Is Natural Selection Stymied by this tactic?

[Soapy Sam]

Define "win".

 

[SteveGrenard]

Define "win".

This has been described by someone above as an evolutionary arms race and this is a good description.

Will the snakes, as clever as they are, wipe out the frogs? Or will the frogs retaliate in time, before extinction, with an additional defense? And how long and at what cost as someone else brought up?

If the snakes wipe out all the poisonous frogs they can easily switch to some other food choice be it rodents or fish if they were available? We don't know if frogs are their only option in their particular habitat which means if they wipe out all their food (the frogs) they too will die. No win situation. Or will they be smart enough to leave enough frogs to assure an indefinite food supply?

Frogs usually get the raw materials for their skin poisons from the bugs they eat. The bugs get it, usually alkaloids, from the plants they eat. I am not sure how they can mount an additional defense. Perhaps by eating a different bug which eats a different poisonous plant.

 

[Soapy Sam]

The term "Arms Race" in this context , (I believe) originated with Richard Dawkins.
It's a useful metaphor, but like all metaphors , has a limit. Human arms races involve consciousness and usually malice on both sides. Each is out to defeat, or maybe exterminate, the other. In this case, neither snake nor frog has any such intent- in fact we suppose neither to be capable of intent.

The question then is are they actually in competition at all? Each snake competes with each other snake. Each frog competes with other frogs. But do they compete with each other?
If the snake can "smell / taste" when the poison is ineffective, the frog might develop a scent which masks this. Or a volatile poison- a nerve gas absorbed via the snake's tongue. It depends how set are the chemical pathways to making poison. Is this something the frog can change relatively easily, or is it so fundamental to frog biochemistry that changing it costs too much?
If all poison becomes ineffective against snakes, the frogs might take the opposite course and stop producing poison entirely, but adopt a lifestyle less open to snake predation.
If the frogs are a major part of snake diet, wiping them out would be a very bad move, snake wise. More likely, as the frogs become rare, the snakes will switch to other prey.

Impossible to say, without knowing all the variables with their relevant weightings. What other predators are out there? What do the frogs eat?

It's pure guesswork Steve. Whatever the outcome, it will be a selective one.

 

[SteveGrenard]

The term "Arms Race" in this context , (I believe) originated with Richard Dawkins. It's a useful metaphor, but like all metaphors , has a limit. Human arms races involve consciousness and usually malice on both sides. Each is out to defeat, or maybe exterminate, the other. In this case, neither snake nor frog has any such intent- in fact we suppose neither to be capable of intent.

This clearly is not human but the intent of each can be implied and it is a life or death situation for both. The intent of the snake is to feed, otherwise starve to death,
the intent of the frog, even in death, is to kill its predator and thus eliminate an enemy
for its fellow frogs. The snake has found a way to beat the frog at its own game.

The question then is are they actually in competition at all? Each snake competes with each other snake. Each frog competes with other frogs. But do they compete with each other?

Clearly they are not in competition with each other in the conventional sense. Each is
competing to stay alive.

If the snake can "smell / taste" when the poison is ineffective, the frog might develop a scent which masks this. Or a volatile poison- a nerve gas absorbed via the snake's tongue. It depends how set are the chemical pathways to making poison. Is this something the frog can change relatively easily, or is it so fundamental to frog biochemistry that changing it costs too much?

Frogs that make poisons and other secretions, noxious or otherwise, are complicated little biochemical factories. It is clearly a genetic ability but see below. There are external factors that come into play.

If all poison becomes ineffective against snakes, the frogs might take the opposite course and stop producing poison entirely, but adopt a lifestyle less open to snake predation.
If the frogs are a major part of snake diet, wiping them out would be a very bad move, snake wise. More likely, as the frogs become rare, the snakes will switch to other prey.

In either case the smart move by the snake is to find something else to eat.

Impossible to say, without knowing all the variables with their relevant weightings. What other predators are out there? What do the frogs eat?

I answered this above but will expand on it. Frogs invariably are all bug eaters....
insects and other arthropods. A few larger species might even eat mice. The millions of bugs one frog eats over X amount of time each contain tiny traces of plant alkaloids
they acquire from eating plants which is what most, yes not all, eat. And not all plants
contain poisonous alkaloids. When very poisonous dart poison frogs were introduced from Panama into Hawaii the frogs were no longer poisonous. The bugs in their diet changed and the plants in the bugs' diet changed. Ditto for captive kept poison frogs. After awhile they are no longer poisonous and their offspring are not poisonous. This is because they are fed different bugs in captivity than they would find in the wild. The point of this explanation is that the frogs may be stuck with the bugs they eat which are stuck with the plants they eat. Thus it would involve a series of changes for the frogs to somehow be modified to produce either stronger posions or none at all.

It's pure guesswork Steve. Whatever the outcome, it will be a selective one.

Yes without a lot more knowledge of the variables in this Australian example it is pure guesswork. I guess what everyone here is saying and the reason I asked, is that natural selection is not blocked or stymied by the actions of this snake and if anything it may be
exemplified by it.

ETA: There is another kind of poison that toads produce as a glandular secretion and it is digitalis-like and predators suffer bradycardia or cardiac arrest if they swallow it. It is also bad tasting so it warns off predators without necessarily killing them. It is clearly genetic since there are no "raw materials" for it in the bugs that the toads eat. A few toads also produce non-lethal (most of the time) hallucinogenic substances which led to the toad licking phemoneon among American and some Australian (licking cane toads) hallucinogen seekers.After a few deaths this practice stopped on its own so clearly the defense worked under this limited toad threat.

 

[Schneibster]

IIRC the correct terminology is "coevolution."

 

[Alkatran]

They assumed snakes couldn't favor frogs without longer lasting poisons. Maybe longer lasting poisons give off a smell snakes will recognize and avoid if easier prey is around.

 

[JoeTheJuggler]

From the article:

Natural selection ceases to operate on an individual after
that individual's death, so frogs will probably never evolve toxins
that last longer in response to the snake's tactic.

What's sad is that the quote is actually from the authors of the article in The American Naturalist not the words of the news writer.

Edit: I removed most of my post upon reading more of the thread and realizing that several people have said what I would've said.

 

[CFLarsen]

Anyone care to wager who will win this? The snakes or the frogs?

Your question reveals a thorough misunderstanding of evolution.

Neither the snakes or the frogs will "win". Species evolve all the time. Those who do not adapt to a new environment will die off. In the time it takes for some of the snakes to evolve this particular trait, some of the frogs will have evolved some other traits that will protect them from some of the snakes.

There are also many other factors that will influence how both will evolve. It isn't a question of two stable species slugging it out in a closed environment, until one becomes extinct.

Why may the author have been premature in citing this interesting set of circumstance as unbeatable by the frogs?

 

[Lucky]

From the article:

Natural selection ceases to operate on an individual after
that individual's death, so frogs will probably never evolve toxins
that last longer in response to the snake's tactic.

What's sad is that the quote is actually from the authors of the article in The American Naturalist not the words of the news writer.

It does seem incredible that academics, presumably in the field of evolutionary biology, could make such a blunder, doesn't it? I was seriously gobsmacked, so I decided to investigate further - and we may be doing them an injustice.

Richard Shine is a professor of evolutionary biology, and head of a research group working on the evolutionary ecology of reptiles. Ben Phillips is a post doc. From the order of the names it's likely that the post doc did most of the work and wrote the paper. However, it seems that the paper isn't published yet, and the article linked to in the OP is based on this press release.

The quoted passage isn't attributed to anyone, and we can't be sure the press release was written by the authors of the paper - could be a more junior member of the group. Anyway, I'm confident it wasn't the professor.

 

[Dancing David]

...so long as the cost to the frog of creating the long lasting toxin is not too great.

The cost can be extreme as long as they reproduce.

 

[Dancing David]

This is a very good example of how even scientifically educated people think they understand natural selection far better than they actually do. The authors are making a basic Lamarckian error, and should ask themselves how being poisonous to a predator can ever be a survival advantage. After all, in their words, this "only becomes effective after the frog has died". What difference can it make to the individual frog whether or not the snake also dies? (And how, by the way, is it any different from the snakes evolving immunity to the poison? It's just a rather interesting example of an evolutionary arms race between species, one that evidently involves learnt behaviour.)

The general answer (not necessarily frogs/snakes) is that predators have learnt (or, in some cases, evolved) to avoid prey that are (or appear to be) poisonous. Being poisonous confers no direct advantage on the individual, as the trait never manifests itself unless the individual is eaten, but advertising itself as being poisonous can confer a powerful advantage. It's actually a very complex subject, as we need to consider many complicating factors such as the co-evolution of poison and advertisement, kin and population selection, and, as Darat mentions, mimicry.

Let me emphasise: becoming effective only after the individual's death is absolutely not a problem for natural selection. In Steve's example the actual problem for the frogs is that the poison has ceased to work. Individuals that are (or appear to be) poisonous will eventually lose their survival advantage, because the predators will learn (or, in other examples, evolve) not to avoid this prey. Therefore the frogs will, through natural selection, evolve other defence mechanisms, e.g. different poisons (the arms race could resume if the poison's timing changes or becomes less predictable), or changing their habitats or habits. Or possibly not, in which case they may become extinct.

That's natural selection for you.

And the other key to this is that frogs (some species) use a large amount of individuals as part of their reproductive strategy. A particuar frog might die but if the sibling cohort lives due to the death of that individual then the genes get passed on. A poisonous prey species does not always kill the predator, if they make them sick, so they won't eat other memebrs of the species, the trait gets passed on. (I think you know that, I was not contradicting you.)

 

[Dancing David]

On the issue of how the snakes learn how long to wait, it is necessary to know that they have extremely keen olfactory senses. I surmise they can smell (even "taste")the difference between a potent poison and one which has lost its potency. Snakes actually smell as well as taste with their tongues, picking up odor molecules with each flick and thus retrieved draw it back into an olfactory organ in the roof of their mouth known as Jacobson's organ.

The odor or taste difference, in a manner of speaking, could be a zeitgeber or "time giver."



http://en.wikipedia.org/wiki/Zeitgeber

I suggest that in this case it falls under the definition where "pharmacological manipulation" is concerned.

Anyone care to wager who will win this? The snakes or the frogs?

There is no win, only reproduction, or not.

 

[Dancing David]

This clearly is not human but the intent of each can be implied and it is a life or death situation for both. The intent of the snake is to feed, otherwise starve to death,
the intent of the frog, even in death, is to kill its predator and thus eliminate an enemy
for its fellow frogs. The snake has found a way to beat the frog at its own game.

There is no intent in evolution. This is the error of deterministic thinking as applied to evolution. The species's morphology is blind to the future. There is only reproduction. The survival of an individual is not tantamount, the reproduction is all that matters.

Clearly they are not in competition with each other in the conventional sense. Each is
competing to stay alive.

On an individual level yes, in the sense of natural slection, no.

 

[Unalienable]

I was thinking: Maybe one day the frogs will evolve a poison which does not degrade after death. If the frog's body decomposes before the poison does, it should be a fairly snake-proof frog.

But then I realized the point of the article. HOW can they evolve a poison that doesn't degrade after death? A gene that makes the poison survive after death will not be selected for. Or will it?

Maybe there is some kind of a "selfish gene" situation that can explain why frogs could evolve a poison with a long shelf-life, just like some animals are seen to "commit suicide" to help save siblings and children. Or maybe there isn't any such explanation (and that's why they don't). Hmmm interesting.

 

[Lucky]

There is no intent in evolution. This is the error of deterministic thinking as applied to evolution. The species's morphology is blind to the future. There is only reproduction.

Indeed, and the linked article is a good example of how that kind of muddled thinking can lead to scientific error. My view is that it generally does no harm to (metaphorically) ascribe intent or strategy to a gene, but if applied to an individual or a species it obscures what is actually going on in natural selection.

I was thinking: Maybe one day the frogs will evolve a poison which does not degrade after death. If the frog's body decomposes before the poison does, it should be a fairly snake-proof frog.

But then I realized the point of the article. HOW can they evolve a poison that doesn't degrade after death? A gene that makes the poison survive after death will not be selected for. Or will it?

Maybe there is some kind of a "selfish gene" situation that can explain why frogs could evolve a poison with a long shelf-life, just like some animals are seen to "commit suicide" to help save siblings and children. Or maybe there isn't any such explanation (and that's why they don't). Hmmm interesting.

You are making the same mistake as the linked article: failing to realise that your argument implies that evolved protective toxicity isn't possible at all. Think about it - the argument doesn't apply specifically to further refinements such longer-acting poisons, but to any predator deterrent that only operates after the prey's death.

For simplicity, let's stick to the scenario of a lethal poison in the prey (not merely a nasty taste), and a genetically-controlled avoidance behaviour by the predator (not a learned response). The crucial point is that the poison can only confer a survival advantage by being associated with a reduced chance of being eaten in the first place. This happens when the prey advertises its toxicity, usually by a distinctive appearance. A selection pressure on the predator is set up, which favours individuals that avoid the prey for whatever reason (they don't have to "know" that it's harmful).

Provided there continues to be a real association between the toxicity and the advertisement (i.e. not just false advertisement and mimicry), the selection pressure on the predator will be kept up, and the avoidance behaviour will continue.

The really interesting question is how the toxicity/advertisement association can have got going to begin with, and the answer must surely involve kin selection, as you suggest.

 

[CFLarsen]

I was thinking: Maybe one day the frogs will evolve a poison which does not degrade after death. If the frog's body decomposes before the poison does, it should be a fairly snake-proof frog.

But then I realized the point of the article. HOW can they evolve a poison that doesn't degrade after death? A gene that makes the poison survive after death will not be selected for. Or will it?

Maybe there is some kind of a "selfish gene" situation that can explain why frogs could evolve a poison with a long shelf-life, just like some animals are seen to "commit suicide" to help save siblings and children. Or maybe there isn't any such explanation (and that's why they don't). Hmmm interesting.

Think about the ladybug.

Ladybugs have bright colors, mostly red or yellow. This is a sign to other animals: "I don't taste well!" And they don't: They taste like crap, and can even be poisonous to some birds and lizards. So, animals generally won't eat ladybugs.

If a ladybug is eaten, it won't do that particular ladybug any good. It will, however, help other ladybugs not to be eaten by the same animal in the future - thereby securing the genes of the eaten ladybug. And if the animal that ate the ladybug can teach its own offspring to stay away from ladybugs in the future, all the better.

Even if the single specimen perishes, its genes can still be continued.

 

[JoeTheJuggler]

The quoted passage isn't attributed to anyone, and we can't be sure the press release was written by the authors of the paper - could be a more junior member of the group. Anyway, I'm confident it wasn't the professor.

That is heartening--that it might be mostly the fault of the science news writer for attributing the quote to "the authors".

 

[JoeTheJuggler]

Think about the ladybug.

Ladybugs have bright colors, mostly red or yellow. This is a sign to other animals: "I don't taste well!" And they don't: They taste like crap, and can even be poisonous to some birds and lizards. So, animals generally won't eat ladybugs.

If a ladybug is eaten, it won't do that particular ladybug any good. It will, however, help other ladybugs not to be eaten by the same animal in the future - thereby securing the genes of the eaten ladybug. And if the animal that ate the ladybug can teach its own offspring to stay away from ladybugs in the future, all the better.

I think Unalienable's question points out that, as Lucky said above, it's more complicated than this.

In the ladybug situation, the bird eats the foul-tasting ladybug and learns to avoid ladybugs. That advantage doesn't select for the new gene since the bird avoids all ladybugs. The bird doesn't eat up ladybugs that lack the gene, for example.

(Also I don't think you need to postulate predators teaching their offspring to avoid a certain type of prey.)

Selection can take place at the population level that doesn't happen at the individual level. The point of the "selfish gene" is protecting the gene, not necessarily the individual organism. I share many genes with close relatives (not just offspring), and fewer with more distant ones.

If one of my genes (likely to be in my nearer relatives) helps teach predators in the area to avoid my relatives, that gene is more likely to be preserved than the version in another population that doesn't teach predators to avoid its relatives. Eventually, my population (long after my noble martyrdom) will be more fit than other populations, and "we" can spread out to their territory.

Unalienable, you were on the right track when you brought up the selfish gene and how altruism might be selected.

Edit: and I think it's even more complex than what I've described.

 

[dogjones]

Think about the ladybug.

Ladybugs have bright colors, mostly red or yellow. This is a sign to other animals: "I don't taste well!" And they don't: They taste like crap, and can even be poisonous to some birds and lizards. So, animals generally won't eat ladybugs.

This puzzles me. How is possessing bright colours an automatic advertisement for poison?

 

[CFLarsen]

I think Unalienable's question points out that, as Lucky said above, it's more complicated than this.

In the ladybug situation, the bird eats the foul-tasting ladybug and learns to avoid ladybugs. That advantage doesn't select for the new gene since the bird avoids all ladybugs. The bird doesn't eat up ladybugs that lack the gene, for example.

Yeah, but that in itself is beneficial to those who aren't being eaten, too. Think of the many parasitic species there are - e.g., the sabre-toothed blenny. Mimic (even accidentally) something that's beneficial to species close to you, and you might just benefit yourself.

(Also I don't think you need to postulate predators teaching their offspring to avoid a certain type of prey.)

Not necessarily. It could also be that they develop a distaste for red/yellow bugs.

Selection can take place at the population level that doesn't happen at the individual level. The point of the "selfish gene" is protecting the gene, not necessarily the individual organism. I share many genes with close relatives (not just offspring), and fewer with more distant ones.

If one of my genes (likely to be in my nearer relatives) helps teach predators in the area to avoid my relatives, that gene is more likely to be preserved than the version in another population that doesn't teach predators to avoid its relatives. Eventually, my population (long after my noble martyrdom) will be more fit than other populations, and "we" can spread out to their territory.

Unalienable, you were on the right track when you brought up the selfish gene and how altruism might be selected.

Edit: and I think it's even more complex than what I've described.

Evolution is both very complex and very simple.