Also, some prey animals are very resistant to poison. The same way evolution selects for a snake that can kill its lunch in one go, there’s evolutionary pressure for the erstwhile meal to have higher tolerance for snake poison. A few million years of evolution, and now you’ve got a frog or fish that can take hundreds of times more poison than a human.
Actually, that’s another question that has been circling in my mind for a while. It may be better if it gets its own thread, though. Can you build a tolerance against anything? Are there any poisons that work in a way you cannot build a tolerance against it?
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How awesome is that!
Turtle, killer of the deadliest jellyfish!
No, there are some toxins you can’t. Cyanide, for example, kills by binding to hemoglobin more tightly than oxygen. Kills too quickly for the body to get rid of it. Other toxins act in ways that the body CAN build a tolerance for. Rattlesnake venom, for example. It depends on the biochemical process the toxin disrupts, and also if the toxin accumulates or is rapidly flushed from the body. Arsenic accumulates, so as you get more and more from small doses it builds up until it reaches toxic levels that then kill you.
You’re thinking of carbon monoxide.
Because it’s better to have a super poison that can kill right away instead of a pretty good poison that can kill something after it kills you?
No, I’m not. They both work the same way.
Obviously, more potent poisons must be more expensive or there wouldn’t be a point to making less potent ones. The more interesting question is, if such super-poisons exist, why has not every creature evolved to have them?
As far as evolution is concerned, good enough is good enough.
To back up the “good enough is good enough” explanation, look at the Komodo dragon. Evidence now shows that Komodos are in fact poisonous and don’t just kill from bacteria. But the poisons take days to kill many of the prey species, so it is clearly a very weak poison for the job. Surely a better poison could kill in minutes or hours, right?
But Komodo dragons are cold blooded. They don’t need to eat very often and have no problem waiting a few days (or weeks) for their next meal.
So… what’s the difference between a Komodo that bites, waits a few days and then eats and a Komodo that bites, eats and then waits a few days? There just isn’t that much selection pressure between the two options - either way, they’ve got more food than they can eat, and either way, they could go weeks between big meals. The effectiveness of the poison just isn’t that important.
You seem to be confusing two different things. The post you quoted was referring to a population evolving a tolerance. That is very different to an individual building up a tolerance.
A population can develop a tolerance to any poison, by the very definition of poison. Poisons cause chemical disruption to biological systems. Since the chemistry of individuals varies base don genetics then it’s always possible to evolve a tolerance to a poison.
An individual can build up a tolerance (technically an acclimation) to any poison that I am aware of. In the case of poisons such as arsenic or snake venom the degree of tolerance can be extremely high, to the extent that an individual can, within a lifetime, develop a resistance to levels of toxin many times higher than what would would be acutely fatal to a non-acclimated individual. In the case of other toxins the level of acclimation may be much smaller, maybe only a few percent better than anon-acclimated individual.
That isn’t true in any way.
A great many animals, plants and microbes are resistant to cyanide. It has been well established that microbes can evolve a cyanide resistance quite rapidly, and there is no reason to believe that animals can’t likewise develop resistance.
Cyanide doesn’t “kill too quickly for the body to get rid of it”, like all poisons the time to death depends almost entirely upon dose and mode of exposure. If ingested in food even a fatal dose of cyanide can take days to be fatal. The vast majority of cases of cyanide intoxication are, of course, not fatal at all.
How is this in any way different to cyanide toxicity? Doesn’t cyanide also depend on the biochemical process the toxin disrupts? Isn’t that why animals with lower oxygen demands and higher anaerobic scope are more resistant to cyanide?
Except that it is well and truly established beyond any doubt that humans can very easily build up a tolerance to arsenic, and can consume low doses for decades with no ill effects.
Well, no. That doesn’t really make any sense. Traits don’t evolve just because they don’t have any cost. Traits evolve because they provide a net benefit. If a more potent venom has no benefit over a less potent one then the more potent form will never evolve. Simple as that.
For example, puss catterpillar venom causes pain, but is never fatal. But it is 100% effective in causing predators to let go. If a catterpillar did evolve venom that was instantly fatal, it would still only have the effect of causing 100% of predators to let go. It wouldn’t confer any additional advantage, even if it cost no more than the current venom. Venom that causes pain is just as good as venom that causes death for the purposes that venom is used for.
The same goes for snake venom. Given its prey and mode of hunting, rattlesnake venom is perfectly good at subduing prey. It allows a rattlesnake to eat 95% of the prey that it strikes with no injury to itself. A rattlesnake with venom as potent as that of a taipan would still only have a 95% chance of subduing the prey that it strikes with no injury to itself . It would have absolutely no advantage over its brethren, even if the more potent venom cost no more. So the venom can’t possibly evolve.
In short, it’s not a case of there being no point in making the less potent venom. It’s a case of there being no selective advantage in making the more potent.
Two reasons.
Firstly because they confer absolutely no advantage whatsoever. Given its prey and mode of hunting, what possible advantage would a tiger gain from having venom equivalent to a taipan? It still takes 10 minutes to incapacitate the prey, by which time the prey has either escaped or been subdued. Tiger hunts simply don’t last 5 minutes, so a super venom that can bring down man sized prey in 10 minutes is absolutely pointless.
Secondly, because no evolutionary pathway exists. IOW you can’t get there from here. Toxins don’t spring out of the ground fully formed, they develop through selective pressure.
Proto snakes were constrictors, and they took half an hour to kill their struggling prey by suffocating it. A snake that evolved a venom that killed the prey in 29 minutes had developed an actual survival advantage, and evolution could then work on that advantage to make it more potent. A pathway was open to more potent venom. Similarly the proto-spider was probably a parasitic mite that was already injecting its host with salivary enzymes. A mite that was parasitising prey many times its own size had an obvious advantage in making the prey sluggish to avoid being groomed off. The evolutionary pathway was open to mites developing better and better toxins.
How does a tiger develop such a trait? If tiger developed venom that would subdue an animal 29 minutes after it was bitten, how would that give it any advantage at all over other tigers? Even if it was absolutely cost free, it has no advantage, so it would never be selected for and thus never able to be improved upon.
This seemed odd when I read it because you would think most prey would wander off before it got sick enough to die, but a show I watched last night said the same thing. On this show, a “reptile hoarder” lived with Komodo dragons loose in his home. On Friday he showed his cow-orkers a nasty bite he had just gotten. Monday he didn’t show up for work. They found him a week later, dead, partially eaten.
No they don’t. Carbon monoxide binds tightly to hemoglobin, stopping your blood from carrying oxygen. Cyanide interferes with cell metabolism, preventing your cells from producing energy.
Yup, exactly right. Carbon monoxide actively out-competes oxygen’s affinity for the heme molecule, with the end result being in ability to deliver oxygen to your blood. Your perfectly healthy tissues starve.
Cyanide is a much more insidious toxin; it binds with enormous affinity to most metals, and is a tiny ion capable of slipping into the deep crevices of a protein’s active site. In particular it kills by interrupting cytochrome oxidase and essentially clogs up the electron transport chain and renders you unable to utilize oxygen. But it also interrupts a wide array of metalloproteins - I wouldn’t be surprised if it exhibits a similar action to carbon monoxide in the blood - maybe that’s what Cheshire Human was referring to?
Cyanide resistance, as is typical for these sorts of things, seems to be achieved by using other cytochrome oxidases less vulnerable to its disruptive effects.
Well, rattlesnake venom is a complex mixture of poisons, enzymes, and other proteins with a wide disruptive range, some of which are just nonspecific proteases that just start chopping everything up. I imagine resistance for these will be more difficult to evolve - particularly given that most of the prey that get subjected to that kind of selective pressure subsequently become dinner.