Camoflage, how do they know what colours to use?

old_hat

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I got into this forum by reading a thread about brains and something came up which i thought deserved a thread of its own. Its about camouflage. This is what i think i know (its probably a bit wrong):

Many of the cephs seem to be able to do amazingly complicated things with their skin, like creating optical illusions (for example of false depth to hide the shape of their profile) due to some kind of two layered system of millions of cells in their skin and changing patterns and colours in less than an eye blink.

From videos it seems like they can match the colours of their surroundings with amazing precision.

And to top it all when they are not using this to be more or less invisible they send each other messages with their skin (this bit isn't for this thread)

Controlling all of this involves loads of processing power and a sophisticated brain.

Right now to the point ... In the thread i mentioned before it came up that almost all species (except the firefly octopuss?) are colour blind.
So how the heck do they figure out what colour they are supposed to be?
And if they dont use their eyes to asses their surroundings for this purpose what system do they use?
I am in shock and awe.


(As an asside feel free to put me right if any or all of this is a load of balls but please only if you also have something to add to a discussion about the main question.)
 

robyn

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Hi old_hat. Welcome!

I am definitely not an expert on comouflage, but it is known that cephs used the light polarisation to match their colour patterns, rather than the colour itself, given that they can't see colour. Lydia Mathger (in Roger Hanlon's lab) has done some beautiful work on polarisation vision in cuttlefishes. The Hanlon group has also shown that at least in cuttlefishes, all of their camouflage is based on three basic body patterns, which can be adapted to suit the substrate and environment.

I think I have copies of their recent papers, so let me know if you would like to read more. (I think there is some info and some great videos on Roger's webpage also).
 

mucktopus

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Every type of octopus has certain colored chromatophores that they can use to create body patterns. For example, they may have yellow, dark-red, and brown chromatophores respectively, or only purple. For some octos (such as O. cyanea) this creates excellent color camouflage, and for others (such as O. bocki) camo is very limited. They use their excellent BW vision to match the contrast and shades using the colors they happen to have in their skin. Because their predators can see color, certain color combinations have been selected for survival in certain habitats. If an octo had a mutation with a better color match (to its habitat) than its siblings, that it should be more likely to survive and reproduce because the fish won't see it as well. This predation pressure has probably had a very strong influence over the evolution of octopus skin.
 

monty

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:welcome: to TONMO!

Interesting report on the polarization giving them help estimating the color; I didn't know about that one. In Hanlon & Messenger's earlier book, they also mention that a lot of the color matching comes more from reflected light from the environment: the animal controls the intensity, and just reflects the light similarly to other things that are around, but passively. It's been shown that if they're put on a sufficiently non-natural color scheme that they can't see like we can, they won't even come close to matching it.

The way the "match the environment color" works in a bit more details is that the lowest level of skin has "leucophores," which are big, inactive white reflectors, that reflect whatever light is in the environment. Then, there are usually 3 layers (typically) of chromatophores under the animal's control, where each layer is a darker shade, so the first layer is amber, the second brown, and the topmost black or dark red-brown. In the colors of light where they normally live, filtered to blue-green by the water, this scheme turns out to do very well at matching colors, probably because the reds and yellows in the pigments are well-tuned to matching color of things of about that brightness in the conditions where the animal lives.
 
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How much of the skin activity is controlled by the brain itself versus the rest of the nervous system? I ask because of the way the physical movement/control of the arms is the same after being severed and isolated away from the brain. Seems more like an automatic reaction to its environment instead of a thought process, which would be involuntary and not depend on eyesight. Then again considering the communication aspect of it...

Sorry if I'm butting in on your thread old_hat. While I understand the use and ability, I too wonder how they manage to control such a complex feature seemingly instantaneously and without effort.
 

monty

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Animal Mother;112958 said:
How much of the skin activity is controlled by the brain itself versus the rest of the nervous system? I ask because of the way the physical movement/control of the arms is the same after being severed and isolated away from the brain. Seems more like an automatic reaction to its environment instead of a thought process, which would be involuntary and not depend on eyesight. Then again considering the communication aspect of it...

Sorry if I'm butting in on your thread old_hat. While I understand the use and ability, I too wonder how they manage to control such a complex feature seemingly instantaneously and without effort.

It's all coordinated by the brain. I think all coleoida (certainly most) have optic lobes for visual processing and chromatophore lobes that control the body patterning, and lesion studies have shown that they're both needed. Blind animals can also no longer match their environments. Some cephs do have secondary visual organs not in their eyes, that are mostly used for things like countershading in open-water squids, to make their bellies match the light level from above so they can't be seen in silhouette from below, and sometimes vice-versa for their dorsal surface matching the darkness of water below.

I seem to recall that the chromatophore lobes actually have a map to the body, but I'm not certain about that. I don't remember if each chromatophore has a little local control as well, or if it's controlled directly by the brain. Certainly, for other body parts, there's a lot more local control: the arms and even the individual suckers each have local ganglia that can do simple control, and the brain does more high-level instructions than controlling all the details. I suspect that chromatophore control wouldn't do this, though, since it's more important to have the visual input converted to a body pattern that has to be consistent across the whole body rapidly than to have autonomy or just communication with neighbors... as opposed to the suckers, which can make reasonable decisions on their own: if it tastes bad, drop it, and if it tastes good, grab it and pass it toward the mouth, that sort of thing.

Lots of good questions in this thread, it's fun stuff...
 

Jean

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I've also read somewhere (naturally I can't remember where or when :roll:) that some species have colour receptive pigments in the retinal cells, so perhaps some can see colour but not using the traditional mammalian receptors????

J
 

monty

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Jean;112966 said:
I've also read somewhere (naturally I can't remember where or when :roll:) that some species have colour receptive pigments in the retinal cells, so perhaps some can see colour but not using the traditional mammalian receptors????

J

The only one I'm aware of is the firefly squid, which has 3 pigments (arranged in 2 colors on one area of the retina, and a different one in the other; I forget if it's top/bottom or front/back split)

As far as I've checked (and I've looked pretty hard) all other cephs have only been found to have one type of rhodopsin pigment. If anyone knows of any exceptions other than the firefly squid, I'd love to hear about it, though!
 
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I read somewhere (Possibly in Octopus and Squid by Jasque Cousteau) that some octos were reported camoflaging when they were blind. However, I did not see this behavior with my O. Hummellincki. Once his eyesight was gone he no longer tried to match his surroundings, and generally only changed color while he was eating or resting.
 

Jean

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monty;112969 said:
The only one I'm aware of is the firefly squid, which has 3 pigments (arranged in 2 colors on one area of the retina, and a different one in the other; I forget if it's top/bottom or front/back split)

As far as I've checked (and I've looked pretty hard) all other cephs have only been found to have one type of rhodopsin pigment. If anyone knows of any exceptions other than the firefly squid, I'd love to hear about it, though!

That's probably what I'm thinking of :biggrin2: brain is scrambled this am no :coffee: and I'm trying to remember what I know of sediment textural analysis so I can help teach it this pm :roll: :goofysca:

J
 

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