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Aug 20, 2021

Hiding in plain sight: explaining intentional camouflage

As the parent of a three year old, I have seen “Finding Dory” approximately 74 times. It’s an instance of the sequel being better than the original, mostly because it uses the species-distinct characteristics of the animals to greater comedic effect than “Finding Nemo” does. There’s the clam who never shuts up. And a nerdy beluga who calls his echolocation abilities “the world’s most powerful pair of glasses” and then neurotically worries about breaking them. But the best character in “Finding Dory” is Hank, the cantankerous octopus who desperately wants to move to Cleveland where he believes he can live in solitude. In the meantime, Hank uses his impressive camouflage capabilities to escape his crowded tank.

During one of many opportunities to dwell on the characterization of Hank, I wondered whether Disney had represented his abilities accurately: Can an octopus change its color and patterning immediately and at will, as Hank does? How do the mind and body interact in order to change their physical appearance? What about chameleons and other animals that change color?

Octopuses belong to a group called cephalopods, which includes squid and cuttlefish. In response to a threat or when stalking prey, several cephalopods can intentionally adjust their appearance to blend in with the background. Flatfish—flounders, halibut, and others whose eyes are on one side of their heads—also camouflage themselves to escape predators or hunt. Chameleons, contrary to popular belief, don’t typically change color to camouflage themselves. Instead, they change color to communicate aggression or desire to other chameleons, or to regulate their body temperature by assuming colors that reflect or absorb more heat.

Considering their color changing abilities, it may come as no surprise that chameleons see color as well as ultraviolet light, giving them a wider spectrum of color perception than humans. Cephalopods, though, are another story.

It was long thought that octopuses could not detect color and thus that their camouflaging was involuntary. This was a reasonable conclusion, because octopuses only have one type of photoreceptor, and can therefore only see in black and white. But a 2016 experiment and publication by a father-son duo (Alexander Stubbs, a graduate student at UC Berkeley, and Christopher Stubbs, an astrophysicist at Harvard) revealed that octopuses can detect color, they just can’t see it. Thus, there is thought, or intentionality, behind their color changing.

Cephalopods detect color through their pupils which, instead of being round, are U-shaped, W-shaped, or dumbbell shaped and which, therefore, allow light to enter from various directions. The drawback of such pupils is that they don’t contract to a focal point, so they are less able to see refined edges, and these elongated pupils see much more blurring than would generally be considered desirable. But, this blurriness, or chromatic aberration, is full of information: different color wavelengths are perceived as more or less blurry, allowing a cephalopod to understand the differentiation among colors in its field of view. That is, it can’t see yellow, but it might recognize something yellow as being “fuzzy” whereas it might recognize something red as relatively distinct. As Alexander Stubbs put it, “Intriguingly, using chromatic aberration to detect color is more computationally intensive than other types of color vision, such as our own, and likely requires a lot of brainpower. This may explain, in part, why cephalopods are the most intelligent invertebrates on Earth.”

Chameleons and cephalopods not only detect color differently, but they assume their color changes somewhat differently, too. A cephalopod senses danger or a prey candidate, looks at his surroundings for a serviceable backdrop upon which he can disguise himself, and then employs color changes by way of neuromuscular control of his chromatophores, or cells that produce color. So, in the same way that you might decide to crouch in response to a threat, an octopus deploys his chromatophores to match the colors (and sometimes the textures) of his environment.

Chameleons, on the other hand, depend on one particular type of chromatophore, called iridophores, to change the texture of their skin. The layer containing iridophores is iridescent, composed of pigmented nanocrystals that reflect light. When a chameleon is excited in some way or another, it tenses its skin, causing changes in the structure of these crystalline iridophores, so that their skin changes color by reflecting different wavelengths of light.

Chromatophores exist in a few other true camouflagers, too. Flatfish like flounder, sole, and halibut likewise intentionally change color, but the mechanism of their chromatophores is distinct, and it takes longer (upwards of ten minutes, depending on the species) for the fish to assume the color of the ocean floor that they’re matching. Part of the rapidity of cephalopod transformation is due to its being muscularly controlled. Flatfish take longer to camouflage because their chromatophores are controlled hormonally, and it takes time for the hormones to effect the pigment blooms and contractions that produce colors in the skin. ​​Juvenile pygmy seahorses change color over a longer period of time, with the change taking several days, but when they choose a background to replicate, they stay there and permanently change to match its colors. It is unknown whether they can change their color thereafter.

Of course, there are some animals who rely on camouflage but whose bodies never change. Tigers, several ground nesting birds, walking sticks, and moths are examples of creatures whose physical traits have evolved to match the environments in which they typically live. But this passive adaptation is, for me, less fascinating than that of animals like flatfish who adapt dynamically to their environments. And, in the hierarchy of what’s interesting from a cognitive perspective, those species who accomplish their camouflaging through intensive brainpower are at the top of the pyramid. Here’s to you, cephalopods!

References: https://royalsocietypublishing.org/doi/10.1098/rsif.2008.0366.focus https://royalsocietypublishing.org/doi/10.1098/rstb.2008.0254 https://royalsocietypublishing.org/doi/10.1098/rsos.160824 https://www.nationalgeographic.com/animals/fish/facts/flatfish-flounder-sole-haddock https://www.nature.com/scitable/topicpage/cephalopod-camouflage-cells-and-organs-of-the-144048968/ https://www.mpg.de/12363924/1017-hirn-080434-elucidating-cuttlefish-camouflage https://www.scientificamerican.com/article/how-do-squid-and-octopuse/ https://www.wired.com/2014/04/how-do-chameleons-change-colors/ https://www.nature.com/articles/s42003-019-0465-8 https://news.berkeley.edu/2016/07/05/weird-pupils-let-octopuses-see-their-colorful-gardens/ https://www.nature.com/articles/ncomms7368 https://www.cco.caltech.edu/~brokawc/Bi11/cephalopods.html https://www.kqed.org/science/22700/pygmy-seahorses-masters-of-camouflage http://www.bioflux.com.ro/docs/2017.1049-1063.pdf https://www.nature.com/articles/ncomms7368 https://www.pnas.org/content/113/29/8206 https://pubmed.ncbi.nlm.nih.gov/11762491/

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