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Researchers Evolve A Complex Genetic Trait In The Laboratory
ScienceDaily ^

Posted on 02/13/2006 5:01:39 PM PST by FlameThrower

Researchers Evolve A Complex Genetic Trait In The Laboratory

Duke University biologists have evolved a complex trait in the laboratory -- using the pressure of selection to induce tobacco hornworms to evolve the dual trait of turning black or green depending on the temperature during their development. The biologists have also demonstrated the basic hormonal mechanism underlying the evolution of such dual traits.

Frederik Nijhout shows the "polyphenic" hornworm he and Yuichiro Suzuki evolved. (Photo Credit: Les Todd)Their experiments, they said, offer important insight into how complex traits involving many genes can abruptly "blossom" in an organism's evolution.

The researchers -- Professor of Biology Frederik Nijhout and graduate student Yuichiro Suzuki -- published their findings in the Feb. 3, 2006, Science. Their work was funded by the National Science Foundation.

The complex traits, or "polyphenisms," they studied are instances in which animals with the same genetic makeup can produce quite different traits, or phenotypes, in different environments. For example, genetically identical ants can develop into queens, soldiers, or workers, according to their early hormonal environment. Or, the same butterfly can assume very different coloration in winter or summer. A kind of polyphenism is also likely at work in mammals -- for example in the seasonal development of antlers or changes in plumage or coat colors, said Nijhout and Suzuki.

While biologists have understood the basic machinery underlying polyphenisms, the mystery remained how such complex traits, which involve mutations in multiple genes, could evolve and persist.

"It's long been known that polyphenisms are controlled by hormones, with the brain sensing environmental signals and altering the pattern of hormonal secretions," said Nijhout. "In turn, these hormonal patterns turn sets of genes on or off to produce different traits. However, we understood only the developmental mechanism, and how it is possible with a single genome in an animal to produce two very different phenotypes," he said.

"There had been theoretical models to explain the evolutionary mechanism -- how selective pressures can maintain polyphenisms in a population, and why they don't converge gradually into one form or another," said Nijhout. "But nobody had ever started with a species that didn't have a polyphenism and generated a brand-new polyphenism. Such a demonstration could offer important insights into the evolutionary mechanism underlying such traits."

In their experiments, Suzuki and Nijhout chose a species of finger-sized tobacco hornworm, Manduca sexta, which normally produces only green larvae. Because a related species, Manduca quinquemaculata, develops black or green larvae when exposed to lower or higher temperatures, the researchers theorized that they could use temperature shocks to evolve a similar polyphenism in M. sexta.

Suzuki and Nijhout conducted their experiments on a black mutant form of M. sexta, which is black because of lower production of a key hormone called juvenile hormone. They subjected the black mutant caterpillars to heat during a critical period, and over multiple generations selected for two different lines of mutant caterpillars. One polyphenic line was selected to show increased greenness on heat treatment, and one monophenic line selected to show decreased color change upon heat treatment.

After rearing and selecting ten generations of caterpillars, with about 300 caterpillars per generation, the researchers found that they had, indeed, created the two distinct strains. The polyphenic strain would develop a green color at higher temperatures, altering abruptly at a temperature of about 28 degrees C. (83 degrees F.) In contrast, the monophenic strain remained black at all temperatures.

The researchers could compare these strains to understand the origin of the polyphenism. Their experiments revealed that it was the level of juvenile hormone in the caterpillars that regulated whether they would turn black or green.

For example, by applying a spot of juvenile hormone extracted from a green caterpillar to a black caterpillar during a critical period, Suzuki could produce a green spot on that caterpillar.

Also, by tightening a tiny noose around a developing caterpillar's head to prevent the juvenile hormone -- produced in the head -- from flowing to the rest of the body of the heated polyphenic worm, Suzuki could prevent the caterpillar from turning green.

According to Nijhout, the generation of polyphenism in the caterpillar demonstrates an evolutionary phenomenon called "genetic accommodation." In this process, a mutation in a regulatory pathway such as a hormonal pathway changes the hormonal level to bring it closer to a threshold level that could be affected by environmental variation.

Thus, the black mutant hornworm had "dialed-down" levels of juvenile hormone, so that the caterpillar's color-producing machinery would be more likely to be affected by temperature. By selecting for a temperature-sensitive strain, the researchers established polyphenism in the caterpillar.

"Our work is really the first demonstration that genetic accommodation actually can happen," said Nijhout. "In this case, it happens in the laboratory by artificial selection; but as with all such experiments, we assume that this is a microcosm of what is actually going on in nature."

Nijhout theorized that such "homeostatic" mechanisms that maintain, for example, the color of a caterpillar, can act to mask a great deal of mutations present within the genetic machinery.

"Homeostatic mechanisms tend to stabilize a phenotype such as color and, therefore, allow the accumulation of underlying, covert mutations just as an electrical capacitor acts to accumulate charge. And eventually, these mutations could 'break out' of that constraint to produce a sudden phenotypic change; and one way for them to break out is for a mutation to happen -- for example, one that alters a hormonal level -- releasing all this variation.

"The reason this 'capacitor' concept is important in understanding evolution and the origin of complex traits is that the common model is that a new trait gets started by a fortuitous single mutation," said Nijhout. "And while that likely happens, we believe that another important mechanism involves the accumulation of many mutations in many genes without any apparent effect because they are buffered by a homeostatic mechanism; then all of a sudden one of them alters the homeostatic mechanism and lots of genetic variation suddenly explodes and is revealed as a tremendous increase in the phenotypic variability of the species. This variation then serves as raw material for selection to mold a new adaptive trait. And so that's why we think these kinds of experiments demonstrate an important novel mechanism for the evolution of novel traits."

In further studies, Nijhout and his colleagues will seek to determine whether the type of evolutionary mechanism they demonstrated in the laboratory also occurs in nature. Also, they will seek to demonstrate the phenomenon of the genetic 'capacitor,' in which mutations can accumulate 'invisibly' without obviously affecting a trait, and whether natural selection tends to filter out deleterious mutations in such cases.


TOPICS: Philosophy
KEYWORDS: evolution; genetics
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To: CarolinaGuitarman
No, I mean, define *kind*. Specifically. And scientifically.

Websters, Second College Edition, New World Dictionary of the American Language

----kind----

1. [Archaic] (a) origin (b) nature (c) manner; way
2. a natural group or division (the rodent kind) sometimes used in compounds (human-kind)
3.essential character
4. sort; variety: class

Is that specific and scientific enough for you.

Because species is used now as the word of the day does not cancel out the word "kind" as a scientific word. Because you do not want to acknowledge it as a scientific word does not void it. Definitions 1(a), 2, and 4, clearly state it in a scientific way.
21 posted on 02/14/2006 1:07:15 PM PST by Creationist (If the earth is old show me your proof. Salvation from the judgment of your sins is free.)
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To: Creationist

"No, I mean, define *kind*. Specifically. And scientifically."

*Kind* has no scientific meaning at all.

" Is that specific and scientific enough for you."

No, it's incredibly vague and has nothing to do with biological classification.

" Because species is used now as the word of the day does not cancel out the word "kind" as a scientific word."

Yes it does.


22 posted on 02/14/2006 1:09:28 PM PST by CarolinaGuitarman ("There is grandeur in this view of life...")
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To: CarolinaGuitarman
Kind is a scientific term. A german shepard is a kind of dog. A robin is a kind of bird. It is an interchangable word with species. I do not use the word species because it is a new word created by evolutionist to distant themselves fromt the Biblical term kind.

Websters, Second College Edition, New World Dictionary of the American Language ----kind---- 1. [Archaic] (a) origin (b) nature (c) manner; way 2. a natural group or division (the rodent kind) sometimes used in compounds (human-kind) 3.essential character 4. sort; variety: class

This definition is of the word kind it can be use in place of the word species and still convey to a person what is meant in a conversation even with a scientist.

Definition no. 4 clearly states everything that would be said about a German Shepard, It is a sort of dog, it is a variety of dog, it is a class of dog. You are just lying to yourself when you deny that kind is a scientific term, look up very old scientific documents they used the word kind not species, because the word species was not created.

The word species is used to distance yourself from the Bible.
23 posted on 02/14/2006 7:01:36 PM PST by Creationist (If the earth is old show me your proof. Salvation from the judgment of your sins is free.)
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To: Creationist
"Kind is a scientific term."

No, it really isn't.

"It is an interchangable word with species.:

No, it's is very, very different. For instance there are over 1,000 species of Birds. Saying an organism is a *Robin* is not the same thing as saying it's a bird. *Bird* is not a synonym for a particular species. It's the name of a class.

"I do not use the word species because it is a new word created by evolutionist to distant themselves fromt the Biblical term kind."

Species is a word that predates evolution. You are very confused.

" The word species is used to distance yourself from the Bible."

No, it's the tern that has been used for hundreds of years to designate a particular biological population.
24 posted on 02/14/2006 7:15:48 PM PST by CarolinaGuitarman ("There is grandeur in this view of life...")
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To: CarolinaGuitarman
Websters, Second College Edition, New World Dictionary of the American Language ----kind---- 1. [Archaic] (a) origin (b) nature (c) manner; way 2. a natural group or division (the rodent kind) sometimes used in compounds (human-kind) 3.essential character 4. sort; variety: class

The word kind has been around longer and has the original meaning of organisms that are of the same kind.

We have the dog kind. Within the dog kind we have the German Shepard kind, which if you read above the definition clearly states sort, variety, class. We have the Chesapeake Bay Retriever kind, sort, variety, class, of a dog.


We have the bird kind. A chicken is a kind of bird, sort, variety, class. Within that kind we have Rhode Island Red kind, sort, variety, class. The Japanese Silky kind, sort, variety, class. We have the cat kind. A Siamese kind, sort, variety, class. We have the Manx kind, sort, variety, class.
25 posted on 02/14/2006 10:38:01 PM PST by Creationist (If the earth is old show me your proof. Salvation from the judgment of your sins is free.)
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To: Creationist
Kind has no scientific meaning. Period.

" The word kind has been around longer and has the original meaning of organisms that are of the same kind."

Circular argument. You are saying *kinds correctly describe kinds*.

"We have the dog kind. Within the dog kind we have the German Shepard kind, which if you read above the definition clearly states sort, variety, class. We have the Chesapeake Bay Retriever kind, sort, variety, class, of a dog."

There are 35 species in the family canidae.

"We have the bird kind. A chicken is a kind of bird, sort, variety, class. Within that kind we have Rhode Island Red kind, sort, variety, class."

There are over 10,000 species of birds in the world. Including ostriches, penguins, hummingbirds, and owls. Claiming they all speciated in the last 4,000 years from the two or so *bird kinds* on the ark is preposterous.

"We have the cat kind. A Siamese kind, sort, variety, class. We have the Manx kind, sort, variety, class."

There are 36 species of wild cats. Including the lion, tiger, bobcat, ocelot, domestic cat. The domestic cat will not (cannot) breed with a lion. They are fundamentally different species. Saying they are the same *kind* and thinking that is in any way specific enough is insane.

The problem with your *kinds* is that they shift constantly depending on who you are asking. Species on the other hand describes a real biological community. That is why, when presented with the task of categorizing organisms, most *primitive* peoples, with no concept of western science or knowledge of our classification systems, will correctly identify what science has discovered to be species. That's because species are real divisions, while *kinds* are figments of a creationists imagination.
26 posted on 02/15/2006 3:37:04 AM PST by CarolinaGuitarman ("There is grandeur in this view of life...")
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To: CarolinaGuitarman

There are 35 kind of dog in the dog kind.


27 posted on 02/15/2006 5:29:26 PM PST by Creationist (If the earth is old show me your proof. Salvation from the judgment of your sins is free.)
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To: Creationist
"There are 35 kind of dog in the dog kind."

Before you said the *kind* was *dog*. Now you are changing that to 35 *kinds*. Or are you saying that *kind* can describe EACH of the 35 AND be used to describe *dog* in general? Sorry, that type of sloppy logic doesn't cut it. The family canidae has 35 SPECIES. *Kind* is as relevant to modern biology as *humours* is to medicine. In other words, it has no scientific meaning.
28 posted on 02/15/2006 5:34:49 PM PST by CarolinaGuitarman ("There is grandeur in this view of life...")
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To: CarolinaGuitarman
will this make you happy there are 35 varieties of the dog kind. Simple enough for a layman and descriptive enough for a scientist.
29 posted on 02/15/2006 6:26:33 PM PST by Creationist (If the earth is old show me your proof. Salvation from the judgment of your sins is free.)
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To: Creationist
"will this make you happy there are 35 varieties of the dog kind. Simple enough for a layman and descriptive enough for a scientist."

They are all separate, non-interbreeding species. *Kind* is not a scientific word.
30 posted on 02/15/2006 6:38:42 PM PST by CarolinaGuitarman ("There is grandeur in this view of life...")
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To: CarolinaGuitarman

Dogs are not interbreeding. New one on me.


31 posted on 02/16/2006 10:41:21 AM PST by Creationist (If the earth is old show me your proof. Salvation from the judgment of your sins is free.)
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To: Creationist
Foxes don't breed with wolves. Both are in the family canidae. You know, the one you said were all *dog kind*.

I notice you skipped over your claim for *bird kind*. Since there are 10,000 known species of birds, it makes any claim that even a small number were on the alleged Ark ludicrous. How did that many species come about in 4,000 years from just a few *kinds*? *Kinds* has no scientific meaning.

While we are talking about the Ark, how did all these animals and plants (Noah would have had to bring thousands of species of plants on board, since most would have died out in a world wide flood) get reintroduced around the world after the flood waters receded? Remember, there are only 8 people to do this job. Most animals can't migrate that far on their own; there is of course the immense difficulty of going over the oceans. How did the koala get onto Australia? How did ANYTHING get to Australia? Or Hawaii, or Alaska, or ... you get the picture. :)
32 posted on 02/16/2006 10:56:26 AM PST by CarolinaGuitarman ("There is grandeur in this view of life...")
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To: Creationist

Oh, almost forgot. There are over 5 to 6 million insect species. Can you tell me how many *kinds* of insects there are? How would one make such a determination? And how did Noah take care of these *kinds* on the Ark? You DO know that most would not have survived a global flood that last for months, right? Most are very highly adapted to a particular environment, especially the plants they eat or the prey they catch.


33 posted on 02/16/2006 11:16:09 AM PST by CarolinaGuitarman ("There is grandeur in this view of life...")
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To: DManA; FlameThrower; gleeaikin
How did it evolve if its genome didn't change?
they studied are instances in which animals with the same genetic makeup can produce quite different traits, or phenotypes, in different environments.

You're misreading the passage, although admittedly it's not as clear as it could be. It's not saying that the evolved versions had the "same genetic makeup" as the originals, it's saying that the evolved version was situationally able to produce two different traits out of the same (new) genetic code.

34 posted on 02/16/2006 11:46:34 AM PST by Ichneumon
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To: Creationist; CarolinaGuitarman; FlameThrower
Variation within it's kind does not mean evolution.

It most certainly does. Why don't you toodle off and learn some biology before you attempt to lecture us again?

But while you're at it, feel free to define "kind" in a way that can be objectively determined. Is the vertebrate taxon a "kind"? Why or why not, and how have you determined this? How about "mammals"? "Eukaryotes"? "Eutherians"?

"Carnivores"? "Ungulates"? Share your wisdom with the people who do this kind of thing for a living, they're just dying to acquire the hard-won insights of someone who has read a few creationist pamphlets.

A Doberman and Pekingese are still dogs.

But they are no longer the same, genetically or phenotypically, as their ancestors. Nor are they even the same species as their more distant ancestors, the wolves. that's evolution.

A Shetland and a Clydesdale are still horses.

But they are no longer the same, genetically or phenotypically, as the ancestral horse from which they descended. That *is* evolution. It's not *speciation*, but then no one but clueless anti-evolutionists think that evolution consists only of speciation.

A short person and tall person are still humans.

No one said they weren't. Enjoy beating up that straw man.

35 posted on 02/16/2006 11:53:36 AM PST by Ichneumon
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To: muawiyah
This is no more evolution than that which occurred when I watched a neighbor install a fuel injector on a 1957 Chevy.

Wrong, but thanks for playing. Your analogy fails on every level.

36 posted on 02/16/2006 11:55:03 AM PST by Ichneumon
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To: bvw; Creationist; CarolinaGuitarman
He did define "kind", definition by a list of examples is a valid way to make a definition.

No, it isn't, since it provides absolutely no method by which other groups can be similarly classified -- i.e., determined whether they too are a "kind" or not.

Nor did he even state how he determined (if he actually did, which is unlikely) whether the items in his laundry list really are "kinds" or not. What criteria is he using, other than "whatever I feel like saying at randomly and slapping the label 'kind' on"?

This is what separates actual science from creationist ramblings.

The definition of "species" is quite variale,

True, for good reason -- contexts vary. For example, living things can be classified by their ability to interbreed, whereas obviously that is an impractical way to classify extinct animals, since you can't test dead things by attempting to breed them.

and about as specific as that simple list, btw. Same order of magnitude of specificity.

Utterly false, but thanks for revealing your utter lack of knowledge on this topic. Biological definitions of species involve testable criteria, not just laundry lists of "we call these few things a species, now guess what else might qualify" like "Creationist's" cop-out.

37 posted on 02/16/2006 12:01:12 PM PST by Ichneumon
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To: Ichneumon
the evolved version was situationally able to produce two different traits out of the same (new) genetic code.

I'm quite curious as to what this "new genetic code" might be?

Perhaps aug is now a stop codon?

38 posted on 02/16/2006 12:59:06 PM PST by tallhappy (Juntos Podemos!)
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To: Ichneumon
I suggest you take a gander at the article on viruses in this month's Discover magazine. Quite interesting stuff.

There's a "hint" that changes in critters are much more akin to putting fuel injectors in '57 Chevys than anyone ever imagined.

39 posted on 02/16/2006 1:18:35 PM PST by muawiyah (-)
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To: CarolinaGuitarman
Quick, which is the correct term: "specieation" or "speciation"?

You can find both terms used in scientific peer reviewed journals. I prefer to use the one that suggests folks are into this for the purpose of turning obscure knowledge into real money, probably via foundation or government research grants.

40 posted on 02/16/2006 1:22:25 PM PST by muawiyah (-)
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