Opalescent coastal squid (Doryteuthis opalescens) are some of the most advanced shapeshifters on Earth. These curious cephalopods are wrapped in a special skin that can be precisely matched to a kaleidoscope of colors.
Scientists have long been fascinated by this squid’s remarkable camouflage and communication. New research has brought us even closer to figuring out how to set up such an eclectic wardrobe that allows them to hunt near the brightness of the shore, slip unseen by predators, or even evade aggressive suitors through a pair of fake testicles to flash.
Previous studies have shown that the opalescent squid has a complex molecular machine in its skin: a thin film of stacked cells that can expand and contract like an accordion to reflect the full visible spectrum of light, from red and orange to yellow and green to blue. and violet.
These little grooves look a bit like what you see on a compact disc, researchers say, and reflect a rainbow of colors as you tilt it under the light. But just like a CD, this skin also needs something to amplify its colorful noise.
When researchers tried to genetically manipulate the skin of this squid, they noticed that something wasn’t right.
The ‘motor’ that tunes the grooves in the squid’s skin is powered by reflective proteins, which respond to various neural signals and drive reflective pigment cells.
Synthetic materials containing reflectin proteins have displayed an iridescent look similar to what we see in squid, but these materials could not flicker or flicker in the same way.
Something was clearly missing, and recent studies within live squid and genetic engineering have shed light on the mystery. It turns out that reflectin proteins can only shine brightly when enclosed in a reflective membrane shell.
This envelope encloses the accordion-like structure, and if you peek under it, you can begin to see how it works.
Reflectin proteins are usually repelled interchangeably, but a neuronal signal from the squid’s brain can turn off that positive charge, allowing the proteins to clump close together.
When this happens, it triggers the overlying membrane to push water out of the cell, reducing the thickness and spacing of the grooves, splitting the light into different colors.
This collapse between the grooves also increases the concentration of reflectin, which allows the light to reflect even brighter.
Thus, the authors explain, this complex process is “dynamic [tunes] the color while at the same time increasing the intensity of the reflected light “, and this is what makes the opalescent squid sparkle and flicker, sometimes with color and sometimes not.
Cells in the squid’s skin, which reflect only white light, also appear to be driven by the same molecular mechanism. In fact, the authors think this allows the squid to imitate the sun’s glittering or dappled light on waves.
“Evolution has so superbly optimized not only color matching, but brightness matching with the same material, protein and mechanism,” said biochemist Daniel Morse of the University of California, Santa Barbara.
Engineers have been trying to recreate the remarkable skin of the opalescent squid for years, but never quite got there. The new investigation, which was supported by the United States Army Research Office, helped us figure out where we went wrong.
On their own, thin reflective films cannot deliver the full power of light control that we see in squid, the authors conclude, because it seems like we are missing that coupled amplifier.
“Without that membrane surrounding the reflectins, there is no change in the brightness of these artificial thin films,” says Morse.
“If we want to capture the power of the biological, we need to add some sort of membranous envelope to allow reversible brightness tuning.”
The study is published in Applied Physics Letters