Download News: Splitting two birds with one gene Posted by Elie Dolgin

News:
Splitting two birds with one gene
Posted by Elie Dolgin
[Entry posted at 17th June 2009 04:04 PM GMT]
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A single base pair change that turned a colorful bird entirely black probably guided the formation of a new
species, researchers report in the August issue of The American Naturalist.
"It looks like we have a single mutation that's driving speciation in these
birds," J. Albert Uy, an evolutionary biologist at Syracuse University in
New York, who led the study, told The Scientist. "It's one of the first if
not only examples of this kind of thing in vertebrates."
Eighty years ago, the late Harvard zoologist Ernst Mayr visited the
Solomon Islands in the South Pacific and marveled at the variation in
plumage color of the Monarch flycatcher (Monarcha castaneiventris), a
small, insect-eating songbird with a long, fanned tail. In particular, two
flycatcher populations that lived on islands eight kilometers apart
caught Mayr's eye. One had a chestnut-colored belly with an iridescent
bluish-black backside, and the other was all black, or "melanic." Mayr
discussed these birds as an archetypal example of speciation in action in
his 1942 opus Systematics and the Origin of Species, but he didn't know
what was driving the two birds apart. Now, Uy thinks he has the answer
-- a single nucleotide substitution in a gene underlying plumage color.
Uy and his colleagues sequenced the coding region of the melanocortin
1 receptor (MC1R) gene, a G protein-coupled receptor that regulates
melanin production, in the chestnut-bellied and melanic birds as well as
Melanic (above) and chestnutthree other subspecies of Monarch flycathers. They discovered three
nucleotide differences, but only one affected the amino acid sequence. bellied (below) Monarch flycatchers
Image: J. Albert Uy
Strikingly, all the melanic birds had the derived amino acid change,
whereas the chestnut-bellied birds and the three other subspecies all had the ancestral sequence. The
researchers also used stuffed taxidermic mounts to test the birds' ability to recognize their own subspecies and
found that the two groups of flycatchers consistently preferred their own kind. Together, these results
indicate that the single genetic swap probably set speciation in motion, Uy said.
"I think we do have a speciation gene because this substitution creates a different physical appearance for the
bird, which in turn causes the birds to recognize members" of its own subspecies, Uy said. "We're catching
them right now in the act of becoming new species."
Daven Presgraves, an evolutionary biologist at the University of Rochester, New York, who was not involved in
the study, agrees that MC1R probably counts as a speciation gene, but pointed out that the ultimate test
would be to show that the gene directly influences mate choice. Nonetheless, the "study is as strong as we can
reasonably expect," he wrote in an email, because mate choice trials are "nearly impossible for monogamous
birds on remote islands." Uy, who is now building aviaries and applying for licenses to keep the tropical,
endangered birds in captivity, plans to carry out mating trials, but conceded that it "may take five years" or
more.
Uy is also investigating the genetic basis of another all-black subspecies that lives on a separate island some
150 kilometers away from the other melanic population but which does not have the same mutation in the
MC1R gene. He intends to sequence the "next group of candidates" -- genes that encode proteins that interact
with the MC1R to control pigmentation. Slowly but surely, "we are now getting at the underlying basis of
species divergence" in these birds, Uy said.