Spiky Sight - Sea Urchins Use Whole Body As Eye
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- Опубликовано: 12 май 2010
- / sciencereason ... Spiky Sight - Sea Urchins Use Whole Body As Eye
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Sea urchins don't seem to have any problems avoiding predators or finding comfortable dark corners to hide in, but they appear to do all this without eyes. So how do they see? It appears that sea urchins may use the whole surface of their bodies as a compound eye, and the animals' spines may shield their bodies from light coming from wide angles to enable them to pick out relatively fine visual detail. Divya Yerramilli and Sönke Johnsen from Duke University explain that if this is the case, sea urchins with densely packed spines will have better vision than sea urchins with sparsely packed spines, so they decided to test the vision of Strongylocentrotus purpuratus sea urchins, with tightly packed spines, to find out how well they see.
Placing individual urchins in a brightly lit arena with a 6 cm or 9 cm diameter dark disk on the arena's wall, the team viewed the shadows of the moving animals from beneath the arena's white floor. Would the sea urchins see the disk and respond to it, or would they be oblivious to the disk's presence? Recording 39 urchins' responses to the disk at different positions around the arena's perimeter, the duo saw that the urchins wandered randomly around the arena when the 6 cm diameter disk was in place; they didn't respond to it. But it was a different matter with the 9 cm diameter disk; the urchins either raced toward it or fled in the opposite direction.
Calculating the visual angle of the 9 cm diameter disk from a sea urchin's perspective, Yerramilli and Johnsen suggest that the sea urchin's visual resolution is at least 10 deg. And when the pair calculated the sea urchin's visual resolution based on the animal's spine density, they found that it could be as good as 8 deg., but not good enough to see the smaller 6 cm diameter disk.
But why did some of the sea urchins career toward the disk while others turned away? Yerramilli and Johnsen suspect that it depends on the sea urchin's interpretation of the dark object. Some of the animals may interpret the object as a predator and flee, while others identify it as shelter and head towards it. What is more surprising is that the urchins' vision is as good as Nautilus and horseshoe crab vision, which is quite impressive for an echinoid that has turned its whole body into an eye.
• jeb.biologists.org/cgi/content...
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I am always struck with awe and astonishment when science advances and sheds light on such intriguing phenomenon. One day the human race will rid itself of evidence lacking beliefs and will be unhindered to march the scientific process forward into new and wonderful frontiers.
@waltermh111 Who was criticizing? Questioning other possibilities is not criticism. In fact, it is a tribute to the researchers for having opened such interesting avenues of research.
@spirous
They said there was almost no reaction at all to the smaller disk from them, but ALL of them reacted to the larger disk. This plainly suggests some kind of knowledge of their part of the larger disk.
@spirous This is how it works.
The smaller disk is worthless to the urchens. Its too small to be a danger, but too small also to be helpful to it.
They know the urchin was reacting to the larger disk because they had a full 360 degree movement to go in, but they happened to go straight toward, or straight away from, the disk.
They would also likely stop at the disk, showing they acknowledge its existance, instead of going around it
They would likely go away a certain distance, to a safe point
@HongKongGhost Density of the spikes could make a huge difference. It would depend on whether each spike collects small pieces of data or if the spikes serve as a redundancy mechanism but that each spike has the capacity to collect the information independently. I'd really like to learn more. Had they tried putting the objects nearby in an environment with and without light? Perhaps it's some kind of electrical field sensation rather than light such as mormyrid fishes use to detect prey.
@waltermh111 In addition, I edited peer-reviewed scientific articles, and some scientists negated their own findings by not ruling out variables. It IS their job to do so. I merely posit questions wondering if they did so. Good science often opens up avenues of further research. This brief media blip told just enough to indicate that this could be so here, as well.
@werecow2003 I hope it's valid; the discovery of examples of distributed photon detection (sight without specific organized macro-structures) is way cool.
@spirous I agree that the video was not good scientific reporting. Nonetheless, the concept is fascinating.
I'd like to see the results on that project. This movie doesn't give very logical reasons to believe that the urchins detected the objects, since the announcer said some move toward the object and some move away. I'd like to find out how they differentiated the two opposite movements as other than random and not causal.
@laraesque Either way, the ability to smell over long distances is largely dependent on current I would think, just as with wind direction in the air or strength to dispurse over wide distances.
even dogs smells are infinite.
So to repeat, the idea of smell is testable. Also, what smell would the plates have that the other components of the cage not have that would make the urchins react to it?
That its a certain material?
Score another one for the scientific process!
@laraesque Yes, that was my first reaction too. I can imagine doing a statistical analysis of their motions that could reveal a distinct nonrandom pattern, but it did sound a bit odd the way it was phrased.
That bunch of spikes sees what you do there.
Does anyone know the specific sea urchin at 0:43 mark? I've seen them all over Maui water during dives but can't find out their specific names. Thank you!
How do they know why the urchins reacted to the disk the way they did? I hate assumptions. Cool that they can see with thier spikes though.
Damn, lifeforms are cool.
@waltermh111 Be difficult? No, I have a science background. I am asking probing questions. I am very curious about this fascinating study. The media always reduces science to the lowest common denominator, and there are so many interesting possibilities here. To say something is made "not to smell" is to say that no molecules can volatilize into the environment. Dogs can smell miniscule amounts of chemicals in the air. The disks, whether plastic or teflon or resin, might give off molecules.
damn that thing looks cool
@spirous Even then, to happen to go exactly away may be a coincidence, but I am sure they tried this test a few dozen times, or maybe far more, and not just one or 2.
@waltermh111 I am curious what made you react so strongly to my questions? The media pick up on many studies, some of which are valid, some of which are not. I always question.
wow
"My feeling is that the density of the spikes matter".
That does not sound very scientifically thorough.
It's sight, Jim, but not as we know it. :P
@waltermh111 That is a good hypothesis for the motivation for movement, but not for the nature of detection or even if the methodology was sound enough to support that the objects were what really caused the reaction. Was this sight? I.e., detection of photons? Or was another sense involved (chemical, i.e., smell or disturbance of electric fields, as in mormyrid fishes)? I'd love to read the whole study, rather than this media blip.
Wow, I wouldn'tve though urchins to have a complex enough brain to see images. o.O
@drche420 - it happens, no problem. :-)
@laraesque Dogs react to smells of certain kinds, not simply to metal that has a metal smell.
As to your credintials.
As a scientist you should know that appeal from authority does not win a case.
Its irrelevent what your credentials are if your criticising a study before reading it fully.
I dont expect the news report to give in depth coverage of the whole study, just to get people curious to follow up on it, or consider it an amusing thought and move on.
no way
@laraesque If you were curious, you would seek out the report before insulting the scientists or analysing a simple news report summarising the study.
You didnt help us by speculating and calling out the study itself based on only a summary news report.
Dogs can smell chemicals, sure. I get what your getting at, but we understand what it takes to smell, or might the urchins have a new way of smellng we dont know about?
I would challenge you to call it smelling then.
@waltermh111 And what did I say that was insulting? I work with scientists every day. Asking questions not answered in the media report in an open forum cannot be insulting to the scientists. Please let me know what you thought was insulting on behalf of the scientists? i thought someone here might have more familiarity with the report. My questions about smelling were the same as the articles proposition about sight. Instead of photon detection, I proposed molecule detection.
@Forserean
I am a robot. Am I not cool?
@TheBeyonder77
ha ha ha.. you should open vote on it
HOW DARE YOU! THESE ARE NOT JUST "BALLS OF SPIKES"! THESE ARE BEAUTIFUL DEMON SPAWNS!!
@Maxdwolf It is pretty self evident that when each and ever premise and explanation, conjecture by "experts", on the evidence "for" evolution can and has been refuted by more plausible answers that actually follow the evidence and does not project any belief on the evidence. That is what I do. That means the the "theory of evolution" is a religion based on mythological beliefs and nothing else.
@drche420 - don't know where you got the impression I was in any way religious. I've been an atheist all my life. The comment you've replied to is me exposing the religious comments made in other places by GoodScienceForYou, who is one of those creationist whackos that likes to claim he isn't religious to make his anti-evolution garbage sound more plausible.
@laraesque you are just trying to be difficult.
Smell? The disks would not be made to give scent. You think they wouldnt think of that? This is what they do for a living. Its a basic disk. I assume they can also detect for electric fields as this is a controlled environment. This is again there job. Thats the point of controlled environments. To keep out extra variables.
It is best to read the study, but your doubting their study before even reading it.
@GoodScienceForYou Given your tendency to promote theories of your own without evidence, this is rather ironic.
@Maxdwolf I don't promote theories. I come up with better plausibilities and back it with the evidence. I don't believe in anything that is not absolutely proven. If any belief can be destroyed by evidence that is what I do. Now tell me where is your absolute evidence for evolution, that fish ultimately evolved into humans. It must be physical, irrefutable, and have no opinions from believers in the Evodelusion religion.
@Forserean life is the leading cause of death
@GoodScienceForYou "...refuted by more plausible answers that actually follow the evidence and does not project any belief on the evidence. "
None of your idiocy is more plausible. None of it conforms to the evidence. ALL of it projects your religious belief.
GSFY quote: "We are honest Christians who believe in God and believe in what is taught".