Understanding Squid Camouflage

No other animal can match the speed and range of coloration found in squid camouflage. (Photo credit: Jeff Rotman / Alamy)

Given their soft bodies, squids cant rely on a hard shell to protect them from predators. Instead, these cephalopods use a sophisticated system of camouflage to help keep them safe from detection.

Though researchers have long-recognized this unique ability, they were not sure exactly how a squid managed to control its rainbow-like coloration until now. Researchers at the Marine Biology Laboratory in Woods Hole, Massachusetts recently discovered that nerves embedded in the squids skin control the animals coloration and speed of change from one color to another. According to a press release about the findings, [this] work marks the first time neural control of iridescence in an invertebrate species has been demonstrated.

Embedded in a squids skin are pigmented organs and iridescent cells. The pigmented organs are called chromatophores, which make patterns from brown, red, and yellow colors. The squid is able to contract or expand these organs on command, which creates varying patterns on its skin.

Beneath the layer of chromatophores are groups of iridescent cells called iridiphores. These cell groups reflect light and add shades of blue, green, and pink to the skin. As with chromatophores, a squid is able to control the actions of its iridiphores. The chromatophores and iridiphores work together to create patterns on the squids skin that can rapidly change in color, contrast, and brightness.

For 20 years we have been wondering how the dynamically changeable iridescence is controlled by the squid, researcher Roger Hanlon said in a press release about the study’s results. At long last we have clean evidence that there are dedicated nerve fibers that turn on and tune the color and brightness of iridiphores. It is not an exaggeration to call it electric skin. The complex nerve network distributed throughout the squids skin instantly coordinates tens of thousands of chromatophores with iridescent reflectors for rapidly changing behaviors ranging from camouflage to signaling.

In addition, unlike its predators, squids can see polarized light. The same structures that produce iridescent colors in the squids skin also polarize light. Because the polarized light does not affect the squids camouflage, the animals can use it to communicate with one another and remain undetected.

The scientists focused their study on the longfin inshore squid, Doryteuthis pealeii. To understand how a squid controls the iridiphore mechanism, they traced a highly-branched network of nerves and stimulated the nerves with electricity. The scientists found that they could activate color shifts in the squids skin from red and orange to yellow, green, and blue over a time period of just 15 seconds. These results indicate that the nervous system controls each iridiphores color and the speed of change from one color to another. Scientists have yet to determine how a squid chooses a certain color which is a particularly interesting aspect of its camouflage, as squid themselves are colorblind.

The scientists hypothesize that it is not the exact colors that are important to the squid, but instead the relative brightness and darkness of its coloration that is significant.

More to Explore
Camouflaged communication the secret signals of squid
MLB Scientists Discover Nerves Control Iridescence in Squid’s Remarkable ‘Electric Skin’
Squid’s Remarkable “Electric Skin” (video)
NOAA FishWatch: Longfin Squid
NOAA:Longfin Inshore Squid, Loligo pealeii, Life History and Habitat Characteristics

What Do You Think?