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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

by 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.

by dboat 12y ago

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.