A study led by Leila Deravi of Harvard University has provided new details on the adaptive camouflage of a peculiar marine animal called cuttlefish.
The Common cuttlefish, Sepia officinalis. Image credit: © Tennessee Aquarium.
The common cuttlefish (Sepia officinalis), or European common cuttlefish, is a cephalopod native to the Mediterranean Sea, North Sea, and Baltic Sea. It grows up to 0.5 m in length and 4 kg in weight.
This marine creature can rapidly alter both the color and pattern of its skin, helping it blend in with its surroundings and avoid predators. It uses pigmented, neurally controlled chromatophore organs to change its appearance in response to visual clues.
To regulate its color, the cuttlefish relies on a vertically arranged assembly of three optical components: the leucophore – a near-perfect light scatterer that reflects light uniformly over the entire visible spectrum, the iridophore – a reflector comprising a stack of thin films, and the chromatophore.
This layering enables the skin of the animal to selectively absorb or reflect light of different colors.
“Chromatophores were previously considered to be pigmentary organs that acted simply as selective color filters. But our results suggest that they play a more complex role; they contain luminescent protein nanostructures that enable the cuttlefish to make quick and elaborate changes in its skin pigmentation,” said Ms Deravi, who is the first author of a paper published in the journal Interface.
When the cuttlefish actuates its coloration system, each chromatophore expands; the surface area can change as much as 500 percent.
Ms Deravi with colleagues showed that within the chromatophore, tethered pigment granules regulate light through absorbance, reflection, and fluorescence, in effect functioning as nanoscale photonic elements, even as the chromatophore changes in size.
“The cuttlefish uses an ingenious approach to materials composition and structure, one that we have never employed in our engineered displays,” said co-author Prof Evelyn Hu from Harvard University.
“It is extremely challenging for us to replicate the mechanisms that the cuttlefish uses.”
“For example, we cannot yet engineer materials that have the elasticity to expand 500 times in surface area. And were we able to do so, the richness of color of the expanded and unexpanded material would be dramatically different – think of stretching and shrinking a balloon. The cuttlefish may have found a way to compensate for this change in richness of color by being an ‘active’ light emitter, not simply modulating light through passive reflection.”
The biologists believe their findings could have applications in materials for paints, cosmetics, military camouflage and consumer electronics.
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Leila F. Deravi et al. 2014. The structure–function relationships of a natural nanoscale photonic device in cuttlefish chromatophores. J. R. Soc. Interface, vol. 11, no. 93; doi: 10.1098/rsif.2013.094
