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What amazes me is the question: what kind of evolutionary pressure would drive creatures to develop stings and venom this viscious. I would have thought nature

by srean 12y ago

What amazes me is the question: what kind of evolutionary pressure would drive creatures to develop stings and venom this viscious. I would have thought nature would stop optimizing once a sting is a good enough deterrent. It is as if someone said, no, I would optimize the crap out of this chemical weapon. I have always been intrigued by how much does the effect generalize across the victim species. Consider tarantula wasps, their sting take pain and suffering to new heights (for humans). But really what the wasps use it for, primarily, is to temporarily immobilize a tarantula so that it can lay eggs on it. The hatchlings end up eating the tarantula. If temporary immobilization is the main use case (surely not the only use case), must it be this painful. Is the tarantula in as much pain and if so what purpose is that serving ? It seems something that gives them a pleasure trip makes more sense.

aylons 12y ago
A few layman hypothesis: * A more powerful venom will work faster and more reliably. * This is not only a very powerful, but also a very efficient venom. More efficient venom reduces manufacturing costs (as only a few molecules are needed). * Chance probably have played a role here. Black widows hardly had any pressure to evolve a specific venom against humans. As our nerve system is based on the same basic molecules as every other land creature, but not the same structure, a venom that is good enough to kill a mouse may have a devastating (albeit non-fatal) effect on us. I'm already speculating, so I may be cruel: maybe the spider wants to paralyze the mouse, but keep him alive for a few days so the flesh stays fresh as they eat it.
- aptwebapps 12y ago
  "I'm already speculating, so I may be cruel: maybe the spider wants to paralyze the mouse, but keep him alive for a few days so the flesh stays fresh as they eat it." Another layman here, but I believe spider venom is designed to pre-digest food to some extent, rather than to keep it fresh.
  - ArkyBeagle 12y ago
    Snake venom of the rattlesnake variety certainly is; the fangs are the first line of the digestive system. Black mamba venom is a neurotoxin. It's remarkable how diverse venom is.
thret 12y ago
I imagine that while it doesn't need to be this vicious for humans, they have evolved this to deal with other large animals. Humans tend to avoid getting bitten so we haven't evolved the defences other animals have. We are pretty weak creatures all things considered. Have you seen that youtube clip of a honey badger attacking a poisonous snake? He is bitten repeatedly. He falls unconscious, and later wakes up and continues eating the snake. That's the kind of predator poison gets stronger and stronger for.
karmajunkie 12y ago
The same evolutionary pressure that drives some predators to develop defenses against the merely painful versions of the venom...
ArkyBeagle 12y ago
Just skylarking: - Spiders have huge litters. - It may be that the evolutionary path is more driven by the enzyme chemistry than the efficacy of the venom. Mighta come up with a nasty version and then change more or less stopped, purely by accident. Evoluton arrives at solutions, not optima. - Given the general proximity these spiders tend to have with humans, their prevalence could be completely accidental. See also grackles, other creatures that are symbiotes to us. Now I wonder what the metabolic load from producing venom in venomous creatures works out to.
- kghose 12y ago
  Small point - I think it's called a brood.
sopooneo 12y ago
I wonder if the devastating effect on us may be a sort of coincidence. It's chemical code running on a different (but similar) biological chip-set than evolved for, and just happens to unleash hell on our human hardware.
dboat 12y ago
Nature doesn't "optimize" like that exactly. Naturally selection is a process of random mutations. The ancient ancestor of the first black widow might not have been some peculiar middle ground between benign and lethal, yet the random mutation of offspring which proliferated merely happened to be highly deadly. Along that vein, I wonder if there have been random black window mutations since which have been even more lethal, but since this did not present a significant survival advantage, they did not live long enough to become a distinct species.
- melloclello 12y ago
  There's a paper on latrotoxins available, "Molecular Evolution of α-Latrotoxin, the Exceptionally Potent Vertebrate Neurotoxin in Black Widow Spider Venom": http://mbe.oxfordjournals.org/content/30/5/999.full http://mbe.oxfordjournals.org/content/30/5/999.full It's way over my head though and I actually have no idea if it's backing up or refuting your claim.
- kybernetyk 12y ago
  > Nature doesn't "optimize" like that exactly. Exactly. A stronger venom doesn't only mean that the spider can kill prey more efficiently. It also means that those individuals with the stronger venom mutation have higher chances of breeding. They can kill more efficiently and faster and thus have higher chances to survive long enough to reproduce. In evolution the mutation that leads in the long term to higher chances of reproduction usually wins.
- ronaldx 12y ago
  > The ancient ancestor of the first black widow might not have been some peculiar middle ground between benign and lethal, yet the random mutation of offspring which proliferated merely happened to be highly deadly. This is possible but not very likely in reality. We expect evolution to be incremental, for the following reasons: First of all, it's very unlikely that any mutation would get to "Surprise! Lethal!" venom unless the species is already geared up to produce something venom-like, and also to store venom and to protect itself from its own venom. There's a whole bunch of new functions that are needed to be venomous, and it's vanishingly unlikely that they will all suddenly appear at the same time, even at evolutionary scale. IMO mutations normally have small positive effects and large negative effects: they are more likely to delete or - if you're lucky - alter some existing function and very unlikely to build a whole new function (compare: a small random change to your computer code). Even if super-lethal venom was to somehow appear overnight, then in order to reach 100% prevalence it must provide such an immediate advantage that the non-lethal spiders die out and only super-lethal spiders proliferate. But the non-lethal spiders were surviving pretty well in order to reach that point. So, there's no reason to believe the non-lethal spiders were in particular danger or that lethal venom was needed - normally, the "Surprise! Lethal!" variant line would just quietly die out (as almost all variants do) leaving the wild non-lethal type. As I say, the random mutation explanation is possible but not really practical. A far more plausible scenario is an "arms race" - where venomous functions develop over time, while predators and prey develop immunity over time - as the predators (honey badger) start evolving coping mechanisms, stronger venom is needed.
Houshalter 12y ago
Purely speculation, but perhaps the target species evolved defenses. So it evolved a more potent venom. Another evolutionary arms race that results in highly optimized weapons. It just happens we have similar biology to the target species and none of the defenses.
ronaldx 12y ago
> I would have thought nature would stop optimizing once a sting is a good enough deterrent. I believe you are probably right about this: but the spider venom was probably developed in an arms race with some {predator/prey} species. In your 'tarantula hawk' example, the venom must work on the tarantula, and the tarantula must do its evolutionary best to protect itself from the venom. This combination allows the venom to become extremely effective. Or, given that it's the black "widow", maybe the venom is a result of sexual selection[0], which tends to have crazily extreme results. A spider fetish, if you like. But, the sting/venom is not designed for humans (it just happens to work on them), and humans as a species have no reason to develop better protection. Humans typically aren't a target of the bites and almost always recover with no long-term effect. It isn't really designed to work on humans. But, it still hurts (and maybe that's a nice side benefit for a reclusive spider). [0] https://en.wikipedia.org/wiki/Sexual_selection https://en.wikipedia.org/wiki/Sexual_selection
Intermernet 12y ago
I often wonder this when thinking about the local fauna here in Australia. So much of it can kill a mammal of human size ridiculously quickly, but there really isn't anything in the fossil record to warrant such destructive power. It's like the insects and snakes (and lots of other animals) of Australia got caught up in the equivalent of a cold war that has led to mutually assured destruction on both sides.
syllogism 12y ago
In the case of the Sydney funnelweb, it's pure coincidence. The spider is much more toxic to primates than any other type of animal, but evolved in Australia, with no primates. The "selection" that's going on here is in our attention: our gaze fixates on the species that have poison or venom that's particularly potent against us, out of the thousands of species that have poison or venom of some sort. (Source: Somewhere in this otherwise sort of stupid video: https://www.youtube.com/watch?v=myh94hpFmJY https://www.youtube.com/watch?v=myh94hpFmJY )

by srean 12y ago

aylons 12y ago

A few layman hypothesis: * A more powerful venom will work faster and more reliably. * This is not only a very powerful, but also a very efficient venom. More efficient venom reduces manufacturing costs (as only a few molecules are needed). * Chance probably have played a role here. Black widows hardly had any pressure to evolve a specific venom against humans. As our nerve system is based on the same basic molecules as every other land creature, but not the same structure, a venom that is good enough to kill a mouse may have a devastating (albeit non-fatal) effect on us. I'm already speculating, so I may be cruel: maybe the spider wants to paralyze the mouse, but keep him alive for a few days so the flesh stays fresh as they eat it.

aptwebapps 12y ago
"I'm already speculating, so I may be cruel: maybe the spider wants to paralyze the mouse, but keep him alive for a few days so the flesh stays fresh as they eat it." Another layman here, but I believe spider venom is designed to pre-digest food to some extent, rather than to keep it fresh.
- ArkyBeagle 12y ago
  Snake venom of the rattlesnake variety certainly is; the fangs are the first line of the digestive system. Black mamba venom is a neurotoxin. It's remarkable how diverse venom is.

thret 12y ago

I imagine that while it doesn't need to be this vicious for humans, they have evolved this to deal with other large animals. Humans tend to avoid getting bitten so we haven't evolved the defences other animals have. We are pretty weak creatures all things considered. Have you seen that youtube clip of a honey badger attacking a poisonous snake? He is bitten repeatedly. He falls unconscious, and later wakes up and continues eating the snake. That's the kind of predator poison gets stronger and stronger for.

karmajunkie 12y ago

The same evolutionary pressure that drives some predators to develop defenses against the merely painful versions of the venom...

ArkyBeagle 12y ago

Just skylarking: - Spiders have huge litters. - It may be that the evolutionary path is more driven by the enzyme chemistry than the efficacy of the venom. Mighta come up with a nasty version and then change more or less stopped, purely by accident. Evoluton arrives at solutions, not optima. - Given the general proximity these spiders tend to have with humans, their prevalence could be completely accidental. See also grackles, other creatures that are symbiotes to us. Now I wonder what the metabolic load from producing venom in venomous creatures works out to.

kghose 12y ago
Small point - I think it's called a brood.

sopooneo 12y ago

I wonder if the devastating effect on us may be a sort of coincidence. It's chemical code running on a different (but similar) biological chip-set than evolved for, and just happens to unleash hell on our human hardware.

dboat 12y ago

Nature doesn't "optimize" like that exactly. Naturally selection is a process of random mutations. The ancient ancestor of the first black widow might not have been some peculiar middle ground between benign and lethal, yet the random mutation of offspring which proliferated merely happened to be highly deadly. Along that vein, I wonder if there have been random black window mutations since which have been even more lethal, but since this did not present a significant survival advantage, they did not live long enough to become a distinct species.

melloclello 12y ago
There's a paper on latrotoxins available, "Molecular Evolution of α-Latrotoxin, the Exceptionally Potent Vertebrate Neurotoxin in Black Widow Spider Venom": http://mbe.oxfordjournals.org/content/30/5/999.full http://mbe.oxfordjournals.org/content/30/5/999.full It's way over my head though and I actually have no idea if it's backing up or refuting your claim.
kybernetyk 12y ago
> Nature doesn't "optimize" like that exactly. Exactly. A stronger venom doesn't only mean that the spider can kill prey more efficiently. It also means that those individuals with the stronger venom mutation have higher chances of breeding. They can kill more efficiently and faster and thus have higher chances to survive long enough to reproduce. In evolution the mutation that leads in the long term to higher chances of reproduction usually wins.
ronaldx 12y ago
> The ancient ancestor of the first black widow might not have been some peculiar middle ground between benign and lethal, yet the random mutation of offspring which proliferated merely happened to be highly deadly. This is possible but not very likely in reality. We expect evolution to be incremental, for the following reasons: First of all, it's very unlikely that any mutation would get to "Surprise! Lethal!" venom unless the species is already geared up to produce something venom-like, and also to store venom and to protect itself from its own venom. There's a whole bunch of new functions that are needed to be venomous, and it's vanishingly unlikely that they will all suddenly appear at the same time, even at evolutionary scale. IMO mutations normally have small positive effects and large negative effects: they are more likely to delete or - if you're lucky - alter some existing function and very unlikely to build a whole new function (compare: a small random change to your computer code). Even if super-lethal venom was to somehow appear overnight, then in order to reach 100% prevalence it must provide such an immediate advantage that the non-lethal spiders die out and only super-lethal spiders proliferate. But the non-lethal spiders were surviving pretty well in order to reach that point. So, there's no reason to believe the non-lethal spiders were in particular danger or that lethal venom was needed - normally, the "Surprise! Lethal!" variant line would just quietly die out (as almost all variants do) leaving the wild non-lethal type. As I say, the random mutation explanation is possible but not really practical. A far more plausible scenario is an "arms race" - where venomous functions develop over time, while predators and prey develop immunity over time - as the predators (honey badger) start evolving coping mechanisms, stronger venom is needed.

Houshalter 12y ago

Purely speculation, but perhaps the target species evolved defenses. So it evolved a more potent venom. Another evolutionary arms race that results in highly optimized weapons. It just happens we have similar biology to the target species and none of the defenses.

ronaldx 12y ago

> I would have thought nature would stop optimizing once a sting is a good enough deterrent. I believe you are probably right about this: but the spider venom was probably developed in an arms race with some {predator/prey} species. In your 'tarantula hawk' example, the venom must work on the tarantula, and the tarantula must do its evolutionary best to protect itself from the venom. This combination allows the venom to become extremely effective. Or, given that it's the black "widow", maybe the venom is a result of sexual selection[0], which tends to have crazily extreme results. A spider fetish, if you like. But, the sting/venom is not designed for humans (it just happens to work on them), and humans as a species have no reason to develop better protection. Humans typically aren't a target of the bites and almost always recover with no long-term effect. It isn't really designed to work on humans. But, it still hurts (and maybe that's a nice side benefit for a reclusive spider). [0] https://en.wikipedia.org/wiki/Sexual_selection https://en.wikipedia.org/wiki/Sexual_selection

Intermernet 12y ago

I often wonder this when thinking about the local fauna here in Australia. So much of it can kill a mammal of human size ridiculously quickly, but there really isn't anything in the fossil record to warrant such destructive power. It's like the insects and snakes (and lots of other animals) of Australia got caught up in the equivalent of a cold war that has led to mutually assured destruction on both sides.

syllogism 12y ago

In the case of the Sydney funnelweb, it's pure coincidence. The spider is much more toxic to primates than any other type of animal, but evolved in Australia, with no primates. The "selection" that's going on here is in our attention: our gaze fixates on the species that have poison or venom that's particularly potent against us, out of the thousands of species that have poison or venom of some sort. (Source: Somewhere in this otherwise sort of stupid video: https://www.youtube.com/watch?v=myh94hpFmJY https://www.youtube.com/watch?v=myh94hpFmJY )