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Opalescent Coastal Squid (Doryteuthis opalescens) are among the most sophisticated shapeshifters on the planet. These curious cephalopods are wrapped in a special skin that can be precisely adjusted to a kaleidoscope of color.
Scientists have long been fascinated by this squid’s remarkable camouflage and communication. New research has brought us even closer to how they can shed such an eclectic wardrobe that allows them to hunt near the brightness of the shore, sneak past unseen predators, or even escape from aggressive contenders by showing a pair of false testicles.
Previous studies have shown that the opalescent squid has a complex molecular machine in its skin: a thin film of stacked cells capable of expanding and contracting like an accordion to reflect the entire visible spectrum of light, from red and orange to yellow and green, passing through blue and purple.
These tiny grooves are much like what you see on a compact disc, researchers say, reflecting a rainbow of colors when you tilt it under the light. But just like a CD, this skin also needs something to amplify its colorful noise.
When the researchers tried to genetically modify the skin of this squid, they noticed that something was wrong.
The “motor” that regulates the grooves in the skin of the squid is driven by reflectin proteins, which respond to different neural signals and control the reflective pigment cells.
Synthetic materials containing reflectin proteins showed an iridescent appearance similar to what we see in squid, but these materials could not sparkle or sparkle in the same way.
Something was clearly missing, and recent studies of live squid and genetic engineering have shed light on the mystery. It turns out that reflectin proteins can only glow if they are enclosed in a reflective membrane envelope.
This envelope is what encloses the accordion structure, and by looking below you can begin to see how it works.
Reflectin proteins are usually repelled by each other, but a neural signal from the squid’s brain can turn off this positive charge, allowing the proteins to clump together tightly.
When this happens, it triggers the overlying membrane to push water out of the cell, reducing the thickness and spacing of the grooves, which divide the light into different colors.
This sagging between the grooves also increases the reflectin concentration, which allows the light to reflect even brighter.
Thus, explain the authors, this complex process “dynamically [tunes] color while simultaneously increasing the intensity of the reflected light ”, and this is what allows the opalescent squid to sparkle and sparkle, sometimes with color and sometimes not.
Squid skin cells, which reflect only white light, also appear to be driven by this same molecular mechanism. In fact, the authors believe this is what allows the squid to mimic the glittering or speckled light of the sun on waves.
“Evolution has optimized not only the color adjustment, but also the brightness adjustment so well using the same material, the same protein and the same mechanism,” says biochemist Daniel Morse of the University of California at Santa. Barbara.
Engineers have tried for years to mimic the remarkable skin of the opalescent squid, but never quite succeeded. The new research, which was supported by the United States Army Research Bureau, helped us understand where we were going wrong.
On their own, the thin reflectin films cannot provide all of the light-controlling power we see in squid, the authors conclude, because it appears that we are lacking this coupled amplifier.
“Without this membrane surrounding the reflectins, there is no change in the brightness of these artificial thin layers,” explains Morse.
“If we are to capture the power of the biological, we have to include some kind of membrane-shaped enclosure to allow reversible adjustment of the brightness.”
The study was published in Letters of Applied Physics.
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