Hindsight is often said to be 20/20. While the theory of ecological speciation—the idea that new species arise due to changes in their environment—has seemed plausible in hindsight, proving it through experiments has been challenging until now. In a recent study published in Science, biologists from the University of Massachusetts Amherst have uncovered a significant link between ecology and species formation in Darwin’s finches, well-known inhabitants of the Galápagos Islands, Ecuador. Previous research showed that the beaks of these birds adapt to shifting environmental conditions, and these beak adaptations influence their singing. However, until this study, no one had successfully experimentally demonstrated that these changes contribute to the formation of new species. The unique aspect of this finding? The predictions of future finches.
Recent research from UMass published in Science reveals a connection between ecological conditions and the emergence of new species in Darwin’s finches, renowned inhabitants of the Galápagos Islands, Ecuador. Earlier studies have established that the shapes of the birds’ beaks change in response to their environments, and these alterations affect their songs. The current study indicates that changes in songs driven by beak evolution can influence how species recognize one another, thus promoting species differentiation.
“I’ve been studying these finches for 25 years,” remarks Jeffrey Podos, UMass Amherst biology professor and lead author of the paper. “In my first publication on them back in 2001, I demonstrated that variations in the beaks of Darwin’s finches lead to differences in their songs, and I suggested that since these birds use songs for attracting mates, alterations in song related to beak evolution might spur ecological speciation.”
However, during that time, Podos lacked definitive experimental proof to validate his theory that environmentally induced changes in beak shapes were responsible for creating new finch species. Documenting speciation is challenging because it is a historical process. Observing it as it happens would be akin to capturing lightning in a bottle. To tackle this, Podos designed a study that incorporated simulations and had valuable prior data to work with.
He recognized that beaks can evolve to be either robust for crushing tough seeds or remain more delicate, allowing for quicker movements needed for elaborate singing. “Performing an intricate song, like that of the swamp sparrow, requires considerable motor skill,” explains Podos, “and a large, powerful beak simply can’t manage the movements required.”
Taking advantage of extensive quantitative studies conducted over decades on how Darwin’s finch beaks adapt due to various environmental changes, Podos realized he could predict future beak transformations. He selected drought as an ecological factor, known to favor thicker-beaked finches. He also understood that he could foresee and simulate how the finches’ songs would evolve during successive drought episodes.
“In essence, we created the calls of future finches,” states Podos.
Generally, thicker beaks lead to slower songs and a narrower range of frequencies. Each drought event is expected to produce beaks that are progressively thicker, which in turn is likely to slow their singing and reduce the bandwidth of their songs further.
In their findings, Podos and his team returned to a population of Darwin’s medium ground finches and played them the simulated calls of their future counterparts.
“We observed that there were no changes in the birds’ reactions to our adjusted calls even after the simulated songs had altered as if there had been three drought events,” comments Katie M. Schroeder, the paper’s co-author, who conducted this research during her doctoral studies under Podos at UMass Amherst. “However, after six drought events, the songs had changed to such an extent that the finches hardly responded at all.”
These results imply that, due to the connections between beak shapes and songs, a completely new species of Darwin’s medium ground finches could potentially evolve following six significant droughts in the Galápagos.
“Our research isn’t a groundbreaking shift in concept,” states Podos, “but rather an empirical and experimental validation of ecological speciation and its feasibility.”
This study received support from the Charles Darwin Research Station, Galápagos National Park Service, and the U.S. National Science Foundation.
