Scientists sequence the genome of Darwin's finches

Large ground finch (Geospiza magnirostris) on Daphne Major island, Galpagos B. R. Grant

For more than four decades, the husband and wife team of Peter and Rosemary Grant travelled to the isolated Galapagos archipelago to watch evolution unfold in front of them.

They were studying some of the 15 species of Darwin's finches, so named because the famed naturalist observed them during the 1830s on his trip aboard the H.M.S. Beagle. Over the years, they noticed the beak size changed among species in response to its food supply - one species developed a smaller beak to take advantage of different seeds - which demonstrated evolution was happening much quicker than Darwin could ever have imagined.

Now, they have tapped the power of sequencing technology to understand the genetic underpinning of these changes. For the first time, scientists have sequenced the genomes of all the famous finches that inspired Charles Darwin's theory of natural selection.

In a study reported Thursday in Nature, the Grants, along with Leif Andersson of Uppsala University and several other authors, detailed the results from sequencing the genome of 120 birds from all of Darwin's finches.

For the DNA, the Grants provided drops of blood samples collected since 1987. They were especially interested in range of beak sizes, which had caught Darwin's eye because they were so much more diverse than the birds he had seen in Europe.

Comparing two species with blunt beaks and two with pointed beaks, they identified 15 regions of the genome as being very different. Six of these contained genes that previously have been associated with craniofacial and/or beak development.

Most significant, they found that genetic variation in the ALX1 gene is associated with variation in beak shape not only between species of Darwin's finches but also among individuals of the medium ground finch.

"This is a very exciting discovery for us since we have previously shown that beak shape in the medium ground finch has undergone a rapid evolution in response to environmental changes," Princeton University's Rosemary Grant said. "Now we know that hybridization (interbreeding between species) mixes the different variants of an important gene, ALX1."

The scientists also were able to show hybridization between a warbler finch and the common ancestor of tree and ground finches goes back more than 500,000 years and 800,000 years.

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Scientists sequence the genome of Darwin's finches