Tuesday, February 17, 2015

Darwin's Finches Get Their Genomes Sequenced



Among the most widely known scientific experiments is Charles Darwin's finches. In 1831-1836 aboard the HMS Beagle, Darwin traveled to the Galapagos Islands where he would study the variation in beaks in endemic bird species. This helped lead to Darwin's theory of evolution by natural selection. Researches have now been able to bring modern genetic technology to this timeless experiment and sequence the genomes of all fifteen species of Darwin's finches, and pinpoint the gene responsible for the renowned beak variations. The study has also redrawn a family tree of the birds.

As the story goes, Darwin observed the physical characteristics of the finches and noticed that their beaks were adapted to the types of food they ate; for example, some had thin, sharp beaks for collecting pollen and nectar (like the Cactus finch), while other had strong, thick beaks for cracking nuts (like ground dwellers such as the Large ground finch). It's a prime example of "adaptive radiation", where a species deviates from a single ancestor as a response to selective pressures, and new species emerge.

With the tremendous amount of progress made in DNA sequences and genetic testing, geneticist Leif Andersson along with a team of scientists, analyzed samples from 120 birds and were able to redraw the family tree of the finches, connecting the dots between branches and indicating gene exchange. The team discovered mixing of genes between species, indicating crossbreeding, and "were able to pinpoint the genes responsible for beak morphology." One of the genes, ALX1, is known to control facial development in vertebrates. This is one of the genes that helped finches rapidly adapt their beak structures to the environment. This was seen as recently as the 1980's, where a drought changed the food supply and the birds had to adapt. 

Other scientists have pointed out that beaks differ in many more ways than just being pointed or blunt. However, studying the ALX1 gene even further will reveal exactly what the gene controls, in this case, specialized beaks.

I really enjoyed this article because Darwin's finches experiment has always fascinated me and when combined with modern genetic technology, it's really exciting to find out what controls variation in beak types. Charles Darwin would be amazed at how far his initial study has come!

Original Article
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