The Evolving Peppered Moth Gains a Furry Counterpart

NY Times ^ | 6-17-03 | CAROL KAESUK YOON

[Pharmboy]

H. E. Hoekstra
Evolution has allowed some rock pocket mice,
pictured on light and dark rocks, to produce
distinct fur that helps disguise them.

In the deserts of the Southwest, among the towering saguaros and the spiny cholla cactuses, rock pocket mice hop and dash in search of a meal of seeds. But while these mice may seem to scamper haphazardly across the desert floor, their arrangement in nature is strikingly orderly.

Nearly everywhere these mice are sandy-colored, well camouflaged as they scurry across beige-colored outcrops. But in some areas, ancient lava flows have left behind swaths of blackened rock. There the same species of rock pocket mouse has only dark coats, having evolved an entirely distinct and, for their surroundings, equally well-disguised pelage.

Now, in a recent study in The Proceedings of the National Academy of Sciences, researchers report identifying the gene responsible for the evolution of dark coat coloration in these mice, pinpointing the DNA sequence changes that underlie this classic story of evolutionary change, the cute and furry counterpart to the famous case of the peppered moth.

Researchers say the study is the first documentation of the genetic changes underlying an adaptive change where the evolutionary forces were natural. Scientists point out that other well-known cases involve evolution caused by humans; some have suggested that those changes may be atypical of natural evolutionary change, since they have typically involved intense, directed pressures destroying most of a population, like the spraying of pesticides or the application of antibiotics.

"This work is very important," said Dr. Mike Majerus, an evolutionary geneticist at Cambridge University, who was not part of the study. "Here man is just not involved. The sandy and lava flow substrates are entirely natural phenomena."

Other well-studied examples of human-driven adaptive change include the evolution of pesticide resistance in insects after widespread spraying and the increase in the numbers of dark-winged forms compared with light-winged forms of the peppered moth in the United States and England after industrialization turned air sooty and polluted.

Dr. Michael W. Nachman, a population geneticist, along with colleagues at the University of Arizona, Dr. Hopi E. Hoekstra and Susan L. D'Agostino, studied mice living on Arizona's Pinacate lava flow in Arizona and on light-colored rocks nearby. The researchers were able to take advantage of decades of meticulous work in which other scientists identified some 80 genes that affected coat color in laboratory mice.

On close examination, the light-colored rock pocket mice could be seen to have a type of hair coloration similar to standard, sandy-colored laboratory mice. In this pattern, known as agouti, the hair is black at the base, yellow in the middle and black again at the tip. The dark-colored rock pocket mice had completely dark hairs.

Researchers knew that mutations in a few well-known coat coloration genes in laboratory mice could cause such complete darkening of the hair, and they began by looking at two genes known as agouti and Mc1r. When they looked at DNA sequences in light and dark mice, changes in the agouti gene did not appear to be associated with light-colored fur versus dark-colored. Still, the researchers found that a certain cluster of mutations at Mc1r could be found in every dark-colored mouse.

"It's a textbook story," Dr. Nachman said. "Now we have all the pieces of the puzzle together in a natural setting."

Dr. Nachman noted that while the new study points to the Mc1r gene as the key to turning mice dark on the Pinacate lava flow, the team also found that dark mice on another lava flow in New Mexico did not share those mutations.

"So the same dark color has evolved independently in the two different populations," he said, "through different genetic solutions to the same evolutionary problem." Dr. Nachman said changes in another gene, perhaps the agouti gene, could be responsible for dark coloration in the New Mexico's Pedro Armendaris lava flow.

One could easily imagine that coloration would be of no consequence to the rock pocket mice, as they are nocturnal, darting about under the desert night sky. But researchers, working early in the last century, released light and dark mice on light and dark backgrounds in an enclosure at night and found that owls, a major predator of mice, could easily spot a mouse on a mismatched background.

Dr. Nachman noted, however, that these early researchers did not use rock pocket mice in their study, but instead used a species in which the dark and light forms were actually much less distinct.

As a result, he said, "we think the owls are discriminating even more strongly in our species." He said tiny bits of rock pocket mouse were often found in pellets at owl roosts.

Dr. Majerus said many kinds of animals showed light and dark forms, from deer mice to squirrels and chipmunks. There are even black ladybugs.

"A lot of the dark forms show an association with a particular type of substrate they're on, or the frequency of burning and charring of the trees in the woodlands," he said, noting that it would be interesting to do genetic studies in other animals, to see how many genetic solutions these other animals have come up with to turn dark.

But while many dark forms are abundant and can be studied at scientists' leisure, Dr. Majerus said that of the peppered moth was slowly disappearing.

So while there is nearly unanimous praise for the increasingly clean air in industrialized regions of the United States and Britain, there may be, at least for some scientists, a downside. "We've got about 15 or 16 years," Dr. Majerus said, "before those black forms, if they continue to disappear at the current rate, disappear completely."

[Pharmboy]

Although they left out the hijinks surrounding the pepper moths, this is a nice illustration of why Darwin was one of the nost brilliant people to ever walk the planet.

[Pharmboy]

Ping

[Grut]

So, when do we start seeing hunter-orange deer?

[balrog666]

Ping, baby, ping!

[Pharmboy]

Not a bad question...

[Pharmboy]

Thanks...I meant to ping Patrick, but you did it first.

[blam]

Thanks for the ping. Bump

[DallasMike]

Although they left out the hijinks surrounding the pepper moths...

It's like doing a biography of Hitler and leaving out the nasty bits about World War II. But, hey, this is the New York Times writing here!

[Aric2000]

But that's impossible, evolution is fake, it is NOT science, no matter what evidence you have.../creationist mode

This is ANOTHER example of microevolution at work, soon the usual suspects will get in here to have their say. See above.

[Al Simmons]

*Sigh* What they described is NATURAL SELECTION (ie, the light colored mice on dark lava flows get eaten, the dark ones do not and reproduce, and *voila!*)

Evolution would be having the rats turn into flying fish or something similar. And that ain't happenin'.

[Aric2000]

Clueless about evolution placemarker.

WHY, OH WHY, do creationists INSIST that evolution says something that it doesn't?

Please study the concept a bit yourself before spouting nonsense.

Thanks,

[plusone]

How is a tan mouse any different than a brown one? What's the big deal here? Why do the evo's hold up such trifling stuff as proof of their theory? Is this the best that they've got?

[Aric2000]

It shows Microevolution at work, without Microevolution, there is NO macroevolution.

A bunch of micros, make a macro, therefore Microevolution is very important for us to understand.

So, why is it that one mouse is dust colored and the other is dark colored? Why is it that one gene has been twisted in order to create this difference, and why is ANOTHER gene turned in another creature to create the same effect.

IT IS VERY IMPORTANT, it shows exactly what natural selection would do, because if it was DESIGNED, then most likely you would find the SAME gene twisted in the EXACT same way to get the SAME effect.

By showing that the gene sequences are different, it shows that natural selection is indeed the most likely cause.

Besides the fact that it is fun to see natural selection working as expected in the natural world, the more examples there are, then the Theory of Evolution becomes even stronger then it is.

Any of you others wish to add anything, or correct anything?

[Dimensio]

Evolution would be having the rats turn into flying fish or something similar.

No, it doesn't. Only idiots and liars make this claim.

[Dimensio]

How is a tan mouse any different than a brown one? What's the big deal here?

It's an example of selecting for a specific genetic variant within a species based upon environmental factors, similar to the peppered moth study. This is somewhat important because it does show that mutations can be beneficial (the genetic variant is caused by mutation) and because some creationists -- either through dishonesty or ignorance -- claim that the peppered moth study is a hoax either in its entirety or in its conclusions. For example, gore3000 claimed that the peppered moth study is held up as an example of speciation, even though he's yet to provide a single reference that presents the study as such "proof" (he then lied about me, claiming that I'd made a statement to the effect that I'd never heard of the study, when I backed him into a corner on the issue).

[Dimensio]

So, when do we get creationist cranks claiming that it used dead rats glued to rocks and sand and that the fact that the photographs were somewhat set up "proves" that the study was a sham?

[plusone]

Fair enough. And I agree that natural forces will force a species to adapt to its environment. I beleive in, what is called 'micro evolution'. But it is a huge leap to suggest that such small changes will result in a species transcending into anothr, and over long periods of time, will become something entirely different. This is my complaint with 'macro evo'n', that there seems to be no proof of it. Micro, yes, we can see this. (Selective breading has been going on for thousands of years, and though it is ID, it still shows what variance there exists within a species. But that is all. There is a certain amount of 'free play' within the genetic structure that allows this partial divergence, it is how a species can adapt. It is what Darwin saw with the finches on the Gallopagos. But this is just adaptation, varietization, etc. How do you go the next big step and link this to general, macro evo'n? What evidence is there to support such a claim?

[longshadow]

multi-spectral mouse placemarker

[ALS]

Darwin was a plagiarist.

[plusone]

Just for fun, what is your opinion about those fossilized human prints found in the Polluxi (sp) river bed?