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Re: snake/spider venom



David Marjanovic <david.marjanovic@gmx.at> wrote:

> Besides, selection would act _against_ snake venom being overkill
> for 65 million years.

I don't know what made you say that...  Anyways, the original
suggestion was that snake venom might be more toxic than it needs to
be because extinct animals (e.g. dinosaurs) might have been less
susceptible to it.  There is no need for such exotic explanations...
There are animals alive *today* that are relatively less susceptible.
Basic pharmacological mechanisms pretty much guarantee that targeted
toxins will produce an arms race between the animal that produces the
toxin and the target for which the toxin is developed.

The most widely known example of this is between _Taricha_ (a newt
which secretes Tetrodotoxin in its skin) and _Thamnophis_ (the garter
snakes that eat the newts).  Tetrodotoxin is the stuff secreted by
puffer fish also -- its the stuff you have to look out for if you ever
eat fugu.  It's a really nasty poison for almost all animals (it
blocks sodium channels in cell membranes).  But garter snakes eat
newts like candy:

http://www.pbs.org/wgbh/evolution/library/01/3/l_013_07.html

Less well known but more on point, California ground squirrels have
protease inhibitors that interfere with the effectiveness of
rattlesnake venom.  You can download a couple of references on this
here:

http://chemac239.ucdavis.edu/~jebiardi/BiardiCV.htm

If that's not enough for you, you might consider looking into the
natural history of snake-eating snakes.  King snakes are legendary for
their resistance to snake venom.

While it might be fun to speculate that snake venom has toxicity
targeted to extinct animals, there's no reason to search so far
afield.  I've never looked into this for spiders, but I suspect there
are similar stories for them as well.

-- 
Mickey Rowe     (rowe@psych.ucsb.edu)