Spider Coloration, not just structural

On the boards I've noticed in many many many threads, especially those about the possible existence of 'albino tarantulas', the statement that spider coloration comes from reflectance from the shape of the cuticle and not pigmentation. Many say outright spiders lack pigments! Therefore albinism is impossible, because it implies a lack of pigment or the specific pigment melanin. (Search albino or albino tarantula and you'll see what I mean!)

While I don't particularly care about whether or not albino tarantulas exists, I would like to point out that spiders do use three major classes of pigments for coloration, in the cuticle, hypodermis, and in the hairs. Also other unclassified and unstudied pigments are utilized by spiders, this includes Theraphosids. So let's put an end to this rumor that seems to be pervasive around the boards that spiders lack any pigments.

The relationship between the pigments in hairs and those in the hypodermis is at present unknown but might prove to be of considerable phylogenetic and taxonomic interest. Indeed, why some taxa utilize hairs while many others use hypodermal pigments is not clear.

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This quote if from the paper I cite below, and while I don't want to publish quote and quote after quote from the paper here, I did try to grab a sentence in which it showed pigments exist both in the hairs and hypodermis.

Here are a select few more, supporting my earlier statements:

Unlike the chromes of many other invertebrates, those of spiders have been relatively little studied from a biochemical point of view. Only three major classes of pigment, ommochromes, bilins, and guanine, have been positively identified to date (66).

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Other pigments, apparently unrelated to these major classes, have
been detected in spiders but have not been fully characterized.

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So the argument about the possibility of 'albino tarantulas' should continue sans the 'fact' that spiders lack pigments and coloration is due simply to shape of hairs and cuticle.

G.S. Oxford and R. G. Gillespie. (1998) EVOLUTION AND ECOLOGY OF SPIDER COLORATION Annual Review of Entomology Vol. 43: 619-643

A point of clarification for guanine. Any color from guanine is due tor defraction of light and it has no inherent color to it. It has a high refractive index partly due to the fact it forms planar crystals that stack. The chances are very good guanine will always be present as it also necessary component of DNA. Its also used to give the pearlescent quality to shampoos and lotions.

Ommochromes would almost always be present as they result from tryptophan metabolism. So for them not to be present would mean there is a metabolic defect and probably seriously affect surviability of the t. So it is unlikely that you could have a t that lacks them.

Not familiar enough with the bilins but they are highly conjugated systems so it is well within reason that they have inherent color.

Though overall it is still highly improbably to have an albino t.

I got just a tiny tiny headache from reading all that......... Interesting read though.

More on Ommochromes from the paper I cited above.

Ommochromes are derivatives of the amino acid tryptophan via kynurenine and 3-hydroxykynurenine and are responsible for a wide variety of colors (yellows, reds, browns, and black). Different colors are produced by different combinations of ommatins and ommins, and they may also depend on the redox state of the pigments and on the nature of conjugated proteins

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Ommochromes are usually deposited as pigment granules within the cells of the hypodermis, immediately beneath the cuticle (66, 137), but in a number of species both xanthommatin and ommins can also be present in considerable amounts in the digestive mass

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And here is some info on Bilins, also thanks to that paper.

Bilins are blue or green pigments that consist of a linear arrangement of pyrroles. The green coloration of Micrommata virescens (Heteropodidae) is a result of micromatabilin in the hemolymph, interstitial tissues, and yolk of oocytes (68, 71). As with ommochromes, the final color produced is a function of both the pigment and its conjugates (65).

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I believe it is fairly rare to have any kind of natural albino in most taxa, it just so happens that selective breeding selects for this trait once it is found. But once again, I don't want to debate albinism in tarantulas I just wanted people to know that this 'fact' they keep throwing around about spiders lacking pigments is false.

Ok now you are getting crazy, I am going to go out on a limb and say that was over most people's heads, mine at least...... I get the general idea, but if I follow my mothers rule and looked up every word I did not know the exact meaning of, id be screwed.

Thoth said:

Though overall it is still highly improbably to have an albino t.

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It is overall highly improbable to have any albino, they are natural selected against, and there for do not happen often.

As for the albino, color variation does happen. We will need to wait a few months to find out the extent.
thedarkfinder.

ps albinism is a polygenic so there is going to be levels to it. Some are going to have to be lighter some darker. Depending on the state of the allele.

I think lucanidae's point is well made.

The 'myth' / urban legend here is that an albino T is biologically impossible and he has quite effectively showed evidence to prove that statement wrong.

The fact that an albino T occurring in nature is improbable is not related to his original statement.


The mechanism for color may be different in T's than let's say GoldFish.

BTW thanks for making me grab my Biochem book, I found a fiver marking a page.

amazing stuff. thanks for posting it. for about the first six months i was in the exotic invert hobby i was very confused about the stuff i found concerning the mechanisms for coloration in inverts and made a mistaken inference that the cuticle reflects all light so pigment coloring wasn't a mechanism, but some other ppl pointed stuff out that made me see the error of my ways.

this would have set me on the straight path from the get go


oh, btw... did this have anything to do with the B. smithi color experiment thread? that smithi thread got the old wheels turning in my brain again. fun stuff to think about.

Albino Tarantula

Lets just leave it at, Nothing's impossible, only improbable. Cause I got a headache now too.

Right, but we arent really talking about albinism right now.

Anybody have any other "facts" they see around these boards that they believe might be just as much as a myth as "spiders lack pigments"?

...Pass the aspirin :wall:

Great post, thanks for sharing and realy doing your homework! So who wants to write a grant proposal so we can fund a complete sequencing of the threaphosid genome, and identify all the alleles that affect pigmentation?

BTW - remember that *pigmentation* does not mean exactly the same thing as color or "perceived color" That's what spectrophotometers are for.

Its a reasonable mistake to make particularly seeing how that phenomenum (i.e. color due to diffraction rather than pigments) is not that uncommon and is shared by certain species of birds and fish as well other non arthropods. Though all said and done there is still a structural component to t color.

Though it would be an interesting look at ts under polarized light and with polarized lenses to see if can be determined which colors and how much color is due to diffraction (not to mention what new ones might appear under such viewing conditions)

In nature most albinos are selected against because they are easy prey and rarely survive long enough to breed. With ts it may be different because 2 of the 3 major classes of pigmentation are tied to key metabolic processes, whose lack would lead to death (actually it would never develop). Possibly all 3 are but again I need to look bilin pathways. I should have been clearer with my original statement but it was written at 3 am.

I don't know where I implied albinism monogenic unless thats out there for just for general edification.

Hey Nerri are we entitled to a cut of the five seeing it was because of us, you found it.

Pigmentation is linked to neccessary biological pathways, now THAT is a real scientific explanation of why albinism dosen't occur in Theraphosids. I'm glad I decided start this thread, because it has provided me a much more fullfilling answer to that particular question. Thanks Thoth.

Wait a sec

Whoa, wait a second. While Thoth's speculation is reasonable, it is based on the _known_ classes of pigments. As the original citations mentioned, there are many more unstudied pigments. The very fact that they have not been thoroughly examined implies that said pigments are not known participants in any important metabolic pathway. As such these pigments might be relatively unimportant. Hence, none of the above is evidence against theraphosid albinism, scientifically speaking. That is, of course, unless the 3 described pigment classes are necessary for coloration, in which case others would be irrelevant.

Btw, albinism is certainly not always selected against in the long term. For example, melanin is a required pigment in Substantia Nigra that is affected during Alzheimer's disease in mammals. I.e. albino mice can't suffer from Alzheimer's disease.

While I don't particularly care about whether or not albino tarantulas exists, I would like to point out that spiders do use three major classes of pigments for coloration, in the cuticle, hypodermis, and in the hairs.

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Yes, ok, well, let's not get too far from the original purpose of this thread. We aren't talking about albinism in tarantulas really, just trying to destroy the myth that tarantulas lack pigment.

Also, albinism is highly selected against in nature. Only one large population of albinos is known to exist; that is white tailed deer on a military base (they aren't even albino really, they have dark eyes...but since you are in Ithaca you should take a day to drive out and see them!).

Just because albinism may help one disease (as is your mouse example) this doesn't mean it won't be selected against. Going along with your mouse example...albinism effects mouse eyes. So the tradeoff is between having better eyes when you are younger (being able to find food, avoid predators, and find mates more effectively) or lacking these qualities just so you could possibly survive longer into old age. The existence of aging tells us that natural selection favors traits that help us when we are young even if they are detrimental when we are older. Also, anything that is hunted by a visually guided predator has almost zero chance of long term survival for albinos.

As I said before, Thoth's explanation isn't our end all be all explanation, but it certainly is better than saying 'tarantulas can't be albino because they lack pigments.'

I agree in general. However, I can't stop myself from pointing out potential flaws in scientific arguments.
Also, my point with the mouse example was that, in theory, albino humans would be immune to Alzheimer's disease, a rather common debilitating condition. The experiment was done on mice, in whom the disease was induced - obviously there is no selection for albino mice as they don't get Alzheimer's naturally anyway...

Even still, a human in natural conditions (say 10,000 years ago) would be much more reproductively fit if they had normal skin pigmentation and died of disease later in life as opposed to the stresses induced on the body by albinism early on which would probably lead to less reproduction..... and a decreased life span anyways....

Point being, mutations as extreme as albinism are selected against nearly 100%. Thus, if an individual linked genes and processes so that albinism could never occur in its offspring, it would be more fit than others in its species whose offspring had the potential to produce unfit mutants.