…and this is a 
Evolving snake fangs
Category: Development • Evolution • Molecular Biology • Organisms • Science
Posted on: July 31, 2008 10:05 AM, by PZ Myers
Ontogenetic allometry in the fang in the front-fanged Causus rhombeatus (Viperidae) displaces the fang along the upper jaw. Scale bars, 1 mm. We note the change in relative size of the upper jaw subregions: i, anterior; ii, fang; iii, posterior. d.a.o., days after oviposition.
I keep saying this to everyone: if you want to understand the origin of novel morphological features in multicellular organisms, you have to look at their development. "Everything is the way it is because of how it got that way," as D'Arcy Thompson said, so comprehending the ontogeny of form is absolutely critical to understanding what processes were sculpted by evolution. Now here's a lovely piece of work that uses snake embryology to come to some interesting conclusions about how venomous fangs evolved.
Basal snakes, animals like boas, lack venom and specialized fangs altogether; they have relatively simple rows of small sharp teeth. Elapid snakes, like cobras and mambas and coral snakes, are at the other extreme, with prominent fangs at the front of their jaws that act like injection needles to deliver poisons. Then there are the Viperidae, rattlesnakes and pit vipers and copperheads, that also have front fangs, but phylogenetically belong to a distinct lineage from the elapids. And finally there are other snakes like the grass snake that have enlarged fangs at the back of their jaws. It's a bit confusing: did all of these lineages independently evolve fangs and venom glands, or are there common underpinnings to all of these arrangements?
Let's start by looking at the phylogenetic tree and different fang arrangements. As you can see, those snakes with fangs at the back of their jaws (Natrix natrix, second from top) are interposed between one group of snakes with front fangs (the elapids, top), and another group with fangs in front (the vipers, third from top). We can imagine all kinds of scenarios that would produce that condition — front fangs are primitive, and Natrix secondarily lost them, or the fangs of all three are of independent origin and this is an example of convergence — but to resolve the question we need to look at some evidence. We need to examine embryos.
(Click for larger image)
a, Phylogeny. b, c, Adult skulls: lateral views (b); palate, schematic ventral views (c; maxilla coloured, fangs circled). Asterisks indicate species studied by electron microscopy. The evolutionary changes leading from an unmodified maxillary dentition to the different fang types in advanced snakes are indicated at the nodes: (1) continuous maxillary dental lamina, no specialized subregions—ancestral condition for advanced snakes; (2) evolution of posterior maxillary dental lamina—developmental uncoupling of posterior from anterior teeth; (3) starting differentiation of the posterior teeth with the venom gland; (4) loss of anterior dental lamina and development of front fangs.
This is where we begin to see some underlying unity. Vonk and others used sonic hedgehog staining to visualize the dental primordia in snake embryos (O Sonic Hedgehog, is there no process in which you are not involved, nothing in which your expression is not enlightening?) and mapped out the pattern of tooth generation. They identify an odontogenic band, a thin strip of tissue that gives rise to teeth, and note an interesting peculiarity: there are subdivisions into independent anterior and posterior dental lamina, and ablating the anterior lamina does not perturb the development of the posterior lamina. In essence, the snakes simply have a couple of separate tooth-generating zones in their embryonic jaws.
The cool observation is that even in front-fanged snakes, it is the posterior zone that generates the fangs. It is also this same primordium that buds off a tube and a sac that will make the post-orbital venom gland — even in the front-fanged snakes, they have a gland located way back behind the eye to produce venom.
These observations are diagramed below. The unspecialized dental lamina, the part that sprouts the generic small pointy teeth, is in green; the specialized posterior dental lamina, which makes fangs and the venom gland, is in orange. In all the venomous snakes, the venom gland is a tube that first extends forward, and then curls back to make the bulk of the gland even more posteriorly. The important point is that all of these snakes use the same small posterior scrap of embryonic odontogenic tissue to make fangs and glands — we can make a pretty solid argument that these structures are all homologous.
(Click for larger image)
Derived from serial sections. Left-hand side of the upper jaw is depicted, and only epithelial components are shown. Purple, shh expression; grey, tooth buds; green, unspecialized maxillary dental lamina; orange, specialized maxillary dental lamina that bears fangs. The specialized dental lamina is dilated into a bifurcated epithelial sac, the lateral part giving rise to the venom duct and venom gland by growing rostrad, then turning caudad to reach the post-orbital region. In Elaphe obsoleta (a–c) and Natrix natrix (data not shown), fangs develop rostrally and caudally alongside the base of the venom duct; in Naja siamensis (d–f) and Trimeresurus hageni (g–i) the rostral part regresses, remaining visible only as the dental ridge, whereas in b and c this part bears fangs and fuses with the anterior dental lamina. The unspecialized dental lamina in E. obsoleta (a–c) and the outgroup Liasis mackloti (j–l) starts developing anterior and grows caudad.
Now hang on, you may be thinking, if all the fangs develop at the back of the jaw, how do they end up out front in the front-fanged snakes? We can find the answer in development, too. Remember that the two tooth generating zones, front and back, are independent, and the front one can be repressed without disturbing the development of the posterior zone. In the front-fanged snakes, the anterior part of the upper jaw lacks sonic hedgehog expression, and the posterior teeth move forward naturally as part of the allometric expansion of the jaw in embryonic growth. This is sweet: not only does development reveal a homology, it also exposes the process that led to a morphological difference.
Here is the authors' summary:
Our results suggest a new model for the evolution of snake fangs. A posterior subregion of the ancestral tooth-forming epithelium became developmentally uncoupled from the remaining dentition, resulting in posterior and anterior dental laminae that are developmentally independent. This condition is retained in the non-front-fanged snakes, such as the grass and rat snake. This model would imply that the front-fanged elapids and viperids have independently lost the anterior dental lamina, which is supported by the lack of shh expression anterior in their upper jaws.
…
The developmental uncoupling of the posterior from the anterior tooth region could have allowed the posterior teeth to evolve independently and in close association with the venom gland. Subsequently, the posterior teeth and venom gland could have become modified and formed the fang-gland complex--an event that underlies the massive radiation of advanced snakes during the Cenozoic era.
The key innovation in snake evolution was a subtle one, an uncoupling of two tooth-generating regions that opened the door to more flexibility in the modification of the jaws. The fang/venom gland complex probably evolved once in the common ancestor of these groups, but the elapids and vipers independently stumbled on a secondary change, the suppression of the anterior region, that allowed the posterior fangs to move forward to make a more effective poison delivery system.
Vonk FJ, Admiraal JF, Jackson K, Reshef R, de Bakker MAG, Vanderschoot K, van den Berge I, van Atten M, Burgerhout E, Beck A, Mirtschin PJ, Kochva E, Witte F, Fry BG, Woods AE, Richardson MK (2008) volutionary origin and development of snake fangs. Nature 454:630-633.
Life Science
Comments
Ooh, PZ, I just love it when you talk biology! Seriously, thank you for yet another fascinating item.
Posted by: Pat Silver | July 31, 2008 10:18 AM
Does this affect the story of Adam and Eve?
Posted by: TSC | July 31, 2008 10:18 AM
Octopus loves Mr. Potato Head
Posted by: John Emerson | July 31, 2008 10:26 AM
Posted by: freelunch | July 31, 2008 10:26 AM
PZ has been one upped! :O
http://www.catholicleague.org/release.php?id=1468
Posted by: Mike | July 31, 2008 10:29 AM
It's a big confusing:
It's a big confusing what?
Posted by: Richard Smith | July 31, 2008 10:35 AM
Dang fangs. I love the name Sonic Hedgehog :)
#5 : a play about virgins and biscuits...
Posted by: LaTomate | July 31, 2008 10:42 AM
I'd be curious as to what evolutionary circumstances led to the development of such a thing as a fang to begin with? I have no trouble grasping the evolutionary development of the eye (or in this instance teeth) but how and why did the simultaneous circumstance of a perfect injection machine and poison sac come to pass? There must be some scientific speculation someone could enlighten me about.
Enjoy.
Posted by: Tim Fuller | July 31, 2008 10:46 AM
#5, don't you mean he was upstaged? Badumpbump
Posted by: True Bob | July 31, 2008 10:47 AM
O Sonic Hedgehog, is there no process in which you are not involved, nothing in which your expression is not enlightening?
Segmentation. Some folks were trying to push a role of Hedgehog in segmentation a while back, but the prevailing opinion now is that it's not doing much.
Posted by: Confused | July 31, 2008 10:50 AM
The evolution of venom preceded the evolution of fangs. Venom probably started with the expression of intestinal digestive-enzyme genes in saliva. Such venom can be delivered by ordinary teeth by a bit of chewing (ev4er been bitten by a racer or a watersnake? Gila monsters do it too). That sets up selection pressures for improved (nastier) venom and a more efficient delivery system (fangs).
I could back most of this up with references if I wasn't so damn lazy.
Posted by: Sven DiMilo | July 31, 2008 10:54 AM
>I'd be curious as to what evolutionary circumstances led to the development of such a thing as a fang to begin with? I have no trouble grasping the evolutionary development of the eye (or in this instance teeth) but how and why did the simultaneous circumstance of a perfect injection machine and poison sac come to pass? There must be some scientific speculation someone could enlighten me about.
----------------------
The origin and evolution of the snake venom system has been long been an area of great controversy and acrimonious debate. It has only become recently evident that venom is a basal characteristic of the advanced snakes. All share a common ancestor that had venom glands but used ordinary teeth to chew the venom in. Many lineages independently enlarged the rear-teeth, an improvement but not a spectacular or difficult to achieve one. The true innovation in venom delivery came with the development of hollow-syringe fangs to deliver the venom in a high-pressured manner.
Logically venom preceeded fang as there cannot be a selection pressure for the evolution of intricate delivery systems in the absence of something worth delivering. Fangs and larger venom glands arrived much later,such innovations allowed the snakes to envenomate new prey items, such as being able to efficiently get past the thick fur of mammals or puncture the hard scales of other snakes.
All snakes with hollow front fangs were initially considered to all share a common ancestor but genetic evidence showed that this was not the case. Hollow front fangs instead evolved independently on three separate occasions. Thus a major unanswered riddle was how did they each innovate their arsenal. The natural 'intelligent design' of these unique adaptations has been unravelled for the first time.
This study is a perfect example of the inherent beauty of science, where even a failure can actually lead to an unexpected success. Initially we set out to study the unique glands of the night adder, an African snake with the largest venom glands in the world, massive glands that extend a quarter the length of the body. We bred the snakes to provide eggs to study the developmental genetics of the glands. However, reptile embryos are already partially developed at the time the eggs are laid. Developmental genes are turned on for only a very short period of time. Think of them as the first domino in a long series. The genes for the glands had already been turned on and then off before the laying of the eggs. So that study was a complete bust. However it turned out that we still had plenty of time to study the fang development.
As the venom system is an intricate combined system, a better understanding of one part facilitates the study of the other components. So the implications of this study go well beyond being a clever dental exam.:D
Posted by: Dr. Bryan Grieg Fry | July 31, 2008 10:55 AM
"but how and why did the simultaneous circumstance of a perfect injection machine and poison sac come to pass?"
I'm guessing completely, but sharp pointy teeth=goodness and poison glands=goodness, both give a selection advantage. Mutating the two together is double-plus goodness though.
Posted by: Garulon | July 31, 2008 10:55 AM
-4
Posted by: Sven DiMilo | July 31, 2008 10:56 AM
Now I have Frank Zappa's song Baby Snakes stuck in my head!
Posted by: Cappy | July 31, 2008 10:58 AM
Here are some relevant references to venom preceeding fang. It is of course just sheer wonderful coincidence that they are my papers :D :D :D
Fry BG, Scheib H, van der Weerd L, Young B, McNaughtan J, Ramjan SFR, Vidal N, Poelmann RE, Norman JA (2007) Evolution of an arsenal: structural and functional diversification of the venom system in the advanced snakes (Caenophidia). Molecular & Cellular Proteomics 7(2):215-46
Fry BG, Vidal N, Norman JA, Vonk FJ, Scheib H, Ramjan R, Kuruppu S, Fung K, Hedges SB, Richardson MK, Hodgson WC, Ignjatovic V, Summerhayes R and Kochva E (2006) "Early evolution of the venom system in lizards and snakes" Nature 439(7076):509-632
Fry, BG (2005) "From genome to 'venome': Molecular origin and evolution of the snake venom proteome inferred from phylogenetic analysis of toxin sequences and related body proteins." Genome Research 15:403-420
Fry BG, Wüster W (2004) "Assembling an arsenal: Origin and evolution of the snake venom proteome inferred from phylogenetic analysis of toxin sequences". Molecular Biology and Evolution 21(5): 870-883
Fry BG, Lumsden N, Wüster W, Wickramaratna J, Hodgson WC, Kini RM. (2003) "Isolation of a neurotoxin (alpha-colubritoxin) from a 'non-venomous' colubrid: evidence for early origin of venom in snakes. Journal of Molecular Evolution 57(4):446-452
Fry BG, Wüster W, Ramjan SFR, Jackson T, Martelli P, Kini RM. (2003) "LC/MS (liquid chromatography, mass spectrometry) analysis of Colubroidea snake venoms: evolutionary and toxinological implications." Rapid Communications in Mass Spectrometry 17: 2047-2062
Posted by: Dr. Bryan Grieg Fry | July 31, 2008 10:59 AM
Snakes freak me the eff out. *shudder*
Posted by: astroande | July 31, 2008 11:01 AM
Quid est Sonic Hedgehog?
At least what is it in this context? And how did it get that name? I know about the nintendo game.
Posted by: Lynnai | July 31, 2008 11:04 AM
@17, good, then leave them alone, but don't kill 'em. Being a kid in Florida, I used to go with my foolish friends and catch snakes, scorpions, vinegaroons, whatever. Water snakes in particular are very very aggressive.
I remember getting a snake book from the library, and ogling the B/W pictures all day. I never opened it again, as I had horrific dreams that night.
Posted by: True Bob | July 31, 2008 11:08 AM
Ah, the reading of hardcore science before my second cup of coffee. My thanks to PZ for his clear explanation for us non-biologists, and to Dr. Fry for his follow-up.
Posted by: Nerd of Redhead | July 31, 2008 11:13 AM
Doc Brian, you have a cool job. I grew up near the Other Melbourne (Melbourne HS '80). That's where I caught snakes.
A friend of mine kept a Massassuaga for a while. He took it in a mayo jar to release it. As soon as it poked it's head out, it whipped around and struck him on the arm. Careful with those biters, they have no sense of gratitude.
Posted by: True Bob | July 31, 2008 11:15 AM
#5.) PZ has been one upped! :O
Don't agree. It is just a play about crackers.
I would say that Bill Donohue is a snake, but he is harmless as he has no venom.
Posted by: Qwerty | July 31, 2008 11:17 AM
Lynnai, for those of us without strong science backgrounds, the Wikipedia articles on Sonic Hedgehog and Hedgehog signaling pathway appear to be reasonable. Sonic (Sega, not Nintendo) is a whimsical name for a developmental pathway that relies on genes of the same name to help cells within organisms differentiate properly during development.
Any mistakes in understanding are mine.
Posted by: freelunch | July 31, 2008 11:21 AM
so whats the REASON for the venom to 'evolve'?
GOD!!!!!
you seriously think this just randomly happened? or that 'evolution' (your god) was thinking it needed it and 'evolved' it ....
i love seeing evolutionist talk nonsense, it makes the creation all so much easier to see.
thank god for living in a country where the majority accept gods creation. maybe you should move to soviet union or europe and see how fun they have it there.
Posted by: Kent | July 31, 2008 11:26 AM
As noted by others, it wasn't simultaneous, but they used their teeth to get the venom past the blood barrier. What I don't think was mentioned is that there are various kinds of tooth delivery of venom, ranging from grooves in teeth, to the wonderful hollow fangs of rattlesnakes and other pit vipers.
The point I'm making with that is that there are (currently) stages intermediate to unmodified teeth, to hollow fangs. Presumably the grooves became more efficiently connected to the venom ducts, and became more and more close to being fully enclosed by the tooth. At some point the grooves simply became enclosed, and you then had your hollow fang injection system.
Indeed, when you see something that looks too difficult to evolve because of the problem of all of the simultaneous changes that have to occur, look around to see if they really need to be simultaneous. In nearly all cases, they do not have to be.
Glen D
http://tinyurl.com/2kxyc7
Posted by: Glen Davidson | July 31, 2008 11:29 AM
(.)(.)
Posted by: wÒÓ† | July 31, 2008 11:31 AM
>Doc Brian, you have a cool job.
I reckon so too :D
I am actually currently kicking back at a tropical beach in Colombia taking a break from catching snakes here. Its a dirty job but someone's gotta do it! :D
Posted by: Dr. Bryan Grieg Fry | July 31, 2008 11:31 AM
Did Kent just ask people to move to a non-existent country? Bit behind the times, no?
Posted by: Stephen Wells | July 31, 2008 11:31 AM
Oops, should have proofed it. Here's the correction I need to make:
Glen D
http://tinyurl.com/2kxyc7
Posted by: Glen Davidson | July 31, 2008 11:32 AM
Posted by: Sven DiMilo | July 31, 2008 11:33 AM
I don't love seeing creationist morons talking nonsense because they don't know the first thing about what evolutionists actually say (let alone have any intelligent objections to it).
Natural selection is not random. See if that simple fact can stick to your thick skull.
Glen D
http://tinyurl.com/2kxyc7
Posted by: Glen Davidson | July 31, 2008 11:35 AM
One more thing, Kent.
How about telling us how and why "God" chose to design venom systems that have killed so many of his "children".
Then write to Behe and tell him how malaria is a purposeful arrangement of parts (as he defines design to be). It would be interesting, because he has never explained anything with respect to design, yet tells us that Plasmodium falciparum was designed. It just doesn't fit his definition of design, nor does snake venom.
IOW, we're still waiting for a coherent ID hypothesis, let alone one that has evidence in favor of it.
Glen D
http://tinyurl.com/2kxyc7
Posted by: Glen Davidson | July 31, 2008 11:40 AM
I swear, I get all giggly when one of the study's authors actually drops in to give us a Special Feature Behind The Scenes.
Also, what about vampires?
Posted by: StuV | July 31, 2008 11:42 AM
Kent, your comments are idiotic. Go get a book on evolution & read it before shooting your big mouth off.
You could read Darwin's "On the Origin of Species...", just to see how simple an idea evolution by natural selection really is, when you put all the components together as Darwin & others did in the mid-nineteenth century. It was an idea whose time had come, and Darwin put in arguments that have stood the test of time, & been verified by subsequent research in genetics, etc.
There has been nothing to refute the theory of evolution by natural selection.
You've been conned by religious leaders. There aren't any gods.
Posted by: Richard Harris | July 31, 2008 11:46 AM
Kent blathered
>so whats the REASON for the venom to 'evolve'?
>GOD!
HAHAHAHAHAHAHAHA
That statement is so ridiculous I don't even know where to start. So God caused an invasion of snakes from Asia to Australia once Australia drifted close enough? Resulting in a massive diversification of the lineages and unique changes in the venom? God caused the egg-eating sea snakes to start losing their venom as they no longer needed it for prey capture? We even have transitional forms in the Australian Brachyurophis genus of Shovel-nosed snakes where some feed on lizards, some on lizards and lizard eggs while others specialise on just lizard eggs. The latter have atrophied venom glands relative to the former.
Wow. I just love how after scientists bust their butts in the lab for years to answer a riddle, it is always dismissed with the catch-all 'Guddit'. That is infantile logic at its finest. We are studying modern uses of ancient toolboxes. As oppossed to recently evolved tools such as yourself. Go back and play in your sandbox and I hope the cat crapped in it! :D
Posted by: Dr. Bryan Grieg Fry | July 31, 2008 11:46 AM
Maybe you should move to a state where they have a school system? Then you wouldn't be nearly illiterate and ignorant.
1. gods creation should be god's creation. And usually fanatics capitalize god as God, proper name and all.
2. The Soviet Union collapsed a decade ago. It doesn't even exist. To move to the Soviet Union, one would need a time machine. Communism collapsed also. You need to update your list of things to be frightened of.
3. The standard of living in Europe is as high or higher than the USA in most countries. The crime rate is generally much lower, educational levels are higher, and social problem rates are lower. Many Americans live in Europe by choice. More would but the Europeans have a problem with illegal migrants from the US. They keep sneaking across their borders to take low wage jobs from the natives.
Posted by: raven | July 31, 2008 11:48 AM
"... maybe you should move to soviet union or europe and see how fun they have it there."
Umm, have you ever been to any part of Europe?
Wait, what am I saying? Of course not. Nevermind.
James W (in London, in Europe)
Posted by: James W | July 31, 2008 11:49 AM
#24
"so whats the REASON for the venom to 'evolve'?
GOD!!!!!"
Oh! Kent! Is that you? Did they let you out of jail already? Hmm, I can understand that. Even jail wardens must get tired of your preaching after a time.
Oh, by the way, did you know there's no more Soviet Union? I'm sorry I have to break the news to you. I know how hard it can be to live without an arch-villain to hate. But I see you still have godless Europe, so it should be ok. By the way, it's where I live and, yes, it's rather nice. Myself, when I read the news about this or that crazy religious bigot in the US, I'm glad there's an ocean between us. Well, I'm not so much worried by the existence of the crazies than by the fact that they're sometimes backed by local authorities, police forces, military officers, even the government. That's pretty bad.
And did you know that evolution doesn't "think"? It's not an entity, you know, like your god. It has no thoughts, and no beard too. It's just a natural process with certain properties. Sure, creation is much easier to understand. Fairytales generally are easy to grasp. You can dismiss evolution as "nonsense", but it just goes to show that you haven't a clue about what it is. But there are so many books explaining it clearly! Why don't you try to read one or two? Go on, learn, and then come back later and we can discuss...
Posted by: Christophe Thill | July 31, 2008 11:51 AM
>Also, what about vampires?
Do vampire bats count? One of the things I am doing down here is comparing the evolution of vampire bat anticoagulants. There are three genera (each monotypic)
- one specialises on mammals
- one specialises on birds
- one prefers birds but will take mammals
The first two have anticoagulants that hit perfectly their respective prey blood coagulation systems. The coagulation cascades are not identical so this is key to how the third one affects both birds and mammals but not a efficiently a either of the specialists. We are seeing how they overcome the differences in the prey blood.
We use virginal maidens as bait. In short supply around here though :D :D :D Although I am funding my research by having a 'second hand virgin shop' with half off all slightly used merchandise. :D :D :D
Posted by: Dr. Bryan Grieg Fry | July 31, 2008 11:53 AM
Dr Fry,
Thank you very much for commenting on the post during your holiday. An absolutely fascinating read!
Posted by: Andrew | July 31, 2008 11:55 AM
Too cool, thank you PZ and a special thanks to Dr. Fry for his very enlightening additions. I am amazed at the stunning coincidence that all the papers cited by Dr. Fry were also authored by him. I also think w owe him a debt of gratitude for all the grueling field work he does, don't forget the sun tan lotion Dr Fry.
My only problem with the post was that the hue of green & orange used in the diagram was to a partial color blind person such as myself totally indistinguishable.
Kent, congratulations you manged to be wrong in every sentence. That has to be some sort of record
Posted by: Natasha Yar-Routh | July 31, 2008 12:00 PM
"but how and why did the simultaneous circumstance of a perfect injection machine and poison sac come to pass?"
See some nice pictures of how a hollow fang that can inject poison is simply a tooth that folded back over a poison-delivering groove
http://www.austmus.gov.au/factsheets/snake_fangs.htm
Back in 1950, Karl Schmidt published Modes of Evolution Discernible in the Taxonomy of Snakes in Evolution, Vol. 4, No. 1 (Mar., 1950), pp. 79-86
http://www.jstor.org/stable/2405535
He talked about how snake venom is basically just elaborated digestive secretions, and how hollow fangs are folded-back teeth. It is interesting to read his phylogenetic speculations in light of the latest findings.
Once you've got a longitudinally enrolled tooth with some nifty nasty chemicals trickling down it, it isn't much of a trick to increase the secretions and develop a holding sac and some muscles to squeeze the poison into the fang.
Posted by: N.Wells | July 31, 2008 12:00 PM
@Tim Fuller #9
I've read in some book (I'm pretty sure it was Wonderful Life) that the armors of the (plated) burgress shale fishes were not bony but toothy. And it seems that a bit before that some kind of sea-worm with bizarre toothy structure is found in the fossil record (one of the first animals with solid parts). So I guess the circumstances were first "feed" (lamprey like, or maybe by simply being a more efficient killer worm), and actually arose before the appearance of bones.
@Confused #11
I'm pretty sure I read (on pharyngula even, when there was all that hubhub about the platypus' genome decoding) that snake (and platypus) venom come from immune system proteins (β-defensins), not intestinal ones.See http://scienceblogs.com/pharyngula/2008/05/the_platypus_genome.php
Posted by: Masklinn | July 31, 2008 12:01 PM
It didn't occur to me that kent could be Kent Hovind but the resemblance is uncanny. I didn't know they had internet access in the federal prison system.
Doesn't look like the diploma mill Ph.D. was worth much.
Posted by: raven | July 31, 2008 12:03 PM
Careful with those biters, they have no sense of gratitude.
And how would *you* feel about being stuffed in a mayo jar?I know my little garter is very unhappy about cage cleaning time.
In fact the garter is a perfect example of what we were talking about... it has slightly venomous saliva, but no delivery system except chewing. On the small prey items that it feeds on it keeps the prey from struggling too much during swallowing, and helps them avoid injury.
Oh, the venom is related to other colubrid venoms and garters have rear fangs, too.
Posted by: Graculus | July 31, 2008 12:09 PM
>I'm pretty sure I read (on pharyngula even, when there was all that hubhub about the platypus' genome decoding) that snake (and platypus) venom come from immune system proteins (β-defensins), not intestinal ones.
The origin of venom proteins is actually much more widespread than that. What has to be stressed however is that absolutely none of them are modified saliva proteins. This is because the reptile venom gland, for example, is not a modified saliva gland. It is an entirely new structure with no homology to anything elee out there.
Venom systems are a key evolutionary innovation and have arisen independently in divergent animal lineages. The most extensively studied venoms are from the medically-important snakes (atractaspidids, elapids and vipers), yet venom systems are also present in other lineages including lizards, mammals (e.g. Platypus and Slow Loris), teleost fish (e.g. Catfish, Stonefish), cartilagenous fish (e.g. Stingrays, Port Jackson Shark, Chimera), molluscs (e.g. Octopus, Cone Snails), cnidarians (e.g. Blue-bottle, Box Jellyfish), echinoderms (e.g. Crown of Thorns Starfish, Flower Sea Urchin) and \several arthropod lineages (e.g. Centipedes, Scorpions, Spiders, (example) and (example). Modes of venom delivery are equally diverse and include barbs (e.g. Stingrays), beaks (e.g. Blue-ring Octopus), fangs or modified teeth (e.g. Centipedes, Water Shrews, Snakes, Spiders), harpoons (e.g. Cone Snails), nematocysts (e.g. Box Jellyfish), pinchers (Pseudoscorpions), proboscis (Assassin Bug), spines (e.g. Catfish, Port Jackson Shark, Stonefish), spurs (Platypus) and stingers (e.g. Ants/Bees/Wasps, Scorpions) indicating considerable morphological innovation in the evolution of venom systems. Furthermore, the use of the venom ranges from defense to predation (or a combination of both) and sites of action include virtually all major physiological pathways and tissue types reachable by the bloodstream (e.g. Fry 2005).
We have shown that venoms evolve via a process by which a gene encoding for a normal body protein, typically one involved in key regulatory processes or bioactivity, is duplicated and the copy selectively expressed in the venom gland. The proteins recruited range from all over the body includig blood, antimicrobial and even brain neurotransmitters. The newly created toxin type evolves via the birth-and-death model of protein evolution, in which a toxin multigene gene family is created by further gene duplication events followed by the deletion of some copies and conversion of others to non-functional copies or pseudogenes. As a result paralogous groups of genes are generated across taxonomic lineages where the gene duplication event occurred prior to their divergence. These evolutionary patterns are similar to those observed for multigene families involved in the adaptive immune response such as immunoglobins and major histocompatibility complex genes, a process which is thought to contribute to an organism's ability to react to a wide range of foreign antigens. In an analogous manner, animal venom toxins must react with diverse compounds in their prey. The birth-and-death model of protein evolution generates suites of toxins that allow the predators to adapt to a variety of different prey species.
The newly created toxin multigene families preserve the molecular scaffold of the ancestral protein but modify key functional residues at the tips of loops to acquire a myriad of newly derived activities. These toxins have an unusual combination of precise specificity and extreme potency, characteristics that make them particularly amenable for use as investigational ligands or as leads for drug design and development. An early example of this is the development of an ACE (Angiotensin Converting Enzyme) inhibitor drug, Captopril, based upon a small snake venom peptide (teprotide). This and other related peptides contained a tri-peptide sequence (Phe-Ala-Pro) upon which the side chain interactions with ACE were modeled. This discovery led to the creation of a multibillion dollar drug class based upon a snake toxin. More recently, the applicant has filed a patent application for the use of novel venom natriuretic peptides in the treatment of congestive heart failure. Showing how human medicine benefits from study of evolution. However if the happy-clappys still insist on rejecting evolution, then they cannot benefit from the fruits of the labour. Enjoy your aneurism dickhead.
Despite this extraordinary diversity in the structure and function of animal venom systems, several protein groups have been independently recruited for use as venom toxins in multiple lineages. These include CAP proteins [CRISP, Antigen 5 (Ag5) and Pathogenesis-related (PR-1)], Peptidase S1, PLA2 (phospholipase A2), natriuretic peptide and kunitz peptides. CAP proteins have been independently recruited for use as a toxin by reptiles, stinging insects (Hymenoptera) and cone snails and is a major allergenic protein in saliva of hematophagous insects. Natriuretic peptides have been recruited into the venom of the platypus, and into reptile venoms. The PLA2 and kunitz peptides have been recruited in disparate lineages, being present in the venoms of reptiles, cone snails and insects. They are also one of the major toxin types secreted by toxic arthropods that are blood meal specialists (such as ticks). The recurrent recruitment of homologous venom toxins across this taxonomic spectrum suggests structural or functional constraints on the evolution of animal venom.
What I am working on now is a general theory of how venom evolves. New insights into the evolution of venom systems and the medical importance of the associated toxins cannot be advanced without recognition of the true biochemical, ecological, morphological and pharmacological diversity of venoms and associated venom systems. A major limitation of the study of venom proteins has been the very narrow taxonomical range examined. As a consequence, several major animal groups with known or suspected venom systems have remained largely unexplored. The mollusc lineage Cephalopoda (including squids, cuttlefish and octopuses) is one such major clade. With approximately 800 known species, cephalopods represent an important element in marine trophic systems worldwide, displaying an impressive variation in shape, size (from 2 cm to over 10 m) and habitat (benthic to abyssal, tropical to Antarctic). So I am currently collecting specimens from all ecotypes. I was in Antarctica this year and got 254 specimens, including two giant octopuses. After I am done suntanning in South America I will be in Asia enjoying dim sum while collecting octopuses there.
Cheers
B
Posted by: Dr. Bryan Grieg Fry | July 31, 2008 12:12 PM
maybe you should move to soviet union or europe and see how fun they have it there.
Just awful. Actual 36-40 hour work weeks, 27 paid days off a year (and sick days don't count against that), affordable health care, affordable schools, public transportation that gets you somewhere, representative democracy...
Awful.
Posted by: StuV | July 31, 2008 12:16 PM
Thanks, greatly, Dr. Fry for your additional information.
Posted by: freelunch | July 31, 2008 12:19 PM
From snake venom to the virginity of bats in 40 posts. Yes, this is a day for giggling!
Posted by: StuV | July 31, 2008 12:19 PM
Somewhat OT, but clearly an issue related to this and the various "Kents" of this world who prefer story-telling to science. And more important than any old crackers, btw. Bleeding Kansas still has to contend with yahoos opposed to science, and it's quite an issue right now:
Science is limited, Martin. That's why it's called "science", not "whatever you want". It follows the rules of evidence, and pays heed to what is known about causation and regularity.
Wait till Hinduism is being taught in science class. You'll suddenly realize that science is limited to proven methods and to realistic inferences, and is not a vehicle for spreading unfounded myth.
Anyway, there's no telling what will be in Kansas after the election.
Glen D
http://tinyurl.com/2kxyc7
Posted by: Glen Davidson | July 31, 2008 12:20 PM
Very interesting information there, Dr. Fry.
Glen D
http://tinyurl.com/2kxyc7
Posted by: Glen Davidson | July 31, 2008 12:22 PM
But not "Ontogeny recapitulates phylogeny", right? :P
Posted by: Spinoza | July 31, 2008 12:25 PM
This just keeps getting better and better. First a great post on the evolution of fangs in snakes with comments from one of the authors, then a quick excursion into vampire bats and now a overview of the evolution of venom's in general. I love me the science posts.
Dr Fry, you do have one of the coolest jobs in the world. Could you use the help of an aging trans-women who's Biology degree is far in the past but who is very good with computer networks?
Posted by: Natasha Yar-Routh | July 31, 2008 12:29 PM
Neat! Looking at the phylogeny, I see that 'Colubridae' has finally been split up; I've heard for the longest time that it's paraphyletic. But where do the bizarre side-stabbing atractaspidids fit in?
[Never mind: this link indicates that they're related to the lamprophiids (or boodontids?), and these two are in turn related to the elapids. Or wait, are the atractaspidids considered part of the lamprophiids in this Vonk et al. (2008) study?]
I was also not aware that ALL the former 'colubrids' possessed proper fangs.
Dr. Brian Fry was also involved in the study that discovered the prevalence of venom in many lizards as well:
http://en.wikipedia.org/wiki/Toxicofera
So the use of venom was probably already widespread among lizards*, including those ancestral to snakes. My guess is that it would have been used to subdue prey (like the Gila monster?), or to start the digestion process in the mouth, or even as an added 'kick' when biting in self-defence when threatened by a predator.
*lizard is used here as a layman's term, because after all, snakes are a highly specialised and diverse lineage of lizards.
If this is the case, then I am also wondering if the more basal snakes like typhlopids, aniliids, boids and pythonids, acrochordids, xenopeltids etc. actually lost their venom glands, or whether they possess weak venom.
It would be nice to see if the other venomous rear-fanged 'colubrids' from the other families such as Homalopsidae are also examined to see if the development of the fangs is the same.
Dr. Fry: I had no idea the egg-eating sea snakes had lost their venom! (Are you referring to Emydocephalus?)
Posted by: Hai~Ren | July 31, 2008 12:30 PM
Awesome! Thanks for the extra details and the background info, Dr. Fry!
Posted by: Spaulding | July 31, 2008 12:31 PM
In case anyone is interested in what an Antarctic giant octopus looks like, here me with one of first of the two specimens.
http://www.venomdoc.com/images/Bryan&giant_octopus.jpg
As you can tell by my grin, I am rather pleased in a very White Hunter sort of way! I didn't even know that Antarctica had giants until the that one came up in the nets!!
Posted by: Dr. Bryan Grieg Fry | July 31, 2008 12:31 PM
Sir sir please sir!
Can we have one on jellyfish venom ere long? Especially these weird killer jellies whose toxins are so damn deadly, in such tiny amounts, I assume they must be catalytic somehow.
CD
(pants expectantly)
Posted by: Chris Davis | July 31, 2008 12:32 PM
# 37
(in London, in Europe)
lol. way to bring it down to their level.
i for one would love to live in London. at least i would have decent health care.
#24
argument boils down to... I don't understand this. Therefore it is nonsense. Therefore the explanation I do understand is better. Therefore the explanation I do understand is true.
flawless logic.
I don't mean to dis biology... but I'm more of a sociology/social psychology kindof guy. Just wanted to know if neone knew of anybody like PZ who was blogging on peer reviewed sociology articles?
Posted by: Timothy Wood | July 31, 2008 12:33 PM
This work shows us the wonderful integration of species divergence in the genes, in the development of morphologies and in the rocks of our world. Science at its finest, explaining the story of life and of course us! What is so scary about this to some humans? Why must they cling to this skyhook they call god?
Rather than continually ridiculing them, how about if we try to explain their responses? Dennett's DDD and "Breaking the Spell" suggest wonderful evolutionary tools to help us study and understand these believers in gods. Let's extend the key evolutionary idea: "Everything is the way it is because of how it got that way," to the religious. Maybe these gods actually exist: as powerful and effective memes, infecting minds, turning the hosts (the other kind) to machines for spreading and infecting others. Let's put these believers under our microscopes and naturalize them.
Thereby neutralize them.
The Naturalist.
Posted by: TheNaturalist | July 31, 2008 12:36 PM
Thanks Bryan for your commentary and response. I particularly liked this sentiment:
As for my "ungrateful biters" remark, even though the mayo jar was only for transport, I told my friend he deserved it and was a dumbass. I'd have bit him, too, FFS. 2 weeks of horse serum and home from school wasn't punishment enough.
Posted by: True Bob | July 31, 2008 12:40 PM
>Neat! Looking at the phylogeny, I see that 'Colubridae' has finally been split up; I've heard for the longest time that it's paraphyletic.
Yep, they were a taxonomical dumping ground for anything that wasn't obviously a elapid or viperid. Based of course on cursory morphological studies. Its all being properly sorted by genetic studies. DNA is everything, the rest is just details! :D :D :D
>But where do the bizarre side-stabbing atractaspidids fit in?
They are distinct from the elapids, no question of that, and ditto with the viperids. They represent the third evolution of hollow-front fangs.
>[Never mind: this link indicates that they're related to the lamprophiids (or boodontids?), and these two are in turn related to the elapids. Or wait, are the atractaspidids considered part of the lamprophiids in this Vonk et al. (2008) study?]
The phylogeny is stable. The relative naming of higher order relationships is a matter of philosophy: whether to lump or split. Lumping keeps the shared evolutionary history obvious while splitting recognises unique derivations.
>I was also not aware that ALL the former 'colubrids' possessed proper fangs.
They don't. Have a look at our 'Evolution of an Arsenal' paper for the insane dentition diversity.
http://www.venomdoc.com/downloads/2008_BGF_Evolution_of_an_Arsenal.pdf
All the variants are there that you'd expect to emerge with active evolutionary tinkering.
>Dr. Brian Fry was also involved in the study that discovered the prevalence of venom in many lizards as well:
http://en.wikipedia.org/wiki/Toxicofera
Yep. That was a fun study. Anytime I get to mess with komodo dragons is a good day! So much for the 'toxic bacteria' hypothesis of komodo dragon bites!!!
>If this is the case, then I am also wondering if the more basal snakes like typhlopids, aniliids, boids and pythonids, acrochordids, xenopeltids etc. actually lost their venom glands, or whether they possess weak venom.
Watch this space. We are actually writing up exactly that study right now!!
>It would be nice to see if the other venomous rear-fanged 'colubrids' from the other families such as Homalopsidae are also examined to see if the development of the fangs is the same.
Live-bearing lineages are going to be nightmares to study in this regard.
>Dr. Fry: I had no idea the egg-eating sea snakes had lost their venom! (Are you referring to Emydocephalus?)
and Aipysurus eydouxii as per two of our other papers:
Li M, Fry BG, Kini RM (2005) "Putting the brakes on snake venom evolution: the unique molecular evolutionary patterns of Aipysurus eydouxii (Marbled sea snake) phospholipase A2 toxins." Molecular Biology and Evolution 22(4):934-941
http://www.venomdoc.com/downloads/2005_BGF_Aipysurus_eydouxii_PLA2.pdf
Li M, Fry BG, Kini RM (2005) "Eggs only diet: the shift in preferred prey by the Marbled sea snake (Aipysurus eydouxii) resulting in a loss of postsynaptic neurotoxicity." Journal of Molecular Evolution 60(1):81-9
http://www.venomdoc.com/downloads/2005_BGF_Aipysurus_eydouxii_3FTx.pdf
Cheers
B
Posted by: Dr. Bryan Grieg Fry | July 31, 2008 12:44 PM
@#19: Man, I can't even look at a snake. I had to fold over any pictures of snakes in biology textbooks in school so I wouldn't see or touch them.
The study is pretty cool though, as long as I don't have to see pictures.
Posted by: astroande | July 31, 2008 12:47 PM
i understand this very well, you get indoctrinated into believing in your evolution god, so you do no longer need to accept the consequences of your actions. hitler, stalin, mao, you name it.
OF COURSE i dont know or been anything, i accept the grace of god, SO OBVIOUSLY i know nothing.
and i have BEEN to europe, i SEEN how 'nice' they have it there. and I AM HAPPY to be AMERICAN and glad to get back to this wonderful country of ours and thankful for everything we have. internet? cars? airplanes? the best heathcare system in the world? the best military in the world? microsoft? oh, and what are you using now mr london? a COMPUTER? the INTERNET?
and maybe you have a cellphone there to?
GOD BLESS AMERICA
Posted by: kent | July 31, 2008 12:48 PM
I never even got to ask the question, and it was answered. I was wondering where the spitting cobra came into this. I see now it is an earlier developed evolutionary model (unless I misunderstood all that I read).
Posted by: Ignorant Athiest | July 31, 2008 12:49 PM
>Can we have one on jellyfish venom ere long? Especially these weird killer jellies whose toxins are so damn deadly, in such tiny amounts, I assume they must be catalytic somehow.
I assume you are referring to Irukandji jellyfish? They are another perfect example of evolution. They live on the reefs, where long tentacles and big bells would be catastrophic. So instead they have tiny tentacles, small bells and have the stinging cells concentrated on the bell instead of the tentacles. The venom hits the heart about 20 minutes after a sting, producing effects very similar to a heart attack. I remember we were dive collecting one time on the barrier reef. On the first dive of the day, someone in another group had a heart attack. He was a bloke in his late 30s and it was an easy drift dive with an 18 meter bottom. I reckon he got smacked by an irukandji-type. The reason I say 'type' is that it appears there are multiple species. One mate of mine was going to name one after his ex-wife, calling it Carukia angelinii. Describing the envenomation as a 'short but painful experienc