Stick insect forces evolutionary rethink
- Thread starter Adam
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though the feature disappered and reapeared the genes were always there, not really a major change for the little critter... just a oddity of evolution not a changing factor
i guess it all depends on how wings are made, i.e. how easy it is to shut down the developmental program for making a wing. If there is a master control gene for stick insect wing development and it is easily shut down by mere downregulation for some signaling molecules and it would be just as easy to upregulate this signaling molecules again and voila! the wing is back.
If the wing is lost because there are some essential mutations of an important gene for wing development, then it would be more difficult. Then these mutations would have to be undone. But this is also not impossible. There was a publication some time ago in which they showed that evolutionary mutational changes could be reversed in Drosophila by merely changing the environment back to the original one.
i shall try to look it up later if I have time and I shall also try to read the original stick insect article.
If the wing is lost because there are some essential mutations of an important gene for wing development, then it would be more difficult. Then these mutations would have to be undone. But this is also not impossible. There was a publication some time ago in which they showed that evolutionary mutational changes could be reversed in Drosophila by merely changing the environment back to the original one.
i shall try to look it up later if I have time and I shall also try to read the original stick insect article.
paulsamuel
Registered Senior Member
wings
the assumption is a wingless common ancestor. what if wings evolved before the branching off of the stick insects. then, one would have a winged common ancestor, and at that point it doesn't matter how many times they're lost and winged stick insects are the ancestral state; wingless, the derived state.
i'll read the paper and update.
BTW; Journal reference: Nature (vol 421, p 264)
the assumption is a wingless common ancestor. what if wings evolved before the branching off of the stick insects. then, one would have a winged common ancestor, and at that point it doesn't matter how many times they're lost and winged stick insects are the ancestral state; wingless, the derived state.
i'll read the paper and update.
BTW; Journal reference: Nature (vol 421, p 264)
I read the paper now.
it is quite a nice paper and the conclusions are really important for our understanding of evolution. But for anyone in the field of developmental biology the results were not shocking. They were within expectation. It is nice though to actually see it confirmed, to see the flexibility of the developmental program reflected in evolution. I think that evolutionists, or just people outside the field of biology, might have been more 'shocked' by it than we were.
and as he authors say really nicely:
'Thus, wing loss does not seem to be an evolutionary dead end, and the ability to regain a wing over evolutionary time means that lineages have the adaptive advantages of being both winged and wingless.'
all because of the flexibility of development.
it is quite a nice paper and the conclusions are really important for our understanding of evolution. But for anyone in the field of developmental biology the results were not shocking. They were within expectation. It is nice though to actually see it confirmed, to see the flexibility of the developmental program reflected in evolution. I think that evolutionists, or just people outside the field of biology, might have been more 'shocked' by it than we were.
and as he authors say really nicely:
'Thus, wing loss does not seem to be an evolutionary dead end, and the ability to regain a wing over evolutionary time means that lineages have the adaptive advantages of being both winged and wingless.'
all because of the flexibility of development.
insects the exception????
nobody is posting on the most interesting topic that has surfaced lately in biology, therefore i shall be the moderator and try to get things started again.
could the insect wing possibly be an exception to the rule, or do we have to rethink our ideas on evolution? Is the development of the insect imaginal discs that make the difference?
nobody is posting on the most interesting topic that has surfaced lately in biology, therefore i shall be the moderator and try to get things started again.
could the insect wing possibly be an exception to the rule, or do we have to rethink our ideas on evolution? Is the development of the insect imaginal discs that make the difference?
No it is not a exception... it does not require any change to evolution. This is perfectly valid under evolution because the genes were always there nd nothing was truly lost and redesigned.
I don't understand the very beginning of this one:
Why is it a rule of evolution that complex anatomical features cannot re-evolve?
It's certainly not the case that, after a feature is lost, it leaves behind some memory of its existance so that the feature can never come back.
Other than thinking it pretty neat, I wouldn't think it all that crazy if the stick insect evolved wings again--even if the genes for the original wings had mutated totally out of recognition.
What am I missing here, people?
Why is it a rule of evolution that complex anatomical features cannot re-evolve?
It's certainly not the case that, after a feature is lost, it leaves behind some memory of its existance so that the feature can never come back.
Other than thinking it pretty neat, I wouldn't think it all that crazy if the stick insect evolved wings again--even if the genes for the original wings had mutated totally out of recognition.
What am I missing here, people?
reverse mutations have been a know fact for decades now! I don't get this either!
a classic notion in evolution was that mutation happen at random. Natural selection can only work with the genetic variation that is present in a population based on these mutations. And natural selection is what shapes the structure of an animal, i.e. the entire animal. If a structure has a favourable shape it might be more beneficial and hence selection will favour this shape during evolution. And with the shape the specific genetic variation is also favoured that specifies this shape.
Obviously if there is a serious mutation in a gene that is necessary for making a wing than you have a problem reversing to the original state of the gene, because mutations happen at random. Mistakes caused by this random mutation could pile up before the original mutation is changed back.
The stick insect wing evolution is clearly saying: this can not be right! Stick insects re-evolved wings all the time. Therefore there must be something else going on than just changing a simple mutation back.
If a wing structure would re-evolve out of the blue than we would expect that it would look different from the normal insect wing (because wings of bats and birds evolved independently and they look completely different.)
Maybe we can discuss in a bit more detail here how this is possible, and possibly on such a level that even I and non-scientists can understand it. As I gather not everybody is that well informed about the field of developental biology and I fear that the answer lies exactly here.
spuriousmonkey is that a order? give me some time here so that I can dig up old research and edit this with more possibilities
Once again I think that it is wrong to say this is a problem in evolution!
-If a mutation helps by making a gene dysfunction this usually means that the gene now produces a proteins that fails to produce the phenotypic effects it use to display. Rarely do genes get deactivated by a mutation to their start codon. This means that that the gene no longer produces a working product but is still is producing protein. As a result if that gene is needed again then mutations that helps revitalizes the phenotypic effects of the original gene will take place.
-Also damage to an Opteron or promoter (master gene that controls the transcription of many other) could halt the production of many genes without mutating them individuals. If this dormant Opteron is activated these old genes can be restarted.
-Because of the effects of hormones and Opteron chains it can be easily proposed that a slight change in hormone levels that trigger the wing genes in this stickinsect results in the difference between no wings and wings.
Once again I think that it is wrong to say this is a problem in evolution!
-If a mutation helps by making a gene dysfunction this usually means that the gene now produces a proteins that fails to produce the phenotypic effects it use to display. Rarely do genes get deactivated by a mutation to their start codon. This means that that the gene no longer produces a working product but is still is producing protein. As a result if that gene is needed again then mutations that helps revitalizes the phenotypic effects of the original gene will take place.
-Also damage to an Opteron or promoter (master gene that controls the transcription of many other) could halt the production of many genes without mutating them individuals. If this dormant Opteron is activated these old genes can be restarted.
-Because of the effects of hormones and Opteron chains it can be easily proposed that a slight change in hormone levels that trigger the wing genes in this stickinsect results in the difference between no wings and wings.
i'm not ordering anyone...just trying to stimulate discussion.
I wanted to raise some discussion because I'm not sure everybody actually realizes the problems that lie behind losing a comlex structure and regaining it. I don't say this because I think it is impossible for mutations to reverse or anything like this, but because I think that there is no easy answer to this problem.
There are several problems going on in the reapparence of complex structures we could address. I will now pick a specific one. Is it common that complex structures are lost and regained? I think that there has been the suggestion that for instance eyes have evolved multiple times during evolution. I do not know if it is known if eyes have been lost and regained during evolution. To be honest I can't quite remember any of such studies, which indicates the importance of this paper.
Now the question becomes more interesting. We know of one example and the question becomes if this is an exception or a rule? If there are special circumstance at play with the evolution of stick insects, or just plain common mechanisms?
Let's think about a structure I know more about, teeth. Teeth are quite flexible in their shape and can dissappear and reappear by mutating certain genes. Therefore, if there are teeth present it is reasonably easy to make other teeth appear and dissappear.
Now lets look at an example where teeth have dissappeared all together: birds. Yes, birds used to have teeth, but they gave them up during evolution, possibly because they are too heavy. No bird has ever regained teeth, even flightless birds that have no weightrestrictions. Yet no teeth will re-emerge. Possibly because the beak shape is satisfactory for survival, or is it because there is something other going on. I do know from one studies that it is possible to make birds with teeth, but it isn't published yet, so i can't really talk about it. The only thing i can tell you is that it isn't very easy to do so and there are some problems with the teeth.
Therefore is the wing of the stick insect an exception? The article mentioned the possibility that the developmental regulatory system of the wing is maintained in the stick insect, because a basically similar version is used to make the lef of the animal. Therefore, this situation could be analogous to teeth. If there are other teeth around, in case of the stick insects, legs, then re-emergence of a similar structure is easy, because the regulatory system is kepy intact.
paulsamuel
Registered Senior Member
reply
it appears that spurious monkey likes this topic, so i will add my views.
apparently, there is confusion regarding the ability of populations to re-evolve a characteristic that's been lost.
complex morphologies, once lost cannot generally be re-gained (see Muller's ratchet). This is due to epistasis (many genes responsible for a single phenotypic character) and genetic drift.
Take a single base mutation in a gene. The probability of a nucleotide mutating into another nucleotide is 3X the probability of a back mutation to the original.
There might be 50 structural genes responsible for wings in this insect species, as well as maybe 10 regulatory genes, and maybe 10 developmental genes (I'm guessing, but these numbers are probably not that far off, but even if they are my point will not be affected). A single base mutation at any one would result in winglessness. Once winglessness occurs, the other genes (and all the other sites within each gene) would be free to vary due to drift (except for those genes that are pleiotropic, i.e. have more than one function). The liklihood that, once changed, all the genes simultaneously revert back to functional is nil; Muller's ratchet.
The authors are well aware of this and cite some other selective force keeping the winged genes intact while the population is wingless. They propose a developmental trigger turning wingless on and off while other genes are maintained due to pleiotropic effects.
Alternatively, which I don't believe they have fully explained away, is that wingedness is the ancestral state and that loss of wings occurred multiple times (I believe they underestimate the relative difficulties between loss and gain of wings). It appears to me that losing wings is easy, re-evolving them unlikely, therefore adding many more instances of wing loss, while dumping all wing gains is as likely (or more so) than the proposed pathways.
Resolution could occur by looking at some fossil ancestral species, and trying to determine the times of wing loss and gain, or finding some of the genes for wingedness and comparing them among and between winged and winglwess species.
it appears that spurious monkey likes this topic, so i will add my views.
apparently, there is confusion regarding the ability of populations to re-evolve a characteristic that's been lost.
complex morphologies, once lost cannot generally be re-gained (see Muller's ratchet). This is due to epistasis (many genes responsible for a single phenotypic character) and genetic drift.
Take a single base mutation in a gene. The probability of a nucleotide mutating into another nucleotide is 3X the probability of a back mutation to the original.
There might be 50 structural genes responsible for wings in this insect species, as well as maybe 10 regulatory genes, and maybe 10 developmental genes (I'm guessing, but these numbers are probably not that far off, but even if they are my point will not be affected). A single base mutation at any one would result in winglessness. Once winglessness occurs, the other genes (and all the other sites within each gene) would be free to vary due to drift (except for those genes that are pleiotropic, i.e. have more than one function). The liklihood that, once changed, all the genes simultaneously revert back to functional is nil; Muller's ratchet.
The authors are well aware of this and cite some other selective force keeping the winged genes intact while the population is wingless. They propose a developmental trigger turning wingless on and off while other genes are maintained due to pleiotropic effects.
Alternatively, which I don't believe they have fully explained away, is that wingedness is the ancestral state and that loss of wings occurred multiple times (I believe they underestimate the relative difficulties between loss and gain of wings). It appears to me that losing wings is easy, re-evolving them unlikely, therefore adding many more instances of wing loss, while dumping all wing gains is as likely (or more so) than the proposed pathways.
Resolution could occur by looking at some fossil ancestral species, and trying to determine the times of wing loss and gain, or finding some of the genes for wingedness and comparing them among and between winged and winglwess species.
Re: reply
quite nice post paulsamuel. Let me add a few things. The development of all organs is regulated by the same groups of regulatory genes. For instance, the Hedgehog signalling pathway, Wnt (=wingless) pathway, TGF-beta (decapentaplegic in Drosophila) signalling, notch signalling, FGF signaling, also TNF signalling, and I am probably forgetting several. These are all signalling pathways, which means that there is a ligand that activates a receptor, and the receptor activates a specific signaling cascade inside the cell, which may or may not activate the transcription of certain genes.
The same regulatory pathways are used in all developing organs! Let me stress that again. These regulatory systems will be around, even if a complex structure is lost. I don't have an exact number for how many genes we are talking about here, but more than 10 for sure...depends on the organism, since humans have for instance 21 FGFs homologues alone.
Then there are the master regulatory genes. Without it an organ will not develop and ectopic expression (expression in an abnormal place) will induce an ectopic organ (an organ where it shouldn't be.) The most famous example of this is Pax6, the master regulaory gene for eye development, which the authors mention. And for drosophila wingless could be considered to be a master control gene, although it isn't for vertebrates since there are amny wingless homologues (is named WNT) and none specific for wingdevelopment (of course).
For teeth there doesn't seem to be a master control gene. They tried to find it but never did.
the question is on what level the mutations are taking place to make it possible for the wing to reappear.
one level i didn't mention here, but has been mentioned somewhere else in this thread is on the level of the promotor.
quite nice post paulsamuel. Let me add a few things. The development of all organs is regulated by the same groups of regulatory genes. For instance, the Hedgehog signalling pathway, Wnt (=wingless) pathway, TGF-beta (decapentaplegic in Drosophila) signalling, notch signalling, FGF signaling, also TNF signalling, and I am probably forgetting several. These are all signalling pathways, which means that there is a ligand that activates a receptor, and the receptor activates a specific signaling cascade inside the cell, which may or may not activate the transcription of certain genes.
The same regulatory pathways are used in all developing organs! Let me stress that again. These regulatory systems will be around, even if a complex structure is lost. I don't have an exact number for how many genes we are talking about here, but more than 10 for sure...depends on the organism, since humans have for instance 21 FGFs homologues alone.
Then there are the master regulatory genes. Without it an organ will not develop and ectopic expression (expression in an abnormal place) will induce an ectopic organ (an organ where it shouldn't be.) The most famous example of this is Pax6, the master regulaory gene for eye development, which the authors mention. And for drosophila wingless could be considered to be a master control gene, although it isn't for vertebrates since there are amny wingless homologues (is named WNT) and none specific for wingdevelopment (of course).
For teeth there doesn't seem to be a master control gene. They tried to find it but never did.
the question is on what level the mutations are taking place to make it possible for the wing to reappear.
one level i didn't mention here, but has been mentioned somewhere else in this thread is on the level of the promotor.
paulsamuel
Registered Senior Member
reply to spuriousmonkey
thnks for the reply
i know tons about evolutionary biology, but i admit to being weak in developmental biology and evodevo. i vow to correct this inadequacy
cheers
thnks for the reply
i know tons about evolutionary biology, but i admit to being weak in developmental biology and evodevo. i vow to correct this inadequacy
cheers
Re: reply to spuriousmonkey
well, i don't know much about evolutionary biology.
but it might be really interesting to look at two different species of stick insect, both with wings, but wings that are supposedly evolved on two separate occasions, and see what the regulatory differences actually are. I'm sure it would be a 'nature' paper.
Originally posted by paulsamuel
thnks for the reply
i know tons about evolutionary biology, but i admit to being weak in developmental biology and evodevo. i vow to correct this inadequacy
cheers
well, i don't know much about evolutionary biology.
but it might be really interesting to look at two different species of stick insect, both with wings, but wings that are supposedly evolved on two separate occasions, and see what the regulatory differences actually are. I'm sure it would be a 'nature' paper.
paulsamuel
Registered Senior Member
reply
crap, we should be PI's! we could publish that!
crap, we should be PI's! we could publish that!
I shall be a party pooper and bring the bad news now...
there might be some practical problems...
we need to have molecular markers...the probes that work for drosophila might not necessarily work for our stick insects, which would mean that we need to clone those genes. Unless we find some nice antibodies that work with other species as well.
we need two colonies of stick insect species and not just 2, 2 proper ones.
and we need some funding.
there might be some practical problems...
we need to have molecular markers...the probes that work for drosophila might not necessarily work for our stick insects, which would mean that we need to clone those genes. Unless we find some nice antibodies that work with other species as well.
we need two colonies of stick insect species and not just 2, 2 proper ones.
and we need some funding.