Adaptive Camouflage Helps Blend Into the Environment

Biological Strategy

Cuttlefish

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Image: Photo by Francis Nie on Unsplash / CC BY - Creative Commons Attribution alone

Send Light Signals in the Visible Spectrum

The visible spectrum is the portion of the electromagnetic spectrum that the human eye can detect. Visible light can be thought of in two ways–light as illumination (such as that used by fireflies) and colors that result from light being absorbed or reflected. Living systems use light for a variety of purposes. Sometimes, they use it to make themselves highly visible (like a peacock showing off his brilliant feathers to a potential mate). Other times, they use it to become virtually invisible (like an owl hiding in plain sight when it rests during the day). When a living system sends a light signal, it must create that light or color in an energy- and material-efficient way. Living systems create and enhance color using such strategies as non-toxic pigments, structures that bend and absorb different wavelengths, and chemical processes that create bioluminescence.

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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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Protect From Animals

Animals–organisms that range from microscopic to larger than a bus–embody a wide variety of harms to living systems, including other animals. They threaten through predation, herbivory, defense, and parasitism, and they compete for resources such as water, nutrients, and space. Any given living organism commonly faces threats from a variety of animals, requiring strategies that effectively defend from each. Trout and other bony fish, for example, escape predators by having scales made of very thin, flake-like pieces of bone covered with slippery mucus. They also have behavioral strategies such as camouflage, fast swimming, and twisting and turning to achieve release from a predator’s grip.

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Cephalopods

Class Cephalopoda (“head-foot”): Nautilus, squid, octopus, cuttlefish

Cephalopods are unique among mollusks, and even within the animal kingdom. They are lauded for their large brains and complex behaviors and are considered the most intelligent invertebrates. Among 800 species in 45 families, all are carnivorous and live in marine ecosystems. They all have a set of arms or tentacles, but only the nautilus retains an exterior chambered shell. Many species have chromatophores, which allow them to change color for defense, camouflage, or courting. They range from the size of a fingernail to just longer than a city bus (the mysterious giant squid).

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The skin of cuttlefish changes color rapidly using elastic pigment sacs called chromatophores, in order to evade predators.

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Introduction

The idea of turning invisible is so intriguing to us humans that every generation invents new superheroes and villains with this ability in the stories we tell. But it’s not really fiction. In the real world, cephalopods such as cuttlefish can use dynamic camouflage to blend in with their surroundings on demand. No matter the background, in a matter of seconds, poof, they’re gone.

The Strategy

Cuttlefish are able to match colors and surface textures of their surrounding environments by adjusting the and iridescence of their skin, which is composed of several layers.

On the skin surface, chromatophores (tiny sacs filled with red, yellow, or brown pigment) absorb light of various wavelengths. Once visual input is processed, the cephalopod sends a signal to a nerve fiber, which is connected to a muscle. That muscle relaxes and contracts to change the size and shape of the chromatophore. Each color chromatophore is controlled by a different nerve, and when the attached muscle contracts, it flattens and stretches the pigment sack outward, expanding the color on the skin. When that muscle relaxes, the chromatophore closes back up, and the color disappears. As many as two hundred of these may fill a patch of skin the size of a pencil eraser, like a shimmering pixel display.

A line drawing shows how muscles pull on chromatophores to enlarge the area of color.

A simplified representation shows how cuttlefish use muscles and chromatophores to control their coloration.

The innermost layer of skin, composed of leucophores, reflects ambient light. These broadband light reflectors give the cephalopods a ‘base coat’ that helps them match the brightness of their surroundings.

Between the colorful chromatophores and the light-scattering leucophores is a reflective layer of skin made up of iridophores. Iridophores use structure to reflect incoming light, to take advantage of other colors provided by the environment. Iridophores selectively reflect light to create pink, yellow, green, blue, or silver coloration.

The combination of these skin layers allows cephalopods like the cuttlefish to blend in quickly with virtually any background.

Diagram showing three layers of cuttlefish skin in cross section

Cuttlefish adjust the pigment and iridescence of their skin using a variety of structures in multiple layers of their skin.

Watch this video from PBS Deep Look to learn more about how cephalopods use adaptive camouflage:

The Potential

Technologies which control how much an object stands out or blends in have many different potential applications. “Smart” crosswalks, for example, could help to make crossing pedestrians more obvious to drivers and self-driving vehicles, and a truly smart phone being sought by its owner could change its color to contrast with the couch cushions it’s tucked between. The chromatophores of cuttlefish also give us the idea of materials that change colors with force or bending. This could be very helpful in everything from visual indicators of car tires getting low on air, to structural elements of bridges deforming and indicating they’re in need of repair.

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Last Updated March 17, 2020

References

“The cuttlefish, octopus, and squid are the undisputed champions of camouflage… They can instantly modulate their color, shading, patchiness, mottling or stippling, transparency, heat, and even bioluminescence, light-polarity, or iridescence…” (Woolley-Barker 2012: 12)

Magazine article

Learning from the Master Shape-Shifter: Cephalopod Technologies

Zygote Quarterly | Tamsin Woolley-Barker

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Reference

Book

The Design in Nature

17/01/2002 | Yahya Harun

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Reference

“Cephalopods have such remarkable camouflage primarily because of their chromatophores – sacs of red, yellow or brown pigment in the skin made visible (or invisible) by muscles around their circumference. These muscles are under the direct control of neurons in the motor centres of the brain, which is why they can blend into the background so quickly. Another aid to camouflage is the changeable texture of cuttlefish skin, which contains papillae – bundles of muscles able to alter the surface of the animal from smooth to spiky. This comes in pretty useful if it needs to hide next to a barnacle-encrusted rock, for instance.

“The final part of the cuttlefish’s camouflage portfolio comes from leucophores and iridophores, essentially reflecting plates that sit underneath the chromatophores. Leucophores reflect light across a wide range of wavelengths so can reflect whatever light is available at the time – white light in shallow waters and blue light at depth, for example. Iridophores combine platelets of a protein called reflectin with layers of cytoplasm to produce iridescent reflections rather like those of butterfly wings. Iridophores in other species, like some fish and reptiles, produce optical interference effects that shift the light towards blue and green wavelengths. Cuttlefish can turn these reflectors on or off in seconds to minutes, controlling the spacing of the platelets to select the colour. They can also combine these iridescent hues with those of the chromatophores to make shimmering purples and oranges, for example.” (Brooks 2008:28)

Journal article

Do you speak cuttlefish?

New Scientist | 26/04/2008 | Michael Brooks

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