Talk:Chromatophore

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Contents

[edit] Merge

I'm proposing that a number of chromatophore stubtype stubs be merged into this as a more comprehensive article. A number of issues - translocation, development, integrative function - are better served by explanation together than in individual articles. Rockpocket (talk) 17:35, 26 May 2006 (UTC)

I'm good with the mergers. - UtherSRG (talk) 17:58, 26 May 2006 (UTC)
Thanks. I'll leave it up for a few more days for comment, especially since i have requested peer review anyway, then go with consensus. Rockpocket (talk) 18:28, 26 May 2006 (UTC)
The information in this article is already better than those, and I see no reason to keep three stubs with incomplete information when they can point to a better page. In this case, be bold! -- Kim van der Linde at venus 16:42, 28 May 2006 (UTC)

[edit] Unofficial review

Ok, I have read the article on request of Rockpocket. I am truly impressed by the amount of data, the many references and the knowledge of the editor(s) who wrote this. I tink the general sructure is a good one, although I think I would add a seperate section with the general lightbreaking/absorption/etc mechanisms so that people have an idea when you start talking about specifics. Each type than can be describe in detail. In each section, I would very carefully try to build it up from the obvious and general interesing towards the specific and specialist interesting. I have the feeling that at current, this is often mixed, which is perfectly okay for a specialist audience of biologists and chemists, but not for the general public. I think that this is tha main weakness of the article, in that it is not really accessable to a lay-audience. This will unfortunately require a major effort to get right, but I am sure that if that works, this article cn become a worthy featured article candidate. In this line, I would also try to resturcture the sentences somewhat, some of them are quite complex. For nice prose, that is not a requirement, I personally would even say, to the contrary. For questions on specific sections, sentences and wording, please bother me. -- Kim van der Linde at venus 04:32, 31 May 2006 (UTC)

I too have read the article and my sentiments are similar to KimvdLinde. Good work that poses no problems for those with some bio background; a bit difficult for a typical casual reader with a high school education. Rockpocket, we need to decide the level of sophistication that should be expeceted of the reading audience. I haven't been around WP long enough to be able to gauge this myself. I'd be happy to go over each section with you starting this upcoming weekend (I am being crushed with work right now). But if you can let me know what our audience target level is, it would be quite helpful. Just off the top of my head, I saw a few minorly inconsistent (but not inaccurate) phrasings and a few places where an in-line definition could be used. Also, a few spots made references that seemed to lack antecedents but I could have simply read the stuff too fast last night or have forgotten them since then. As I said, I'd be happy to try a section by section approach to make sure we're on the same wavelength. You've done a lot of work here and I don't want to sidetrack you with minor issues. Ande B. 05:04, 31 May 2006 (UTC)
Thank you both. As i mentioned at Kim's talk page. The level of sophistication is something that i'm struggling with, both on this article in particular and the project in general. I'm so used to writing for, and interacting with, specialist audiences that i find it difficult to judge when language and concept are too technical or complex. I'm loathe to 'dumb down' too much - i believe we shouldn't overly restrict our language just because most of the population have a terribly limited working vocabulary - but i agree that if an intelligent layman is finding it tough then it can clearly be improved. Taking your comments on board, i think i'll go through each section and try and reorder, simplify sentence structure, and generaly try and make it more accessible. I very much welcome any specifics you could offer Ande, when you have the time of course, and a section by section approach would be super. I'll continue tinkering away in the meantime. Rockpocket 05:18, 31 May 2006 (UTC)

[edit] In response to the request on the science help desk, some nitpicking from a non-expert.

  • In the second sentence "poikilothermic", is used while in the section "Classification" it says "cold blooded". Later in the article, "poikilothermic" appears again. It is preferable that only one synonym be used, and since the article is so dense with terminology, "cold blooded" might be more reader-friendly.
  • Are you sure that "chromforo" is the correct italian spelling? It doesn't look right to me (is there an "o" missing?), but I don't speak the language.
  • Why is "chromato-cytes" hyphenated?
  • The phrase "pterinosome and carotenoid vesicles" appears with no definition of the word "pterinosome", although I assume it is an might be an adjective describing a vesicle containing pteridines (although the "-some" ending suggests a small body). If my assuption is correct, "vesicles containg pteridines and vesicles containing carotenoids" could have been more reader-friendly.
  • dihydroxyindole is mentioned in the Chromophore page, as well as on the Adenochrome and Melanin pages, but has no page of it's own. Should there be one?
  • The sentence "In 1995 it was demonstrated that the vibrant blue colours of mandarin fish are not structural in nature" does not make sense. Does a colour have structure? I suppose this is the schemochrome/biochrome distiction again, but the wording could be improved.
  • "Both types of dermal melanophores are extremely important in physiological colour change." delete "extremely", "enough" "important" is a strong enough word.
  • If the distinction is not essential, I suggest that orthologue be replaced with homologue, with a link to Homology (which is a well-developed page). I didn't know what "orthologue" meant before following the link, but would have had no problem with "homologue".
  • The sentence "Often repetitive waves of colour changes are observed as over 1 million neurons controlling the muscular contractions are patterned in the basal and peduncle lobes of the brain." is difficult to read, and I am not sure that I understand exactly what it means. At first reading, it seems to suggest, absurdly, that neurons are moving around, forming a pattern. Does it refer to the mapping of neurons, like the mapping of sensory input on the human cerebral cortex? The sentence is too busy, trying to say too many things at once. Maybe splitting it will help.

As stated in the heading, this is nitpicking. Thank you for drawing my attention to a beautiful article. --vibo56 18:27, 31 May 2006 (UTC)

Thank you so much for your very helpful comments, vibo56. I think almost all of them will improve the article and will incorporate them when i get the chance later today. I have made a few specific comments in response.
  • Sangiovanni, G. (1819). Descrizione di un particolare sistema di organi cromoforo espansivo-dermoideo e dei fenomeni che esso produce, scoperto nei molluschi cefaloso. G. Enciclopedico Napoli. 9, 1–13. You are absolutely right. Well spotted.
  • Chromato-cyte is hypenated in a clumsy attempt to show how the nomenclature differentiates between the cells of cold and warm blooded animals. The term is redundent actually. As there is only one type of cell, the melanocyte, the term chromato-cyte is actually never used in practice. Perhaps it would be better if it were not mentioned at all.
  • Structual colours are those generated by schemochromes, i concur that that is not clearly explained though.
  • The homologue/orthologue/paralogue thing is tricky. They all indicate different things and, from a phylogeneticists point of view, the distinction is very important, especially when talking about evolutionary conservation of function. However, since orthologues and paralogues are types of homologue, it would not be incorrect to refer to them as homologous. If it would make it an easier read, i'm not against changing it.
  • Good point about the neural patterning. It was meant to indicate that the neurons are thought to be positioned in a brain map that recapitulates the positioning of the chromatophores they innervate, so the pattern of neuronal activation matches the pattern of colour change. I'll try and reword and explain that better.
Thanks again! Rockpocket 19:29, 31 May 2006 (UTC)
Just a thought, not dreadfully important, but could we put something to the effect of "...ectothermic ('cold-blooded')..." to clarify things? I'm afraid I only know so much about Biology, so I don't know if in all that above this has been clarified already (only know so many terms), but if not something like this could satisfy both a need for correct, thorough termonology in the article and keep it reader friendly. Russia Moore 20:24, 30 July 2006 (UTC)

[edit] Compare these first sentences

  1. Chromatophore is the collective term for pigment-containing and light-reflecting cells found in amphibians, fish, reptiles, crustaceans and cephalopods.
  2. Chromatophores are pigment-containing and light-reflecting cells found in amphibians, fish, reptiles, crustaceans and cephalopods.
Both of these possibilities are correct, but the latter is preferable, because this is an article about chromatophores themselves, not an article about the word "chromatophore". However, if you do use the former version, you will need to use italics for the word chromatophore in order to clarify that you are talking about the word itself, and not about the thing the word describes (chromatophores). Otherwise readers may for a moment think that "a chromatophore is a collective term", whereas what you really mean is "chromatophore is a collective term"; this ambiguity is unnecessary, and can be problematic considering that we have many articles that are indeed about words and terms themselves, of which this is not one. -Silence 20:50, 23 July 2006 (UTC)
You make a good point. Rockpocket 23:16, 23 July 2006 (UTC)

[edit] The colour of octopi, the color of octopuses

To the editors who have been changing, or plan to change, colour to color: the article is currently consistant in its use of colour, it should remain that way per WP:MOS#National_varieties_of_English. Also, i notice the inevitable edits regarding the plural of octopus have begun. As the article on the subject states:

Fowler's Modern English Usage states that "the only acceptable plural in English is octopuses", and that octopi is misconceived and octopodes pedantic.

This source is consistant with opinion in the cephalopd community [1]. Hopefully this should save us all some reverting over the next 24 hours, but i doubt it. Rockpocket 02:52, 30 July 2006 (UTC)

[edit] nice work!

How refreshing to see a well-researched (and referenced) article about a non-fiction topic in the "Featured" spot. Great work! -- Mikeblas 06:58, 30 July 2006 (UTC)

On behalf of myself and the other contributors - thank you, Mike! Rockpocket 07:54, 30 July 2006 (UTC)

Yes, fine work done on this article. Very appreciative reader.Christian Roess 15:36, 30 July 2006 (UTC)

I wonder if Bulbasaur has Chromatophore too... --Xyz or die 17:04, 30 July 2006 (UTC)

[edit] Difficulty with words / concepts / scientific explanations

Some of the terms used and the explanations for colour production in biological systems puzzle me. Different authors seem to use the same term to mean different things. I am unsure about an "authoritative source" for some of the terms, and of how things "fit together".

Hi. I'll address you questions one by one.

Whence Chromatophore?: Chromatophore is said to be derived from "chromoforo", yet the term chromophore generally refers to the color producing part of a molecule in a cell, not a whole cell. In the phytochrome article it even says says "phytochrome is a protein with a bilin chromophore". Phew! When did "-at-" come to mean a cell; rather, does that "-at-" mean anything?

Chromatophore is correctly defined in the article, as i understand it from the literature. I have heard the term chromophore used to refer to the molecular moeity that produces colour, though it is rarely used in the context of pigments within chromatophores. I don't know the liguistic development of the terms, though Joe Bagnara (in Comparative Anatomy and Physiology of Pigment Cells in Nonmammalian Tissues in The Pigmentary System: Physiology and Pathophysiology, Oxford University Press, 1998. ISBN 0195098617) - who is probably the world authority in chromatophores - defines the term as being developed from "chromoforo". Thats good enough for me. Rockpocket 02:54, 6 August 2006 (UTC)

Iridescence: What makes an an iridophore an "irido"-phore? Iridescence is defined in WP as an optical phenomenon characterized as the property of surfaces in which hue changes according to the angle from which the surface is viewed. In which case Rayleigh scattering, producing a Tyndall effect, should not produce iridescence as I understand it (the sky is uniformly, non-iridescent blue, the classic example of the Tyndall effect). A diffraction grating mechanism seems a more likely explanation for the shimmer effect. But then, is an iridophore necessarily iridescent? I assume that is what the name means, but in this field I cannot be sure...

Good question. The problem here is in defining, what actually is an iridophore? Is it defined by the colour it generates (i.e. iridescence), is it defined by the mechanism through which it generates colour, is it defined by the schemochrome (guanine) or is it defined by the species it is found in? I'm not sure there is agreement in this. From its name, it was obviously first described as the "iridescent cells", but since it was a biologist and not a physicist that named them whether they are truely iridescent is up for debate. It would appear to me that what biologists regularly call iridophores are not necessarily, technically, iridescent. But the biological literature describes them as such and the threshold for inclusion in Wikipedia is verifiability, not truth, i guess we have to go with that. Rockpocket 02:54, 6 August 2006 (UTC)
Iridiscence The explanatiton of iridiscence is wrong in this article, because it cannot be ascribed to the Tyndall effect (Rayleigh Scattering), but it is due to constructive and destructive interference. The guanine crystals are analogue to to iridescent clouds which also consist of small platelike crystals. The orientation of the plates produces various mother of pearl colours in fish as well as clouds. Rayleigh scattering is responsible for the blue colour of the sky. Probably the white color of the fishes belly is due to light scattering, just like the white color of a normal cloud. For iridiscent colors look at the color of a morpho buttefly's wing, the eye of the three spined stickleback and the color of the bleak. I think the text in this respect has to be changed, because it is inconsistent with the explanation at the morphs page. In fact colors of butterflies can be even more advanced, by the use of photonic crystals and fluorescence(http://newton.ex.ac.uk/research/emag/butterflies/pdf/Vukusic_nireus_paper.pdf)

I also came across a dutch site which adresses the matter concerning the blue color of birds plumage. I suppose it is not readable for you, but it contains a list of english reference articles. PS I was using and translating your article as a basis for a dutch article about chromatophores, when I noticed this mistake. The article as a whole serves as a good basis however for an article. My primary interest is in fish and I am busy photographing a bit of fish iris, scales etc. Maybe when I think it makes sense and I am satisfied I will add some pictures to the dutch page, which is still not ready. Keep up the good work! Viridiflavus 12:16, 19 April 2007 (UTC)

Cell or organ (or both): I am similarly unsure about the why chromatophore is defined as a cell at the beginning of the article, and then used to refer to something else further on. In the different contexts the word seems to refer either to a cell, a group of cells, or an organ. So, when unqualified, to which one of these does the term chromatophore "correctly" refer? In this regard, I have come across the terms iridophores (as a type of chromatophore), iridocytes and iridosomes used in a hierachical sense, e.g. "iridophores made up of irodocytes containing iridosomes". [1] I infer from this "a collection of cells" with "individual cells" having "specific organelles" inside them. Or are the terms iridophore and iridocyte interchangable? In cephalopods "chromatophore" seems to be routinely used to describe an organised collection of cells, e.g. "The chromatophore organs of Lohgo are each composed of five types of cells." [2] Of these 5 types of cells only one seems actually to change colour. This seems to mean that chromatophores are not necessarily "pigment-containing and light-reflecting cells", but should be referred to as "structures", or "organs", or "collections of cells". Or should one explain that there is a difference in the use of the word, depending on what is being described, or what qualifying term is used - "cell" or "organ"?

Your examples sound very much to me as if the authors are making primary definitions. The vast majority of the literature explicity describes chromato-phores as pigment bearing cells of poikilotherms, melano-cytes as the pigment bearing cells of endotherms (though occasionally some refer to them all as chromato-cytes thus the terms are interchangable to some degree) and chromato-somes as the pigment-containing intracellular vesicles. In terms of cells or organs, nowhere in the article do we say that chromatophores are organs or groups of cells. We explain that cephalopods have complex multicellular 'organs' the contain chromatophores among other cells. That seems pretty clear to me. The use of the term "chromatophore organs" in the literature is just lazy writing, i think, meaning "the organs that contain chromatophores". As for the Australian Journal of Zoology paper, that is very perplexing to me. It would appear they are defining an iridophore as a aggregation of iridocytes. I have never heard this hierachical nomenclature before, the terms have always been used interchangably, in my experience, to describe single cells [2] [3] [4] (and in the interest of full disclosure, i should add the i have a PhD on the subject of chromatophore biology, though i have never read that particualr paper). Seeing as the journal is hardly high profile, i'm willing to write that off as a novel definition, which sometimes occurs in the literature when the reviewer is not on the ball. Rockpocket 02:54, 6 August 2006 (UTC)

Leucophores not Chromatophores?: This beautiful illustration, adapted from Cloney and Brocco[2] carries the comment: "The leucophore reflects whatever color of light illuminates it. There is no color discrimination and no effect on the color by the angle of illumination. Under white light the leucophores appear to be white. The leucophores, therefore, simply produce scattered reflection of ambient light." And, reading futher, it seems as if leucophores are not simply a sort/class of chromophore, but a different thing: "The leucophores sometimes occur in dense patches that appear as white spots on the cephalopod when seen under white light and when not obscured by chromatophores." So do I deduce that leucophores are not chromatophores? And then why aren't they called leuc-at-ophores, with xanthophores being called xanth-at-ophores - by analogy with chomophore / chromatophore?

Leucophores most certainly are chromatophores (in that they are neural crest derived and from the same multipotent precursor lineage, in vertebrates at least [5]). Some people studying cephalopods differentiate between the biochrome containing cells (melanophores, erythrophores, xanthophores) which they define as chromatophores and the schemochrome containing cells (leucophores and iridophores) which they they don't tend to group together (though i guess they might be though of as schemophores). To confuse matters further, they call bioluminescent cells photophores and discuss them alongside the other schemochrome containing cells. I must admit, i'm not familiar with the developmental source of these cells in invertebrates, so i can't say whether they are making these definitions based on anything other than arbitrary terms. The vertebrate cells are much more widely studied and it is clear that are all developmentally related, thus are grouped together as chromatophores. My guess is that the cephalopods are from the same origin, and thus they should probably be grouped together as in the vertebrates. Nevertheless, I guess we could explain how the same terms mean different things in the cephalopod world. Though it could start to get very confusing. Rockpocket 03:19, 6 August 2006 (UTC)
You make a fair point about why they, and the other subtypes, are not call leuco-at-ophores, i guess i can only offer the fact that the naming scientists were not consistant in their nomenclature. Rockpocket 02:54, 6 August 2006 (UTC)

Why still Rayleigh?: For non-iridescent colours, should one not, in discussing the production of different colours, mention coherent scattering by the mechanism of constructive interference [3] as an alternative explantion for colour production (vs Rayleigh / Tyndall, which seems these days to be less popular an explanation [4]) ? Though the work using Fourier analysis [5] is to date mostly with birds and mammals, it seems to be overturning much of the previous theory about structural colours - and chromatophores are being studied in this way.

You have a point here. I've long suspected that the Rayleigh / Tyndall explanation was an oversimplification. Unfortunately most of the specific chromatophore literature continues to use this explanation (as you mention, the avian and mammalian side of things have moved forward). If you can find some literature specific for chromatophores then by all means add it. I think there is even an argument that we could use the principle of what was found in bird and mammals and extrapolate to chromatophores. Unfortunately, like most biologists, the physics of light relfection/refraction is somewhat beyond me thus i was always happy to tow the Rayleigh / Tyndall line, which i just about understand. Rockpocket 02:54, 6 August 2006 (UTC)
  1. ^ Griffiths DJ, Winsor H, and Luongvan T. Iridophores in the Mantle of Giant Clams. Australian Journal of Zoology (1992) 40(3) 319 - 326
  2. ^ a b Cloney RA, Brocco SL. Chromatophore Organs, Reflector Cells, Iridocytes and Leucophores in Cephalopods. American Zoologist (1983) 23(3):581-592.
  3. ^ Prum RO, Torres, RH. Structural colouration of avian skin: Convergent evolution of coherently scattering dermal collagen arrays. Journal of Experimental Biology 2003 206: 2409-2429.
  4. ^ Kathryn Phillips. Blue, but not sky blue. The Journal of Experimental Biology 2003, 206, 2297
  5. ^ Prum RO, Torres RH. A Fourier Tool for the Analysis of Coherent Light Scattering by Bio-Optical Nanostructures. Integrative and Comparative Biology 2003 43(4):591-602

--Seejyb 21:32, 5 August 2006 (UTC)

Thanks very much for your input. Rockpocket 02:54, 6 August 2006 (UTC)

[edit] Tapetum lucidum

Another possible concept problem for this article! In the eyes of many vertebrates, the choroid includes a reflective tissue layer that, as far as I can make out, consists of leucophores. The problem is that they are not called leucophores. In fact, they don't seem to have any specific name, getting by with "tapetal cell" etc. At present, the article says the leucophore, is found in some fish, particularly in the tapetum lucidum; well, if tapeta lucida have leucophores in a fish, then surely they have them also in the many other vertebrates with tapeta lucida. --Una Smith (talk) 05:23, 4 June 2008 (UTC)

I looked at this beautiful illustration (link found above) and AFAIK leucophores do not occur in any form of tapetum lucidum. If they do occur, please tell me in which taxa. Else, my edits to this article need to be reworked. Is it fair to say this?: Tapetum lucidum cells (meaning the cells containing reflective crystals) are iridophores, but they produce white light, not iridescence, because the light source is a point source (the lens of the eye) and the cells themselves are oriented uniformly with respect to the source. --Una Smith (talk) 05:33, 4 June 2008 (UTC)
As I understand it, mammals generate a similar effect using collagen, riboflavin and zinc cysteine, but don't have specific neural crest derived cell types in the tapetum lucidum. Fish use the guanine or uric acid stacks. I don't honestly know whether the cells in the fish tapetum lucidum are technically leucophores or iridophores, but I know the cells in mammals are neither. When I wrote this article, I tried to keep the terms strictly within biological context (that is, to describe the cell types based on their developmental origin and molecular composition) rather than use the terms as descriptors of general function. Your explanation, above, makes sense to me. Rockpocket 05:50, 4 June 2008 (UTC)
In at least 2 of the 4 anatomical types of tapetum lucidum, reflection is from crystals of guanine, or from stacks of crystals of guanine. Life is sooo messy... I am feeling a strong urge to put quotes on "white light", and edit the article to explain (more clearly) that leucophores don't reflect white light per se: they reflect the same spectrum of light as shines on them. How do tapetum lucidum cells fit in the melanocyte bin, BTW? --Una Smith (talk) 06:11, 4 June 2008 (UTC)
Perhaps, but my understanding of the literature is that are restricted to teleosts and elasmobranches. Do you have a source suggesting that guanine is the reflecting material in tetrapods?
There is some debate about the origin of mammalian tapetum lucidum cells. Some claim they are modified melanocytes (PMID 6766689), while others claim they are modified from connective tissue (PMID 356534).
Feel free to address the leucophore section in more detail if you can. the schemochromes aren't really my area of expertise, so those sections could probably do with some work. Rockpocket 06:48, 4 June 2008 (UTC)
PMID 6833116 states in intro "Amongst the reflective materials noted in tapeta cellulosa are guanine / hypoxanthine crystal plates, riboflavin crystal plates and rodlets of varying composition." But I think the type of crystal is a tangent. How about organizing the iridophore/leucophore section as follows? Iridiphore: subsets iridescent and retroreflective: retroreflective subsets tapetum lucidum and leucophore? In a TL all the crystals are oriented in the radial plane wrt the light source. In a leucophore, I gather, there are many crystals, oriented every which way, and only those crystals oriented in the plane of the light are reflective. --Una Smith (talk) 13:46, 4 June 2008 (UTC)
That source appears to make the comment in reference to "vertebrate" tapeta cellulosa, which would include fish, of course. I'm not sure the value in specifically describing tapetum lucidum as a subset of iridophores in this article. Odd schemochrome types are found in all sorts of organs in all sorts of tissues, I don't really see what we should focus on this type, especially since we don't seem to have a source that really explainswhat those cells are. That said, in light of the info you provide, I so think we could explain the differences between leuco- and iridophores better.
Either way, if you wish to have a go at improving this section, please do so. However, since this is a featured article, it might be better to draft amendments to the section here first, in an effort to keep the article as stable as possible. Rockpocket 17:14, 5 June 2008 (UTC)