Posted on 05/31/2005 12:03:06 PM PDT by 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.
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.”
What about cows and chickens? Do you think they existed thousands of years ago?
Huxley claimed that given enough time, a money at a typewriter could generate the works of William Shakespere.
But this article shows that significant changes can happen in one generation.
The reason I posted those links was so that you could improve your understanding of how science works. Nothing in science is "proved." Theories can be dis-proved, but never proved. Theories are supported by making predictions which observations then demonstrates are accurate. That's been the unbroken history of evolution. But if you want to cling to your personal -- and incorrect -- conception of science, that is your decision
Oh, for your further information -- should you care -- there are numerous sciences that rely on observation, not reproducing results in a lab. For example: astronomy, geology, anthropology, paleontology, climatology, archeology, and cosmology. And of course, evolution.
One further thought (and a few links), then I'll leave you to do as you like: Evolution makes numerous predictions, which always work out:
All present and fossilized animals found should conform to the standard evolutionary tree. And they do.
Fossilized intermediates should appear in the "correct" chronological order on the standard tree.
Many organisms should retain vestigial structures as structural remnants of lost functions.
Species that are more closely related should share a greater portion of their DNA.. Excerpt:
[A]n hypothesis of evolutionary relationships is provided by the fossil record, which indicates when particular types of organisms evolved. In addition, by examining the anatomical structures of fossils and of modern species, we can infer how closely species are related to each other. When degree of genetic similarity is compared with our ideas of evolutionary relationships based on fossils, a close match is evident.
This thread is doing a terrific job of flushing out the folks who flunked biology class (or clearly should have). Keep up the good work.
I don't know. Neither does anyone else. We may never know. and you know what....what difference does it really make anyway? On a philosophical level, of what importance is it whether evolution is true or not? Obviously we can't prove it, as I've demonstrated, so it is merely a belief. Why hold this belief as opposed to another? I don't really care about how chickens, cows, sharks, or people came into existence. I deal with the present and the future. As for the future, if evolution is an ongoing process, some species should have been spotted in the process of changing from one species to another by now. And none has as far as I know. So maybe we should just consider evolution (and variations upon evolution) as one theory which may or may not be proven with the passage of time and the demonstration of an actual change from one species to another through some significant mutation.
I can't; it's too boring. Like teaching remedial math, year after year. And too often seeing the same students come back again and again.
That is just a bunch of BS. And you can stop talking down to me, Perfesser. Obviously any real science can be proven. We know that electricity works because we have actual inventions that harness it and prove that it works repeatedly. We know that the atom exists because we've split it. We don't know that evolution is true because we have seen NO PROOF of it. Proof is very simple and only exists in one of two ways. You can either re-produce a physical result or you predict a result. A theory ceases to be a theory once you can predict (consistently, not once, of course) results based on it, or re-produce physical experiments from it. So please, come off the high horse. Evolution for most of you folks is merely a substitute for a religious belief. That's fine with me, but don't tell me about the proof as THERE IS NONE. Maybe if our species continues to exist for a sufficient length of time, there will be proof, but right now, it's just part of a belief system.
No! No! No! No! We all know that all mutations are killers. It's in the talking points. These scientists must be lying. </creo_mode>
Your arrogance becomes neither you nor your argument, by the way. You'll win few converts with that approach, Perfesser.
***For example, consider all the events throughout history...***
I think you meant this post for someone else...
> Genetic analysis? I don't think so.
Riiiiiiiiiiiiight.
Look: there's a reason why the animals we look most like - the great apes - have gene codes most like ours.
> I cannot imagine that it is an ongoing process
Your failure of imagination puts strictures on neither the natural world nor God to create biodivesity via mutation and natural selection.
Nothing significant happened here. A fish is still a fish. Big deal. When a fish turns into an ostrich, send up a flare.
> What different species did the prehistoric shark evolve into?
The Great White and the Whale Shark for two. These did not exist 30 million years ago. They do today. Megalodon existed 2 million years ago. It does not today. Evolution and extinction occur.
did it ever stop being a fish?
> How do I renounce my faith
I dunno. Maybe you fill out a card.
Any doctor who has worked in a maternity ward can tell you that a simple genetic change can make a major and often hideous difference between the child and his parents. Most of the time these differences are fatal but not always.
We just don't talk about it.
"Your failure of imagination"
PRECISELY!!!!! You have just proven my point. I have written repeatedly that the theory of evolution is an exercise in...IMAGINATION. and here you are berating me for a "lack" of imagination. In short, also, a lack of faith - as what is imagination, but faith in something that cannot be proven. Imagination is NOT science. It might at some point lead to something that is part of science, as Jules Vernes imagination no doubt helped to pave the way for some experiments and inventions, but it is not, in and of itself, science. It is in fact, ANTI-science. It is part of a belief system.
Revelation 4:11
See my profile for info
Perhaps you are being militantly unaware. We have something like the fossil record we would expect, given our models of geography and evolution. Will the catch be that none of those morphologically and chronologically in-between things are intermediate species as you define the term?
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