National Geographic

Lizard “Sees” With Its Skin For Automatic Camouflage

When Domenico Fulgione placed Moorish geckos on dark surfaces, he saw what he had seen for years. These spiny, hand-sized lizards changed colour. Within an hour, their typical creamy white complexions transformed into blacker hues that better matched their environment.

And then Fulgione blindfolded the geckos.

They still changed colour. How does an animal adjust its colour to match its environment, when it can’t see that environment at all?

Fulgione’s team found an important clue when they repeated their experiment and bandaged the geckos’ torsos, rather than their heads. This time, their camouflage failed. They could see perfectly well but with their flanks covered, they were less effective at matching their surroundings than their unrestrained or blindfolded peers.

Skin of the same gecko, placed on white (left) and dark (right) surfaces.

Skin of the same gecko, placed on white (left) and dark (right) surfaces.

These bizarre results started to make more sense when the team analysed the gecko’s skin. They found that the skin is rife with opsins—light-sensitive proteins that are the basis of animal vision. When light enters your eyes, opsins in your retinas respond by triggering chemical reactions that send signals to your brain. That’s how you see. The Moorish gecko has plenty of opsins in its eyes too, but the team also found these proteins all over the skin of its torso. It’s especially common in the lizard’s flanks, and in cells called melanophores that are filled with dark pigments.

The researchers think that the flank opsins can respond to surrounding light levels and automatically adjust the gecko’s colour. If they’re right, the lizard has a kind of distributed vision that is independent of its eyes, and perhaps its brain. In other words, it can “see” with its skin.

This isn’t a new concept. Some cells in the skin of fish like tetras and tilapias can change colour independently, thanks to their own opsins. And in 2010, Lydia Mäthger and Roger Hanlon found that cuttlefish also have opsins all over their skin. These relatives of squid and octopuses excel at quickly matching the colour of their skin to their surroundings. And yet, they’re colour-blind. Perhaps cuttlefish are also using opsins in their skin to sense light without having to involve their eyes?

But the presence of opsins means little on its own. In all of these animals, scientists still need to show that the opsins are actually responding to light, that they are sending signals to other parts of the body, and that these signals are causing changes in colour. For the geckos, there’s another mystery: why are most of the opsins on the lizard’s flanks, when it’s the back that changes colour most dramatically?

Reference: Fulgione, Trapanese, Maselli, Rippa, Itri, Avallone, Van Damme, Monti & Raia. 2014. Seeing through the skin: dermal light sensitivity provides cryptism in moorish gecko. Journal of Zoology http://dx.doi.org/10.1111/jzo.12159

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There are 6 Comments. Add Yours.

  1. cbranch
    July 16, 2014

    Regarding your last question, could it be as simple as the fact that the flanks are positioned to “see” the color of the surface while the back, which needs to match the surface, is pointed away from it?

  2. Caitlin Syme
    July 17, 2014

    My thoughts exactly! And there’s no point having opsins on the belly, as the body would be blocking light and making the surface appear darker.

  3. Alex
    July 18, 2014

    I think that makes sense cbranch. Caitlin, perhaps the camoflage system of the gecko has evolved through natural selection to calibrate the input from the opsins to take into account the fact that they will be receiving less light due to the shade from the gecko’s body, which should be fairly easy to do seeing as the amount of shade should be fairly constant. Also I am very naive about how the camouflage and opsins work, maybe it is only important to get the general colour right, and the shade is not so critical. Very interesting.

  4. SignedbyScience
    July 18, 2014

    What is also very cool about camouflage is how other organisms might have evolved to “see” through it. There was a study in 2005 (Saito et al.) that showed how monkeys with dichromatic vision (as opposed to trichromatic vision) were able to “see” camouflaged animals. The monkeys with trichromatic vision, which is similar to the normal human vision, were not able to see these animals.

  5. Richard Dashnau
    July 18, 2014

    Here in Texas we have Mediterranean Geckos (Hemidactylus turcicus) I’ve often observed a similar color change (whitish pink to darker brown or “bark color”). But this seemed an automatic reaction to being placed into bright light and happened regardless of the “background” the gecko was placed upon. Geckos out foraging at night show this “pink” color; but bringing them into light bright enough to-photograph them, for instance-would cause the skin to darken after a few minutes. *Why* this would happen has been a mystery to me.

  6. Edgar Carpenter
    July 19, 2014

    The light sensors in our skin are mainly sensitive to infrared light, so we don’t call it ‘seeing’, but if ‘seeing’ is light perception, we see with our skin too. It’s pretty common in the living world, isn’t it?

    The more interesting thing here is the chromatophores in their skin. Chromatophores would be extremely useful and fun for humans – for one thing, all this kerfuffle that’s been going on for the last thousand years about skin color would be made obsolete.

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