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Spitting cobras' sharp-shooting secrets
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by tigers9 on January 21, 2009
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http://www.msnbc.msn.com/id/28774770/
Spitting cobras' sharp-shooting secrets
Process is like a baseball pitcher psyching out batters before a throw
By Jennifer Viegas
Discovery Channel
updated 10:22 a.m. PT, Wed., Jan. 21, 2009
Spitting cobras spew blinding venom toward the eyes and face of victims with surprising accuracy, and now researchers know how they do it.
Venom spitting — a defense mechanism only — is a two-part process that's part muscle and part like a baseball pitcher psyching out batters before winding up before a throw, indicates a new study published in the latest issue of Physiological and Biochemical Zoology.
"Since the venom can cover a distance of over 6.5 feet, and the snakes appear to be very accurate, it is presumed to be a good deterrent," said Bruce Young, an associate professor of biology at Washburn University and lead author of the study.
For the study, Young and colleagues Melissa Boetig and Guido Westhoff analyzed adult, captive specimens of the red spitting cobra, the black-neck spitting cobra and the black-and-white spitting cobra.
Equipped with a special visor to protect his eyes, Young had the indelicate task of taunting the snakes by moving his head in front of them. The visor was outfitted with a custom-made accelerometer system allowing a computer to track the movements of Young's head in three dimensions.
During one experiment, the researchers also anesthetized some of the snakes and implanted electromagnetic leads to monitor a muscle that controls the venom gland, as well as the movements of the snake's head and neck.
The scientists found that before a spitting cobra releases its venom, a muscle contracts, displacing tissue barriers in the snake's fangs that normally prevent the flow of venom. More muscle contractions increase pressure within the venom gland, propelling a stream of venom out the fangs.
The spitting wind-up explained, the snakes' accuracy was still a mystery.
"When we looked carefully at the data, we found that the cobras always spat shortly after I changed the direction my head was moving," Young said.
He added that when he was moving his head, the snake was also rotating its head, winding itself up before the impending hurl.
"This really boils down to geometry," Young explained. "Since I am moving linearly at a distance from the snake, the snake need only make slight angular movements to follow me. Once the cobra starts spitting, it accelerates the movements of its head, and this enables the snake to actually 'lead' its target and spray the venom to where it thinks the target's eyes are going to be."
The researchers further discovered that spitting cobras don't release their venom as a stream, mist or cloud. The liquid poison instead sprays out in distinctive geometric patterns, typically consisting of paired ovals. The scientists suspect this increases the overall area covered by the spray, heightening the snake's chances of hitting the eyes.
Aside from causing temporary or permanent blindness, the venom, if it penetrates the open eye, can enter the victim's body, sometimes leading to additional systemic problems.
Aaron Krochmal, assistant professor of biology at Washington College, also studies snakes.
Krochmal told Discovery News that the new study "is, quite simply, top notch," and that "there are some very interesting and important findings."
Young and his team are now focusing on the snakes' vision in relation to its reaction time.
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RE: Spitting cobras' sharp-shooting secrets
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by FSB on January 24, 2009
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Thanks, Z, for the interesting article, and this is something I've been putting some thought to recently. Mostly, I'm interested in finding out what sort of visual cues the snakes use to locate the eyes... is it the eyes themselves that are the target, or are they programmed by instinct to aim for the face since that is where the eyes are located?
It would be interesting to devise a study something like the one used on herring gulls, which have a red spot on the beak which the chicks peck at to induce their parents to regurgitate a meal. The study utilized models of gull heads with the red spot moved to various locations to determine if it was the spot itelf, or the location of the spot, that cued the chicks' pecking.
With spitting cobras, I think a similar approach could be used employing dummy heads of various animals, including ones that would be a familiar, natural threat in a certain snake's home range, such as wildebeests or other large ungulates. The eyes could be moved to various locations on the dummy head, or removed alltogether, to determine if there is any effect on the snakes' aim. Also, how do spitting cobras react when defending themselves against a threat from an ophiophagus snake? Squirting venom at a snake's eyes would be useless, since all snakes have built-in safety goggles.
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RE: Spitting cobras' sharp-shooting secrets
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by AquaHerp on January 24, 2009
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If I recall, that has been published a few years back. 2004 or 05 I am thinking.
DH
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RE: Spitting cobras' sharp-shooting secrets
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by tigers9 on January 24, 2009
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paid text:
http://www.journals.uchicago.edu/doi/full/10.1086/595589
paid PDF text:
http://www.journals.uchicago.edu/doi/pdf/10.1086/595589
abstract:
http://www.journals.uchicago.edu/doi/abs/10.1086/595589
Physiological and Biochemical Zoology 82(1):80–89. 2009.
© 2009 by The University of Chicago. All rights reserved.
1522-2152/2009/8201-8135$15.00
DOI: 10.1086/595589
Functional Bases of the Spatial Dispersal of Venom during Cobra “Spitting”*
Bruce A. Young1,†
Melissa Boetig1
Guido Westhoff2
1Department of Biology, Washburn University, Topeka, Kansas 66621; 2Institute of Zoology, University of Bonn, Poppelsdorfer Schloss, 53115 Bonn, Germany
Spitting cobras expulse venom toward the face and/or eyes of potential predators as part of their defensive repertoire. Evaluating the accuracy of the cobras is difficult because the spit venom does not land as a point but rather is distributed, in some cases widely, in complex geometric patterns on the surface of the target. The purpose of this study was to explore the functional bases of the venom’s spatial distribution. Using a combination of spatial analysis of “caught” venom, morphology, high‐speed digital videography, and electromyography (EMG), three hypothesis were evaluated. Two of these hypotheses—that the spatial distribution was due to differential venom pressure produced by the contractile activity of the adductor mandibulae externus superficiali and that the spatial distribution was produced by the morphology of the venom canal within the fang—were both rejected. The third hypothesis—that the spatial distribution was due to rapid rotational movements of the head about the vertebral column—was supported by analyses of EMG activity within the cervical axial muscles and by predictions of venom‐distribution patterns based on these cephalic displacements. These results suggest that the ability to “spit” venom is a unique suite of specializations involving both the axial and the cephalic systems.
Accepted 7/11/2008; Electronically Published 12/1/2008
Cited byDominique Adriaens and Anthony Herrel. (2009) Functional Consequences of Extreme Morphologies in the Craniate Trophic System. Physiological and Biochemical Zoology 82:1, 1-6
Online publication date: 1-Jan-2009.
Abstract-Full Text-PDF Version (168 kB)
This paper was a contribution to the symposium “Functional Consequences of Extreme Adaptations of the Trophic Apparatus in Craniates,” organized by Dominique Adriaens and Anthony Herrel, at the Eighth International Congress on Vertebrate Morphology, Paris, France, 2007.
Corresponding author; e‐mail: bruce_young@uml.edu.
More articles:
http://www.journals.uchicago.edu/toc/pbz/current
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RE: Spitting cobras' sharp-shooting secrets
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by Cro on January 26, 2009
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Doug is right, there was a study in 2005 that tried to determine if the eye was the actual target.
http://www.sciencedaily.com/releases/2005/02/050212194818.htm
If I remember correctly, many years ago, there was a study that was on one of the National Geographic / Discovery / Nature type shows were people wore a face mask, and allowed cobras to spit at them. Some of the masks were entirely blank, and others had a single eye painted on them, and others had a pair of eyes painted on in different positions. I almost want to say it could have been on one of the Mutual of Omaha Shows ? I will try to find something about study.
Best Regards
John Z
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