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Newly Discovered Gene Sheds Light On Evolution Of Darwin's Finches

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It’s evolution in action: species competing for the same food and resources tend to diverge from each other to decrease competition. Now scientists have recently identified a gene answering for variations in the beak size among Darwin’s finches, a glaring example of this evolutionary mechanism.

An example of adaptive radiation, Darwin’s finches appeared on the Galapagos around two million years past and evolved into 18 different species with various sizes, beak shapes, songs, and feeding practices. Evolutionary biologist Charles Darwin observed these birds while visiting islands while on board the HMS Beagle in the 1830s.

Now, researchers from Uppsala University and Princeton University identified the HMGA2 gene as one that influences beak shape and drives changes in that part of the birds’ anatomy. They showed that through having a smaller beak, medium ground finches more ably consume tiny seeds and thus better compete with large finches, which eye bigger seeds and thus leave the smaller ones alone.

This transition in beak morphology likely happened after a severe drought from 2004 to 2005, when competition for food intensified among various finch species. Work done by study authors Peter and Rosemary Grant from Princeton, for example, found that the medium ground finch moved away from the beak size of the large ground finch.

“[T]he 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 two scientists who carried out field research in the area for 40 years.

The researchers discovered that during that episode of drought, the medium ground finches’ average beak size turned smaller due to a high death rate among those with large beaks, which could not fiercely compete with the larger species.

The team saw that 61 percent of the surviving birds had genes coding for a smaller beak, while only 37 percent of those who perished had the same genotype. This gene contribution to survival, according to lead author Leif Andersson, is among “the highest yet recorded for an individual gene” occurring in nature.

HMGA2 affects body size in dogs, horses, other animals, and even humans, and is involved in cancer development as it affects a crucial factor in metastasis and progression of the disease.

“[T]his gene pops up in many different species as a gene affecting growth and in humans also as a gene affecting dysregulated cell growth in cancer,” added Andersson.

However, it is not yet exactly known how the gene works in Darwin’s finches or in humans, entailing further investigation.

The findings were published April 22 in the journal Science.

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