Researchers Trace Evolution to Relatively Simple Genetic Changes

Howard Hughes Medical Institute ^ | 25 Narcg 2005 | Staff

[PatrickHenry]

In a stunning example of evolution at work, scientists have now found that changes in a single gene can produce major changes in the skeletal armor of fish living in the wild.

The surprising results, announced in the March 25, 2005, issue of journal Science, bring new data to long-standing debates about how evolution occurs in natural habitats.

“Our motivation is to try to understand how new animal types evolve in nature,” said molecular geneticist David M. Kingsley, a Howard Hughes Medical Institute investigator at the Stanford University School of Medicine. “People have been interested in whether a few genes are involved, or whether changes in many different genes are required to produce major changes in wild populations.”

The answer, based on new research, is that evolution can occur quickly, with just a few genes changing slightly, allowing newcomers to adapt and populate new and different environments.

In collaboration with zoologist Dolph Schluter, at the University of British Columbia, Vancouver, Canada, and Rick Myers and colleagues at Stanford, Kingsley and graduate student Pamela F. Colosimo focused on a well-studied little fish called the stickleback. The fish — with three bony spines poking up from their backs — live both in the seas and in coastal fresh water habitats all around the northern hemisphere.

Wild populations of stickleback fish have evolved major changes in bony armor styles (shaded) in marine and freshwater environments. New research shows that this evolutionary shift occurs over and over again by increasing the frequency of a rare genetic variant in a single gene.

Sticklebacks are enormously varied, so much so that in the 19th century naturalists had counted about 50 different species. But since then, biologists have realized most populations are recent descendants of marine sticklebacks. Marine fish colonized new freshwater lakes and streams when the last ice age ended 10,000 to 15,000 years ago. Then they evolved along separate paths, each adapting to the unique environments created by large scale climate change.

“There are really dramatic morphological and physiological adaptations” to the new environments, Kingsley said.

For example, “sticklebacks vary in size and color, reproductive behavior, in skeletal morphology, in jaws and teeth, in the ability to tolerate salt and different temperatures at different latitudes,” he said.

Kingsley, Schluter and their co-workers picked one trait — the fish's armor plating — on which to focus intense research, using the armor as a marker to see how evolution occurred. Sticklebacks that still live in the oceans are virtually covered, from head to tail, with bony plates that offer protection. In contrast, some freshwater sticklebacks have evolved to have almost no body armor.

“It's rather like a military decision, to be either heavily armored and slow, or to be lightly armored and fast,” Kingsley said. “Now, in countless lakes and streams around the world these low-armored types have evolved over and over again. It's one of the oldest and most characteristic differences between stickleback forms. It's a dramatic change: a row of 35 armor plates turning into a small handful of plates - or even no plates at all.”

Using genetic crosses between armored and unarmored fish from wild populations, the research team found that one gene is what makes the difference.

“Now, for the first time, we've been able to identify the actual gene that is controlling this trait,” the armor-plating on the stickleback, Kingsley said

The gene they identified is called Eda, originally named after a human genetic disorder associated with the ectodysplasin pathway, an important part of the embryonic development process. The human disorder, one of the earliest ones studied, is called ectodermal dysplasia.

“It's a famous old syndrome,” Kingsley said. “Charles Darwin talked about it. It's a simple Mendelian trait that controls formation of hair, teeth and sweat glands. Darwin talked about `the toothless men of Sind,' a pedigree (in India) that was striking because many of the men were missing their hair, had very few teeth, and couldn't sweat in hot weather. It's a very unusual constellation of symptoms, and is passed as a unit through families.”

Research had already shown that the Eda gene makes a protein, a signaling molecule called ectodermal dysplasin. This molecule is expressed in ectodermal tissue during development and instructs certain cells to form teeth, hair and sweat glands. It also seems to control the shape of - bones in the forehead and nose.

Now, Kingsley said, “it turns out that armor plate patterns in the fish are controlled by the same gene that creates this clinical disease in humans. And this finding is related to the old argument whether Nature can use the same genes and create other traits in other animals.”

Ordinarily, “you wouldn't look at that gene and say it's an obvious candidate for dramatically changing skeletal structures in wild animals that end up completely viable and healthy,' he said. "Eda gene mutations cause a disease in humans, but not in the fish. So this is the first time mutations have been found in this gene that are not associated with a clinical syndrome. Instead, they cause evolution of a new phenotype in natural populations.”

The research with the wild fish also shows that the same gene is used whenever the low armor trait evolves. “We used sequencing studies to compare the molecular basis of this trait across the northern hemisphere,” said Kingsley. “It doesn't matter where we look, on the Pacific coast, the East coast, in Iceland, everywhere. When these fish evolve this low-armored state they are using the same genetic mechanism. It's happening over and over again. It makes them more fit in all these different locations.”

Because this trait evolves so rapidly after ocean fish colonize new environments, he added, “we wondered whether the genetic variant (the mutant gene) that controls this trait might still exist in the ocean fish. So we collected large numbers of ocean fish with complete armor, and we found a very low level of this genetic variant in the marine population.”

So, he said, “the marine fish actually carry the genes for this alternative state, but at such a low level it is never seen;” all the ocean fish remain well-armored. “But they do have this silent gene that allows this alternative form to emerge if the fish colonize a new freshwater location.”

Also, comparing what happens to the ectodysplasin signaling molecule when its gene is mutated in humans, and in fish, shows a major difference. The human protein suffers "a huge amount of molecular lesions, including deletions, mutations, many types of lesions that would inactivate the protein," Kingsley said.

But in contrast, “in the fish we don't see any mutations that would clearly destroy the protein.” There are some very minor changes in many populations, but these changes do not affect key parts of the molecule. In addition, one population in Japan used the same gene to evolve low armor, but has no changes at all in the protein coding region. Instead, Kingsley said, “the mutations that we have found are, we think, in the (gene's) control regions, which turns the gene on and off on cue.” So it seems that evolution of the fish is based on how the Eda gene is used; how, when and where it is activated during embryonic growth.

Also, to be sure they're working with the correct gene, the research team used genetic engineering techniques to insert the armor-controlling gene into fish “that are normally missing their armor plates. And that puts the plates back on the sides of the fish,” Kingsley said.

“So, this is one of the first cases in vertebrates where it's been possible to track down the genetic mechanism that controls a dramatic change in skeletal pattern, a change that occurs naturally in the wild,” he noted.

“And it turns out that the mechanisms are surprisingly simple. Instead of killing the protein (with mutations), you merely adjust the way it is normally regulated. That allows you to make a major change in a particular body region - and produces a new type of body armor without otherwise harming the fish.”

[VadeRetro]

Nice chart. But you're text is full of "might have" and "may have". Just like Urey-Miller and others presented as facts.

That would be on the ancestors of single-celled organisms, an area currently refered to as "abiogenesis." I believe you were dumb-dumbing on whether there has been any evolution at all, such as whether alligators have always existed, etc. The use of "maybe" in describing the best interpretation of real evidence is not usually considered a failing. Creationist "maybe"-counting is a bogus rhetorical trick which only highlights that religion can't be about what science is about. Religion can't allow itself to be wrong about anything. Science converges on the truth by being free to follow the evidence.

Don't get me wrong, I don't have a dog in this hunt either way.

Funny. Most people bending over backward to deny the obvious have something of an agenda. You argue just like a baloney-spouting creationist. Did you realize that?

I think many of you lose credibility when you call people ignorant or simple minded for having a different guess about how it all started than the so called experts.

I can't make points with people who don't follow evidence. Nor can I portray you as any more ignorant or simple-minded than you're willing to make yourself. Hint: you need a new tactic besides not knowing beans about what you're proclaiming to be wrong.

[longshadow]

Festival of Festivals placemarker

[mysterio]

You will have to do more than present straw man arguments to disprove this theory.

Evolution is real, and it takes nothing away from God. I'm sorry that you can't see that.

[garybob]

Actually, none of those "problems" even address what would stop microevolution from becoming macroevolution over time. Those are just problems with making a straw-clutching you-can't-make-me-see-ist admit there's no limiting mechanism.

Absurd. If you cannot define it, detect it, or measure it, how do you study its evolution, if any? Indeed, how do the sciences, based on physics, handle the physically undetectable?

[VadeRetro]

Superstition= useful (to those same people)

There isn't much to talk about if you think Occam's Razor and physical evidence are superstition and some decrepit creation myth is science.

[mysterio]

No, the theory of evolution does not attempt to explain the origin of life. It only explains the development from single celled organisms to modern life over billions of years. I'm sure this has been explained to you already. If not, read the theory. I will debate you on this topic, but I won't debate misconceptions presented purposely to make your argument more dramatic.

[Alamo-Girl]

Thanks for the ping!

[mysterio]

Evolution is measureable. I work in biotechnology, and I often see genetic recombination in large scale DNA preps. I work with natural antibiotic resistance genes. The fact that any bacteria have these genes is evidence of a beneficial mutation.

Here's how it works. You have a large population with constant genetic recombination. Sometimes that recombination results in a mutation. Many mutations are harmful to the organism and make it less able to compete. In the case of antibiotic resistant bacteria, the environmental pressure of mass antibiotic treatments selected for resistant organisms. Multiply that times 3.5 billion years, and you have large scale evolution.

[VadeRetro]

Absurd. If you cannot define it, detect it, or measure it, how do you study its evolution, if any?

A spectacularly ignorant argument. We detect it. It's called faunal succession. It's called the Fossil Record. Then we have the evidence from molecular biology and embryology which points the same way. 29+ Independent Lines.

Indeed, how do the sciences, based on physics, handle the physically undetectable?

The ether, or creationist IQs? Science is about what is detectable, and evolution fits in just fine.

[blueblazes]

Don't make assumptions, buddy. I am neither disturbed by evolution nor a believer in the Adam & Eve story. Apparently many of you are extremely disturbed by my challenge to your belief system. I simply don't subscribe to YOUR religious tenet of evolution. There is no proof as I have cited repeatedly in this thread about evolution. It is merely a theory based on physical similarities of various animals throughout the fossil record. There is NO SCIENTIFIC PROOF of evolution. The only SCIENTIFIC way to prove or disprove anything is either to re-produce a physical result through experimentation consistently, or to consistently predict a result. Neither of those applies to evolution, it is merely a theory. That's all, despite all your genuflections in its direction, and your insulting and arrogant behavior towards those who don't sing the hosannas of evolution. Evolution doesn't even have the benefit of direct observation on its side - no species has EVER been observed by humans as evolving into anything other than another form or variation of the same generally recognizable species. Lions and tigers and bears have always been recognizable as lions and tigers and bears even if you go back as far into the fossil records as their earliest ancestors. Even those animals that you point to as intermediates cannot be proven as they may have existed as species in their own right and you are just basing your theory upon how the creature "looks" or the resemblance it bears to something else.

Moreover, if evolution were an ongoing process it would still be going on and someone in recorded human history would have noted SOME species somewhere on earth evolving into a totally different species. That has NEVER been recorded anywhere on earth that I am aware of. Show me a species recorded somewhere within the past 2000 years that has evolved into something that is totally different and unrecognizable from what it was originally -not just a variation of the same general plant or animal.

For those of you who argue so ludicrously about the role of imagination in science I might say that the earth was seeded by space aliens who planted all of these creatures or tinkered with their DNA. There are people who have the "imagination" to believe this and for all I know, they might be right if imagination is your major criteria rather than scientific proof.

What really irritates me is not the THEORY of evolution or the THEORY of creationism. A theory is a theory is a theory without proof to back it up. It might be right or wrong or something of both. What irritates me is the attitude of you "scientific" fanatics who are just as narrow-minded and fanatical as the religious folk you deride and insult. You are all far too arrogant, insolent and insulting to those who disagree with you. You are far too sure of yourselves and your "theory". I think it is based upon your need to find some explanation of how creation and particularly mankind evolved as most of you reject religion (which is fine with me) and you have a need to fill the vacuum of the creation story and "explain" things. There is no more validity to your explanation than there would be to listening to the creation stories of many primitive peoples throughout the world. I don't want to see things "explained" - I want to see them proven. And if they can't be proven, just say that this is what you believe and allow others to believe as THEY will.

There have been many other people throughout time who thought they also had the answer to everything - including those who believed in the flat earth or that the earth was the center of the universe. These people were willing to kill or imprison those who disagreed with them. In time, they were proven to be wrong. Perhaps some day, you will be proven to be wrong as well.

[garybob]

It only explains the development from single celled organisms to modern life over billions of years. I'm sure this has been explained to you already.

It has been told to me, but what has never been explained to me is:

Evolution breaks down into at least three logically separable components: First, that life arose by chemical accident; second, that it then evolved into the life we see today; and third, that the mechanism was the accretion of chance mutations.

The first, chance formation of life, simply hasn’t been established. It isn’t science, but faith.

The second proposition, that life, having arisen by unknown means, then evolved into the life of today, is more solid. In very old rocks you find fish, then things, like coelacanth and the ichthyostega, that look like transitional forms, and finally us. They seem to have gotten from A to B somehow. A process of evolution, however driven, looks reasonable. It is hard to imagine that they appeared magically from nowhere, one after the other.

The third proposition, that the mechanism of evolutions is chance mutation, though sacrosanct among its proponents, is shaky. If it cannot account for the simultaneous appearance of complex, functionally interdependent characteristics, as in the case of caterpillars, it fails. Thus far, it hasn’t accounted for them.

[VadeRetro]

Don't make assumptions, buddy. I am neither disturbed by evolution nor a believer in the Adam & Eve story.

Medved.

[VadeRetro]

... that the mechanism was the accretion of chance mutations.

No anti-Es ever say it right. Ever.

If you don't know what evolution is, how do you know it's wrong? You don't know what it is.

[darbymcgill]

Recall, I'm not the one who espoused the alligator theory, he's one of your guys. I don't recall you calling him names.

I told you I don't have a dog in the hunt. You suggest I'm a liar. Did I call any of you Darwinists baloney throwers?

Where is your evidence of Urey-Miller to Shania Twain. You expect everyone to accept by faith that because some chemicals in a lab coalesce into carbon based amino acids etc. and then there was lightening of un-heard of proportions or a meteor. Is that the scientific proof you rely on?

If you don't like using maybe counting then stop using maybe or might as a replacement established fact. You want everyone to accept your theory just because you know a lot about it. Tell us how you differ from the Pope or any other religious expert who thinks they know more than you do about Creationism.

They could simply say you don't follow the evidence and you try to to refute an issue of which you are ignorant.

[garybob]

A spectacularly ignorant argument. We detect it. It's called faunal succession.

The problem getting answers from bigoted blowhards is that one never gets a concrete, non-metaphysical, demonstrable answer.

[mysterio]

No, evolution is not my religion. I believe in God. That is my religion.

It seems that the only thread to your argument is twisting the scientific method. By your definition, nothing is a fact. Gravity is a theory. It doesn't make gravity any less real. Evolution is real, too.

I'm sorry you are so resistant to this. Much of the constant negativity you are having to endure is due to the frustration of the scientific minds here. It's like trying to explain to someone that the earth revolves around the sun, and they just absolutely refuse to accept it.

But that's fine. You have a right to your opinion, and I have the right to tell you that the science is totally on my side. But you don't have a right to present straw man after straw man and expect to be taken seriously.

[garybob]

If you don't know what evolution is, how do you know it's wrong? You don't know what it is.

That's been the gist of your argument all along...call everyone who disagrees with you names and claim that you alone know the truth.

[VadeRetro]

Recall, I'm not the one who espoused the alligator theory, he's one of your guys. I don't recall you calling him names.

Did you read what I said on the subject? You're not doing very well here in the reading comprehension department.

I told you I don't have a dog in the hunt. You suggest I'm a liar. Did I call any of you Darwinists baloney throwers?

You're not very credible there, no. You seem to have learned all your science from Duane "Goo to you via the zoo" Gish of ICR. I don't know how to help you with that. You walk like a duck, look like a duck, and quack like a duck. That makes me think you're a duck.

Where is your evidence of Urey-Miller to Shania Twain.

Hey! "Goo to you, via the zoo!" I didn't peek, either! Really.

You are so bogus! And to think there's another guy on the same thread talking Duane Gish and supposedly HE's not one either.

Yeah.

If you don't like using maybe counting then stop using maybe or might as a replacement established fact.

Hey, if you don't like science, try religion. It'd be right up your alley.

Out for the night. Just leave the next of "You can't make me see"-isms on the thread and I'll get to them when I get to them.

[VadeRetro]

No really, you don't know the mechanism of evolution, but you know the mechanism doesn't work. You're bludgeoning with your ignorance. The really bad news is you aren't doing creationism wrong. You're doing it right.

Out for the night.

[mysterio]

Here's your example of observed speciation by a human.

While studying the genetics of the evening primrose, Oenothera lamarckiana, de Vries (1905) found an unusual variant among his plants. O. lamarckiana has a chromosome number of 2N = 14. The variant had a chromosome number of 2N = 28. He found that he was unable to breed this variant with O. lamarckiana. He named this new species O. gigas.

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