Evolution in colubrids

[Ace]

My cousin is a perfect example of this. She used to play with snakes in the backyard when she was a toddler, her mom would freak out. now she's terrified of snakes.

This is how I actually started my collection. I had found a gartersnake In my yard and brought it in to show the kids to show them snakes aren't "nasty little critters" Once they figured out it was a real snake they cleared out of the room faster than if I would've yelled "FIRE!". So, I did research, found a species I liked (Kings) and picked one up at the next show. Now snakes are just second nature to them. My son's considered the reptile expert in his class . They're aware there are dangerous species and not to pick up wild ones.

Dr. Fry: First off welcome to Ssnakess!
Second: You state "As for potential legislative problems, there's only one way to counteract this, and thats of course through education." This may be easier said then done. Considering your research has just changed many of the things we "THOUGHT" we knew of many of the species we know. Your research basically sought to find out if there was or wasn't venom in these species. The problem is it didn't go to the point of figuring the potency of these venoms.(as I understand it anyway) Till that's done many legislatures will base their laws on just the "venomous or non-venomous" aspect of your research. Not whether they're dangerous or harmless venoms.

[Invictus]

I have a question for the good Dr.

Would it be fair to say that even if all snakes do possess venom, that certain colubrids (corns and kings, for example) lack a delivery system for this venom? Or have you discovered that even corns have the ability to inject venom?

[BoidKeeper]

I was think of asking the same question but couldn't get it worded right.
Thanks,
Trevor

[Dr. Bryan Fry]

Hi Ace

This paper is part of a series (two others are in press and should be out soon (in the next couple weeks), two more have just been sent in and a few more projects are being finished up in the lab).

We did test the venoms and they are just as toxic as the comparative range of elapids (and some are staggeringly toxic, approaching death adder level). The venoms are just as complex.

Some of the snakes (such as Psammophis and Telescopus) have massive venom yields coming from staggeringly big glands. So, we have a range funning from small yeilds (ie radiated rat snakes) to massive yields (Telescopus), pretty inefficient delivery (radiated rats again) to very efficient (Psammophis).

The American Elaphe-types (e.g. Pantherophis/Pituphis/Lampropeltis) have recently undergone a secondarly loss of the gland and reverted back to the more primative condition of constricting. This allowed them to switch from an amphibian/reptile diet to a rodent diet. The venom delivery wasn't up to scratch for this task. This is of course what drove the development of highly effective fangs on at least four separate occasions (the Elapidae, Dispholidus in the Colubrinae, the Atractaspidae and the Viperidae).

The toxins themselves include the archetypal cobra-style toxins (three-finger toxins and Type I phospholipase A2 toxins) as well as a myriad of other sorts (including the M12B metalloprotease type for example that is responsible for the devastating action upon the blood by Dispholidus, Rhabdophis and Thelatornis, is widespread in all the Colubroidea venoms (including vipers)).

This of course means that the entire conept of Duvernoy's gland is toast. Same venom, same gland.

Check out the scary size of these glands. Bloody huge!

Psammophis mossambicus
http://www.venomdoc.com/ryan/Snakes/Glands01.jpg
http://www.venomdoc.com/ryan/Snakes/Glands02.jpg

Telescopus dhara
http://www.venomdoc.com/ryan/Snakes/Glands03.jpg

Where this all gets very cute is that none of the existing antivenoms do touch them. So while they are less likely to get you, if they do you are screwed.

Certainly not what we expected when we started this all.

Cheers
BGF

[Dr. Bryan Fry]

Hi Invictus

They do have a delivery mechanism and some of them can deliver it quite well. However fangs are of course a vast improvement and this is of course what drove the development of fangs. Just like the ability to make noise in the primate far preceeded our voice box but this advanced piece of architecture was a tremendous modification. Fangs evolved separately on four separate occasions but came much later than the potent venom. There could be no strong selection pressure for the development of fangs unless there was already a potent, complex venom worth delivering.

Cheers
B

[BoidKeeper]

Links did not work for me. So were venom glands found in colubrids that we deem as harmless?
Thanks,
Trevor

[Ace]

The American Elaphe-types (e.g. Pantherophis/Pituphis/Lampropeltis) have recently undergone a secondarly loss of the gland and reverted back to the more primative condition of constricting. .

I thought this meant they were the few that didn't have venom because they no longer had Duvenroy (or now venom) glands?

How do you test the degree of toxicity of the venoms? As I understand it (I'm by no means a scientist) these snakes only carried parts of the venom proteins that previously more dangerous snakes have. How do you conclude the venoms just as deadly? Do certain venom proteins carry certain levels of toxicity? Are some more toxic at lower levels than others?
Sorry for all the ???'s, just trying to make sense of your study, and I'm not well versed in the venomous side of snakes .

I think part of the confusion may be the use of the term venom and real differences between what is venom, what is toxic saliva, and is there a real difference between the two. The other confusion will be the definition of venomous used, whether glands, delivery system, use for prey aquisition, defense, and other questions defining the parameters of venom, poison, venomous, and poisonous. Welcome to the site Dr. Fry

[Dr. Bryan Fry]

Hi mate

Thie ancestor of this clade of American (but not the Asian) 'Elaphe-types) lost the venom gland as it evolved (devolved?) to become a more efficient feeder on rodents. This lineage is one of the very few that doesn't have it. Trimorphodon (lyre snakes) share a common ancestor with these snakes and do have the gland.

As for how we tested the venom, our initial tests have been on the neurotoxicity, using the same assays we've used in the past for death adders, sea snakes, etc. Some of the venoms are very very toxic. Effects upon the blood will be the next major pharmacological area to be investigated. In the meantime I'm sequencing as wide of a diversity of toxins as possible in order to study how they evolved.

The various 'colubrids' share at leasat six toxin types with the elapids and have no doubt evolved new ones of their own just as the elapids have developed new ones as well. Some toxin types are more toxic than others, and the 'colubrids' contain at least three of the most toxic (three-finger toxins, phospholipase A2 and M12B metalloproteases (this last group is the toxin type widespread in viper and elapid venoms that the boomslang uses to exert its devastating effect upon the blood chemistry and toast the ability to clot).

Cheers
B

[Dr. Bryan Fry]

Hi Reverendsterlin,

These venoms are true venoms. The concept 'toxic saliva' was used when 'colubrids' were thought to have evolved toxic secretions independently. However what we've shown is that venom originated only once and that some toxin types (4-6) are shared amongst all the lineages, including the vipers. The 'colubrids' share these six with vipers and elapids and further share at least an additional two with the elapids. It is the same venom gland.

Venom was a key evolutionary step for prey capture. The next step was a refinement of the gland and delivery mechanism. This was through the development of a musclar compressor set to create a high pressure delivery system terminating in long fangs (typically hypodermic-needle like). This has happened independently at least four occasions.

Cheers
B

[Simon R. Sansom]

Dr. Fry,
Are you able to observe the developement/evolution of the venom-delivery system in the fossil record?

Simon

[Dr. Bryan Fry]

Hi Simon

Not the venom glands they are soft tissue. We can however physically watch the emergence of different dentition types in the fossil record. Also, by mapping the presense of certain toxin types over the genetic tree of the animals themselves we can map the evolution of these toxin types. Further to this phylogenetic analysis of a toxins present in more than one lineage can also provide evidence for a single recruitment event.

Cheers
B

[Jeff_Favelle]

Holy crap, I just saw Brian on TV!! Way cool. Talking about Taipans or something. Great stuff man!

[Simon R. Sansom]

Jeff, I was just sitting here thinking about how amazing it is that we can have a group dialogue with the top man in the field when he's on the other side of the world!

Great Stuff!

Simon

[Jeff_Favelle]

I would have to say amazing as well Simon. For all the bad that technology does, its still pretty cool sometimes eh?