Scientists Also Discovered How Squid Camouflage in Shimmery Shallows Was Exquisitely Optimized.

 

(Maia Valenzuela/Flickr/CC BY 2.0)


Inshore squid (Doryteuthis opalescens) are among the most evolved shapeshifters on the world. These fascinating cephalopods have a distinctive skin that can be precisely calibrated to a rainbow of colors.

The extraordinary camouflage and communication abilities of this squid have long captivated scientists. New research has taken us closer to understanding how they manage to dress in such an eclectic manner that helps them to hunt near the shore, sneak past predators unnoticed, and even elude hostile suitors by flashing a pair of fake testes.

According to previous research, the opalescent squid's skin contains a complex molecular machine: a thin film of stacked cells that can expand and contract like an accordion to reflect the entire visible spectrum of light, from red and orange to yellow and green, blue and violet.

According to the researchers, these tiny grooves are similar to those found on a compact disk, reflecting a rainbow of colors as you tilt it under the light. This skin, like a CD, needs something to amplify up the colorful noise.

When scientists tried to genetically manipulate the skin of this squid, they found something wasn't quite right.

Reflectin proteins, which respond to different neural signals and regulate reflective pigment cells, are the ‘motor' that tunes the grooves within the squid's skin.

Synthetic materials containing reflectin proteins have an iridescent appearance similar to that of squid, but they do not flicker or shimmer like squid.

Something was obviously missing, and new research involving living squid and genetic engineering has shed light on the mystery. Reflectin proteins, it turns out, can only shine brilliantly when wrapped in a reflective membrane envelope.

The accordion-like mechanism is enclosed by this envelope, and peering under it, you can see how it functions.

Reflectin proteins are normally repellent to one another, but a neuronal signal from the squid's brain may turn off their positive charge, causing them to clump together.

As this occurs, the overlying membrane pushes water out of the cell, causing the grooves to shrink in thickness and spacing, splitting light into different colors.

The concentration of reflectin increases as the grooves collapse, allowing the light to reflect even brighter.

This intricate mechanism "dynamically [tunes] the color while simultaneously increasing the intensity of the reflected light," according to the writers, and this is what causes the opalescent squid to shimmer and flicker, sometimes with color and sometimes without.

The same molecular mechanism appears to drive cells inside the squid's skin that display only white light. In reality, the authors assume that this is how the squid can mimic the sun's glinting or dappled light on the waves.

 

According to biochemist Daniel Morse of the University of California, Santa Barbara, evolution has so exquisitely programmed not only color tuning, but brightness tuning using the same stuff, the same protein, and the same mechanism.

Engineers have been attempting to replicate the opalescent squid's extraordinary skin for years but have never succeeded. The new study, which was funded by the US Army Research Office, has assisted us in determining where we went wrong.

The authors conclude that thin films of reflectin alone cannot deliver the full power of light control seen in squid because we lack the coupled amplifier.

There is no improvement in the brightness of these artificial thin-films without the membrane covering the reflectins, according to Morse.

If we want to harness the biological's strength, we'll need to have a membrane-like enclosure that allows for reversible brightness adjustment.


Originally Published In Applied Physics Letter

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