Why Octopuses and squids can change color?

The common squid
(Doryteuthis opalescens).

Colors in living organisms can be formed in two ways, namely pigmentation or anatomical structure. Structural colors arise from the physical light interaction with biological nanostructures. Many organisms have the ability, but the mechanisms underlying these processes are still poorly understood until now.

Two years ago, a group of researchers from the University of California, Santa Barbara, discovered the mechanism neuro transmitter on the common squid (Doryteuthis opalescens) that could dramatically change color. Accumulation of the neurotransmitter acetylcholine will add phosphate groups to proteins reflectin family. The process of making proteins condense and drive change in the color of the animal.

Scientists dig deeper, to uncover the mechanisms that responsible for the color change on the squid and octopus. The findings are published in the journal Proceedings of the National Academy of Science, on December 31, 2012.

This shows the diffusion of the neurotransmitter applied to squid skin at upper right, which induces a wave of iridescence traveling to the lower left and progressing from red to blue. Each object in the image is a living cell, 10 microns long; the dark object in the center of each cell is the cell nucleus. (Picture from: http://www.nanowerk.com/)

Structural color is very dependent on the density and shape of the material, not on their chemical nature. UCSB research team showed that specific cells in the skin iridocyte squid has the folds of the cell membrane that goes deep into the body's cells. Folds it creates a layer that operates like a Bragg reflector.

Iridocyte membranes consist of lots of tightly packed parallel folds, creating numerous extracellular channels between lamellae containing reflectin proteins (1). The neurotransmitter ACh activates a cascade of signals in the cell that results in reflectin condensation, making the membrane reflective and iridescent (2). Ions released by the condensation of reflectins cross the membrane into the extracellular space, which in turn drives the expulsion of water from lamellae (3). This shrinks the lamellae, changing the thickness of and spacing between the membrane’s deep grooves to reflect light in a variable way that produces colors (4). (Picture from: http://www.the-scientist.com/)

"We know how cephalopod to use the rainbow spectrum for the camouflage colors, so that they can control the transparency, even to the surrounding environment," said Daniel E. Morse, biotechnology expert and Director of Marine Biotechnology Center / Marine Science Institute at UCSB as quoted by ScienceDaily, on July 26, 2013.

Octopus and squid also use that ability to create confusing patterns that interfere with the ability of visual predators. "Control of colors also help coordinate interactions, especially during mating, because they are constantly changing appearance," he said. "Some kind of squid for example, can change to bright red, which means 'stay away', until striped like a zebra, a meaningful invitation to mate." *** [EKA | FROM VARIOUS SOURCES | THE SCIENTIST | SCIENCEDAILY | TJANDRA DEWI | KORAN TEMPO 4302]

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