An international team of researchers from Uppsala University and Princeton University has identified a specific gene that within a year helped spur a permanent physical change in a Darwin’s finch species, the medium ground finch (Geospiza fortis).
The medium ground finch (Geospiza fortis) diverged in beak size from the large ground finch (Geospiza magnirostris) on Daphne Major Island, Galápagos following a severe drought. Image credit: Peter R. Grant.
Darwin’s finches, also known as the Galápagos finches, are a classical example of an adaptive radiation.
According to scientists, their common ancestor arrived on the Galápagos Islands about 2 million years ago.
During the time that has passed the finches 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 utilize different food resources such us insects, seeds, nectar from cactus flowers as well as blood from seabirds, all driven by Darwinian selection.
In a previous study from the same team the ALX1 gene was revealed to control beak shape (pointed or blunt).
In the latest study, the scientists carried out whole-genome sequencing of 60 birds representing six species. These included small, medium, and large ground finches as well as small, medium, and large tree finches.
They identified a gene, HMGA2, and confirmed that it is highly associated with beak size, as well as body size, in medium ground finches, a species with considerable diversity in both body and beak size.
They then analyzed the genomes of medium ground finches that survived a 2004-2005 drought in the Galápagos, finding that the finches with two sets of the small-beak gene variation of HMGA2 were much more likely to have survived compared to finches with the gene variation associated with larger beak size.
The results were published April 22, 2016 in the journal Science.
“We have demonstrated that HMGA2 played a critical role in this evolutionary shift and that the natural selection acting on this gene during the drought is one of the highest yet recorded in nature,” said co-author Prof. Peter Grant of Princeton University.
“Our data show that beak morphology is affected by many genes as is the case for most biological traits. However, we are convinced that we now have identified the two loci with the largest individual effects that have shaped the evolution of beak morphology among the Darwin’s finches,” said lead author Sangeet Lamichhaney from the Uppsala University’s Department of Medical Biochemistry and Microbiology.
The gene HMGA2 is not limited to finches. It has previously been associated with different body sizes in dogs and horses.
“It also is one of the genes most consistently associated with variation in stature in humans, which is determined by hundreds of genes,” said study senior author Dr. Leif Andersson from Uppsala University.
“This research tells us that a complex trait such as beak size can evolve significantly in a short time when the environment is stressful,” said co-author Dr. Rosemary Grant from Princeton University.
“We know that bacteria can evolve very quickly in the lab, but it is quite unusual to find a strong evolutionary change in a short time in a vertebrate animal.”
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Sangeet Lamichhaney et al. 2016. A beak size locus in Darwin’s finches facilitated character displacement during a drought. Science, vol. 352, no. 6284, pp. 470-474; doi: 10.1126/science.aad8786
