Changes in beak size have allowed the iconic Darwin's finches of the Galapagos Islands to expand the types of food available to them. And now, scientists from Uppsala University and Princeton University say they have identified the key gene that regulates the size of those beaks.
In a study published in the journal Science, researchers identify HMGA2 -- a gene typically associated with body size in dogs and horses as well as variation in human size -- as the gene that controls beak size in Darwin's finches.
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Since their common ancestor came to the islands some 2 million years ago, spawning 18 different species, beak size has been a key to the finches' ability to access varied food sources – from cactus flower nectar to seeds to insects.
In a previous finding, study co-authors Peter and Rosemary Grant documented a rapid shrinking of beak size of the medium ground finch on Daphne Major Island, after a severe drought there in 2004 and 2005 left food supplies depleted. Birds with smaller beaks were better able to crack open smaller seeds - the most ample food left after larger seeds had been eaten in prior years by a newer species on the island, the large ground finch.
"Now we have demonstrated that the HMGA2 locus played a critical role in this evolutionary shift and that natural selection acting on this gene during the drought is one of the highest yet recorded in nature," said the Grants, in a joint statement.
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Exactly how does HMGA2 impact beak size? The researchers aren't yet sure.
"The HMGA2 gene regulates the expression of other genes but the exact mechanism for how it controls beak size in Darwin's finches or human stature is unknown," said the study's lead author, Uppsala University's Leif Andersson.
"It is clear that more research to better understand the function of this gene is well justified," Andersson added.