Discussion in 'Physiology and Biology' started by laikadog, Oct 7, 2005.
Are octopuses colourblind? I've heard they are.If so, how do they camouflage themselves so well?
That is truly a most excellent point!!!! The answer? I have no clue!
Yes, laikadog, it appears that many of them are colourblind. As far as I know, every species of octopus examined so far has been found to possess only one visual pigment. Furthermore, behavioural experiments and electroretinograms (which measure the response of the retina to a flash of light) also indicate that octopuses can't distinguish colour. Watasenia scintillans, the Japanese firefly squid, is the only cephalopod I know of that is thought to have colour vision. Still, it might be a little premature to make too many sweeping generalizations.
Your second question is a very good one. Chromatophores come in only a few colours (black, brown, red, and yellow) and the nervous system does not seem to be wired in such a way that an octopus can consciously control which individual chromatophores to expand and contract. Instead, it seems that cephalopods create their patterns by combining several basic 'preset' patterns of colouration. Many cephalopods also have reflecting cells known as leucophores and iridophores. Leucophores reflect the predominant colours of the environment, appearing whitish in white light, bluish in blue light, etc., while iridophores produce blues and greens (through interference or diffraction--I can't recall which). Together, these reflecting cells might aid camouflage simply by passively reflecting the general tones of an octo's surroundings. Perhaps the general success of camouflage is a bit of a statistical thing, where cryptic responses only need to be good enough on average to allow species to avoid too much predation or get just a little bit closer to prey. This article has tons of information about chromatophores and patterning in cephalopods.
Good questions, and I hope they get a bunch of good responses.
Indeed, from an evolutionary perspective it is interesting that octopuses appear to be colourblind. Could it be that all the modern octopus families evolved from ancient deep-water forms who did not need colour vision?
Packard once suggested that the radiation of fishes and reptiles in coastal regions drove the chambered shell cephalopods into deeper and offshore waters. Chambered cephalopods, such as the ammonites and nautiloids, could not reach the deeper waters due to danger of implosion, and prompted the rapid evolution of the coleoids.
Perhaps a gradual recolonisation of shallower waters following the Cretaceous extinction by the colour-blind deeper-water non-shelled cephalopods drove animals that had lost their colour vision back up to repopulate recently vacated waters and fill a vacant ecological niche.
Granted we have the shallow-water Carboniferous octopod Pohlsepia and the Jurassic Proteroctopus, but there is precious little to suggest these were the direct ancestors of the Incirrata, perhaps all modern descendants split from their deeper-water cousins.
I still want to know about the degree of colour perceptivity of marine animals in general. Is colourblindness really as much of a disadvantage as it seems? I had assumed that many (shallow water) reef animals would have good colour vision, given the splendour of their environment, but since cephalopods were initially included in that assumption I'm not sure what to think. Perhaps I need to some more...
I've been looking for an answer to this question, too - how do they match such different colors if they are colorblind. I watched my bimac match different purples - red purple, blue purple, the colors of coralline algae. She couldn't have perceived only shades of gray and matched these colors. So how did she do it? And wasn't some research done recently that showed octos could distinguish red and blue?
That is a very good question and im happy to know the answer to.
Like Um... already stated, the color reflective cells on an octopuses skin surface aid the octo to camouflage in the wild through whatever environment they seem to pass by. However, generally...as stated in books and a wonderful guide called "The Ultimate Guide: Octopus" on discovery, the octopuses, cuttlefish and squid see only few tones of color in terms of being color-blind: Black, white...and shades of grey. Because of these colors, they think the pattern onto their brain, chance their color precisely and know exactly how to blend in with the different shades of greys wether it be plain grey, or darker greys. In general terms, theyan only see alternated color shades of grey...which can be white and black. Through our eyes, red is the color red. In their eyes, red looks like a soft-blackish shade. Instead of changing to red...mentally, they are changing their color and pattern to the blackish shade they see in their environmment. It's very interesting.
Another interesting fact is how octopuses can change different shades of colors when their chromatophores only have pigments of black, brown, red, and yellow. The timing of the contracting and expanding of these pigment cells gives the illusion of a lot more than that. Plus, they have billions apon billions of these sacks...which would surely and easily create illusional patterns of tones not yet seen in nature. I love when they turn black. Beautiful camoulflage. They have to be the masters of camoulflage. Able to alterate skin color, texture AND shape in a fraction of a second is incredible.
For me, the fallacy lies in thinking that one shade of gray corresponds to a particular color. I've even had courses in color theory and have also been interested in Ansel Adams photography (he discussed the gray scale a lot). A particular value of gray in a black and white photo might be green or blue or brown in the actual scene. It doesn't correspond to a single color. I have yet to see a good explanation for this part of the theory.
And this doesnt explain how a blind octopus can match its surroundings. Also I was under the impression that a severed arm would also match its' surroundings, not sure on either of these facts,(I read them somewhere) can anyone confirm if they are true?
Not too long ago someone posted about his octopus being able to recognize colors. He had 2 sets of plastic rings, one set inside the tank, the other set outside. He would hold up one of the rings, and his octo would find the same color ring and hold it up inside the tank. I believe he said tht the octopus could recognise 4 colors so far and he was working on training it to recognize a fifth. Not having seen those sets of rings, and I'm presuming that they are identical, I don't know if the rings have the same tone and intensity. I have some books on color, since I work with color in fiber arts, and do a lot of dyeing. Unfortunately they are all packed right now, so I can't access them, but Nancy is right that several different colors could all share the same tone of gray. Maybe we are making assumptions about octopus eyes based on inadequate information. There has to be something about the physiology of their eyes that make it possible for them to discern colors, even if our current knowledge would indicate color blindness.
Octopuses aren't blind. But if you meant..how an octo going blind or supposadely IS blind as a result of injury, I wouldn't know the answer to that other than the fact that their color-reflective cells aid them in camoulflage.
Nancy, for the green color, I watched a cuttlefish on a video camoulflage itself to try and take on the shades of a rocky bottom filled with blues and greens. The camoulflage failed, however...to the cuttelfish, all the green and blue rocks were all the same shade of grey. And they remained no different from one another to the cuttlefishes eye. To our eyes, the rocks were green and blue...two different shades. So the cuttle took no pattern at all and simply turned into a very, very light greyish color. This probably works for octo's and squids as well.
From what I understand, although most cephs can't see colour, they can discriminate (to a very fine degree) the differences between hue and colour intensity (and patterns but that's another story!). I watched a Discovery doco which had John Forsythe demonstrating that a cuttle can match patterns based on colours of different intensity BUT when he put the cuttle in a tank with a substrate of yellow tiles and green pebbles which had the same intensity the cuttle didn't change. The other was put in a tank with (I think) red tiles and blue pebbles and the cuttle opted for a checkerboard pattern. The tanks were then filmed in black and white and to our eyes (well mine anyway!) the red and blue were different shades of grey and the yellow and green were all one shade of grey! So cephs may have a better ability to match based on tone, hue and intensity.
Oh, yeah I meant an octo that has become blind/ possibly has its eyes covered for an experiment? Just remember reading that somewhere
Yea, thats exactly what I saw on discovery also. I meant yellow and green...not blue and green, sorry Nancy, lol. It explained very well how they can blend in though. I own that tape with that video clip...and its "The Ultimate Guide: Octopus" which I ordered on TV after it aired for 19.99. Im planning on purchasing "Incredible Suckers" and "The Octopus Show" both on The Nature Show website.
Well, these are all good answers. I would also think that this topic also deals with several major factors of octopus sight including sensation and perception, the evolutionary morphology of the cephalopod eye, and properties of light in the ocean.
People always remark about how similar the Cephalopod eye is to the human eye. I prefer to look at the morphological differences and remark about the similarity in function. If you really study the ceph eye, you see it’s more of a highly derived version of the basic mollusc eye, itself a modified pigment cup ocellus similar to those of the flatworms.
Another interesting thought is the idea of the use of the Cephalopod visual pigments like rhodopsin and retinochrome. The rhabodmeres (or cell units of the cephalopod eye – analogous to our rods and cones), house these pigments, which actually move in response to light, unlike our own. This could affect what they perceive as “color” versus what we perceive and see in our own non-aquatic world.
Also, the cephalopod optic lobe is nearly half of the brain, which is a far higher ratio of optic nerve tissue to brain weight than ours. There would have to take a lot of processing power for sight in the Cephalopod eye, which means their visual acuity may be greater than we think.
Color vision isn’t really a necessity in the ocean, though I can see where in certain animals this might be an advantage. Light has weird properties in the ocean, and certain wavelengths (colors) will simply not penetrate far down. You’d be better off collecting light than dedicating your resources toward color vision.
I just can’t shake the feeling that, given that our sight is the sum total of a lot of different factors, the “color vision” of a cephalopod is not that straightforward. There are probably numerous factors that we aren’t seeing at the present time.
Gee John, that's exactly what I meant to say.(yeah, right!)
Thanks, John, very interesting!
Just one note - some octos live close to the shore in shallower water where more light would penetrate. I wonder whether these species would have more use for color perception.
Light filters out very quickly particularly the short wavelengths such as red....which is why many critters are red/orange. Below about 10m they look black and are much harder to see. In fact most photos of coral reefs you see would be blue if the photographer hadn't used a white strobe! So it would be an advantage to see "more" than just colour; hue, saturation, polarisation etc would be more useful visual tools than just colour.
True enough, but I think that what we're looking at from an evolutionary perspective is something building on the original molluscan bauplan. If the eyes of the ancestral forms weren't originally color-sensing, then the derived forms might have the same issues to this day unless acted upon by the right mutations and selective pressures. Think of it as a Newton's Law of Evolution, except without the apples.
Well, maybe Watasenia is one such individual.
Cephalopods notwithstanding, color vision is not nearly as important a factor in most animals than it is in humans. We are strongly biased in our ideas of how other animals see the world by the way we see the world. Some theorists believe that the reason we have the type of color vision that we do is because our monkey ancestors needed to identify different fruits and their levels of ripeness, so our lifestyle of eating fruit in bright sunshine (I wish I actually spent more time eating fruit in the bright sunshine ) really explain our style of vision. Noctournal predators like cats generally are more optimized for seeing movement in very low light levels. I assume deer are color blind and sensitive to movement as well, since hunters can wear colorful vests to not be shot by other hunters and yet can still sneak up on deer. Of course, insects that need to find flowers can gain from color vision, and I understand some stomatopods have 11 or so different visual pigments, so presumably they get some information about spectrum from that.
My point is that it's not even clear what color would mean to most of these animals; certainly it's not the same thing that we see.
I've studied a lot about color in the context of computer graphics and visual psychophysics, and generally find that almost nobody has a good understanding of what color "is"-- there are different aspects of color in many fields. A friend of mine believes that the chemists are the ones who understand color the best, since they use spectroscopy to examine different materials, so they're heavily invested in what the actual spectrum of light is. There are a large number of color models used by the art, print, materials, video, lighting and film fields, all of which have a lot of value in some areas but less so in others-- some concentrate on the pigment properties, some on the spectrum of light, some on human perceptions. There was an attempt to clarify this sort of thing in the creation of the CIE color space, which describes a basis for representing the gamut of colors that the human eye can perceive... it's interesting how much of that falls outside what can be represented with the red+green+blue phosphors of video screens.
My bottom line is that it's quite clear to me, just because of the differences in nervous systems, that any color vision cephalopods may possess is likely to be very different than human color perception. As was pointed out, the spectrum of light in the ocean tends to be quite different than what we get on land. Someone (John, maybe) posted a reference to a fascinating paper a few months ago which discussed a whole bunch of aspects of deep-sea vision, lighting, and color issues-- it's quite interesting... I'll look for the thread when I have a bit more time.
I'm not sure what Jean is getting at by mentioning "hue" as distinct from color-- in my experience, hue is defined as the "normalized" color, in systems like HLS and HSV that try to separate out color from "intensity"/"lightness"/"brightness" and "saturation," so I don't understand how an animal could make sense of "hue" without color vision.
I think the prevailing assumption is that since most cephs seem to only have one visual pigment in their retinas, that they don't have any way to distinguish frequencies-- humans do that by comparing the responses of 3 different pigments, roughly corresponding to red, green, and blue. If there is any alternately proposed mechanism, I've never heard of it.
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