Okay i get the whole concept of evolution, but today in my chemistry seminar my prof was describing how certain toxins have evolved to be effective by attacking specific parts of certain neurons.
My question is: how would evolution work in this case. Either a toxin works or it doesn’t work. Once it works the animal would stop spending the energy to create new venom, but until then i don’t see how evolution would tell the difference between a toxin that is very close to working, and a toxin that is no more harmful than water.
Doesn’t seem like survival of the fittest to me.
Not necessarily. Maybe your toxin only works half the time. That’s still better than no toxin at all–half the time you bite something, it dies, and you get to eat. The other half of the time, you go hungry. Now, along comes another snake, whose toxin has some random variation in chemical structure. His toxin works three times out of four, he gets 50% more rats than you do, and he’s a big, strong, sleek, healthy snake, and all the female snakes want to have his baby. Conversely, a snake who by some genetic quirk produces a “toxin” that isn’t actually toxic at all almost never kills anything, and leads a short and unhappy life.
I wish I could remember the names of a certain snake and salamander species. I saw them on a show a while ago that relates to this question. The salamanders (I think) had a ridiculouly potent toxin that they released through their skin that would kill animals hundreds of times their size, yet the only real predators were this one type of small snake. The snakes in turn could withstand incredible amounts of this same toxin, although there seemed to be lots of other things to eat. These two species evolved these weird traits in response to each other; there was no need for them to have these traits other than the fact that one preyed on the other. Animals usually don’t have qualities that they don’t need or didn’t need at one time; but they don’t come with information tags around their necks that tell us why they develloped these traits - that’s for us to ponder. Animals don’t “spend energy” conciously or even subconciously trying to improve their genetic make-up. Most seems to happen through random mutations… to over simplify:
Snake A was born with weak venom, can’t kill anything to eat, and dies.
Snake B has slightly stronger venom, can kill to eat, and has some kids with Snake C who has similar venom.
One of their kids has really strong venom, out-competes all the other snakes (maybe by being able to kill a different, more numerous prey that was too tough for weak venom), and has LOTS of kids.
Now the only snakes left all have strong venom. Only the best of these can survive, and all the while the prey might be evolving a slight resistance to the venom. And so on and so forth.
Evolution could tell the difference between weak and useless venom like so:
Useless venom does nothing, so naturally that snake doesn’t do very well.
Weak venom might not kill the prey, but could slow it down or make it feel sick enough for the snake to catch.
You don’t need 100% perfection the very first time for a trait to start making it’s way into a species; besides, what’s the definition of something working or not? It can always change - take the example of the devellopment of lungs. They originally started out as another (probably mutated) organ of aquatic animals, which just happened to let them take in a little gulp of atmospheric oxygen. They got better and better to the point that we now have them, although the original blueprints sure weren’t for what we got in our chests. They have been improved upon even more; birds have much more efficient lungs than we do. But if evolution was pre-planned for one specific trait that couldn’t be used in new ways, and just stopped after something was “good enough”, then the world would still be inhabited by slimey amphibians who stick their heads out of the water now and then.
The questions’ benn pretty well answered, but I thought I’d chime in anyway.
Sanke benom, last I herad, was assumed to be modified saliva. It’s primary purpose is to stop the snake being injured by prey by immobilising the animal. A snake with no venom at al would still be an efficient predator, it’s just that occasionally they’d get killed when they didn’t get quite a good enough grip on a rat and it bit them.
Sometime in history a snake ancestor presumably evolved some form of saliva that caused a nasty reaction in the prey. Not a big leap really since saliva contains digestive enzymes anyway. Not a hideously nasty reaction, but one that immobilised a rat in say 2.5 minutes rather than the 3 minutes that it would take to suffocate it. Maybe not a big advantage but probably sufficient that it had slightly more offspring. From there any increase in the efficiency of the venom and delivery system would give some advanatge to the individual until we have the really nasty toxins we have today.
mmmiiikkkeee: I believe the example you’re thinking of referred to the Newts in the genusTaricha, which produce a toxin identical to that found in Puffer-Fish ( known as both tarichatoxin for the newt and tetradotoxin from the family of the fish ), and certain populations of the Common Garter Snake Thamnophis sirtalis ( especially populations of the Red-Sided Garter Snake, Thamnophis sirtalis helleri ).
In addition to everybody else’s comments, I’ll just point out how interesting it is that we see virtually every seeming “step” in the evolution of venom and venom-delivery systems in different species of modern snakes to today. From the very elaborate solenoglyphous ( hypodermic-like “folding fangs” ) system of vipers, to the slightly enlarged, slightly grooved teeth found in certain species of colubrids ( these species will bite and hold on, “chewing” a bit to work their saliva into the prey item ), and everything in between. I would wager that there is quite a bit of evolution in the direction of more venomous species going on as we speak. It does seem to be a pretty natural progression given the advantage of being able to subdue larger prey items. It has been estimated that at least one-third of the huge “non-venomous” garbage can family of the Colubridae has some sort of opisthoglyphous ( rear-fanged ) dentition with associated Duvernoy’s gland.