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Member (Idle past 1691 days) Posts: 53 From: Reno, Nevada, USA Joined: |
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Author | Topic: Foul Tasting Bugs | |||||||||||||||||||||||||||
InGodITrust Member (Idle past 1691 days) Posts: 53 From: Reno, Nevada, USA Joined: |
There are a number of species of insects that use a foul taste for defense. I watched part of a TV program recently that showed one such species with a baby alligator as a predator. The narrator said that after the alligator eats a couple of the bugs, it will learn its lesson and eat no more. Altough the scene may have been staged for TV, they showed the 'gator killing one of the bugs.
Obviously the defense is good for the species as a whole, but how did natural selection come into play in the development of the foul taste, if a couple bugs are killed before the predator learns its lesson? The foulest tasting bug has no better chance of survivng to pass on its genes than any of the other bugs. I'm sure biologists have contemplated this and written about it. Maybe it's even been discussed here at EVC before. But I haven't come across the answer yet. Who has plausible speculation? Edited by InGodITrust, : spelling
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Admin Director Posts: 13018 From: EvC Forum Joined: Member Rating: 1.9 |
Thread copied here from the Foul Tasting Bugs thread in the Proposed New Topics forum.
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Dr Jack Member Posts: 3514 From: Immigrant in the land of Deutsch Joined: Member Rating: 8.4 |
Kin selection.
It's not true that the fowlest tasting bug has no more chance to pass on its genes than any other bug. Also, remember foul taste comes about by exaptation not de novo formulation. Edited by Admin, : Fix spelling: exaption => exaptation.
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Wounded King Member Posts: 4149 From: Cincinnati, Ohio, USA Joined: |
The most obvious explanation, and one that Fisher came up with in the 30s, is that it is propagated through a form of kin selection. While as you say the bug which gets eaten doesn't get any benefit from its being eaten the other bugs in the area do. If we assume that the other bugs in the area are likely to be closely related to the eaten bug, and therefore more likely to share the same genes for noxious taste, then the protection from its noxious taste enhances the survival of those related bugs relative to other unrelated bugs in different regions.
So if you have a whole brood of dozens of foul tasting bugs in an area with a few predators and each predator learns to avoid them after 1 or 2 samplings then losing a moderate proportion of the brood could confer protection on the rest. As to the very inital development of the foul taste, it depends. We might assume that populations of bugs naturally vary in their tastiness and predation acts as a strong form of directional selection favouring less tasty bugs. Alternatively we might posit a novel exceptionally untasty mutation in an individual which would need to survive independent of its tastiness before it could mate and produce a brood in which tastiness could provide some group protection. Of course if we allow that predators sometimes taste noxious prey without killing them then the chances of a rare de novo noxious mutation propagating become much better. TTFN, WK
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PaulK Member Posts: 17825 Joined: Member Rating: 2.2 |
I've been thinking about this, and it seems that while the foul taste alone would provide a limited benefit (until it was very widespread), a foul taste AND an identifying mark (one which predators would recognise) would provide a whole lot more.
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Wounded King Member Posts: 4149 From: Cincinnati, Ohio, USA Joined: |
Sure and the whole concept of the evolution of noxious taste is usually bound up with the development of aposematic signals for letting predators know you are noxious. And from then of course onto various forms of inter and intraspecies mimicry and evolutionary cheating strategies.
TTFN, WK
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Phage0070 Inactive Member |
The reason it does not make sense is that you are thinking of a simplistic explanation of evolution. While it is easy to imagine a single organism being born and exposed to selection pressures, it really works with larger populations and over larger periods of time. For instance:
What would happen is a population of bug would develop into several bloodlines, each with its own mutation. Perhaps some would be slightly larger, or a little bit yellower, or somewhat bad-tasting. Predators would still be willing to eat the bad-tasting bugs, but not as much as they would like the other bugs. This means that there is a clear pressure toward tasting nasty, and also being distinguishable as being an icky one. Predators would be looking for a way to tell the foul-tasting bugs apart from the normal ones, so those that interbred with the yellow strain might survive better than the standard color scheme. Once predators link that color with tasting bad the selection pressure would be toward tasting worse and being more vividly marked. Normal-tasting yellowish bugs might even be more likely to survive despite tasting OK, and become one of the many "fake" poisonous species. Large populations with inherited mutations exposed to slight selection pressures over long periods of time isn't as dramatic as a single organism being eaten or not, but it is more accurate. The key is that even the foul-tasting bugs would get eaten to some extent, but not enough to wipe out their entire bloodline.
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Percy Member Posts: 22480 From: New Hampshire Joined: Member Rating: 4.8 |
One of the side-effects that I find fascinating is that once the bad-tastiness is established, other bug species might experience selection pressure for an appearance closer to the bad tasting bugs.
--Percy
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Dr Jack Member Posts: 3514 From: Immigrant in the land of Deutsch Joined: Member Rating: 8.4 |
Batesian mimicry.
Even more intriguing to me is Mullerian mimicry, where other bad tasting beetles will evolve to look similar to existing ones.
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Huntard Member (Idle past 2317 days) Posts: 2870 From: Limburg, The Netherlands Joined: |
Mr Jack writes:
Well, isn't that kinda the same as Batesian? I mean, if you look like a bad tasting bug, you are much less likely to get eaten, even if you don't taste bad. Now, if you do taste bad, yet look completely different, there's no way to tell you taste bad, except after being eaten. So, it's better to look like each other, whether bad tasting or not.
Even more intriguing to me is Mullerian mimicry, where other bad tasting beetles will evolve to look similar to existing ones.
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Wounded King Member Posts: 4149 From: Cincinnati, Ohio, USA Joined: |
We had quite a few mimicry threads when MartinV was doing the rounds of the boards, see Mimicry and neodarwinism and Mimicry: Please help me understand how.
TTFN, WK
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Wounded King Member Posts: 4149 From: Cincinnati, Ohio, USA Joined: |
The difference is in the honesty of the signal. If you are all signalling honestly it is better for everyone, if only some are signalling honestly then they are weakening the protection of the signal for everyone including the honest signallers.
The basic effect is the same but the underlying evolutionary strategy, mutualism or parasitism, is what makes the difference. TTFN, WK
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Dr Jack Member Posts: 3514 From: Immigrant in the land of Deutsch Joined: Member Rating: 8.4 |
I mean, if you look like a bad tasting bug, you are much less likely to get eaten, even if you don't taste bad. Now, if you do taste bad, yet look completely different, there's no way to tell you taste bad, except after being eaten. So, it's better to look like each other, whether bad tasting or not. Yes, it is, that being why it evolves. I just like it, and there's some really neat traces of regional variation in warning patterns, where the variation between different species in one region is smaller than the variation in the same species across different areas. So you get these (apparently) reasonless cross-species parallel drifts. Edited by Mr Jack, : No reason given.
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InGodITrust Member (Idle past 1691 days) Posts: 53 From: Reno, Nevada, USA Joined: |
Thanks everyone. I'm still thinking this through. Like with many other aspect of evolution, this gets so complicated it is mind-boggling (for me anyway).
IGIT
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RAZD Member (Idle past 1427 days) Posts: 20714 From: the other end of the sidewalk Joined: |
hi Wounded King and Mr. Jack,
Message 3: Kin selection.
Message 4: The most obvious explanation, and one that Fisher came up with in the 30s, is that it is propagated through a form of kin selection. While as you say the bug which gets eaten doesn't get any benefit from its being eaten the other bugs in the area do. If we assume that the other bugs in the area are likely to be closely related to the eaten bug, and therefore more likely to share the same genes for noxious taste, then the protection from its noxious taste enhances the survival of those related bugs relative to other unrelated bugs in different regions. What we see is a mutation that makes a bug taste less palatable for predation. Initially this type of mutation is neutral, as there is no way for predator/s to distinguish the palatable from the less palatable bugs, and so many such mutations can spread by neutral drift within a population. As the mutation/s becomes more predominant within a sub-population (or in the whole population) then we can see a response to the taste in bug selection by the predator/s and subsequent selection for the populations of bugs with less paletable taste, allowing the less palatable taste to become predominant and even reinforced by later mutations for even less palatability. We are seeing more and more instances of mutations that are initially neutral being spread by neutral drift, and then becoming subject to selection, and this could easily be a similar situation. Another group of organisms that exhibit this noxious taste ability are the poison dart frogs of south america.
quote: As far as I know, these frogs do not use their toxins to poison prey (the way some snakes and lizards do), and that it is only defensive. We can also discuss the evolution of color in such populations, once selection pressure for any camouflage or blending into the background to reduce predation has been removed, but that's getting off topic. Enjoy. we are limited in our ability to understand
by our ability to understand Rebel American Zen Deist ... to learn ... to think ... to live ... to laugh ... to share. • • • Join the effort to solve medical problems, AIDS/HIV, Cancer and more with Team EvC! (click) • • •
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