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Geneticists supply heads-up on pigeons' crests

ScienceNOWFebruary 10, 2013 

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Genome sequencing has revealed why some breeds of pigeons have head crests.

JIM RASSOL — MCT

For centuries, pigeon fanciers have cultivated a startling variety of colors, feather arrangements, and behaviors, creating more than 350 breeds used in shows for looks and competitions for how fast they fly, how much they tumble in the sky, or how long they can remain airborne.

After sequencing the rock pigeon genome, researchers have tapped into that diversity to track down the genetic basis of one of the pigeon’s more ostentatious traits: the head crest. The gene could be the same one used in wild birds for head crest features, and its discovery paves the way for uncovering the genetic basis of other important bird traits.

Classical geneticists were intrigued by pigeons, and in 1911, breeding studies by T. H. Morgan suggested that head crests were a simple trait. “But this system has remained remarkably unknown among modern evolutionary biologists and geneticists,” said Hans Ellegren, an evolutionary biologist at Uppsala University in Sweden.

Michael Shapiro, an evolutionary biologist at the University of Utah in Salt Lake City, wanted to bring pigeons into the scientific limelight again.

“We know much more about genetic variation in fish and in mammals than we know about birds,” he said.

Until he came to Utah in 2006, Shapiro had focused on stickleback fish. But then, someone pointed out that the range of traits in those fish was meager compared with pigeon traits and proved the point by showing Shapiro the Encyclopedia of Pigeon Breeds.

“I was just blown away,” Shapiro recalled.

In 2008, Shapiro’s team began collecting blood samples and feathers for DNA analyses and, last year, developed a genealogy of pigeon breeds.

Head crests jumped out as a potentially interesting trait to study. Different breeds boast different designs, from a simple peak to a hood of plumage that buries the head. And breeds with crests were distributed throughout the pigeon family tree. Furthermore, wild birds such as woodpeckers and doves have head crests thought to be important in mate selection and communication.

So Shapiro teamed up with by BGI-Shenzhen in China, which sequenced the pigeon genome. The group also sequenced 40 other pigeon genomes, including breeds with and without head crests as well as two free-living pigeon populations. Those data helped establish the range of normal variation among these genomes.

That led them to a gene called EphB2 that was responsible for the presence or absence of a head crest. A survey of an additional 69 uncrested birds from 57 breeds and 61 crested birds from 22 breeds confirmed that uncrested birds had one version of this gene, and all the crested birds had another version, they reported online recently in Science.

Researchers already know that pigeon head crests form because feathers there grow up toward the head rather than down along the body. The researchers didn’t find any gene activity differences between crested and uncrested birds where and when this feather polarity is established in the embryo. So they think the decision to grow a head crest must be made earlier in development, Shapiro said.

“It’s an interesting example of how a single gene change can have a profound effect,” said Cliff Tabin, a developmental geneticist at Harvard University.

Now, Shapiro’s team is looking at other traits. Beak shape, size and color also vary greatly, and their genetics may be simple to work out.

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