Another question for Dr. Fry...

[Simon Sansom]

Okay, with all of this talk about venomous colubrids lately, I'd like to ask -
What, if any, benefit does the snake derive from having these toxins? For example, is the venom of an Asian rat snake actually of any use in capturing prey? Everything evolves for a purpose, correct? If these toxins are even only present in relatively small amounts, why even have them at all?

... Or am I missing a key point here?

Thanks,

Simon

[Vanan]

Hmm... not Dr Fry and can't really answer your question Simon, but thought I'd add another angle to it.

Maybe that's why the Asian rats are more slender bodied and more racer-like. Could it be that having venom reduces the need of a thick, bulky constrictor type body? Seems like the best way to be, is fast and sleek, to escape predators and chase prey if need be. So if you have venom, then it gives you more freedom to be less muscular for constriction, thus making it less bulky and gives you faster locomotion.

Sorry Simon, don't mean to hijack your post but maybe Dr Fry can answer both at the same time.

[Simon Sansom]

Vanan,
No need to apologize at all, my friend - discussion is what it's all about...That's an interesting point of view. I wonder what the good doctor will
have to say...?

Simon

[Dr. Bryan Fry]

Basically the first venomous snakes were heavy bodied 'swamp monsters' not too dissimilar to the modern day anaconda. In order to move out of the swamps and into grasslands and such required that it become more gracile and athletic. This ment dumping the very muscle that it was using for prey capture, enter venom. From there, seven families or so, evolved out rapidly, all carrying the original toxins. Constriction ended up varying from zero (the vipers) through various amounts of constriction in the other families of 'colubrids', elapids and atrastaspids. Colubrinae includes some that use constriction more then others (eg the American lineage of the ratsnakes reverting back to a more powerful constriction. Obviously advantageous to the new habitat because they flourished on the rodent diet. The venom that was there just wasn't up to scratch. However, some elapids (eg the Australian Brown snakes (Pseudonaja) species do use contriction to hold the prey in place while they drive the fangs into them. A sliding scale.

Even with the ones like Coelognathus radiatus (Radiated ratsnake), which puts out very little amounts of equally potent venom relative to the elapids, basically full strength beer served in a thimble (with varying glass sizes all inbetween, some like Telescopus dhara (Egyptian catsnake, in the Colubrinae family) and Psammophis mossambius (Olive sand snake, in the Psammophiinae family) having massive venom glands (as shown on my webpage with the gland size pictures of these two, scary indeed).

Cheers
B

[Vanan]

Ah, so you think that some snakes are reverting back to constriction and losing the venom. Could that be what most colubrids are "doing", excluding the Boiginae.

With regards to Asian rats, do you think they're moving towards a more successful venom or more towards bulk for constriction.

Damn! I wish I could live a million years, just to see Nature evolve! Psshh!

[Dr. Bryan Fry]

Hi Van

Actually most 'colubrids' are not doing that. The actual diversity within the Colubroidea (advanced snakes) is tremendous, with the 'colubrids' actually being seven different families, some of which are actually 'proto-elapids' in that they are genetically much much closer to a cobra than a corn snake (e.g. the Pseudoxyrhophiinae (any 'colubrid' from Madagascar) as well as the Psammophiinae (Psammophis, Malpolon etc.)). The venom gland size range from small (radiated ratsnakes) to massive (Telescopus dhara and Psammophis mossambicus are two good examples of species from different families (Colubrinae and Psammophiinae respectively) that have massive venom glands).

Not sure what the Asian rats are doing. The venom is quite useful in helping to settle down frogs though.

Cheers
B

[lizardmom]

the info here is awesome, i love learning more and more,
thanks Dr. Fry, wow, info from downunder.this forum is so cool.
you people make my day, i have three kids, i am a stay at home mom, secretary, doctor, therapist., so to learn all this info at home is just amazing.
thanks to all
lizardmom.