How Darwin's Finches Developed Beak Diversity

Charles Darwin's famous finches from the Galápagos archipelago and Cocos island are hallmark examples of speciation and adaptive evolution. Now, new research shows how over the years these birds developed the extraordinary diversity in beak shape that we see today.

Their common ancestor arrived on the Galapagos about two million years ago, and since then the finches have evolved into 15 separate species, each with differing beak shape, among other things. Naturalists believe these birds developed specific adaptations to live in one region or another. For example, on islands where insects are common in trees, the finches learned to live in trees and eat bugs, whereas those on islands where seeds are readily found on the ground adapted to that feeding method. And researchers say that their breaks also evolved accordingly, all driven by Darwinian selection.

That's all thanks to a gene called Alx1, which was recently found by researchers to vary between birds possessing rounded or pointed beaks.

"The most exciting and significant finding was 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 one of them, the medium ground finch," Leif Andersson from Uppsala University, who led the study, said in a press release.

Medium ground finches are known to have undergone significant genetic changes as a result of environmental changes. A severe drought hit the area in the 1970s, making seeds scarce. Those few seeds that did survive, however, were larger and tougher than normal and made it difficult for smaller birds to feed. So within just a generation, beak sizes increased in newborn birds in response.

And these adaptive changes were brought about, researchers now know, by mutations in the ALX1 gene.

"Now we can safely conclude that interspecies hybridization has played a critical role in the evolution of the finches, and has contributed to maintaining their genetic diversity," added Peter Grant, who was involved in the research.

The findings are described further in the journal Nature.

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