Camoflage, how do they know what colours to use?

Discussion in 'Physiology and Biology' started by old_hat, Mar 18, 2008.

  1. old_hat

    old_hat Larval Mass Registered

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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.)
     
  2. robyn

    robyn Vampyroteuthis Supporter

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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).
     
  3. mucktopus

    mucktopus Haliphron Atlanticus Staff Member Moderator

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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.
     
  4. monty

    monty Colossal Squid Staff Member Supporter

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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.
     
  5. Animal Mother

    Animal Mother Architeuthis Supporter

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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.
     
  6. monty

    monty Colossal Squid Staff Member Supporter

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    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...
     
  7. Jean

    Jean Colossal Squid Supporter

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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
     
  8. monty

    monty Colossal Squid Staff Member Supporter

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    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!
     
  9. shipposhack

    shipposhack Haliphron Atlanticus Registered

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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.
     
  10. Jean

    Jean Colossal Squid Supporter

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    That's probably what I'm thinking of :grin: 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
     
  11. Animal Mother

    Animal Mother Architeuthis Supporter

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    I observed the same with my one-eyed O. hummellinki. Color changes were VERY mild, no texture changes at all.
     
  12. DWhatley

    DWhatley Cthulhu Staff Member Moderator

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    AM,
    If a hummelincki did not change pattern and color when the eye was damaged, I would say that is very strong evidence for brain control. Octane does not keep the same pattern or color for a full minute while he is not sleeping.

    I am glad Robyn brought up the polarized vision as I have not seen anything on it in a long time and I wonder if we are not testing color reception the way octos may view it. I keep thinking about the way the larger ones have grabbed at masks and cameras (that reflect light) but I don't know enough about light waves to even suggest an experiment the students who come looking for a project.
     
  13. Animal Mother

    Animal Mother Architeuthis Supporter

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    True. I didn't even think about it until Shippo mentioned it. I thought at the time that Polyphemus probably had an infection of sorts considering the condition of his eye upon arrival (rotting out), and there was no telling what all senses/organs it had damaged, and I didn't know for sure if the lack of skin activity was due to his damaged eye or illness.

    I've been re-reading the articles in my CORAL magazine (Feb. 2005 I think) and the information about the muscle control in Alf Jacob Nielson's article had me all mixed up. I should probably re-re-read it.
     
  14. monty

    monty Colossal Squid Staff Member Supporter

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    That was part of what I got to talking about David Edelman about after his talk a few months ago... I believe that to properly test a lot of this, you have to be able to control brightness and polarization. Although it sounds from Robyn's report like Dr. Hanlon is looking at some relationship between polarization and color choice, I'm puzzled about what it could be... I normally consider them relatively independent, and while it might be possible for the animal to guess a color based on polarization, I don't think it's physically possible for it to actually see color using polarization.
     
  15. DWhatley

    DWhatley Cthulhu Staff Member Moderator

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    Monty,
    My knowledge of color is very basic and less when it comes to polorization but the color we typically see is reflective, ie the light spectrum that is not absorbed by an object and the three primary colors that make up the whole set are red, blue and yellow. But we can also observe light that is filtered (TV or the light from colored lights) and the primary colors change to red, blue and green with the variation being additive. With this simplistic understanding, it would seem that we see color in two different ways so it would seem viable that other forms of acknowledging color are likely.
     
  16. monty

    monty Colossal Squid Staff Member Supporter

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    I don't have time to respond to this in detail, but in brief: the receptor in the eye doesn't know the difference between reflected, transmitted, or emitted photons... when a photon hits the rhodopsin in the receptor cell (rods and cones in mammals, rhabdomeres in cephs) it's just the wavelength that is perceived. Because humans have 3 cones, with chemically different forms of rhodopsin, that respond to wavelengths in roughly red, green, and blue, we get some combination of how many red-ish, green-ish, and blue-ish photons are coming from what we're looking at. (It's generally safe to ignore rods in these discussions, for reasons I won't go into). Since most cephs only have one type of rhodopsin, they can't perceive color in the same way we can: they can't say "this is brighter in blue and dimmer in green" because they only get one signal that mashes it all together, like a black-and-white TV. No matter what kinds of filters and such you put in front of it, you can't figure out what colors were in a black and white movie... if you're Ted Turner, you can *guess* what colors should be there, and "colorize" it, and certainly cephs might, in some sense, be doing that, but there's just not enough information to perceive color directly.

    The polarization is something quite different: in addition to having the wavelength, each photon also has a polarization direction. Humans' rods and cones respond equally well to light polarized in any direction, so we don't notice polarization at all naturally. If we wear polarized glasses and look at a polarized light source, like a puddle or ocean in late afternoon, we can indirectly benefit from most of the glare being polarized so it can be filtered out by the glasses. Cephs, though, while they only have one "color" type of rhodopsin visual pigment, have the villi "fingers" of their rhabdomeres organized in little squares, some of which are oriented vertically, some horizontally, that act like tiny localized polarizing filters, so by comparing adjacent squares, the octopus or cuttle can tell if there is a difference in polarization direction. But this doesn't convey any color information: the polarization is one type of information in the photon, completely independent of the wavelength of the photon that (in the aggregate) we see as color.

    Cuttles might well "know" in the Ted Turner sense that when they see a certain pattern of polarization, that can be identified as a seaweed leaf, and that this means they should try to be more green, but that would be more of an educated guess based on the polarization than because they can see the green-ness directly.

    I believe that many cephs can also actively control the polarization of light that reflects off of them, either to camouflage themselves relative to other critters that can see polarization (like some arthropods) or to signal each other via the polarization without ruining their ability to stay hidden from us inferior vertebrates who don't see the polarization. I know this is somehow done through the iridophores, which reflect polarized light predominantly in one direction, I think through some sort of stacked-plate arrangement that acts sort of like a polarizing filter. I'm not sure how, but I believe they can rotate this stack of plates under active muscular control, similar to the chromatophores. But this doesn't modulate color directly (although it does mess with the iridescent "sheen" colors that we see a lot in squids a bit, but it still depends on the incoming light that's reflected.)

    I have a half-baked article that summarizes what I've read on ceph vision around somewhere, I should probably finish writing that up, and go into this in more detail. Color perception even in humans is a big mess, because different people using it for different things all invent their own ways of describing, explaining, or quantifying it, that usually don't capture what's really going on. I've studied it both from the computer graphics direction and from the primate vision side, and to some extent both of those groups pay attention to what the painters, photographers, filmmakers, TV makers, chemists, printers, and psychophysics people use to describe color, so I'm rather up to my eyeballs in this sort of thing... but humans are horribly biased by being completely immersed in a visual world that's really very different from a lot of other animals: stomatopods have a lot more visual pigments than we do, I think more than 11 in some species, so the "tri-color" business is more of an artifact anyway, plus the rhodopsins' response curves have strange overlap, where there's much more overlap between red and green than blue, but blue response per photon is rather different, and our early visual processing in the retina and early visual path in the brain (lateral geniculate nucleus, IIRC) do things like compare colors to neighboring regions rather than absolutely, leading to many of the kooky color illusions that can fool us.

    :rainbow:
     
  17. shipposhack

    shipposhack Haliphron Atlanticus Registered

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    :shock: How long would the detailed post be?!
     
  18. robyn

    robyn Vampyroteuthis Supporter

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    here are some papers on the mechanisms, for those interested.

    Cuttlefish use polarization sensitivity in predation on silvery fish
    Vision Research, Volume 40, Issue 1, January 2000, Pages 71-75
    Nadav Shashar, Roland Hagan, Jean G. Boal and Roger T. Hanlon

    Three-dimensional structure of an invertebrate rhodopsin and basis for ordered alignment in the photoreceptor membrane
    Journal of Molecular Biology, Volume 314, Issue 3, 30 November 2001, Pages 455-463
    Anthony Davies, Brent E. Gowen, Angelika M. Krebs, Gebhard F. X. Schertler and Helen R. Saibil

    Discriminative responses of squid (Loligo pealeii) photoreceptors to polarized light
    Comparative Biochemistry and Physiology - Part A: Molecular & Integrative Physiology, Volume 142, Issue 3, November 2005, Pages 340-346
    William M. Saidel, Nadav Shashar, Matthew T. Schmolesky and Roger T. Hanlon

    Lack of polarization optomotor response in the cuttlefish Sepia elongata (d'Orbigny, 1845)
    Physiology & Behavior, In Press, Corrected Proof, Available online 31 January 2008
    Anne-Sophie Darmaillacq and Nadav Shashar
     
  19. monty

    monty Colossal Squid Staff Member Supporter

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    I'm not sure, but it would involve a lot more editing, proofreading, and actually looking at books instead of going from memory...

    & thanks for the refs, Robyn!
     
  20. monty

    monty Colossal Squid Staff Member Supporter

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