komodo dragon

#4: Komodo Dragons have antibacterial blood

dr. dolittle — Thu, 19 Oct 2017 17:55:44 +0000

#4: Komodo Dragons have antibacterial blood

Here is the 4th most popular post so far this year:

Picture of a komodo dragon by CC BY-SA 3.0, via Wikimedia Commons

Researchers studying komodo dragons (Varanus komodoensis) at George Mason University discovered 48 previously unknown peptides in their blood that might have antimicrobial properties. Their findings were published in the Journal of Proteome Research. For the largest lizard, these peptides may help prevent the animals from getting infections from their own saliva, which is host to at least 57 species of bacteria. With this number of bacteria, it is easy to understand why they evolved so many defense mechanisms to prevent infections from their own saliva as well as bite injuries during fights with other dragons.

The researchers isolated and synthesized 8 of the peptides and tested their ability to fight infections. Seven of the peptides were found to have antimicrobial activity against Pseudomonas aeruginosa as well as Staphylococcus aureus whereas the 8th peptide showed antimicrobial activity only towards P. aeruginosa. Thus, for humans these proteins may pave the way for the development of new treatments for antibiotic-resistant bacterial strains.

Source:

BM Bishop, ML Juba, PS Russo, M Devine, SM Barksdale, S Scott, R Settlage, P Michalak, K Gupta, K Vliet, JM Schnur, ML van Hoek. Discovery of Novel Antimicrobial Peptides from Varanus komodoensis (Komodo Dragon) by Large-Scale Analyses and De-Novo-Assisted Sequencing Using Electron-Transfer Dissociation Mass Spectrometry. Journal of Proteome Research. In Press. doi: 10.1021/acs.jproteome.6b00857

dr. dolittle Thu, 10/19/2017 - 13:55

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Killing you with poison, not sepsis

razib — Mon, 18 May 2009 20:12:55 +0000

Killing you with poison, not sepsis

Ed Yong has an excellent review of new research which casts substantial doubt on the trivia chestnut that Komodo dragons kill their prey with their extremely pathogen rich saliva. The more prosaic answer seems to be that they utilize poison, not particularly surprising or trivia worthy for a reptile. But the truth is not always sexy.

razib Mon, 05/18/2009 - 16:12

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It's unclear to me whether this substance should be called a "poison" as you have called it, or a "venom". Usually poison refers to a toxin taken through eating or drinking, whereas venom is associated with a bite. But then again, venom is usually injected, and here it seems the toxin is kind of just introduced into a tear-wound via contact with the mouth.

So it's a bit of both?

"The more prosaic answer seems to be that they utilize poison, not particularly surprising or trivia worthy for a reptile."

Pretty large for a venomous reptile, though. That's always trivia-worthy. (heaviest, but not the longest)

Venomous Komodo dragons kill prey with wound-and-poison tactics

edyong — Mon, 18 May 2009 15:00:33 +0000

Venomous Komodo dragons kill prey with wound-and-poison tactics

For the longest time, people believed that the world's largest lizard, the Komodo dragon, killed its prey with a dirty mouth. Strands of rotting flesh trapped in its teeth harbour thriving colonies of bacteria and when the dragon bites an animal, these microbes flood into the wound and eventually cause blood poisoning.

But that theory was contested in 2005 when Bryan Fry from the University of Melbourne discovered that a close relative, the lace monitor, has venom glands in its mouth. The discovery made Fry suspect that Komodo dragons also poison their prey and he has just confirmed that in a whirlwind of a paper, which details the dragon's "sophisticated combined-arsenal killing apparatus".

By putting a virtual dragon skull through a digital crash-test, Fry showed that its bite is relatively weak for a predator of its size - instead it's adapted to resist strong pulling forces. This is a hunter built to inflict massive wounds through a "grip and rip" style that involves biting lightly but tearing ferociously.

The wounds provide a large open area for the dragon to inject its venom and Fry unquestionably showed that the dragons poison their prey. By placing the head of a terminally ill dragon in an MRI scanner, he managed to isolate the venom glands, which turn out to be more structurally complex than those of any other snake or lizard. He even managed to analyse a sample of venom, which is loaded with toxins that prevent blood from clotting and induce shock.

And as the icing on the cake, Fry concluded that Varanus prisca, a extinct close relative of the Komodo dragon probably also had venom glands. Also known as Megalania, V.prisca was three times the size of the Komodo dragon, making it (to our knowledge) the largest venomous animal to have ever lived.

Fry used a CT scanner to create a three-dimensional model of a Komodo dragon's skull and he assessed its properties with a technique called finite element analysis. Engineers use the method to crash-test cars; Fry used it to compare the dragon's skull to that of another giant reptile - the saltwater crocodile. Of the two, the dragon had a much weaker bite, exerting just 39N of force with its jaws compared to the 252N chomp of the croc. If a dragon bit with that much strength, its skull would fracture.

The dragon's skull wasn't much better at coping with twisting or shaking movements either - this is not an animal that can bite and hold onto a prey animal for long. However, Fry found that its skull is highly resistant to pulling forces, and that's the key to its method of attack. Biologists watching these animals have noted that when they bite, they often yank their heads back with powerful neck muscles. Their skulls take the brunt and their sharp, serrated teeth open considerable wounds in their prey.

Other studies using finite element analysis have found that other famous predators, like sabre-toothed cats and great white sharks, do similar things. For their size, they have relatively weak bites but they made up for it with strong neck muscles and very sharp teeth. In all cases, prey start losing blood, but those bitten by the Komodo dragon suffer from another weapon - venom.

Fry used a medical MRI scanner to analyse the preserved head of a dead Komodo dragon and found that it has two long venom glands, running down the length of its jaw. They are the most structurally complex venom glands of any reptile. Each consists of six compartments, with ducts leading from each one to openings between the teeth. Other venomous lizards, like the Gila monster, channel venom down grooves that run the length of their teeth but the Komodo dragon doesn't have these - it just drips venom straight into the wounds that it inflicts.

The venom itself consists of over 600 toxins, a chemical arsenal that rivals those of many snakes. Many of these poisons are familiar and they greatly exacerbate the blood loss caused by the dragon's bite. They cause internal haemorrhaging from leaky blood vessels, prevent blood from clotting and cause muscle contractions and paralysis. Fry calculated that a typical adult dragon would need only 4mg of venom proteins to send a 40kg deer into toxic shock from collapsing blood pressure. A full venom gland packs at least eight times this amount.

If the dragon has venom, you can be sure that it uses it. Venom is so costly to produce that the moment it becomes obsolete, natural selection rapidly does away with it. That's happened in other reptiles - members of venomous families that have developed other ways of feeding (like constriction, or egg-eating) quickly lost their venom system. The glands atrophied, the fangs became smaller and the genes that produce toxic proteins built up debilitating mutations. The Komodo dragon, on the other hand, has strong glands that are loaded with poison.

These results don't discredit the salivary bacteria idea, but Fry has little time for it. For a start, he says that since the dragon was first 'discovered' by Western scientists in 1912, no one has actually documented a case of a dragon victim falling foul of blood poisoning. While dangerous bacteria have been isolated from the mouths of Komodo dragons, no single species has been consistently identified in all individuals. This variability makes it very unlikely that dragons could rely on the presence of toxic bacteria as a reliably strategy to hinge their evolutionary success upon.

One study suggested that the bacterium, Pasteurella multocida, accounted for much of the saliva's killing power, but the researchers didn't find this lethal bug in all the dragons they looked at. P.multocida is rare in reptiles but common in mammals, especially those that are sick or old - exactly the demographic that dragons prefer to kill. As such, Fry believes that the bacteria isolated from the mouths of dragons actually came from the animals they fed on. To him, Komodo dragon victims die not from bacterial sepsis, but from heavy, bleeding wounds that are exacerbated by the toxic effects of the giant lizard's venom.

The dragon's extinct and even bigger relative, V.prisca or Megalania, may have done the same. This giant lizard also had a strong skull but relatively slender jawbones. It was very closely related to the Komodo dragon and the lace monitor, both of which are venomous. And Fry has previously shown that the capacity to produce venom evolved once in the common ancestor of snakes and lizard groups like the iguanas and monitors. There's every reason to think that V.prisca used venom too, which would make it the largest venomous animal to have ever lived.

For more venomous animals, and some truly amazing stories, be sure to check out Bryan Fry's blog Sex, Drugs and Rockin' Venom: Confessions of an Extreme Scientist.

Reference: Fry, B., Wroe, S., Teeuwisse, W., van Osch, M., Moreno, K., Ingle, J., McHenry, C., Ferrara, T., Clausen, P., Scheib, H., Winter, K., Greisman, L., Roelants, K., van der Weerd, L., Clemente, C., Giannakis, E., Hodgson, W., Luz, S., Martelli, P., Krishnasamy, K., Kochva, E., Kwok, H., Scanlon, D., Karas, J., Citron, D., Goldstein, E., Mcnaughtan, J., & Norman, J. (2009). A central role for venom in predation by Varanus komodoensis (Komodo Dragon) and the extinct giant Varanus (Megalania) priscus Proceedings of the National Academy of Sciences DOI: 10.1073/pnas.0810883106; Dragon photos by Chris Kegelman; skull image from paper.

More on komodo dragons and other lizards:

edyong Mon, 05/18/2009 - 11:00

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Seems strange that something so large needs venom, but there you go. Terrific stuff.

Stupidly, I never really thought hard about that whole septic bite thing - I mean, wouldn't that take AGES to kill the prey?

Frank, it might not take ages to kill the prey if the bacteria that infected the wound were toxic enough. The theory I'd heard is that the deer get sick (and blind!) over the course of a few days, and then when it dies the dragons sniff out the carcass nearby and gather and feed. So it is a "bite and wait" strategy. I have no idea if this is true or how this new venom evidence affects the time for the deer to drop or drop dead.

Is there any documentated cases the whole way from bite to devour with these dragons? That would give some good answers. I have also seen a program in which a local man shows a leg bite he got from a dragon, and how these bites take a long time to heal and even then they don't heal well.

@frank
it might take a day or two, but it would be low energy cost.

Fascinatingly enough, no one has ever seen a dragon track a deer for a few day, wait for it to die of infection and then eat it. Every documentary purporting to show this has staged the scenes. In attempt to recreate... something that doesn't actually exist!

What we have seen, however, are sustained frenzied attacks persisting for several minutes until the large prey item is dead from blood loss. The venom supplements the mechanical damage by keeping the bleeding going through anticoagulation and also helping induce shock.

Cheers
B

In the 1990s, I got to visit the island of Komodo with a CA Academy of Sciences group (mostly ichthyologists & their diver friends, looking for various fish species-- no herpetologists on the trip.

The dragons are so amazing. I believed the "dirty mouth" hypothesis at the time.

The venomous mouth theory is so much more parsimonious.

It is an amazing thing to see an old, unproven, but widely held belief be replaced overnight.

> toxic shock from collapsing blood pressure

@Ed

You're describing cardiogenic shock here, not necessarily toxic shock. Failure of circulation secondary to hemorrhage is cardiogenic.

The article however is nice. I always (wrongly) believed the "toxic" saliva theory.

Bryan - Thanks for commenting. Awesome work.

Frank - I think the point is that their arsenal allows them to kill things that are even larger.

J - I concur. All of this reminds me of a story I covered two years ago, where moray eels were found to have a second set of ballistic jaws in their throat, rather like Giger's Alien. And they're animals found in most large aquariums. It just goes to show that even "familiar" species are often nothing but.

Wow, those things are freaking scary dude!

RT
www.privacy-center.de.tc

Fascinating! I'll have to have a look at this paper and see if there are any unusual peptides in the venom.

toxic shock from collapsing blood pressure

@Ed

You're describing cardiogenic shock here, not necessarily toxic shock. Failure of circulation secondary to hemorrhage is cardiogenic.

A quick read of the article leads me to disagree here. Admittedly, I'm a med student, not a physiologist.
Table 1 from the article lists the following in toxins
PLA2(T-III) - thats a platelet inhibitor, which is anticoagulation and would lead to hemorrhage
Kallikrein - increases vascular permeability
Natriuretic - I believe this one is both antiplatelet, AND vasodilator (someone correct me if I'm wrong here).

So, Kallikrein and natriuretic would be vasodilation related shock that decrease blood pressure, rather than hemorrhage leading to decreased blood pressure, so I think that counts as toxic shock.

Reading this makes me wonder what we can really tell about other reptiles - like dinosaurs for example - that we only have palentological data for. Is it possible that those large reptiles also may have had venom? Would we be able to tell by looking at bones if venom glands had existed to help paralyze particularly large prey?

Heather, sadly, venom sacs don't have osteological correlates. The only way you could really tell is if a theropod tooth (I assume it would be a theropod) had a groove or hollow channel in it, which would indicate the presence of venom. So far, that hasn't been found.

Ed, wonderful article. Makes me all the more reluctant to visit the Komodo islands. :-)

The only way you could really tell is if a theropod tooth (I assume it would be a theropod) had a groove or hollow channel in it, which would indicate the presence of venom

And as this story shows, the grooved tooth isn't necessary for venom.

Re-read bits of the post. You're right! That's terrifying. So in a way, it's a simplified version of the gila monster system: the venom is almost mixing in with the saliva, which sops into the wound instantly.

So, damn. I guess there's no way to tell for sure whether theropods had venom systems or not. It would certainly make life easier for the smaller carnivores, like compsognathids and microraptorines. But as we've seen with giant varanids, it's clear that enormosity does not preclude the evolution of venom glands.

I suppose we'd have to use phylogenetic bracketing. No living crocs have venom, and as far as I know, no bird has a venom delivery system (in its mouth). So until we find some osteological evidence for venom in a dinosaur, the only thing we can say right now is "probably not."

So regarding the phylogeny, one of Fry's earlier papers suggested a clade called Toxicofera, which includes all snakes, and some lizards including monitors, iguanas, agamids, chameleons and the two species we've known were venomous for the longest time. I think the idea is that reptile venom evolved once in the origin of this group and has been subsequently lost in some.

Right. Secondarily lost in many groups, and is BEING lost in some right now. Also, chameleons? Whoa!

Ah, varanids, how I love thee.

I did take an accidental bite from an exanthematicus once and didn't notice any ill effects beyond the actual, physical trauma and the amount of bleeding seemed normal.

That was also the last time I fed a varanid by hand (hey, I was young....ish).

Why 600 toxins? That seems overkill. I'm struggling to see how a creature with 599 toxins in its bite might need to evolve the 600th...

Wouldn't 10 or 20 be enough?

There are no toxins listed in this article.

@zutroi67
To be precise, all shock is defined by falling perfusion and, frequently, falling blood pressure...be that septic, hypovolemic, cardiogenic or obstructive shock. Blood pressure falls in septic shock just as it would in cardiogenic shock. And, shock due to blood loss is hypovolemic, not cardiogenic. Cardiogenic would be some defect of the function of the heart itself (like myocarditis).

Reader's Poll: Komodo Dragon Rampages

bleimanb — Tue, 26 Aug 2008 15:40:09 +0000

Reader's Poll: Komodo Dragon Rampages

For centuries local villagers who lived around what is now Komodo National Park in Indonesia fed slaughtered animals to their neighbors, giant Komodo dragons. The locals believe that the dragons are the reincarnation of their ancestors and townsfolk, and would leave offerings of dead meat at the jungle's edge to keep the massive predators at bay. About a decade ago, however, they were forced to stop by their own government working with the American non-profit, the Nature Conservancy. Now they're blaming these groups for a recent spate of Komodo dragon attacks (including the death by bone-smashing of a nine year-old boy last year) and the dragons' venturing further and further into civilian areas.

Aunt Marion? Is that you?

Do yourselves all a favor and read Yaroslov Trofimov's well written article, When Good Lizards Go Bad:Komodo Dragons Take Violent Turn, from yesterday's Wall Street Journal.

Then you tell us... Do you think the forced discontinuation of the centuries-old practice of feeding Komodo dragons has actually done more to hurt them and the humans that co-inhabit the island than help them?

More on Komodo dragons below the fold...

Komodo dragons are the largest species of lizard alive today, reaching up to ten feet in length. They inhabit just a handful of islands in central Indonesia, and their populations have been decimated by human encroachment and their popularity as zoo animals. Subsisting mostly on carrion, the dragons can also be fearsome predators, taking down water buffalo, birds, snakes and once in a while, humans. Their bite has a large concentration of toxic bacteria in it, making their bite particularly dangerous. When hunting they often rely on a single nip and then wait for the prey to die of blood poisoning before consuming it. While eating, Komodo dragons take time to crush the bones of their prey, whether it's dead or alive, by smashing it against rocks or just crunching down on it with their powerful jaws, in order to facilitate digestion. That's so weird! I do the same thing when I'm eating human!

Warning Graphic Violence:

bleimanb Tue, 08/26/2008 - 11:40

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Many societies have a superstitious fear where, if they do not placate an entity with sacrifices, they will face its wrath. I don't know the particulars, but this is one case where that fear could conceivably not be mere superstition.

Wait - so 10 years ago they stopped killing Dragon's (oh and coincidently stopped feeding them) The story left this part out. Now the population of Dragons is a lot higher and coincidently again the population of humans is also a lot higher... Shucks ya think there might be an issue or two more than there used to be?

It has to be dealt with and by the people there, but no I don't think the people feeding the dragons or not had a lot to do with things. Better management meant mroe dragons. Human population growth meant more humans. All in same area. That means more incidents.

Well, wait until a dozen or more children are attacked, killed and eaten and then, with the help of a large-bore rifle, the problem will solve itself in a couple of days.

My dad has a long fluoro light above his back gate. Its always on, because everyone comes and goes at all hours of the night. It also happens to be right near the dogs water bucket, and the pond (untreated spa, anyway). It didn't take the frog people long to realise this insect goldmine - they all line up along the light, picking off insects all night long. Sometimes the big ones sit on the little ones, so the little ones migrate to the rose branches hanging next to the light. He has some seriously fat frogs...

One day the light blew, and dad didn't have time to get a new one for a while (living on a farm, its a 2 hour trip to decent shopping). Even though the light was out, and there wasn't any insects anymore, dad's little handout generation of frogs still lined themselves up along the light, waiting, and looking pretty confused! When they eventually disappeared after a few weeks, it was because winter set in. I really don't know how long they would have waited for the fluoro tube to be replaced in good weather.

The point of that little story was that perhaps the locals have accidentally done a similar thing with their komodo's. These lizards have pretty huge lifespans, and they've learnt to use and perhaps come to expect and rely on the donations from the villagers. Although feeding wild animals often ends in disaster, its an important part of the locals religion and they've been doing it so long that the impact on the dragons ability to survive alone has probably been done anyway. Perhaps the environmental agencies working in the area should be looking at working with the locals to supplement the komodo's diet a little bit, as far away from villages as possible? Just my 2c :)

I saw a komodo dragon recently at the Shedd Aquarium in Chicago. Humongous. The video they show of kd's in action is pretty cool, too. A real beasty beast.

It seems to me that the conservationists are looking at the humans in the situation as outsiders to the ecosystem, as if the people just moved there last week.

If this tradition has been going on for decades or hundreds of years and was effective for most of that time, then it is probably just as necessary for the dragons' survival as the people by this point. Notice that the people, besides not being allowed to leave out the sacrifices, also aren't allowed to hunt the deer in the park anymore, which led to a population surge in the deer, and thus a surge in the dragons, too. Now the dragons are more aggressive because they have more competition with others of their species for survival, and a soft, pink human is an easy alternative to almost anything else. Humans are the equivalent of a bag of Taco Bell to most carnivores.

Which reminds me, I was at the Lowry Park in Tampa zoo a few years back, watching their big dragon sunning himself on a rock. He was absolutely still, and separated from me by a thick pane of glass, so he was only about six feet away. He only moved when a small child toddled up to the glass to peer at him. I was astounded to see that not only did he look towards her, but his eye, which had been dilated as if he were 'staring off into space,' contracted when he was looking at the little girl. Then the head slowly came around and the tongue started going in and out much more quickly. Nothing more exciting happened than that because the little girl wandered off (apparently oblivious to this little drama) but it certainly left an impression on me!

Jenbug, I have likewise noticed that the animals in my local zoo seem fascinated by my slightly-autistic son! I have wondered if his behavior is just so different from the typical human behavior these animals get paraded in front of them every day that they eyeball him to see what his deal is. ;) One day he picked up this Erianthus plume and started waving it around like a parade-leader near to the meercat enclosure. They wigged out!!! All their sentries were brought to bear, until they finally (I guess) decided he wasn't a threat. Even so, they watched him closely! Likewise, our rhinoceros iguanas seem to view him as a threat-- they did that bobbing up and down thing that they do. The tigers, on the other hand, seem to view him as easy prey and stalk him from the other side of the fence. It was very creepy.

My youngest son, who isn't autistic, but has a distinctive way of walking, has always been observed by komodo dragons as "meat" walking. The first time I noticed this was at the Audobon zoo, when my youngest was about 2. However, the dragons at the NW Florida Zoo and at the Atlanta zoo, also have viewed him as tasty (even at age 7).

when my youngest was about 2

The people, besides not being allowed to leave out the sacrifices, also aren't allowed to hunt the deer in the park anymore, which led to a population surge in the deer, and thus a surge in the dragons, too.

Well, wait until a dozen or more children are attacked, killed and eaten and then, with the help of a large-bore rifle, the problem will solve itself in a couple of days.