Changes in the size and form of the beak have enabled different species to utilize different food resources such as insects, seeds, nectar from cactus flowers as well as blood from iguanas, all driven by Darwinian selection. 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 insight was that gene flow between species has played a prominent role throughout the evolutionary history of the Darwin's finches.
The scientists could even trace clear signs of hybridization between a warbler finch and the common ancestor of tree and ground finches that must have occurred about a million year ago. The most striking phenotypic diversity among the Darwin's finches is the variation in the size and shape of the beaks. Charles Darwin was struck by this biological diversity, and compared it with the variety he was accustomed to among European birds such as the hawfinch, the chaffinch and warblers, as documented in his book "The Voyage of The Beagle.
Now we know that hybridization mixes the different variants of an important gene, ALX1," says Rosemary Grant. The ALX1 gene codes for a transcription factor with a crucial role for normal craniofacial development in vertebrates, and mutations that inactivate this gene cause severe birth defects including frontonasal dysplasia in humans. Using modern genetic analyses, they found a molecule that regulates genes involved in shaping the beaks of Darwin finches.
These signals alter the behavior of cells responsible for beak sculpturing. Members of the research team received permission to collect finch eggs from the Galapagos National Park, a group of rocky islands in the Pacific Ocean, about miles west of Ecuador.
Female finches lay clutches of four to five eggs, one per day. To avoid disruption and abandonment of the nests, the researchers took only the third eggs laid. In the Department of Genetics at Harvard Medical School, 26 bird embryos were examined, using gene chips that reveal which genes are most active in the heads of the developing finches. This activity was then matched with the size and shapes of adult beaks. The investigation soon focused on calmodulin as the switch that can turn on genes involved in increasing beak length.
This protein had never before been implicated in the development of the skulls and faces of any birds. Heather Scoville is a former medical researcher and current high school science teacher who writes science curriculum for online science courses. Featured Video. Cite this Article Format.
Scoville, Heather. Charles Darwin's Finches. Artificial Selection: Breeding for Desirable Traits. The Natural History of the Galapagos Islands. Directional Selection in Evolutionary Biology. Your Privacy Rights. To change or withdraw your consent choices for ThoughtCo.
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