The striking variations in the shape and size of the beak of finches on the Galapagos Islands have given naturalist Charles Darwin the idea that the traits of species could evolve over time as they adapt to new environments.
Now, a genome study has revealed a gene that could explain this remarkable variation of the species' beaks. For the new study, which was published in the journal Nature on Feb. 11, Leif Andersson from Uppsala University in Sweden and colleagues sequenced the genome of 120 birds belonging to the 15 species of Darwin's finches.
By comparing the pointed-beak species and blunt-beak species, the researchers have found that the differences in the gene dubbed ALX1 were linked not only with the differences in the beak between species but also with differences within the species medium ground finch (Geospiza fortis), which are known to exhibit fast beak changes in response to drought.
"The most thrilling 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," Andersson said.
ALX1 plays a crucial role in the formation of head and facial bones. The malfunctioning of this gene in humans could lead to deformities such as cleft palates, but in finches a small difference in the gene distinguished birds with stout beak and those with more pointy beaks.
The researchers have found that in one species of finches, the birds that inherited the blunt version of ALX1 from both parents had the bluntest bills while those who inherited a blunt gene from one parent and a pointy gene from the other had intermediate beaks. Those who had two pointy versions, on the other hand, had the sharpest beaks.
The study suggests that interbreeding has allowed the genes to flow across the birds' species, resulting in a variety of beak shapes and sizes. The researchers said that they were able to show that there has been hybridization occurring between the different species throughout the course of their evolution.
"We have previously shown that beak shape in the medium ground finch has undergone a rapid evolution in response to environmental changes," said study researcher Rosemary Grant from the Princeton University." Now we know that hybridization mixes the different variants of an important gene, ALX1."