Tag Archives: chromatophores

Nerve endings, iridescence, and camouflage amongst the squid

Iridescence is a magical thing as far as I’m concerned. I know the scientists at the Marine Biology Laboratory (MBL) in Woods Hole, Massachusetts have mundane reasons for studying the iridescence in squid but I detect a hint of the fascination in the description of their work in the Aug. 27, 2012 news item on ScienceDaily,

Squid skin is extraordinary because it has two ways to produce color and pattern. Pigmented organs called chromatophores create patterns with yellow, red, and brown colors. Underneath the pigments, iridophores, aggregations of iridescent cells in the skin, reflect light and add blue, green, and pink colors to the overall appearance of the skin. Collectively these two groups of skin elements can create spectacular optical illusions with patterns of color, brightness, and contrast change.

“For 20 years we have been wondering how the dynamically changeable iridescence is controlled by the squid,” says study co-author Roger Hanlon. “At long last we have clean evidence that there are dedicated nerve fibers that turn on and tune the color and brightness of iridophores. It is not an exaggeration to call this “electric skin.” The complex nerve network distributed throughout the squid’s skin instantly coordinates tens of thousands of chromatophores with iridescent reflectors for rapidly changing behaviors ranging from camouflage to signaling.”

The Aug. 24, 2012 MBL news release, which originated the news item, provides details about the study,

Working with longfin inshore squid (Doryteuthis pealeii), the researchers took a new approach to investigating the mystery behind the iridophore control mechanism.  By tracing a highly branched network of nerves and stimulating them electrically, they found that they could activate progressive color shifts from red and orange to yellow, green, and blue in just 15 seconds. The findings suggest that the specific color of each iridophore, as well as speed of change, is controlled by the nervous system, as is spatial chromatophore patterning that occurs in the skin layer just above.

The scientists have provided some images to illustrate the process,

Nerves in red can be easily traced among the distinctive chromatophores and iridophores that they innervate. (Credit: Wardill, Gonzalez-Bellido, Crook & Hanlon, Proceedings of the Royal Society B: Biological Sciences)

Neurally stimulated squid iridophore. (Credit: Wardill, Gonzalez-Bellido, Crook & Hanlon, Proceedings of the Royal Society B: Biological Sciences)

They’ve also created a brief, silent video showing the process of becoming iridescent in action,

What I found particularly interesting about iridescence and colour  in squid was this (from the Aug. 24, news release),

How squid choose and hold particular skin colors to help camouflage themselves remains unknown and is particularly interesting because the animals are completely colorblind.

For anyone interested in reading the study, here’s the citation from the ScienceDaily news item,

T. J. Wardill, P. T. Gonzalez-Bellido, R. J. Crook, R. T. Hanlon. Neural control of tuneable skin iridescence in squid. Proceedings of the Royal Society B: Biological Sciences, 2012; DOI: 10.1098/rspb.2012.1374

The article is behind a paywall.

ETA Aug. 28, 2012 1:15 pm PDT: I forgot to mention the ‘camouflage’ part of the headline in the context of this story. The ability to change colour in response to stimulae of one sort of another is often for the purpose of camouflage/concealment, a matter of some interest to the military. In this case (from the Aug. 24, 2012 news release),

The work was funded by grants from the Office of Naval Research (ONR), Defense Advanced Research Projects Agency (DARPA), and Air Force Office of Scientific Research.

I last wrote about squid and camouflage in my Aug. 17, 2012 posting on soft robots.

Camouflage for everyone

The Institute of Physics (IOP) journal, Bioinspiration and BIomimetics, has published an open access article on camouflage inspired by zebrafish and squid. From the IOP’s May 2, 2012 news release

Researchers from the University of Bristol have created artificial muscles that can be transformed at the flick of a switch to mimic the remarkable camouflaging abilities of organisms such as squid and zebrafish.

They demonstrate two individual transforming mechanisms that they believe could be used in ‘smart clothing’ to trigger camouflaging tricks similar to those seen in nature.

The soft, stretchy, artificial muscles are based on specialist cells called chromatophores that are found in amphibians, fish, reptiles and cephalopods, and contain pigments of colours that are responsible for the animals’ remarkable colour-changing effects.

Here’s the video mentioned in the IOP’s May 2, 2012 news release,

The lead author Jonathan Rossiter provides a description of the work (which may help you better understand what you’re seeing on the video), from the May 2, 2012 news item,

Two types of artificial chromatophores were created in the study: the first based on a mechanism adopted by a squid and the second based on a rather different mechanism adopted by zebrafish.

A typical colour-changing cell in a squid has a central sac containing granules of pigment. The sac is surrounded by a series of muscles and when the cell is ready to change colour, the brain sends a signal to the muscles and they contract. The contracting muscles make the central sacs expand, generating the optical effect which makes the squid look like it is changing colour.

The fast expansion of these muscles was mimicked using dielectric elastomers (DEs) – smart materials, usually made of a polymer, which are connected to an electric circuit and expand when a voltage is applied. They return to their original shape when they are short circuited.

In contrast, the cells in the zebrafish contain a small reservoir of black pigmented fluid that, when activated, travels to the skin surface and spreads out, much like the spilling of black ink. The natural dark spots on the surface of the zebrafish therefore appear to get bigger and the desired optical effect is achieved. The changes are usually driven by hormones.

The zebrafish cells were mimicked using two glass microscope slides sandwiching a silicone layer. Two pumps, made from flexible DEs, were positioned on both sides of the slide and were connected to the central system with silicone tubes; one pumping opaque white spirit, the other a mixture of black ink and water.

“Our artificial chromatophores are both scalable and adaptable and can be made into an artificial compliant skin which can stretch and deform, yet still operate effectively. This means they can be used in many environments where conventional ‘hard’ technologies would be dangerous, for example at the physical interface with humans, such as smart clothing,” continued Rossiter.

I wonder what these smart clothes/smart skin would feel like against your personal skin given that we are talking about ‘artificial muscles’. For example, how much movement would your clothing/smart skin have independent of you?

By independent, I mean that everything occurs externally. While we’re not ordinarily conscious of all our physical responses they are stimulated internally and part of a whole body response (even though we may notice only localized responses, e.g., a rash). In the research, there’s an external stimulus and an external response via smart clothes/smart skin.

This is just speculation as I imagine we’re several years away from any field testing of these smart clothes/smart skin, assuming that scientists are able to address all the technical hurdles between a laboratory breakthrough and developing applications.

Thanks to Nanowerk where I first came across this information (May 2, 2012 news item).