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Natural Science Forum / Biology / Biology / October 2004a cyclops gene for slugs?
I've seen pictures of slugs with two eyes - riding on the top of their little feelers - and I've seen pictures of slugs with four eyes - again riding on top of those feelers - but I have never seen a slug with a single eye, on the top of a single feeler. Have researchers located the gene for "polyocularism" (two or four eyes) for the common garden slug? Would this be the same place to find the gene for "monocularism" (the condition of being a cyclops)? This is for a horror movie I am working on. If anybody has some pointers along these lines, I'd be glad to hear about them. >I've seen pictures of slugs with two eyes - riding on the top of their >little feelers - and I've seen pictures of slugs with four eyes - [quoted text clipped - 9 lines] >If anybody has some pointers along these lines, I'd be glad to hear >about them. The problem is that eye, like many body components, are bilateral organs. That is why they come in pairs. Whatever happens during development on one side of the body happens the same way at the corresponding location on the other side. In that circumstance, four eyes is not too difficult: given a set of interacting genes that makes a pair of eyes, just express them a second time and you get another pair. Producing a single structure in the midline requires a whole different scenario. A dozen eyed slug would be a lot easier to accomplish. |>Have researchers located the gene for "polyocularism" (two or four |>eyes) for the common garden slug? Would this be the same place to [quoted text clipped - 7 lines] |The problem is that eye, like many body components, are bilateral |organs. Um, yes . . . at least for mammals. Is it the same way for gastropods? |That is why they come in pairs. Whatever happens during development |on one side of the body happens the same way at the corresponding |location on the other side. In that circumstance, four eyes is not |too difficult: given a set of interacting genes that makes a pair |of eyes, just express them a second time and you get another pair. Does the brain of a slug have a single area for processing all its visual information, or is it 'hemispherical' in nature, with information being processed from left to right, and right to left, and shunting the spare information back and forth, depending on the apparent need to keep track of where it is going? From the slow movement of an earthbound slug, I was hoping that the motion enjoying by swinging its eyestalks, would convey the necessary parallax for an estimation of depth. If that is the case, a single eye on a single eyestalk, can do the same job as two, simply by moving the eye about more. |Producing a single structure in the midline requires a whole different |scenario. | |A dozen eyed slug would be a lot easier to accomplish. That certainly seems to be the case. Do slug eyes have cones and rods? Can they perceive color, or is it all in "black and white" for them? >Does the brain of a slug have a single area for processing all its >visual information, or is it 'hemispherical' in nature, with information [quoted text clipped - 8 lines] >Do slug eyes have cones and rods? Can they perceive color, or is >it all in "black and white" for them? Here is a very general site on vision and its evolution: http://soma.npa.uiuc.edu/courses/bio303/Ch11b.html One specialized paper on vision in a particular snail (though not a slug) is Spatial vision in the prosobranch gastropod ampularia sp Seyer JO, Nilsson DE, Warrant E. Journal of Experimental Biology 201, 1673-1679 (1998) which can be found at http://jeb.biologists.org/cgi/reprint/201/10/1673 The introduction has a lot of information about molluscan vision in general and there is a good bibliography. What appears to be good references for you are MESSENGER, J. B. (1981). Comparative physiology of vision in molluscs. In Handbook of Sensory Physiology, vol. VII/6C (ed. H. J. Autrum), pp. 93-200. Berlin, Heidelberg, New York: Springer. LAND, M. F. (1981). Optics and vision in invertebrates. In Handbook of Sensory Physiology, vol. VII/6B (ed. H. J. Autrum), pp. 471-592. Berlin, Heidelberg, New York: Springer. HAMILTON, P. V. (1991). Variation in sense organ design and associated sensory capabilities in closely related molluscs. Am. Malacol. Bull. 9, 89-91. and especially EAKIN, R. M. AND BRANDENBURGER, J. L. (1975). Understanding a snails eye at a snails pace. Am. Zool. 15, 851-863. The central nervous system of snails and slugs is, indeed, bilateral in organization as it is in all animals except the radial jellyfish/coral/hydra group which doesn't have a CNS at all. One good illustration is http://nighthawk.tricity.wsu.edu/museum/ArcherdShellCollection/Illustrations/Ner vousSystem.html which clearly shows the paired cerebral ganglia (brains) which connect to the eyes through the optic nerve. Invertebrates don't have the funny crossover we do, where the right side of the body connects to the left half-brain and vice-versa. The right eye connects to the right cerebral ganglion, the left eye to the left ganglion. There are connections between the two sides, but nowhere near as extensive as in the corpus callosum of our brain. I really don't know how much depth perception or even image formation there might be in a slug brain. The references cited above indicate that this varies tremendously in different members of the snails (Class Gastropoda). Invertebrate visual receptors don't belong to the rod vs. cone category, but have their own morphology. The fundamental mechanism of light transduction with a rhodopsin-like system is shared, but the neural mechanisms are quite distinct from our own. For instance, our own photoreceptors, the rods and cones, are actually inhibited by light, not excited. Invertebrate photoreceptors are excited by light. I didn't easily see any mention of color vision in snails and slugs -- octopus certainly does have color vision. I imagine that the references cited about would have that information. The illustration at http://manandmollusc.net/advanced_introduction/gastro_ns1.html shows how the torsion in the body of most snails doesn't really affect the organization of the brain (cerebral ganglia). Slugs are weird in that they do have the torsion characteristic of the gastropods but then undergo detorsion which sort of eliminates most of the effects. Probably an important resource for you would be Behavior and Its Neural Control in Gastropod Molluscs Ronald Chase Oxford University Press, 2002 http://www.us.oup.com/us/catalog/general/subject/LifeSciences/Neurobiology/~~/dm lldz11c2EmY2k9MDE5NTExMzE0NA== Note that the octopus is of the same phylum (Mollusca) as the slug. Yet, it is an extremely capable animal with a high metabolic rate and rapid locomotion, a very large and complex brain capable of learning complex tasks, and excellent eyes and vision. You might create monster slugs that evolved along a parallel pathway for your story. Make sure you mention that these creatures now have a good closed circulatory system to support their high metabolic rate. Also, make the foot finely divided into long tentacle-like structures so that it can move quickly by muscle contraction (like an octopus) rather than creeping along a slimy mucus trail (like most snails and slugs). |>From the slow movement of an earthbound slug, I was hoping that the |>motion enjoying enjoyed |>by swinging its eyestalks, would convey the necessary parallax for an |>estimation of depth. If that is the case, a single eye on a single |>eyestalk, can do the same job as two, simply by moving the eye about |>more. And remembering a 'frame' of some kind, for any given degree of movement. Would doing it this way have involved a larger brain to store the different representations of reality? |>Do slug eyes have cones and rods? Can they perceive color, or is |>it all in "black and white" for them? | |Here is a very general site on vision and its evolution: | http://soma.npa.uiuc.edu/courses/bio303/Ch11b.html Thanks, I'll take a look at it. |One specialized paper on vision in a particular snail (though not a |slug) is [quoted text clipped - 6 lines] |The introduction has a lot of information about molluscan vision in |general and there is a good bibliography. It might go over my head a little, but I'll take a look at it. |What appears to be good references for you are | [quoted text clipped - 19 lines] |in organization as it is in all animals except the radial |jellyfish/coral/hydra group which doesn't have a CNS at all. If the eye at the end of the 'feeler' could produce two signals, modulated by the degree of tension on either side of the feeler, then the electrical impulses produced could be delivered to the appropriate lobes of the brain. |One good illustration is | [quoted text clipped - 4 lines] |the left half-brain and vice-versa. The right eye connects to the |right cerebral ganglion, the left eye to the left ganglion. I was wondering about that. Since the brain of the slug consists of two lobes, there would have to be some way of feeding the right signal to the right lobe. That is why I suggested a means of comparing visual input to the left or right tensions on the eye-stalk, and choosing which lobe of the brain gets stimulated. |There are connections between the two sides, but nowhere near as |extensive as in the corpus callosum of our brain. Is this because the eyes on the slug don't deliver as much information as our eyes do? If slugs are so slow because they are starved for information, that might explain why the data isn't delivered as efficiently as I was thinking. |I really don't know how much depth perception or even image formation |there might be in a slug brain. There is bound to be a college out there somewhere, where they are actually studying that sort of thing. If slow processing of imperfect information actually leads to more perfect navigation, then that would be justification for the direction that evolution has taken for that animal. |The references cited above indicate that this varies tremendously in |different members of the snails (Class Gastropoda). Invertebrate |visual receptors don't belong to the rod vs. cone category, but have |their own morphology. The fundamental mechanism of light transduction |with a rhodopsin-like system is shared, but the neural mechanisms are |quite distinct from our own. Hmmmmmm...... A science fiction movie about telepathic slugs comes to mind, appropriately dressed up with the right kind of scientific jargon... |For instance, our own photoreceptors, the rods and cones, are actually |inhibited by light, not excited. Okay. |Invertebrate photoreceptors are excited by light. I didn't easily see |any mention of color vision in snails and slugs -- octopus certainly [quoted text clipped - 13 lines] | Oxford University Press, 2002 |http://www.us.oup.com/us/catalog/general/subject/LifeSciences/Neurobiology/~~/dm lldz11c2EmY2k9MDE5NTExMzE0NA== Lots of incredible links, I'll be sure to take a look at them. |Note that the octopus is of the same phylum (Mollusca) as the slug. |Yet, it is an extremely capable animal with a high metabolic rate and |rapid locomotion, Making the animals faster, does not necessarily make them smarter. Right now, I am thinking of a mad scientist that embarked on a project to increase the size of a slug's brain, with the result that the thing was a bizarre cyclops, with a single eye on a rather long feeler. |a very large and complex brain capable of learning complex tasks, and |excellent eyes and vision. The octopus is a remarkable creature. I'm certain I've seen some documentaries where the animals could be taught how to open jars, turn doorknobs, direct the spray of water from tubes, and put lids BACK on jars. A very highly intelligent animal. Now, I wonder if an octopus could be taught to recognize visual cues for glass jars with "clockwise" threadings (for the lids that are screwed on tight) and distinguish them from glass jars with "counter-clockwise" threadings... |You might create monster slugs that evolved along a parallel pathway |for your story. Okay. |Make sure you mention that these creatures now have a good closed |circulatory system to support their high metabolic rate. Also, make |the foot finely divided into long tentacle-like structures so that it |can move quickly by muscle contraction (like an octopus) rather than |creeping along a slimy mucus trail (like most snails and slugs). It's definitely worth an angle! >If the eye at the end of the 'feeler' could produce two signals, >modulated by the degree of tension on either side of the feeler, >then the electrical impulses produced could be delivered to the >appropriate lobes of the brain. <snip> >I was wondering about that. Since the brain of the slug consists of >two lobes, there would have to be some way of feeding the right signal >to the right lobe. That is why I suggested a means of comparing visual >input to the left or right tensions on the eye-stalk, and choosing >which lobe of the brain gets stimulated. <snip> >There is bound to be a college out there somewhere, where they are >actually studying that sort of thing. If slow processing of imperfect >information actually leads to more perfect navigation, then that would >be justification for the direction that evolution has taken for that >animal. <snip> >Making the animals faster, does not necessarily make them smarter. >Right now, I am thinking of a mad scientist that embarked on a project >to increase the size of a slug's brain, with the result that the thing >was a bizarre cyclops, with a single eye on a rather long feeler. You may not have the right idea about the connection between sense organs and brain regions. You don't send information to the proper lobe depending on what that information contains. The sense organ is simply wired to a specific brain region. All the information from that organ goes to that location. In the slug case, all the information from the right eye goes to the right brain, all the information from the left eye goes to the left brain. If the two brain regions want to communicate further with each other, then that can occur. There are many universities that study brain function in a large variety of slugs. The Nobel Prize in Physiology and Medicine for 2000 was awarded to Eric Kandel (among others) mostly for his studies in a sea slug, Aplysia. There is a tremendous wealth of knowledge on this animal from many labs around the world. Other slugs, the nudibranchs, are also well studied. These are all marine. The land slugs are not particularly well studied, although there has been a lot of work on the edible land snail, Helix. There is a general association between rapidity of movement and level of brain function and organization. It is not a direct cause-and-effect relation. Still, it is hard to develop rapid movement without a very rapid and effective nervous system. However, the slow and relatively modest sea slug is capable of a form of memory and learning. Hence the Nobel Prize! Your crazed scientist would probably be embarked on a project to select for a whole host of related characteristics in order to make a very large and capable animal out of a slug. He (she) would have to increase the metabolic rate to support rapid movement which would require simultaneous changes in the circulatory, respiratory, digestive, and excretory systems. Such changes are necessary in any event to produce large body size. It would have to have simultaneous changes in the nervous system to coordinate complex movements appropriate to deal with rapidly changing environments and stimuli. It would have to have more complex locomotor apparatus to enable precise and coordinated rapid movements. You had also better provide some sort of skeletal system to hold up a large body -- slugs are particularly deficient in that category. If your really want to jazz up your story, do some research on the excessively weird copulatory practices of snails and slugs! I am not sure why you are so fixed on a cylcopean single eye. A giant rapidly moving predacious slug with two eye would be scary enough! Still, if you want to retain some shred of biological credibility, you should fuse the two eyes into a single midline structure. The idea of getting depth perception from swaying back and forth is not at all far fetched. I believe that some birds do that, cocking their heads back and forth and I am sure there are other examples in the animal kingdom. Essentially all animals have feedback from sensors detecting head (or tentacle) and eye position and the visual system so they can figure out what they are seeing as their bodies/head/eyes move. Adding depth perception as part of that ability is no great stretch. Then, again, you have to work out just how much biological realism is necessary for your story. You might do better not to worry about all the fine details. You are bound to miss some (or many) or them and get lots of angry letters from biologists as happened to Jurassic Park. You also have to worry about following too closely the precedents set by the possibly all too similar slime-generating monsters in Ghostbusters or Men In Black! >>I've seen pictures of slugs with two eyes - riding on the top of their >>little feelers - and I've seen pictures of slugs with four eyes - [quoted text clipped - 20 lines] >Producing a single structure in the midline requires a whole different >scenario. Cycloptic mammals are known. I think some farm animals (sheep?) can develop as cyclops if mom eats certain toxic plants. I think that Leroi discusses this in his book Mutants. I vaguely recall that he discussed cycloptic humans. As rn notes, the developmental reason is probably different than in going to multiple eyes, but it can happen. bob >>>I've seen pictures of slugs with two eyes - riding on the top of their >>>little feelers - and I've seen pictures of slugs with four eyes - [quoted text clipped - 29 lines] >As rn notes, the developmental reason is probably different than in >going to multiple eyes, but it can happen. The developmental abnormality is called "cyclopia". One form is synopthalmia in which the two eyes fuse into a single structure. Others result from a rather catastrophic failure of forebrain development (holoprosencephaly). In that case, major portions of the brain fail to form proper bilateral structures and there are multiple midline facial defects. It might be possible to imagine such a defect affecting only the eyes and in such a way as to leave a single functioning eye. In reality, the defect is major and involves so many facial and brain structures. However, the subject matter is fiction or, more likely, science fiction or fantasy, where all kinds of things are possible. |
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