Fang Length Relationships
from
Mark McMahon
on
February 4, 2002
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RELATIONSHIPS BETWEEN FANG LENGTH AND THE TOXIC/DIGESTIVE PROPERTIES IN FRONT-FANGED SNAKES.
The Viperidae in Southern Africa, as is typical of the family, have extremely long venom fangs. The mechanical action of these formidable "needles" would, more often than not, result in massive internal damage when thrust into the prey item, resulting in-or closely followed by- death, due to fatal organ damage.
This ability to stab the prey to death leaves more scope for the development of digestive enzymes in the venom itself, i.e. the evolution of advanced digestive enzymes to aid in digestion, at the expense of underdeveloped toxicity, because the subduing and killing of the prey is carried out by the mechanical action of the bite. This results in a highly developed and effective combination in both immobilising and digesting of prey items. Very large quantities of venom in relation to individual size could also be seen as a resulting development with the intention that a much larger dose of venom would cause toxic shock, again making up for the lack of toxicity, and consequently speeding up the digestive action even further.
The Elapidae family, on the other hand, have developed highly toxic and immediately effective "immobilising qualities" to the venom. This could be interpreted in that the initial immobilisation of prey is more paramount in feeding than is digestion. The function of digestion is thus left up to the internal digestive juices, which could, arguably, be stronger than those of the Viperidae. i.e. the lack of fang length developement has depressed the progressive developement of digestive enzymes in the venom to allow for more advanced developement in toxicity, so that the lack of mechanical killing power can be covered by the injection of a potent and immediately acting toxin.
This can perhaps be seen as motivation that the Viperidae have in fact developed a more advanced venom apparatus as is popularly believed.
Published in "African herp news" the newsletter of the "Herpetological Association of Africa" journal.
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Fang Length Relationships
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by copperhead8814 on February 5, 2002
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Interesting. I've never quite thought about it in that sense. I have a tendency to relate my thinking on snakebite to human victims. The puncture wound cause by a 1 1/2 to 2 inch puff adder or gaboon fang doesn't seem to signifigant, especially when compared to the seriousness of the venom injected. But when you think about fang size relative to the size of the prey, I guess that would be like a man getting stabbed by a pair of hunting knives. Anyway, good article.
Marc
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by scottquint on February 7, 2002
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I think that the most compelling causal factor is the type of prey. All those points are accurate but I do not believe they explain the evolutionart impetus.
Almost all elapids prey upon cold blooded animals. In fact, most feed exclusively on cold blooded prey. Additionaly, the majority prefer other snakes and lizards. Another factor to consider is that many elapids are not particularly strong animals. The picture this paints, for me, is a predator that must subdue a thin bodied, chemically resistant, thick skinned animal that can often over power it. Short, thick fangs are less likely to break off, more likely to penetrated thick skin, are better suited for holding, and are unlikely to overpenetrate. Powerfully Neurotoxic venom acts more quickly on cold blooded animals than hemo/cytotoxins so hanging on becomes less of a liability.
Vipers, on the other hand, are geared towards warm-blooded prey. Longer fangs penetrate deeper into the body where over penetration is not an issue. Long fangs are also much sharper for penetrating hair or feathers. Because most viperids bite and release, longer sharper fangs are going to be more succcessful. Hemo/Cytotoxins act quickly to incapacitate this type of prey.
Overall, the efficiencies of either design will overlap the other, and so some small vipers adapted well to cold blooded prey(most of which have shorter fangs) and many larger elapids harvest warm-blooded prey(Again these often have proprtionally larger fangs).
Again, purely from a causality argument, I suggest the hunting method and prey choices were more important than some of these other effects. In fact, I think that the opportunities presented by efficiencies in these strategies led to further adaptations sch as described in this article.
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by MAMBAMAMA on March 13, 2002
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I am always very pleased and come away with increased knowledge from this site, both article and comments very thought provoking and I learned some new information , what more could you ask for. Thanks
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by Nilesnake on October 9, 2002
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From Gabon I remember the difference in attitude of cobra and viper. The Gabon Cobra is fluorescent yellow. You can see him anywhere within your line of sight. In other words "stay away from me". The Gaboon Viper is mostly immobile during the day. He does not move away when humans are near as do most other snakes. Stubborn or lazy?
We carried an antivenon syringe with a mixture of seven types of snake venom, including the two above, plus Black and Green Mamba, "Cigarette Snake" (a small red viper), Rhinocerous Viper, and one I don't remember.
Relative danger -- a year and a half in the field, at times up to 1000 men working in the jungle every day -- no bites during that time to any of our crew. Our medics treated several local residents, not employees, for bites.
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Anonymous post on January 22, 2003
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I think the length of the fangs came from the hemotoxic properties of the venom. Longer fangs can deliver venom deeper into the tissue, causing more damage, and increecing the chance of puncturing and envenomating a vital organ. Also helping in digesting pray from the inside out. Anyone know if the the venom evolved before the fang lengths grew to the sizes we see today? Or is it the other way around? Also looking for info on the venom of new world vipers compared to old wold?
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by ketill75 on February 10, 2003
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I believe in nature's way of 'developing due to needs'. This theory is supported by many things, for example this last one. A viper bite, with tissue damaging venom will be more severe if the envenomation is located deeper (as you say yourself), while a neurotoxic venom doesn't NEED a more complicated fang structure than it is today. Another example is the common question 'Why is it that the five most (terrestrial) snakes are located in Australia?'. Well, a good theory is enviromental needs. Snakes living in these open grounds with such high competition of food will NEED the prey to die very quickly so he, after the bite, can get to it before another animal (ex. bird) spots it.
A good comparision to this is the Adder (Vipera berus) here in Sweden. With these large rocky and food rich forests, also with few competitors, the snake has a very good chance to track down the prey before someone else takes it. It doesn't NEED to be that venomous... and it isn't.
Then to your question 'which was developed first... venom or fangs', I can give you an answer that isn't a theory but a fact. Venom was the first step. Without real fangs, it can't be injected. But as a mixture with the saliva it's still considered a part of the digestive system. From there, evolution took another step and fangs were developed to use it more effectively.
On a seminar about venomous snakes and spiders, I also was shown an unskinned head of a Grass Snake (Natrix natrix)... with two large venom glands. So in time, the Adder won't be the ONLY venomous snake here in Sweden, as nature seems to be working on the Grass Snake and the Smooth Snake (Coronella austriaca) too.
// Nic
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by ketill75 on February 12, 2003
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Very interesting page concerning fangs:
http://www.amonline.net.au/factsheets/snake_fangs.htm
**Nic
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