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Sci-Tech

Skin that can see is octopus camouflage superpower

A protein in octopus skin is similar to a light-detecting protein found in the eye, enabling the cephalopods' amazing camouflage skills.

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A baby California two-spot octopus. The speckles are its chromatophores. UCSB

Octopuses have some amazing tricks up their sleeves, which is understandable with eight arms and everything. The most amazing of those tricks is its ability to camouflage itself (and there are some videos of that down at the bottom because it's awesome).

We know that the change in the colour of the octopus' skin is affected by chromatophores, light-reflecting and pigment-containing cells that undergo a process called metachrosis. This is when the reflective plates are shifted and the pigment relocated, controlled by complex organs, which causes a colour shift based on what the octopus sees around it with its powerful eyes.

But, as it turns out, the octopus doesn't just use its eyes and brain to process visual information -- it can sense light through just its skin.

Researchers at the University of California, Santa Barbara, have discovered that the California two-spot octopus is able to sense light directly through its skin, without any input from its central nervous system. This is because a family of proteins called opsins can be found in the octopus' skin, discovered by the UCSB team.

Opsins are light-sensitive receptor proteins usually found in the photoreceptor cells of the retina.

"Octopus skin doesn't sense light in the same amount of detail as the animal does when it uses its eyes and brain," said study lead author Desmond Ramirez, a doctoral student in the Department of Ecology, Evolution and Marine Biology. "But it can sense an increase or change in light. Its skin is not detecting contrast and edge but rather brightness."

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Contracted chromatophores (left) and fully expanded (right). UCSB

Ramirez observed the results of the octopus' "seeing skin" by shining a bright white light directly onto the tissue. This caused the chromatophores to expand and change colour, without any input from the eyes or brain. When the light was turned off, the chromatophores relaxed. Ramirez then tried a variety of different light wavelengths from violet to orange. Blue light produced the quickest chromatophore response.

This process, which suggests that the skin's light sensors are connected to the chromatophores, has been dubbed Light-Activated Chromatophore Expansion, or LACE.

"It looks like the existing cellular mechanism for light detection in octopus eyes, which has been around for quite some time, has been co-opted for light sensing in the animal's skin and used for LACE," explained study co-author and EEMB professor Todd Oakley. "So instead of completely inventing new things, LACE puts parts together in new ways and combinations."

Further molecular experiments determined that rhodopsin could be found in the sensory neurons on the surface of the skin tissue. The new discovery helps further understanding of the complex mechanisms involved in octopus camouflage and could prove useful in developing bioinspired technologies.

The next step in the research is to determine whether the protein can be found in the skin of other cephalopods, such as squids and, if so, how octopuses and squids are related.

"Do they all come from the same ancestral source or did they evolve multiple times?" Ramirez said. "What kind of behaviours do the different groups share and what kind of behaviours does the skin sensing light underlie?"

And now for the promised incredible octopus camouflage videos.