According to the journal Science, researchers from Princeton and Uppsala Universities have identified the gene that allows for the rapid evolution of Darwin’s Finches in response to their continuously changing environment on the Galapagos Islands. The gene, HMGA2, seems to be the chief factor in beak size in the finches. This gene is also present in dogs, horses, and humans, playing a role in body size and build.
These finches are a typical example of an adaptive radiation. Since their first ancestor arrived on the islands, they have evolved into 18 recognized species differing in body size, beak shape, song and feeding behavior. Changes in the size and form of the beak have enabled different species to adapt to different food sources, ranging from insects, seeds, nectar from cactus flowers, and even the blood of seabirds.
The medium ground finch diverged in beak size from the large ground finch on Daphne Major Island following a severe drought in 2004-2005. When studying the birds that survived it was found that they were more likely to have a version of the gene that leads to smaller beaks, enabling them to survive the drought. The mechanism by which HMGA2 influences the finch’s beak is not known, but what is known is that it is extremely powerful. Co-author of the Princeton study, Peter Grant, believes that the beak adaptation as a result of the drought is one of the most remarkable examples of natural selection on record.
In a study published last year, the DNA of 120 birds including members of all known species of Darwin’s finches and two closely related species was sequenced. It was found that the species have been evolving in response to their environment ever since arriving on the islands two million years ago. In some cases, different species would hybridize, interbreeding to produce a new trait. The Herald of Everett reports an example of Hybridization was witnessed by the Grants during their stay on Daphne Major when a newcomer to the island, named Big Bird, mated with a medium ground finch. The new hybrid is now seven generations old. These new generations, however, are largely the result of inbreeding, and therefore stand a fair chance of dying out.
Another gene identified in the study was the gene responsible for beak shape called ALX1. The variation of this gene in the bird determines whether the beak would be narrow and pointed or broad and blunt.
“There are multiple genes that contribute,” Leif Andersson, an animal geneticist who worked on the study from Uppsala University said, “but we think that ALX1 is one of the most important, if not the most important factor that has changed on the island.” This, combined with the new study of HMGA2 gives biologists a reasonably good idea of how the finches evolved. Dolph Schluter, a biologist at the University of British Columbia said this opens a new perspective on how species split and gene variants arise. “On the one hand it doesn’t change anything, in that we already knew there was an evolutionary response to competition during that drought, but on the other hand, it changes everything, because we can point to a physical, material basis for that change,” he said.
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