

Principles of Animal Communication, Second Edition

03/08/2011 | Jack W. Bradbury

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Reference

“Many vertebrates can rapidly change colour for camouflage, communication and thermoregulation²^,⁴^,⁵^,⁶^,⁷, but these so-called physiological colour changes are generally mediated by modifications of skin brightness (that is, diffuse and/or specular reflectivity) through dispersion/aggregation of pigment-containing organelles, especially melanosomes, within dermal chromatophores⁶^,⁷. On the other hand, rapid active tuning of skin hue has been described in only a handful of species and generally involves structural, rather than pigmentary, components, that is, multilayer nano-reflectors with alternating high and low refractive indices that generate interference of light waves…

…chameleons have evolved two superimposed populations of iridophores with different morphologies and functions: the upper multilayer is responsible for rapid structural colour change through active tuning of guanine nanocrystal spacing in a triangular lattice, whereas the deeper population of cells broadly reflects light, especially in the near-infrared range. This combination of two functionally different layers of iridophores constitutes an evolutionary novelty that allows some species of chameleons to combine efficient camouflage and dramatic display, while potentially moderating the thermal consequences of intense solar radiations.” (Teyssier et al. 2015:2)

Journal article

Photonic crystals cause active colour change in chameleons

Nature Communications | 10/03/2015 | Jérémie Teyssier, Suzanne V. Saenko, Dirk van der Marel, Michel C. Milinkovitch

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