Stick Insects force Evolutionary Rethink

New Scientist ^ | 15 January 03 | Nicola Jones

[Ahban]

SRC="/img/shim.gif">

Wings could be a passing phase for the giant prickly stick insect (Image: OSF)

Researchers have discovered that on a number of occasions in the past 300 million years, stick insects have lost their wings, then re-evolved them. Entomologists have described the revelation as "revolutionary".

Michael Whiting, an evolutionary biologist from Brigham Young University in Provo, Utah, and his team stumbled upon the finding while examining the DNA of 37 different phasmids, the stick and leaf insects famous for camouflaging themselves against plants, in a bid to work out their family tree.

	The big wing switch

Entomologists have assumed that wings only evolved once in insects. The received wisdom is that a winged ancestor produced the winged phasmids we see today. The 60 per cent of stick insects that do not sport wings will, this thinking goes, have jettisoned them along their evolutionary journey so they could expend more energy on reproduction and less on flying.

But Whiting's analysis shows that the very first stick insect, which appeared 300 million years ago, had already lost its wings and that stick insects re-evolved the structures at least four times (see graphic). The study covers only 14 of the 19 known sub-families of phasmids, so it is possible that wings reappeared even more often.

Beyond repair

Researchers assumed wings could not come back once lost as the genes needed to create them would mutate beyond repair once the wings disappeared. But Whiting says there is evidence from the fruit fly Drosophila that the same genes contain instructions for forming wings and legs.

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Weblinks

Zoology, Brigham Young University

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Nature

If the same were true for stick insects, there would be an evolutionary pressure to stop wing genes from mutating, even in the insects that did not have wings. Those genes could then be turned back on in the future.

Whiting says, however, that while wing re-evolution may seem unlikely to insect researchers, the basic idea of switching regulatory genes off and on is well accepted. Even a single gene can sometimes switch on the growth of a complex structure - studies indicate that a master gene called Pax-6, for example, might control the development of eyes in all creatures that have them.

So Whiting suggests that eyes too could have disappeared and reappeared in animals over time. "I remember sitting down with entomologists and hearing them say 'impossible, impossible, impossible'," he says. But "re-evolution is probably more common than we thought".

[Ahban]

Webbed feet hardly quailfy as a acquiring a complex new structure such as eyes or wings. The hairy South American example applies even less- we all have hair all over our bodies anyway, the only change expressed is the size of the hair.

Til now evolutionists thought that complex structures like wings could not disapper and then come back repeatedly. Now they find that they do, and without blinking an eye they wish to spin finding the exact opposite of what they predicted as evidence for evolution.

During the tens of millions of years the wing genes are not expressed, they are neutral. If neutral, they are subject to mutations that scramble them without hindering the surviability of the organism. The scrambling should prevent the re-emergence of the trait. The odds that those scrambled genes have repeatedly unscrambled themselves, and then got turned on at just the right time, must be astronomical.

[Sentis]

"2) This, once again, is confusing variations (or micro-evolution, if you like), which we can observe, with macro-evolution, which we do not observe"

All evolution is micro-evolution because it occurs in the reproductive cells of multicellular creatures. What this basically means is that any evolution that occurs occurs when a mutation or viral genetic exchange occurs in sperm or egg cells (micro-evolution). (this could also happen in a very immature fetus consisting of only a few cells). This genetic change causes a mutation that will either (for the most part) be deadly to the creature or be beneficial, such as the virus that sometime in the past linked two chromosomes in the human genome. Thus creating a creature with 23 chromosomes and differentiating it from the other apes that had 24. This change probably took place in the sperm or eggs cells which when expressed as offspring resulted in a new species.

[Buckeye Bomber]

What are you talking about? Neutral genes?

Do you understand the process of alleles? Do you understand inheritance? Do you understand dominant and recessive genes? Genes never scramble and unscramble. I'll try to keep this brief.

OK, say a genetic trait is expressed based on one gene (most traits actually occur because of many complex interactions of genes, but I'll simplify here). A gene is made up of two alleles, and simply put, a gene is just a place on a chromosome. Alright, so this allele has two forms: A and a. Since sexual reproduction mixes two genes, producing more variation, we'll assume sexual reproduction rather than asexual. Two creatures mate, and each one donates an allele as part of their part in sexual reproduction (sperm or egg).

Say a mother donates the lowercase a, the recessive gene, and the father donates the A, dominant gene. This will result in a creature with Aa as its gene for this particular trait. If two A's met, they'd form AA. If two a's met, they'd form aa. Since A is dominant, that trait will be expressed in both AA and Aa. Only in aa will the recessive trait be expressed.

But say that the recessive trait is a beneficial variation for a species. Over many generations, the variation that occurs because of aa will become more and more common, due to the increased survival rate that this trait allows. Therefore, more and more members of this species will end up with this trait.

Please, if you have no concept of basic biology, take your religious dogma elsewhere. If you criticize evolution, you better have a better explanation for inheritance than genetics also.

[Buckeye Bomber]

I've read your previous posts on this subject, including the 50 reason to leave evolutionary theory behind. As a college biology student, I can pick apart half of them. I wonder what a real scientist could do to them. You are a dogmatic, illogical nut.

[Sentis]

"The scrambling should prevent the re-emergence of the trait. The odds that those scrambled genes have repeatedly unscrambled themselves, and then got turned on at just the right time, must be astronomical. "

Astronomical in terms of insects is a misnomer. Genes express themselves in a variety of ways and I will not go into it as it takes volumes to explain why genes do what they do and your free to read about that on your own. I'll give a very simple example. Lets say the information for wings is available in 20 % of the population of stick bugs and is spread evenly among those creatures. This information is scrambled in these bugs but as the bugs breed and re-breed among themselves the percentage remains the same but a number of insects slowly increase the amount of genetic information for wings. So after one generation there is a group with 21% of the information needed to develop wings and a population with 19% after 80 generations there will then be a group with 100% of the information and a group with none. Thus those with 100% would be likely to express wings as a result and any offspring would also have that information.

This is a very simple example but it shows how astronomical isn't the word that can be used especially in insect population where generations are measured in months or a year rather than long periods of time.

[Stultis]

it says nothing to how the wing genes came about in the first place

Yeah it did. They are copies, indeed some of the same genes, used to make legs, and also closely related to those used to make mouth part, etc.

Evolution is all about finding new uses for existing parts and existing code.

[Stultis]

One wonders whether this team's parents still cling to even the slightest hope that their once-bright little boys and girls will ever become productive members of society, instead of welfare (research grant) recipients.

Yeah, down with entomology. We can do without it and weather the occassional plague, pestilence and famine.

[gore3000]

Seems the image did not come out properly:

[Ahban]

I am very sorry you feel that way.

As to the"50 Resaons" business, as I don't ever recall posting anything like that. I can't help but wonder if you might have confused me with another poster. If so, your abuse, if it is really necessary, should be hurled elsewhere.

As for the neutral genes business, I only meant that a non-expressed gene can undergo mutations without affecting the viability of the organism. Mutations in an unexpressed gene are by default neutral and I was trying to say this in a shorthand way. Many people on this thread are longtime adversaries whose knowledge I nevertheless respect. They are well able to catch my meaning without the bothersome explanations you are demanding.

As for your questions in an earlier post, I am quite aware of the basic biology facts you outlined, as I am a middle school science teacher by profession.

Good day.

[Physicist]

Wings were lost and then re-evolved at least four times in STICK INSECTS ALONE? Then how many times have wings been re-gained in all families of insects and other creatures? Surely more than dozens. Hundreds? And when these newly re-gained wings pop up out of nowhere, for every time it "takes" and results in a new genus there should be many thousands of examples where a mutation occurs, but is not passed on, or does not entrench itself and create a new population. Yet we have never observed wings, or ANY complex structure, arising out of nothing.

But in this case, it only takes a single homeotic mutation to turn wing development on and off. I suggest you look up the terms "antennapedia complex" and "bithorax complex" with Google.

[f.Christian]

bb...

You are a dogmatic, illogical nut.


24 posted on 01/15/2003 5:18 PM PST by Buckeye Bomber


Evolution is hypothetical . . . unproven - - - NO design // evidence - - - hearsay and you are going to base your life on it ? ? ?

Science . . . laws // design // intelligence // evidence is another matter // game - - - TRUTH ! ! !

[Dataman]

Oh no! Not another evolutionary "rethink."

Evolutionary trial balloon?

Evolutionary reguess?

Maybe it's grant-writing time.

[f.Christian]

"A New World Order emerges on the basis of heroic will. It is not hard to see how appetizing this . . . stew (( link )) - - - was for Hitler."

Spengler replies to readers . . .

"Thanks to Asia Times Online readers [letters below] who elaborated on the mythical pre-history of Middle-earth. My summary was truncated, and Tolkien enthusiasts might fairly raise objections. I note with pleasure that no Wagnerians yet have written to complain, validating the observation that Tolkien has taken back the Ring on behalf of the forces of light. If you prefer Wagner to Tolkien, you might be an Orc, and you should . . . seek (( original article // source )) - - - professional help."

[Ahban]

Numbers! May God bless you sir, for it is a rare evolutionist who is willing to consider them.

I'd like to move furhter with this. Can you help me follow up on this mathematical model?

First you assume that 20% of the population has the information for wings. Do you mean that 20% of the population have the wing gene intact, or that any given individual has 20% of the whole infoset needed for wings? If the latter, does another member of this group have a different 20%?

[xm177e2]

Certainly at least, GOD didn't go taking and giving back wings. This alone should be enough evidence to refute creationist theories.

It's not so incredible that an animal could lose and regain wings like this. Perhaps the winged stick insect suffered a mutation causing his wings not to grow--but the underlying genetic code for the wings remained. Then all it would take is another small mutation of the same kind to reactivate the dormant DNA. Humans have a lot of dormant "legacy" DNA that is useless. That is another refutation of creationism. If God made us, why did he leave remnants of lesser organisms in our DNA?

[xm177e2]

Wings were lost and then re-evolved

They probably weren't "lost," just switched off by another mutated gene. They wouldn't have to be re-evolved from scratch, they would just have to have another small mutation turning them back on.

[Ahban]

Evolution is all about finding new uses for existing parts and existing code.

So is modular or object oriented programming, yet computer programs are the result of intelligent design. This is so for both the modules and objects, and the macro-code written from them.

This implies that the parts were all there to start with, or you had something with the potential to be all of those parts, from the very start. What is the mechanism by which all of this info is added? Do the mechanisms you would suggest operate to add info to genomes at the rate required to explain the diversity of life on Earth throughout history?

I just don't think you have a mechanism. Genes don't change function that dramatically. Even mutated, they do something very close to what they were originally meant to do.

[Stultis]

Insects are presumed to have evolved from segmented worms and, AFAIK, the simplest insects are just vastly more complicated than the most complex worms.

Yes the simplest insects are far removed from worms, but there are other critters that are much closer, particularly Onychophora, a.k.a. "velvet worms". In fact these creatures (similar, albeit marine, forms are found in the Cambrian) are beautifully intermediate between annelids ("worms") and arthropods. They are basically earthworms with a pair of legs on each segment and a primitive head. From this page:

The most primitive-looking of the insects alive today, such wingless species as the silverfish, have lead biologists to believe that insects may have evolved from a creature similar to the Annelida. This supposed ancestor had a segmented, worm-like body with a pair of feet on each segment and may have looked something like the creature in the photo above (a member of the phylum Onychophora, this creature has a worm-like body with a head and antennae and one pair of stubby, telescoping legs on each segment). One hypothesis shows the first five segments of such an animal coalescing to form the head, the next three the thorax, and the remainder being left for the abdomen, as in the diagram below. The concentration of locomotive mechanisms in the thorax would have relieved the hind sections of the need for leg muscles and thus allowed them to develop the complex abdominal organs.

The most commonly accepted theory of the origin of the insects is here illustrated. An organism resembling the modern earthworm may have grown some kind of legs on each segment as a locomotive aid. The development of head, thorax, and abdomen by aggregation of segments followed. Various of the limbs either disappeared or were modified: in the head to become antennae and mouth parts and in the abdomen they probably just disappeared altogether or became pincers or other structures at the end of the body. The theory of the merging of segments is supported by the fact that the thorax has six legs (derived from the pairs on each of three segments), and the head has five ganglia and the thorax three. Ganglia are nerve bundles, of which there is one in each segment of the annelid worms. The ganglia serve the purpose of brains in worms and play a lesser role, subordinate to the brain, in insects.

[ASA Vet]

See what you did? You woke up another one.

[Ahban]

, it only takes a single homeotic mutation to turn wing development on and off

Yes, yes, a fruit fly with the gene turned off can breed in the next generation a winged descendent with them turned on. I see that. But suppose those wings genes were turned off for tens of millions of generations at a time. Wouldn't this mean that mutations in applicable segments of code were by definition NEUTRAL? How then could the original info be conserved though the eons?

I suppose it could happen once or twice by chance, but here you have it happening a minimum of four times in only one insect family!!! It is not the turning on and off of a single gene that has me impressed, but the idea that the same genetic info herocially re-assembled itself multiple times in this one narrow range of life over millions of years.

Please don't pretend as if it is no big deal, for the evolutionary scientists quoted in the article feel that it is quite amazing indeed!