Huber Shares Research on Song Evolution in Darwin's Finches

As part of the Natural Science and Mathematics (NS&M) Colloquium series this semester, Sarah Huber, Biology Professor from Randolph-Macon College, came to visit St. Mary’s to discuss her research on song evolution in her lecture “Song Evolution in Darwin’s Finches” in Schaefer Hall on Oct. 5.

Huber opened the lecture by discussing Charles Darwin’s original research on the finches living on the Galapagos Islands. Initially, Darwin failed to realize that all the birds he was observing belonged to the same species because they had such different outside appearances. They all ate different foods, ranging from having a diet of seeds, to insects or fruit. Over time, a finch’s diet evolutionarily influences the development of its beak size and shape. For example, a finch that is forced by its environment to have a diet of mostly insects will be likely to have a fine and pointy bill.

Previous research shows that the environment in general has a role on the evolution of finches. “We know less about the roll of song [in evolution],” said Huber. “We know that songs differ greatly between birds but it’s unclear what’s driving that difference.”

Most of Huber’s research on the evolution of song in finches is done on the population level, as opposed to doing a comparative analysis. When doing research at the population level, a single species is studied in only one discrete location.

While measuring beak morphology (size and shape of beaks), Huber and her colleagues began to realize that there was a bimodal distribution among the finches. This means that there were finches with large beaks and finches with small beaks, without many existing in the intermediate area between the two extremes.

This got the researchers very excited. They began to wonder, “If you have two different beak sizes, is it possible that selection on beak sizes could potentially be driving song?” said Huber. The songs of the two birds were so distinct that they could be distinguished easily. Huber said, “As we were walking around we could tell the difference between a large beak bird and a small beak bird just by listening.”

Huber explained that finches with a larger beak (a large morphology), would sing songs with a lower pitch and slower notes, whereas a bird with small morphology would sing songs with faster notes and a higher pitch.

Huber also explained how beak size influences the range of movement that a bird has while singing. By closing the beak, the vocal tract is shortened and thus slightly lower notes can be produced. On the other hand, if a bird opens their beak, then they can produce higher frequencies of sound. A bird with a narrow frequency of notes (a small range) does not have to open or close their beak very much. A bird with a smaller beak has smaller muscles that can be moved more rapidly, allowing the bird to sing sweeping frequencies very easily when compared to a larger morphology bird.

Huber further mentioned ecological speciation: when a divergent trait leads to reproductive isolation. This means that if a single trait changes in a population of birds, birds with one form of the trait will only mate with birds of their same trait, and not those with the other trait (who will, in turn, only mate with birds of that trait).

A correlation was found between female beak size and male beak size in mates. Small morphology females were found to mate with only small morphology males. This also causes a lower survival rate of birds with an intermediate beak size, leading to the appearance of the bimodal distribution of beak sizes that Huber found in her research.

A study relevant to the evolution of song is phylogenetics, which shows the pattern of discrete changes in related species over evolutionary time. The closer phylogenetically related two birds are, the more similar their song will be. However, as phylogenetic distance increases, song dissimilarity also increases.

As a disclaimer, Huber also mentioned that stochasticity, random happenstance, could also play a role in the evolution of song. It is possible that specific features of song that change over time may have arbitrary causes.

In reaction to the lecture, sophomore Kevin Tennyson said, “Bird-song evolution is not a subject that I am familiar with, but I thought she presented it well and made me interested in finding out more about it.”

“I thought Sarah did a great job. Charles Darwin would be proud. Her research was really interesting, and she presented it in a way that everyone in the audience could understand, even if they weren’t a biology major,” said senior Julie Frank. Frank went on to say, “In molecular evolution we’ve read about many phylogenetic studies, but I had never seen studies of song evolution before. If we studied the evolution of awesome bird song researchers, Sarah Huber would be an autapomorphy because she is one of a kind.”

The next NS&M Colloquium of the semester will be given by Katherine Socha of Math for America, entitled “Maggie & Milly & Molly & May: Mathematical Stories inspired by the Beach and E.E.Cummings.” This lecture is scheduled to take place on Wednesday, Oct. 19 at 4:40 p.m. in Schaefer 106.

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