Why Scorpions Glow In Black Light.

skinheaddave

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First off, I don't know how practical stripping the chemicals is, as they are an intrinsic part of the exoskeleton. You can remove the fluorescent properties through continuous exposure to UV light, but I don't imagine that this actually removes the molecules -- likely just damages them and removes their fluorescent capability. The real key the experiment, beyond the use of more specimens (given a properly designed study and good statistical practices you might get away with less than 30, or might need more -- I'd like to know where you got this number without an experimental design) would be to set up your controls under a similarily powered light that emmitted in a different portion of the spectrum (but do you compensate for the power difference due to wavelength or not ... hmmm). Alternately, you could expose some to UV light until they lost their fluorescence and then test them in conditions identical to the controls.

Regardless of the practicality, let us assume that the study is done in full, with adequate statistical power, and a significant (statistical and practial) result is found. The question then becomes whether the damage to the molecules results in a more porous cuticle, whether the UV has damaged something other than the fluorescing molecules, whether the trait is adaptively significant to primarily nocturnal animals etc. etc. etc. My point was not that this study provides any answers -- merely that someone else had clearly been thinking about a connection between fluorescence and water retention but had only done a preliminary test and not a proper study.

As for the "no UV light" thing, this is not actually true. Moonlight is actually just reflected sunlight and has a remarkably similar spectrum. Furthermore, according to Kloock's study on avoidance by aerial scorpions (Euscorpius #21), there is at least enough UV light out at night to have a detrimental effect on the scorpions due to their fluorescence -- at least on or around a night with a full moon. While scorpions do tend to prefer moonless nights, they DO come out on lit nights and will occasionally wander around during the day.

It is actually interesting that you mention the aquatic lifestyle, since there are some theories that revolve around that as well.

Overall, a very interesting subject.

Cheers,
Dave
 

fusion121

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lucanidae said:
We should remember that scorpions were orginally acquatic (and HUGE) and perhaps (as suggested by some) the phosphourescent chemicals are a leftover byproduct of from something important to aquatic life. We do see a most bioilluminescence in ocean fauna.
Fluorescence and bioluminescence are fundamentally very different properties, so I don't it as easy as that to draw comparisons to scorpion and other "light using" forms aquatic life. That said this link is very interesting:

http://oceanexplorer.noaa.gov/explorations/05deepscope/background/fluorescence/fluorescence.html

In contrast, fluorescence in the organisms living on the deep sea bottom in the majority of cases seems to be a mere by-product of particular tissue biochemistry and is unlikely to play any particular adaptive role. Such fluorescence is usually weak, is not localized to particular body regions and has a wide featureless spectrum. The most common example of this is green fluorescence of the exoskeleton in crustaceans and other arthropods such as sea spiders
 
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lucanidae

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The above quote is in perfect agreement with my argument, a by-product of a pathway in aquatic arthropods that produces flourescence for no reason.

Maybe scorpions avoid nights when the moon is out because of visible light....not because of UV light. Besides, if flourescing actually helped retain water, then why do fossils of aquatic scorpions glow? No reason for water retention in that case. Why do rainforest scorpions glow? Why hasn't flourescence evolved in other animals that need to retain water in the desert? The point is, there are to many blattant inconsistensies with the water retention hypothesis.

Oh, and 30 is a statistical rule for a good paired test expieriment.
 

fusion121

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lucanidae said:
The above quote is in perfect agreement with my argument, a by-product of a pathway in aquatic arthropods that produces flourescence for no reason.
Yes I'm also in the camp that’s merely a quirk of chemical fate, which may have served a purpose earlier in scorpion evolution. I was merely pointing out that you keep changing terms, fluorescence, phosphorescence ( a sub-set of fluorescence) and bioluminescence all mean different things. The only one relevant to scorpions is fluorescence.
 

skinheaddave

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Maybe scorpions avoid nights when the moon is out because of visible light
Entirely possible. That being said, the Kloock study exhibits that there is a cost associated with the fluorescence (purely a function of the UV light) so a scorpion that bypassed whatever pressures are associated with the visible light would still have a cost associated with the UV light. In other words, UV does have an effect -- doesn't mean it is adaptive, but it does mean you can't use a "no UV at night" argument to dismiss that it may be adaptive.

lucanidae said:
The point is, there are to many blattant inconsistensies with the water retention hypothesis.
Absolutely nothing you have mentioned removes the possibility that the molecules responsible for fluorescence have a function in water retention. It only speaks to adaptation -- not function. I don't know the answers to your questions because, as has been mentioned several times already, there are very few studies of such things and it is hard to provide evidence for adaptive arguments. Perhaps it would be wise to determine if and how fluorescence is linked to water retention (ultimatley probably a doable series of experiments) before we start proposing theories as to the why of it all.

http://ethomas.web.wesleyan.edu/wescourses/2004s/ees227/01/spandrels.html is an interesting article (from some fairly well known scientists ;) ) discussing function, adaptation and where scientists go wrong thinking about them as completely linked. It is entirely possible that scorpion fluorescence has no adaptive function and is simply a byproduct. It is also possible that it was a byproduct to begin but has been selectively maintained in terrestrial scorpions. It is entirely possible that it has a selective cost but has not been selected against because suitable mutations have never occured, there is a more pressing selective pressure in favour or, like the spandrels of San Marco, it is merely a necessary byproduct of another function. It is entirely possible that it was a selective adaption in the first place but has been retained despite the loss of the selective pressure. Point is, we don't know and it is very hard to establish evidence along these lines. All of the adaptive/non-adaptive arguments, however, say nothing of function. It is entirely possible that there is a real and testable reason for scorpions to lose more water under UV light that is, itself, merely a byproduct. It is also possible that the Constantinou & Cloudsley-Thompson test was merely a fluke. You see what I'm getting at here? There are plenty of possibilities and there is no point in drawing conclusions before testing them.

Oh, and 30 is a statistical rule for a good paired test expieriment.
Yeah. It is in my first year stats textbook as a good rule of thumb for the division line between small samples and big samples too. That being said, there are plenty of statistical methods that address issues surrounding smaller group sizes. If we dismissed any group smaller than 30 as insignificant then we'd also have to dismiss an incredible amount of statistically sound studies that have been done to date.

Cheers,
Dave
 
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skinheaddave

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fusion121 said:
Yes I'm also in the camp that’s merely a quirk of chemical fate, which may have served a purpose earlier in scorpion evolution.
And, as you know from our previous discussions, I am of the "you're probably right, but it might be fun to look into" camp. ;)

Cheers,
Dave
 

Alakdan

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I'm enjoying this discussion.

Pardon my ignorance guys.

Are there other arachnids or insects that glow under UV light?

Just a thought, one of the scorps set of eyes is probably sensitive to this luminescence, and this help them see and identify other scorps or prey. Do you think there is a difference between the light wavelength reflected by each scorp specie? Sort of a "signature" glow.
 

skinheaddave

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Alakdan,

I'm enjoying this too. Since I graduated, I don't get quite as many opportunities for exchanging ideas with others -- especially those with an academic leaning -- something I always enjoy.

There are other arachnids and insects that fluoresce to some degree. Some amblypygi fluoresce in certain parts. Some spiders have high UV reflectivity, though they do not actually fluoresce. There was one spider (Micrathena sp.) I ran into in Costa Rica that glowed as brightly as any white T-shirt under my UV light -- really not sure what was going on there or how common it is. There's an early review paper (Lawrence, 1951, I think, but don't quote me on that) that reviewed the matter at the time.

There are a couple theories I've seen surrounding the fluorescence being used as a visual cue etc., but most of them seem poorly supported, especially in light of the scorpion's relatively poor ability to resolve images. There is a theory that has been presented that they use their own fluorescence to aid in navigation -- but as far as I know this one hasn't been tested. Regardless, median eyes and lateral eyes have both been shown to be receptive to the emmitted light and, as already mentioned, Zwicky found that the extraoccular light sense of Urodacus was sensitive to this range.

Cheers,
Dave
 

lucanidae

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On the topic of arachnid UV reflectance; there is a really cool study on thomisid crab spiders of australia whose reflectence effects pollinator choice of flowers, really cool paper.
 

lucanidae

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Chittka,Lars. Camouflage of predatory crab spiders on flowers and the colour perception of bees (Aranida: Thomisidae/Hymenoptera: Apidae) Entomologia-Generalis. 2001; 25(3): 181-187
 

cacoseraph

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lucanidae said:
On the topic of arachnid UV reflectance; there is a really cool study on thomisid crab spiders of australia whose reflectence effects pollinator choice of flowers, really cool paper.
now that *is* interesting... flowers reflect UV to look like targets to bees... this is just spitballing... but i wonder if a part of the cause has to do with certain feeders being attracted to reflected UV making for better fed scorps. course, this kind of clashes with the aquatic origins as i doubt there is much UV making it down into the briney deep =P

i expect as in much of life, there is no single cause, but combo of many different influences
 

TTstinger

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my thoughts

:wall: Ok many Ideas/theories and a whole bunch of big words. Good read though. But what if the reason scorp have a glowing talent is just this. Now think about this as if you were a bug such as a moth. Keep in mind to that we humans really have no way to know how any creature see's the world with it's eyes.

Now a moth flies to light for unknown reasons and no test on earth could ever really tell us why, but they do. does it see that as light or maybe it see's it as dark just maybe the scorp has just developed it's self a lure. Making it's seem like the right place to go when really it will be the death of you.

Basically the scorp has evolved to become a bug attracting light source even with minimal UV not noticeable to the human eye, like the black lights we are so use to. In my mind this make the most sense, being loads of creepy crawlies are attracted to light source's. So in that theory the glowing talent become of some use to the scorp. I just do not think it has to do with keeping moisture.

And futhermore for example purpose my sperm fluorescence under black uv light does that mean the little guy are trying to stay wet. I really think this topic is great for debate but in thee end I think That is all we will learn it make great debate. Oh and the military will make a great bomb that glows under UV or some rad weapon. they are making bullet proof vests out of spider web kinda cool I guess.

Sorry I could not use big words or drawn out terms and as far as test I can't pass a p test. But thats my thoughts on the whole thing, and I don't think UV has really any effects on scorps and If anyone has a scorp that does not glow because of too much UV I want to see it. Please post a pic of this non-glowing scorp please.

Thats my 2 cents and you can take them to the bank or whatever

P.S. you guys are the best
 

skinheaddave

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cacoseraph said:
fed scorps. course, this kind of clashes with the aquatic origins as i doubt there is much UV making it down into the briney deep
True. But in the shallow seas where the aquatic scorps mostly seemed to live, there would be plenty of UV penetrating the first bit of water. So, as with the "no UV at night" argument, it isn't overly compelling.

cacoseraph said:
i wonder if a part of the cause has to do with certain feeders being attracted to reflected UV
TTstinger said:
Basically the scorp has evolved to become a bug attracting light source even with minimal UV not noticeable to the human eye
For the theory that it is an attractant to insects, it may be worth your while to read this:

http://www.science.marshall.edu/fet/euscorpius/p2005_21.pdf

kind of throws a monkey wrench in that one. Plus, remember that we are talking about fluorescence, in which the emmitted light is in the visible blue/green spectrum, not reflected UV.

Cheers,
Dave
 
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TTstinger

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skinheaddave said:
remember that we are talking about fluorescence, in which the emmitted light is in the visible blue/green spectrum, not reflected UV.

Cheers,
Dave
how do you know what is reflected to a bug. Somthing that see's in a way humans can never know, what we can't see maybe they can. There is a world that humans will never see nor will the know with science.
Sometime's the answer is the one staring you in the face but you don't see it cause your trying to hard to prove it with science and tests.

your link did not work, send another.
 

cacoseraph

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skinheaddave said:
True. But in the shallow seas where the aquatic scorps mostly seemed to live, there would be plenty of UV penetrating the first bit of water. So, as with the "no UV at night" argument, it isn't overly compelling.




For the theory that it is an attractant to insects, it may be worth your while to read this:

http://www.science.marshall.edu/fet/euscorpius/p2005_21.pdf

kind of throws a monkey wrench in that one. Plus, remember that we are talking about fluorescence, in which the emmitted light is in the visible blue/green spectrum, not reflected UV.

Cheers,
Dave
pretty experiment. does seem to indicate fluoresence has a negative effect on prey capture

i thought the fluoresence *was* reflecting the UV into visible via some crazy electron/photon intereaction, by definition
 

skinheaddave

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Reflection is when the light basically bounces off something. So UV goes in, UV comes out. Fluorescence is when the energy from the light going in (in this case UV) excites the molecules, which then become less excited, returning light of a different wavelength (in this case, somewhere in the blue-green portion of the spectrum).

how do you know what is reflected to a bug
You stick an electrode in the nerves running from the photoreceptive cells and then expose it to various stimuli. If there is an electric impulse then it senses it, if there is not then it doesn't. That doesn't tell us how the creature percieves the stimuli -- just that it does or it doesn't. We actually know quite a bit about insect senses, as they have relativley simple neurological systems which are much easier to study than more complex systems (mammals, for example). Regardless, the point was that bugs being attracted to reflected UV would be different from bugs being attracted to fluoresced visible light -- you provided a potential explanation to an entirely different thing.

Oh, and the link has been fixed for a while now. Try clicking on it again.

Cheers,
Dave
 

Metzgermeister

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hmm

I was looking though the scorp gallery, and theres a freshly moulted scorpion under a uv light, and it barely glows at all, while the shedded skin is glowing like crazy. Perhaps it has something to do with the hardening of the exoskeleton??:?

(p.s. a glowing scorp would look kinda intimidating to predators, whilst a newly molted one would neatly blend in with the darkness??)

http://www.arachnoboards.com/ab/gallery/showimage.php?i=883&c=502
 
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