Of dragons and microbes

Finally, a photo at the top of the page that can compete with the one of Dr. Smith in the upper right corner!

And, no, I don't deliver that far west, so don't even think about phoning in an order for an extra-large pizza with the small-mammals topping!

Hey, Lenny, did you hear where they found the gene for venom in lizards? Who knows, next they might find it in fish?

G'day BlastfromthePast,

Not sure if I understoond your question. Could you please clarify?

Cheers
Bryan

(Sigh...)

Once again, you didn't understand a single thing you read--like the fact that the genes are found in a clade of snakes and lizards related by common-descent--did ya, Blastie?

Dude, I want one of those SOOOOOOOOOOO bad . . . . ;>

Hey, Lenny, did you hear where they found the gene for venom in lizards?

G'day BlastfromthePast, Not sure if I understoond your question. Could you please clarify?

Once again, you didn't understand a single thing you read---like the fact that the genes are found in a clade of snakes and lizards related by common-descent---did ya, Blastie?

G'head, Blast ---- tell him all about the "frontloaded genes". And tell him all about your, uh, "extensive research". (snicker) (giggle)

I think it's a shame that pure evolutionary articles like this one rarely get more than a dozen comments on PT unless people like Blast make inane statements, while the countless "ID supporter makes a fool of himself" threads routinely break the hundred post mark. To me, this is 10x more interesting than whatever Behe, Dembski, et al. happened to have said in the last 24 hours.

Anyhow, I have a couple questions. When did Varanids evolve? I would assume they are fairly derived lizards. Are there other characteristics they share with snakes that may be lacking in more distantly related lizard species like the geckos and the skinks?

Is the forked tongue you see on our komodo dragon friend up top, evidence of his(her) shared ancestry with snakes, or is it an example of convergent evolution?

Also, have we found any fossil snakes that still retained rudimentary legs, or have they all been completely limbless? I think that evolutionary changes in mode of locomotion are fascinating, and its a shame that the transitionary states of those changes are so rarely preserved in the fossil record. Kind of like the case with bats, where the earliest fossilized bats already have fully developed wings.

Re "Not only are lizards snakes' closest living relatives, but varanids like the Dragons are probably the most closely related living lizards to snakes."

So snakes are a branch within the lizard clade?

Henry

So, does this article mean that this tree-of-life-page will shortly get rewritten? Interesting.

Henry

wasp venom (and) mad time-traveling genetic engineers...

Also, have we found any fossil snakes that still retained rudimentary legs, or have they all been completely limbless?

Other than anal spurs on pythons I mean. I know that some snakes still have vestigial pelvic girdles, I was just interested in what snakes looked like closer to their divergence point from other lizards.

I think it's a shame that pure evolutionary articles like this one rarely get more than a dozen comments on PT unless people like Blast make inane statements, while the countless "ID supporter makes a fool of himself" threads routinely break the hundred post mark. To me, this is 10x more interesting than whatever Behe, Dembski, et al. happened to have said in the last 24 hours.

Hmm, Kwickxml doesn't like me too much...

Anyhow, I know that some extant snakes (like pythons) have vestigial pelvic girdles and anal spurs. I was more interested in seeing what snakes looked like closer to their divergence from other lizards. Basically, what order did they lose their legs, extend their bodies, and shorten their tail. It would be interesting to see transitional snake forms analogous to the transitional cetaceans and non-avian maniraptors that have been recently discovered.

I think the interesting biology articles often go without comment because there's not a lot to add. It doesn't mean that they haven't been read.

In this case, though, one question did come to mind. Is it possible that the komodo dragon's venom plays only a minor role in killing its prey and may even be unnecessary or vestigial? I'm not a biologist, but wouldn't this be consistent with the notion of scaffolding in evolution?

I.e., this kind of "germ warfare" attack is not as simple as it sounds and requires all kinds of adaptations in the lizard. Its ancestors without the same adaptations still had some way of killing their prey. Maybe the komodo's ancestors relied primarily on venom until this gradual bacterial symbosis made it less important, and since then there has been selective pressure to favor komodo dragons that can live with high concentrations of bacteria over the ones that produce the most effective venom.

In other words, it's not that surprising to find venom, and if you didn't, you'd have to wonder what the komodo dragon's ancestors did. Obviously, they couldn't use the tactic of biting and following prey to its death.

Alternatively, it might just be that the notion of killing with a septic bite just sounds too good (in a gross kind of way) to give up easily and that's why it is presented so often. I don't claim to know which.

In this case, though, one question did come to mind. Is it possible that the komodo dragon's venom plays only a minor role in killing its prey and may even be unnecessary or vestigial? I'm not a biologist, but wouldn't this be consistent with the notion of scaffolding in evolution?

What I thought I'd heard was that komodo dragon's 'venom' mostly consists of a lot of virulent bacteria.

I can't say how much bacterial infection plays a role in the killing of a komodo dragon's prey, but the research by Fry's group shows that indeed, these lizards are capable of producing venom, via previously undescribed venom glands. (Carl Zimmer has posted a figure from the Nature paper; the komodo dragon is in the Varanidae group).

Similarity as evidence for evolution? Man, I've never seen this before! Is this a new type of argument?
Yawn... then Zzzzzzzzzzzzz..........

Similarity as evidence for evolution? Man, I've never seen this before! Is this a new type of argument? Yawn... then Zzzzzzzzzzzzz..........

comment #59609: namingerror-recodeasJERKoff#2502345

>When did Varanids evolve?

~140 million years ago.

>I would assume they are fairly derived lizards. Are there other characteristics they share with snakes that may be lacking in more distantly related lizard species like the geckos and the skinks?

Venom for starters ;-) Unique tongue structure as well but how much of this is convergence and how much is shared dervied state is still being teased out.

>Also, have we found any fossil snakes that still retained rudimentary legs, or have they all been completely limbless?

Many of the basal snakes still have pelvic girdles and some like the pythons still have vestigal rear limbs. There are fossils in this regard too. So there is plenty of 'transitional evidence' ;-)

>Is it possible that the komodo dragon's venom plays only a minor role in killing its prey and may even be unnecessary or vestigial? I'm not a biologist, but wouldn't this be consistent with the notion of scaffolding in evolution?

We did a lot of work with the fish-egg eating sea snakes and found that due to the tremendous biological energy cost in producing it, if venom is not being used it is rapidly lost. That is what is making the interpretation of the toxin secretion in iguania so puzzling. The glands are retained in the basal form (smal, thin and putting out bugger all) but the toxins are showing evidence of the same accelerated evolution well characterised for snake venoms. Very curious. We are now testing various forms of different toxin types to get a feel for the bioactivities. This should hopefully shed some light on potential use. In the case of the varanids, however, it is much more obvious that venom is playing a role. The gland is extremely derived, having been changed into something quite special. It now is full encapsulated (sealed) with large duct leading to the base of the big teeth on the lower jaw. Quite considerable amounts of liquid venom is being stored for ready use and the venom is as complex as any snake venom I've previously looked at. The bioactivities we've demonstrated for varanid venom so far are the same sorts that have been previously shown as useful for prey capture in snakes. Killing a prey several days later by bacteria is totally illogical. This dogma was based mostly on conjecture and assumption and the comments almost entirely directed towards non-natural prey items (buffalo and other mammals are introduced species in the islands, the naturally available prey are much smaller and venom would have a much more profound effect). SO the bacteria has been a complete red herring. Of course they have some nasty bacteria around, any carnivore would since they all love to scavenge. Even vultures would have something nice and toxic if you gave them a swab. This doesn't mean that it plays any role in prey capture. It would be too slow to subdue a prey and something that dies later is of no use to the individual animal that bit it. They are not communal so there would be no group selection benefit. In the other varanids, we are seeing changes in the venom relative to the prey type. The same sort of variation also well documented with snakes. So it seems at the end of the day that the venom in varanids is being actively used in prey capture and bacteria, contrary to popular belief, has nothing to do with it. We will be doing lots of field observations in prey capture techniques to reevaluate things from a fresh perspective.

Cheers
Bryan

As some have remarked earlier in this thread, PT's "ID-debunking" posts have tended to garner more commentary than the "straight science" posts.

But when one of the lead investigators takes the time to actively interact with the commentators: that's about as cool as it gets for evolutionary science junkies!

This is taking ultimate advantage of the promised potential of science blogging. It's like being able to discuss the lead guitar figure in Honky Tonk Women with Keith Richards, in near-real time!

Dr. Fry, thanks!

Posted by Steviepinhead on November 23, 2005 05:18 PM (e) (s) ... But when one of the lead investigators takes the time to actively interact with the commentators: that's about as cool as it gets for evolutionary science junkies! ... It's like being able to discuss the lead guitar figure in Honky Tonk Women with Keith Richards, in near-real time! Dr. Fry, thanks!

So it seems at the end of the day that the venom in varanids is being actively used in prey capture and bacteria, contrary to popular belief, has nothing to do with it.

> It's definitely not as good a story though

I think goannas with venom is a ripper of a story ;-)

I think it's a shame that pure evolutionary articles like this one rarely get more than a dozen comments on PT unless people like Blast make inane statements, while the countless "ID supporter makes a fool of himself" threads routinely break the hundred post mark. To me, this is 10x more interesting than whatever Behe, Dembski, et al. happened to have said in the last 24 hours.

Anyhow, I have a couple questions.

When did Varanids evolve? I would assume they are fairly derived lizards. Are there other characteristics they share with snakes that may be lacking in more distantly related lizard species like the geckos and the skinks? Is the forked tongue you see on our komodo dragon friend up top, evidence of his(her) shared ancestry with snakes, or is it an example of convergent evolution?

One of the earliest groups of lizards, the varanoids, were spectacularly successful, spreading into a wide range of environmental niches. The varanoid group contains all of the monitors and their ancestors, plus the North American heloderms (the gila monster and Mexican beaded lizard), the earless monitor from Borneo, and several other groups that are now extinct. One group of early varanoids, known as the mosasaurs, took up a marine existence, developing flippers instead of legs and reaching lengths of over fifty feet. They became a varied and widespread group of animals before dying out in the same mass extinction that killed the dinosaurs. The monitor lizards share a number of distinct features in the structure of their skulls with the modern snakes; both, for instance, possess a moveable quadrate bone at the back of the jaw, and both are missing the quadratojugal bone at the rear of the skull. Snakes and monitors also share a deeply forked tongue which transfers chemical particles to a Jacobson's organ for sensory information. The most snake-like of the living monitors is the earless monitor, a burrowing semi-aquatic lizard found in Borneo. The earless monitor has movable eyelids, but the lower lid sports a clear "window" which allows the monitor to see even when its eyes are closed, protecting it from water and dirt. This is very reminiscent of the snake's brille or eyecap, which is formed in embryonic snakes when the transparent upper and lower eyelids fuse together. The earless monitor also has a number of snakelike features in its skull architecture and, as the name implies, it lacks any trace of an external ear, just as in snakes. It is probable that the earless monitor more closely resembles the saurian ancestor of the snakes than any other living lizard. Based on these similarities, some herpetologists have theorized that an ancient group of varanid lizards began to follow a burrowing way of life, tunneling through loose dirt and sand in search of earthworms and other prey, just as some lizards do today. Over a period of millions of years, the theory goes, these burrowing lizards lost their limbs and their external ears--to help them burrow more easily--and also replaced their eyelids with a clear brille or spectacle to protect their eyes while digging. At about the time that the dinosaurs reached their apex, one group of these burrowing lizards then gave up its subterranean lifestyle and emerged to the surface, where they developed a new legless mode of locomotion and rapidly diversified to invade a large number of ecological niches. Today we classify the various descendants of these legless lizards as snakes. It is thus probable that the monitors are the closest living lizard relatives of the modern snakes. The earliest known fossils of modern-appearing monitor lizards date from the upper Cretaceous period, about 65 million years ago--during the time that the dinosaurs were declining. These early monitors are classified in the genus _Paleosanawa_, which lived in North America, and _Telmasaurus_, which was found in Asia. During that time, these continents were joined together in a single super-continent called "Laurasia". Since then, they have broken into a series of huge "plates" which move around atop the earth's mantle, a process known as "plate tectonics". Skeletons of these extinct varanid lizards have been found at dinosaur nesting sites, indicating that these ancient lizards made their living by raiding nests, just as modern monitors do today. At the end of the Cretaceous, these two genera died out and were replaced by monitors of the genus _Saniwa_, which spread throughout Europe and North America. The modern monitor genus _Varanus_ probably evolved from the _Saniwa_ group approximately 50 million years ago. As the tectonic plates moved away from the equator, however, the climate cooled dramatically, and the monitors, unable to cope with the lower temperatures, disappeared from many areas and were greatly reduced in number and diversity. The _Saniwa_ genus died out, and only the tropical representatives of the _Varanus_ genus remained. Although most of the living monitors and goannas are found in Australia, the earliest known Australian fossils are from the middle Miocene period, about 20 million years ago, indicating that the modern monitors evolved in Europe or North America and reached Australia only relatively recently. Today, the monitors and their relatives have all but died out in their ancestral homes---there are no monitors found in North America or Europe, and only four species in Africa. In Australia, though, they have undergone adaptive radiation and have diversified to almost thirty species, which fill a number of ecological niches. The fossilized remains of the largest known lizard, called _Megalania_, have been found in Australia. This ancient monitor lizard, at a length of 15 feet and a weight of 1,000 pounds, is almost twice as large as the biggest living lizard (the Komodo dragon). _Megalania_ went extinct only 10,000 years ago--a very recent period in geological time. It fed on the rhinoceros-sized marsupial relatives of the koala that lived in Australia at the time.

Also, have we found any fossil snakes that still retained rudimentary legs, or have they all been completely limbless?

What I thought I'd heard was that komodo dragon's 'venom' mostly consists of a lot of virulent bacteria. So its hunting MO (with larger prey, at least) is to bite something one time, then to wander off and wait for its victim to die of septicemia a day or two later. I agree, I'd be very saddened to hear this wasn't accurate.

No really, there was a study (warning: pdf) that showed that kids who who were stung by wasps were twice as likely to become "genetic engineers" than "civil engineers".

>All of this info is a few years old. I'd appreciate any updates that anyone might have. There have apparently been genetic studies which have been interpreted to indicate that varanids are NOT snake ancestors, but the venom research cited here seems to indicate that they ARE.

>The venom findings, I think, would also support an "aquatic" origin for snakes, rather than a "burrowing" origin. My speculation would be that venom first appeared in varanid snake ancestors as a way of disabling fish before they could swim away. This would rather rapidly select for stronger and stronger venoms, since the more potent the venom, the more quickly the fish is disabled and the less far it can swim before it dies

>I suspect there is at least one person here who would disagree with that, though ... . . ;>

Right you are ;-) The data actually supports a terrestrial origin of snakes since the anguimorpha are not the closest relatives, the varanids are not the most basal anguimorpha, and further the anguimorpha are a largely terrestrial group. Lanthanotus having snake-like characters is convergence rather than direct ancestry. Mosasaurs are actually a very derived lineage within the anguimorpha clade. If snakes were aquatic descendents, then genetically they should be rooted deep within the anguimorphs. They aren't. Also, if snakes evolved aquatically, we should logically have basal aquatic snakes lineages persisting or at least extensive evidence of ancient basal snakes. We don't. We do have ancient terrestrial snakes, including those with rear limbs (rumour has it there is a paper about a new terrestrial snake fossil in this regard). Further, aquatic lizards always retain their limbs for steering. In contrast, burrowing lizards have lost their limbs on numerous occasions. A terrestrial origin for snakes is the most parsimonious explanation and certainly the best supported by the data.

The venom results do not contribute to the terrestrial vs aquatic debate but rather show a shared history between snakes + iguania + anguimorpha of venom, evolving in the common ancestor to these three lineages.

>(that's why sea snakes have the most potent snake venom on earth today).

Actually, this is a great myth. Sea snakes do not have the most potent venom on earth. Both the inland taipan (Oxyuranus microlepidotus) and the eastern brown snake (Pseudonaja textilis) both have venom more potent than any sea snake. Both are of course Australian (go Aussie!).

Cheers
Bryan

Dr. Fry and Lenny: Thanks for taking the time to answer my questions.

Fighting the ID Movement's push to get pseudoscience in schools is indeed a worthy cause, but sometimes just discussing cool science findings goes a long way towards winning fence-straddlers over to evolution. The reality of evolution is just as amazing as any creation myth, and you don't even have to suspend your sense of disbelief to swallow it.

The neat aspects of evolution, such as the topic of the thread, are not always apparent when you guys are forced into debunking faulty/circular arguments about the 2LoTD or IC over and over again. That's why I think its beneficial to have articles like this one, in addition to straight forward articles battling the ID movement.

Anyhow, enough of that.

I look forward to seeing future studies on how Varanid venom assists prey capture. Excuse me for being utterly ignorant about neurotoxins in general (my specialty is in avian acoustic communication), but how long does it take for a venom similar to that found in monitor lizards to go into effect? I've seen goannas eat in captivity before, and they can be pretty voracious. I don't think a rat lasts long enough for a venom induced paralysis to offer much assistance in prey capture for the goanna, but perhaps it would be helpful in killing larger prey items in the wild.

Monitor bites can be pretty nasty. I know someone who got a serious infection after being bitten by a crocodile monitor a few years back. Are the infections that often accompany improperly treated monitor bites purely due to sepsis, or does the lizard's venom play a role as well?

I don't think a rat lasts long enough for a venom induced paralysis to offer much assistance in prey capture for the goanna

Monitor bites can be pretty nasty.

Also, if snakes evolved aquatically, we should logically have basal aquatic snakes lineages persisting or at least extensive evidence of ancient basal snakes. We don't. We do have ancient terrestrial snakes, including those with rear limbs (rumour has it there is a paper about a new terrestrial snake fossil in this regard). Further, aquatic lizards always retain their limbs for steering. In contrast, burrowing lizards have lost their limbs on numerous occasions. A terrestrial origin for snakes is the most parsimonious explanation and certainly the best supported by the data.

Both the inland taipan (Oxyuranus microlepidotus) and the eastern brown snake (Pseudonaja textilis) both have venom more potent than any sea snake. Both are of course Australian (go Aussie!).

On a completely different tangent, I have heard tell that the (geographically very widespread) water monitor (_V. salvator_) has now been separated into several different species based on genetic data. Yes?

Monitors were always one of my favorite reptiles to keep. They seem, on a purely subjective basis, to be much smarter than most other herps. You can almost see the gears turning inside their scaley little heads. ;>

The way they move (particularly the smaller arboreal species) is very birdlike -- reminds me a lot of the _Velociraptors_ depicted in "Jurassic Park".

Origin of snakes - a controversy worth teaching!

Just my 2 cents worth. :)

Henry

>That's why I think the "venom evolved to disable fish" angle is so interesting.

Except that venom was not evolved in the varanids, it started in the common ancestor of iguania + serpentes + anguimorpha.

>What is it with you Aussies ---- you have venomous snakes, venomous jellyfish, venomous spiders ... . even venomous MAMMALS. ;>

And lots of venomous lizards ;-) Its a great country indeed. ;-D

As for the taxonomy of V. salvator, yes is has been broken up into a number of full species and no doubt additional refinements will be undertaken.

Cheers
Bryan

Posted by Dr. Bryan Grieg Fry on November 24, 2005 01:56 AM (e) (s) ... >(that's why sea snakes have the most potent snake venom on earth today). Actually, this is a great myth. Sea snakes do not have the most potent venom on earth. Both the inland taipan (Oxyuranus microlepidotus) and the eastern brown snake (Pseudonaja textilis) both have venom more potent than any sea snake. Both are of course Australian (go Aussie!). Cheers Bryan

Comment #59548 Posted by kswiston on November 23, 2005 10:52 AM (e) (s) I think it's a shame that pure evolutionary articles like this one rarely get more than a dozen comments on PT unless people like Blast make inane statements, while the countless "ID supporter makes a fool of himself" threads routinely break the hundred post mark. To me, this is 10x more interesting than whatever Behe, Dembski, et al. happened to have said in the last 24 hours.

or the periodic creationist asserting that ID is not creationism, and being buried under an avalanche of comments wherein top IDers use ID and creationism synonymously.

That's why I think the "venom evolved to disable fish" angle is so interesting.

Except that venom was not evolved in the varanids, it started in the common ancestor of iguania + serpentes + anguimorpha.

Dr. Fry and Lenny: Thanks for taking the time to answer my questions.

>Ya know, if you're gonna keep slaying beautiful hypotheses with ugly facts, then I'm gonna convert to ID, where I can believe whatever I want, in a fact-free environment, and never have to change my mind. ;>

LOL nicely put mate ;-D

Following on from comments up thread, how about putting this thread or one like it on the section in the front page about must read threads? That way people can get a more positive view of the site.