Darwin's finches have been a long-standing icon of adaptive evolution, and now a team of scientists has identified the gene behind their variation in beak shape.
The common ancestor of the finches first arrived on the Galapagos about two million years ago, and since then the birds have evolved into 15 distinguishable species, Uppsala University reported. Changes in beak size have allowed different species to utilize different food sources such as seeds, nectar from cacti, insects and even the blood of local iguanas.
"We have now sequenced 120 birds including all known species of Darwin's finches, as well as two closely related species in order to study their evolutionary history," said Sangeet Lamichhaney, a PhD student and shared first author on the paper. "Multiple individuals of each species were analyzed and for some species birds from up to six different islands were sampled to study variation within and between islands."
One important finding taken from the study was that gene flow between the species played a key role in their development.
"During our field work on the Galapagos we have observed many examples of hybridization between species of Darwin's finches but the long-term evolutionary effects of these hybridizations have been unknown," said Peter and Rosemary Grant, Princeton University. "Now we can safely conclude that interspecies hybridization has played a critical role in the evolution of the finches, and has contributed to maintaining their genetic diversity."
The team looked at two species with pointed beaks and two with blunt beaks. They found 15 regions of the genome that were significantly different among the studied species, six of which contained genes that are believed to be associated with craniofacial and beak development.
"The most exciting 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," said Leif Andersson, Uppsala University, Swedish University of Agricultural Sciences and Texas A&M University, who led the study.
This finding is significant because past studies have shown the beak shape in the medium ground finch has exhibited rapid evolution in response to changes in the environment. The ALX1 gene codes for a transcription factor that plays a role in the craniofacial development of vertebrates. Mutations that inactivate this gene have been known to cause disfiguring birth defects such as frontonasal dysplasia in humans.
"This is an interesting example where mild mutations in a gene that is critical for normal development leads to phenotypic evolution," Andersson said. "I would not be surprised if it turns out that mutations with minor or minute effects on ALX1 function or expression contribute to the bewildering facial diversity among humans."
The findings were published in a recent edition of the journal Nature.
