The octopus is a master of disguise. It can change its appearance to blend in with its environment or to warn predators to back off. This talent isdue to pigment cells called chromatophores in octopus skin. Muscle contraction expands the chromatophores and helps them change the skin color to match its surroundings.
But first, the creature has to sense those surroundings. Not surprisingly, information about the colors in the environment comes in through the eyes. But new research reveals that, for one octopus species at least, the skin itself can sense light and react, with no input from the eyes or brain.
Researchers from the University of California Santa Barbara worked with skin removed from the California two-spot octopus. Not only did the skin respond to bright light, but the scientists found that the skin possesses the same family of light-sensitive proteins, called opsins, typically found in its eyes—which implies that, in the course of evolutionary history, the same molecular mechanism that the eyes employ for light detection got co-opted for use in the skin. The study is in the Journal of Experimental Biology. [M. Desmond Ramirez and Todd H. Oakley, Eye-independent, light-activated chromatophore expansion (LACE) and expression of phototransduction genes in the skin of Octopus bimaculoides]
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Octopus integument was quickest to respond to blue light—which is the color best suited to travel far in water. Study author Todd Oakley said via email of the skin’s capacity that “we hypothesize the light response has some role” in “communication and camouflage.”
The exact nature of that role remains unclear. But this evidence for light-sensing skin brightens up our understanding of how octopuses so effortlessly go incognito.
—Dina Fine Maron
[The above text is a transcript of this podcast.]
