The optical powers of octopus skin, revealed


A recent discovery by a team of biologists from the University of California at Santa Barbara (UCSB) has made the octopus species even cooler than it was before.

Many types of octopi can change the color of their skin, radically altering their appearance. They camouflage quite well, perfectly mimicking grey rocks and rainbow corals in order to nab their prey.

Their skin is like an LCD screen, dynamically shifting the pigments in their skin cells, akin to pixels, to create a wide range of colors.

The envy of stealth cloaking researchers and inspiration for sci-fi writers, this form of camouflage is the closest the animal world comes to invisibility on a macroscopic scale.

Now, thanks to the work of evolutionary biologists Desmond Ramirez and Todd Oakle of UCSB, we have found that the octopi don’t even need eyes to camouflage effectively.

It turns out that their skin naturally reacts to light so as to mimic it.

Though this has been suspected for a while, Ramirez and Oakle are the first to prove it.

They took skin grafts from bimac octopi and grew live cultures from them, then exposed the cultures to light. Using pulsing LEDs, the researchers observed the skin in a petri dish and realized that it changed color despite having no neural connections.

Octopi change their skin color through specialized color-changing cells in their skin, called chromataphores. These cells contain lots of pigment of a certain color, which gives them the appearance of that color.

When the octopus wants to change color, the cell contracts, forcing the pigment to the center, and changing the visibility of the color.

Each cell has a ring of tiny muscles that contract or release according to the needs of the octopus. Chromataphores are present in almost every cold-blooded animal, but only some are able to expand and contract the chromataphores to achieve color change.

The reason that octopus chromataphores change in response to light, without even needing eyes, is thanks to light-sensitive proteins called opsins.

Opsins are found in eyes, and are also pigmented. The important part is that opsins react to light through direct chemical reactions, without needing nerves at all.

Opsins have been thoroughly researched before, since they are found in the eyes of every animal. Even ragworms, known also as ‘living fossils,’ have opsins at the head of their body. It is these opsins that allow octopi skin cells to react so dynamically to changes in background light, even without a connection to the nervous or optical organs.

Interestingly, the chromataphores also react in response to touch as well.

When a light force is applied, the chromataphores contract, indicating that the cells are also sensitive to touch.

This could prove to be a ground-breaking insight into opsins, which were previously thought to be solely light-sensitive.

If the researchers find that the octopus cells are truly sensitive to touch, then it could pave the way for investigation into whether opsins are really mechanical detectors in addition to light detectors.

Researchers are also testing whether the opsins in the skin of an octopus are similar or identical to the opsins of other organisms, or whether they evolved independently.

In order to test both of these ideas, Ramirez and Oakle are planning another series of experiments.

These experiments are designed to test what the opsins themselves react to, so as to determine what behaviors they are part of.



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