Octopus has ‘eyes’ in its skin

Octopuses change the colour of their skin using the same light-sensitive proteins found in their eyes, allowing them to effectively ‘see’ with their skin.

Researchers from the University of California, Santa Barbara (UCSB) studying the Californian two spot, or “bimac,” octopus found that the intelligent molluscs can detect light with their skin using light-sensitive cells called chromatophores, independent of their eyes and brain.

The animals use chromatophores to change the colour of their skin for camouflage, and the cells contain the same family of light-sensitive proteins, opsins, found in human eyes.

“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,” said Professor Todd Oakley, an evolutionary biologist at UCSB.

Professor Oakley’s lab tested how a sample of the octopus skin reacted to a wide spectrum of light, from ultraviolet to orange, and found that the chromatophores responded quickest to blue light. In addition, the light-response is independent of the brain.

Desmond Ramirez, a PhD student at UCSB and lead author on the study, said: “Octopus skin doesn’t sense light in the same amount of detail as the animal does when it uses its eyes and brain, but it can sense an increase or change in light.”

The team is now hoping to find out if other colour-changing molluscs use the same mechanism, and if the mechanism evolved from a shared evolutionary ancestor.

The research is published in the Journal of Experimental Biology.

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