Making Darwin’s finches sing can help establish connections between environmental changes and the emergence of new species

They say “hindsight is 20/20,” but ecological speciation theory (the theory that new species emerge in response to ecological change) seems to hold true in hindsight. Until now, it has been difficult to prove this experimentally.

In a study published in the journal Science, biologists at the University of Massachusetts Amherst identified an important connection between the ecology and speciation of Darwin’s finches, famous residents of Ecuador’s Galapagos Islands.

Previous studies of these birds have established that birds’ beaks adapt to changes in their ecological environment, and that changes in their beaks affect the way they sing. However, until this paper was published, no one had yet been able to show experimentally that such changes cause the emergence of new species. What is the revolutionary key to this discovery? The Ghost of the Finch of the Future.

A new study shows that changes in beak song itself may influence species recognition and thereby facilitate species separation.

“I started studying these birds 25 years ago,” says Jeffrey Podos, a professor of biology at Amherst College in Massachusetts and lead author of the paper. “In my first publication on finches in 2001, I showed that changes in Darwin’s finches’ beaks lead to changes in the songs they sing. And I showed that Darwin’s finches sing to attract mates. We speculated that the song might then change because of the use of beaks.” Something related to beak evolution could possibly catalyze ecological speciation. ”

However, at the time, Podos did not have conclusive experimental evidence to prove his hypothesis that environmental changes in beak shape were driving the emergence of new finch species.

One difficulty is that speciation is a historical process and therefore difficult to document. Being able to watch it happen is like catching lightning in a bottle. As a workaround, Podos devised an experimental study based on simulations that yielded some useful clues.

For example, he knew that beaks could evolve to be powerful for crushing hard seeds, or remain more delicate, thereby allowing the rapid movements needed for more elaborate songs. “Singing a complex song like a swamp sparrow requires considerable motor skills, and the large, powerful beak is too clumsy to manage the necessary movements,” says Podos. .

Thanks to decades of quantitative research carried out by the broader biological community on the exact changes that Darwin’s finch beaks undergo due to various environmental changes, Podos has a good idea of ​​how beaks will change in the future. I realized that I could model something like this.

In this case, he chose drought as the environmental factor, which tends to select for thick-billed finches. And he knew he could predict and simulate how finch songs would change with future drought episodes.

“Essentially, we engineered the future finch song,” Podos says.

Generally, the thicker the beak, the slower the song and the narrower the frequency bandwidth. With each subsequent drought, their beaks are predicted to grow thicker, their speeds to slow further, and their song bandwidth to decrease.

Finally, Podos and his team returned to Darwin’s specific population of mesoterranean finches and let them listen to future finch calls.

“We found that when calls equivalent to three drought events were simulated, there was no change in finches’ responses to the modified calls,” said co-author and co-author of the study at the time. Katie M. Schroeder says. I received my doctoral training under Podos at Amherst College. “But by six droughts, the finches had changed to the point where they were almost unresponsive.”

These findings suggest that an entirely new species of Darwin’s mesoterranean finch, associated with its beak and song, may have evolved in response to six major droughts in the Galapagos.

“Our research is not a conceptual revolution,” Podos says. “It is an empirical, experimental confirmation of ecological speciation and its validity.”