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[News]: Reef Cuttlefish, Sangalaki Island, Indonesia - ScienceBlogs

monty

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#2
very cool video. minor technical nitpick that they not only have no cones, they don't have rods, they have rhabdomeres and they only have one color photopigments. And although the chromatophores are colored differently in each layer, it's not all that mysterious how they match colors: the leucophores reflect the ambient color of the environment, and the colors of the layers of chromatophores are tuned to make their intensity-matching come close to matching the ambient light of things they're matching in the environment in ways that are cryptic to vertebrate color vision. But if you move the cuttle to an environment different from where it evolved, the color matching is "out of tune" and doesn't work at all.
 

sorseress

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#3
Minor nitpicks aside, that is one very cool cuttle video. Very, very nice.:cuttle:
 

DWhatley

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#4
Monty,

Can you layman that a little? When you say "move the cuttle to an environment different from where it evolved" are you speaking of evolution or simply several (or immediate) generations? My interest is in my bandensis'. If their (immediate) parents envionment is crutial to maximizing their color change, should I be investigating the environment "colors" of the Phillipines to maximize their ability and possibly their health or are you saying they can't turn swimming pool blue if the tank was barebones with a blue background since that color is not found on reefs in general?
 

monty

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dwhatley;94378 said:
Monty,

Can you layman that a little? When you say "move the cuttle to an environment different from where it evolved" are you speaking of evolution or simply several (or immediate) generations? My interest is in my bandensis'. If their (immediate) parents envionment is crutial to maximizing their color change, should I be investigating the environment "colors" of the Phillipines to maximize their ability and possibly their health or are you saying they can't turn swimming pool blue if the tank was barebones with a blue background since that color is not found on reefs in general?
The example I was thinking of was that there's a clip on one of the ceph documentaries where someone puts a cuttle in a tank with some of that garishly colored goldfish bowl gravel (like yellow and purple or something" and the cuttle matches the texture, but misses the colors completely. But I tried to generalize it to the idea that studying camouflage in general needs to be done by looking at the environment in which the creature uses it... I would normally say this is over a large number of generations, but there's a famous example of moths in Britain during the industrial revolution who rapidly changed their coloration over a small number of years to match the soot spewed by coal-fired industry, so I guess it can change on a pretty rapid timescale. Of course, in a tank, there's no penalty for having bad camouflage, because there are no predators, so there's not a lot of selection pressure to adapt the camouflage to the tank, while the moth example presumably happened because once there was a lot of soot in the environment, all the light-colored moths were eaten by sharp-eyed birds before they had a chance to reproduce.

I suspect (but this is theoretical handwaving, not based on any actual research) that the colors and layering of the chromatophores has evolved over a very long time, since coleoids have been hiding from vertebrate predators since the time of the dinosaurs (although I'm not sure at what point their predators developed color vision) so I wouldn't expect any short-term changes in animals over a few generations.

Really, though, my objection to the idea that it's mysterious that an animal without color vision can match colors well is that there are plenty of examples in nature of camouflaged animals whose constant body patterning is cryptic to color vision, but the animal doesn't see colors... people get confused because cephs can actively change their patterns, but they don't actively change how the colors of the patterns look, so there's a constant component of the coloration of chromatophores and leucophores that hides from color vision, and the patterns, changes over time, and such are actively controlled by the animal, and are optimized to dovetail with the coloration in the environment the animal lives in. There's a picture in Hanlon & Messenger of an octopus that has the nerve controlling its chromatophores cut on one side, and it actually matches a blue background better on the side where it has no control over the chromatophores, which pretty much shows that the color matching is just done by reflecting light in ways that match the color of the environment, not by the choice of the animal. The part the ceph has direct control over is more the brightness (the dark-or-light) patterns (which have coloration, but the animal doesn't control that) and the polarization (which we can't see, but cephs and some arthropods can.)

In Sepia officinalis it's been noted that there are ripples of slight change in color that happen a few times a second, which you can see if the animal is in the tank. I think this is an adaptation to match the ripples in the water over the sandy areas where they live in the wild, because the waves make rippling shadows on the sandy bottom, so this probably makes the animal less visible to birds, particularly if the animal can see the shadows around it and adjust its timing to fit. But when you're studying the animal in a tank in a lab, there aren't waves producing the ripples, so in that context, the ripples make the animal more visible, even though they were cryptic where it normally lives.

Since I'm not too satisfied with my explanation, here's a quote from Hanlon & Messenger (p.71) that may help:

If octopuses are colour blind... how could they change colour to match the background? The answer may be that they do not change colour with the chromatophores but rather the brightness (or luminance) of their skin. In the process of adjusting the brightness, they reveal more or fewer of the underlying reflecting cells and it is these that assist the animal in matching the background in colour.

Octopuses cannot use their chromatophores to match all the colors in their world because their pigments are restricted; they are black, brown, red, orange, or yellow, never green, cyan, blue or violet. Such chromatophores could never match the blues of a limestone grotto or the greens of algae in a shallow pool. Yet in life octopuses can take on the colour of their surroundings...
 

DWhatley

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#6
Monty,

Thanks for the reference. I started to reply differently but retrieved my copy from under a stack of papers and reviewed the section you mentioned. I really do need to bring this book closer to the surface of my reading list :oops:
 

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