Octopuses are incredibly fascinating creatures: intelligent and clever, strange organ configuration (to me at least), and some really exotic forms of sensory perception.
Octopuses are part of the cephalopod family, with their cousins, squid, cuttlefish, and nautiluses. Fossil impressions of octopuses show evidence that these creatures have been around more than 200 million years, and so they have had plenty of time to evolve some really unique adaptations!
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| No octopus to see here! (Flikr 808_Diver) |
The skin of an octopus has several layers of cells that work together during color changes. One layer of skin contains chromatophores, which are tiny fluid-filled sacs that contain different pigments of colors. If the muscles around the sac squeeze it shut, then it hides the pigment. If the sac expands, then the color shows through. Opening and closing these different sacs of color can give an octopus a wide range of colors for its skin color (a little like a digital pixel display). Another layer of skin contains iridophores, which work to reflect surrounding light, especially green and blue colors. The base layer of skin contains leucophores, which is like a white background for all the other colors. Some octopuses have photophores, which give them special bioluminescent ability.
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| A close-up of squid skin, where the wide-open chromatophores reveal brownish colors (Creative Commons, via wikipedia) |
More deeply (as my neighbor asked me): does an octopus think about it and "try" to look like its surroundings, or does an octopus innately change color and texture without thinking about it?
Without being able to directly ask an octopus about whether its camouflaging ability is conscious or sub-conscious, some experts have tried to study this. One study found that an octopus tends to choose a particular object to imitate (a rock or piece of coral) rather than its entire surroundings, suggesting there is some thought behind camouflage. This suggests that at least some octopuses are using their vision to match its surroundings.
On the other hand, in addition to seeing light with their eyes, octopus skin could perceive light or color as well. Octopus skin cells contain opsin proteins, which are special sensors that allows their skin to detect color and light. That's not to say that octopuses can "see" with their skin, but their skin can pick up enough information about their surroundings so that they can change shape and color to mimic their environment without using their brains.
So maybe camouflaging is a little more innate than conscious!
So can octopus skin change color without the octopus thinking about it? Actually, yes, sort of: Skin that has been removed from an octopus (ouch!) can change color on its own, but its much slower than usual, suggesting that some neural input from the brain assists in color changing and camouflaging.
As if all this wasn't crazy enough, some species of octopus are color-blind. Or are they? A recent paper suggested that while an octopus might only have one photoreceptor (only see in black-and-white), their unique pupil shape (U-shaped) could allow them to interpret color though chromatic abberation. However, this work is only one possible model that remains to be proven.
If only we could just ask an octopus.
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| Octopuses have been found to build and carry shelter materials. They can also open doors and screw-topped containers. Don't ever underestimate an octopuses ability. (Creative commons, via pxhere) |
Other awesome references:
https://www.nationalgeographic.com/science/phenomena/2014/08/18/adaptive-colour-changing-sheet-inspired-by-octopus-skin/
https://ocean.si.edu/ocean-life/invertebrates/how-octopuses-and-squids-change-color
https://www.nature.com/scitable/topicpage/cephalopod-camouflage-cells-and-organs-of-the-144048968
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