Getting Ruff with Pigeons
Posted by Richard Conniff on February 5, 2013
How do breeders develop such colorful and varied pigeons? To find out, the normally reclusive Charles Darwin immersed himself in the hobby, frequenting the taverns and other low abodes where fanciers met and becoming “hand & glove with … Spital-field weavers & all sorts of odd specimens of the Human species, who fancy pigeons.”
Now a University of Utah researcher has taken on the same question more directly, with genetic analysis. He traced the efflorescence of spectacular pigeon head ornamentation to a change to a single gene. Here’s part of the story, from Carl Zimmer’s account in today’s New York Times:
… pigeon breeders produced crests on the birds on five separate occasions. The scientists compared the genomes of the crested pigeons with one another, as well as with other pigeons and with chickens, turkeys and other species. They hunted for mutated genes unique to the crested breeds, and found that all of them shared precisely the same mutation in precisely the same gene, EphB2.
Bird embryos develop placodes, little disks of tissue on their skin from which feathers will grow. The scientists found that in ordinary pigeons without crests, EphB2 became active on the bottom edge of the placodes; in crested pigeons it was active on the top edge.
The experiment suggests that EphB2 tells the placode which way is up. In most pigeons, it instructs the feathers to grow down the neck; but the mutation changes the location where EphB2 switches on, effectively turning the feathers upside down and producing a crest.
“They grow the wrong way,” Dr. Shapiro said. “They’re even pointing the wrong way in the embryo, before they become feathers.”
The new research suggests that the crested version of EphB2 arose in a surprising way. It mutated only once, rather than five separate times.
Dr. Shapiro came to this conclusion in part because he found that it takes two copies of the mutant gene to reverse the feathers. When the mutation arose, it was passed down invisibly from pigeon to pigeon. Only when two carriers happened to mate did they suddenly produce a crested chick.
Along with Zimmer’s text, check out Bailey’s colorful photo series.