Light Sensors in Cephalopod Skin

Squid, cuttlefish, and octopuses possess vision machinery in their skin.

By | May 21, 2015

FLICKR, JERRY KIRKHARTTwo studies—one on squid and cuttlefish, another on octopuses—published in the Journal of Experimental Biology last week (May 15) demonstrate that the skin of color-changing cephalopods harbors molecules used in vision, perhaps explaining how the organ detects light.

In the case of the squid and cuttlefish, researchers from University of Maryland Baltimore County and the Marine Biological Laboratory in Woods Hole, Massachusetts, found that the animals’ chromatophores—the cells that stretch out to expose their colorful pigment or pinch in to hide it—express opsins. And in the study on the octopus, scientists at the University of California, Santa Barbara, observed that illuminating a patch of skin caused the chromatophores to expand. In octopuses, however, it was the cilia that contained opsins.

“[O]ur data suggest that a common molecular mechanism for light detection in eyes may have been co-opted for light sensing in octopus skin and then used for LACE [light-activated chromatophore expansion],” M. Desmond Ramirez and Todd Oakley of UC Santa Barbara wrote in their report on octopuses.

While both studies identified vision machinery in the skin, they did not show that the animals “see” using it.

“All the machinery is there for them to be light-sensitive but we can’t prove that. It’s been very frustrating,” Tom Cronin, a vision researcher at the University of Maryland who was part of the squid and cuttlefish study, told National Geographic’s Not Exactly Rocket Science. “We don’t know if they contribute to camouflage or are just general light sensors for circadian cycling or are driving hormonal changes. They have a job to do but we don’t know what it is.”

 

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Avatar of: JonRichfield

JonRichfield

Posts: 135

May 22, 2015

Hmmm...

I don't know whether this is relevant, but for what it is worth, the Southern African dwarf chameleons (Bradypodion species, and in particular B. pumilum, the species that I have the most experience of), turn pale in the dark.

Now, one might assume that this is mediated through visual stimuli, but a chameleon basking with the sun shining on one flank will be dark on that side and pale on the shady side. OK, still maybe cerebral control...?

BUT, if the lizard has been sitting still in the sun for many minutes with one leg against its flank, and it then begins to walk, it reveals that the skin that had been shaded is conspiculously pale, like the flank on the shaded side. Obviously there is some sort of direct photic stimulation that is not cerebrally mediated.

What we now need is for some intrepid experimenter to expose the shaded side to a high intensity light spot for several minutes to see whether the skin develops a dark spot.

And to try different colours of light.

Hmmm...

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