jayant
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Dedicated to Biospeleological Research www.cave-biology.org
Posts: 18
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Post by jayant on Apr 4, 2008 10:44:52 GMT -5
Stories about cavefish are like buses - you get a seeming infinity of nothing and then loads turn up at once. Just 10 posts ago, I wrote about a study which found that you can restore sight to blind cavefish by cross-breeding individuals from different caves. The different populations lost their eyes through changes to different sets of genes and in the hybrids, each faulty version was paired with a working one. As a result, the hybrids had fully formed and functional eyes despite having lived in darkness for a million years. Now, a new study shows that the larvae of blind cavefish can detect light (or more accurately, shadows) too, even without working eyes. Complete Article cave-biology.org/forum/index.php?topic=636.0
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Post by Azurerana on Apr 6, 2008 15:22:23 GMT -5
Defining "blind" is the operant word. Cavefish being able to detect light is not news. Cavefish have always been defined as blind, because they have no visual acuity, not because they "see" only black.
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jayant
Beginner
Dedicated to Biospeleological Research www.cave-biology.org
Posts: 18
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Post by jayant on Apr 7, 2008 0:25:00 GMT -5
Defining "blind" is the operant word. Cavefish being able to detect light is not news. Cavefish have always been defined as blind, because they have no visual acuity, not because they "see" only black. Its not absolutely correct. Cavefish being blind can detect light. And the receptor may be an extra occular (eye) system, may be pineal or dermal itself. The working capacity of their rudiment eyes are always a news.
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Post by Azurerana on Apr 7, 2008 20:11:32 GMT -5
Dear Jayant,
This is not to criticise your work in determining why cavefish remain light sensitive, so please do not take it that way. It is just that cavefish where I live (both A. rosae and T. subterraneus) in the adults have long been known by cavers to be able to detect light. This is firsthand, and anecdotal, of course, however, I have myself played 'hide and seek' with T sub specimens with my headlight and the fish in their natural environment. Old incandescent lights have a 'bright spot' and a dimmer circle of light surrounding them. T. sub will flee the bright inner light, but if you look at them obliquely, using only the dimmer outer circle, they will remain motionless as if they were unseen.
Both A. rosae and T sub are farther removed from surface species than the Mexican "cave tetra" with which you are working -- A. rosae being further along the dark adapted line, but both species do still react to the light. Neither has eyes. These fish will also retreat under ledges if given the chance, and T sub shows some very wide variety in adaptability, morphology and habits between caves. I also know of a sinkhole where T. sub thrives outside (albeit in perpetual shadow at the bottom of a karst window. We did not norm the study to account for possible affects of vibration, but our trials were standing still, and moving only our heads.
Perhaps this may suggest some further experiments for you in using variable light and cavefish adults in your work. I am not a biologist; however I do have an undergraduate geology degree, and know quite well that a mere reported anecdote does not science make. Feel free to pursue any lines of study off this suggestion.
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jayant
Beginner
Dedicated to Biospeleological Research www.cave-biology.org
Posts: 18
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Post by jayant on Apr 8, 2008 8:25:45 GMT -5
Dear Azurerana, The behaviour of cave fish (whether blind or with regressive eye sight) with light has been found to be peculiar. Our several experiments (already published) shown that at a particular time the cavefish (our experimental model Nemacheilus evezardi comes to light zone irrespective to the availability of food (at light zone). However, our group have repeated the same study with different light intensities, frequencies etc. But at this moment it is hard to say why they are photophilic even lying in dark from generation to generation. So behaviour of each species various as per their ambient environments. -Regards.
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