They say hindsight is always clear, and while the theory of ecological speciation—which suggests that new species develop due to environmental changes—appears to be validated with the benefit of hindsight, proving it through experiments has been challenging until now. Recent research has highlighted a significant link between ecology and speciation in Darwin’s finches, renowned inhabitants of the Galapagos Islands in Ecuador. Earlier studies established that these birds adapt their beak shapes to different ecological conditions, which in turn influences their vocalizations. However, prior to this study, no one could experimentally demonstrate that these adaptations lead to the creation of new species. The breakthrough in this research comes from examining the potential “ghosts” of future finches.
They say that hindsight is 20/20, and though the theory of ecological speciation — which holds that new species emerge in response to ecological changes — seems to hold in retrospect, it has been difficult to demonstrate experimentally, until now. In research recently published in Science, biologists from the University of Massachusetts Amherst have identified a key connection between ecology and speciation in Darwin’s finches, famous residents of the Galápagos Islands, Ecuador. Prior work on these birds had established that birds’ beaks adapt to changing ecological environments, and that beak changes affect how the birds sing. But, until this paper, no one has yet been able to experimentally show that such changes drive the emergence of new species. The innovative key to this discovery? The ghosts of future finches.
In a recent study published in Science, researchers from UMass have established a connection between ecology and the development of new species in Darwin’s finches, well-known inhabitants of the Galápagos Islands, Ecuador. Earlier studies have shown that these finches alter their beak shapes in response to different ecological environments, which also influences their songs. The new findings demonstrate that changes in song due to alterations in beak shape can affect species recognition and, consequently, lead to the separation of species.
“I began studying these birds 25 years ago,” says Jeffrey Podos, a biology professor at UMass Amherst and the principal author of the paper. “In my first research on the finches back in 2001, I showed that the birds’ beak changes result in song alterations, and I suggested that since they use songs to attract mates, these song changes associated with beak evolution might actually trigger ecological speciation.”
However, at that time, Podos lacked direct experimental evidence to support his theory that environmentally-induced beak shape changes were responsible for the formation of new finch species. The challenge lies in the fact that speciation is a historical process, making it difficult to observe. Witnessing it unfold in real-time would be akin to capturing lightning in a bottle. To tackle this, Podos designed an experimental study based on simulations and had valuable insights to guide him.
He understood that beaks can either evolve to crush hard seeds effectively or remain more refined, allowing for the intricate movements required for complex singing. “Singing a detailed song, like that of the swamp sparrow, demands excellent motor skills,” explains Podos, “and a big, powerful beak is simply too unwieldy for such precise movements.”
Thanks to years of extensive quantitative research on how the beaks of Darwin’s finches respond to various environmental factors, Podos realized he could predict future changes in beak shapes. He focused on drought as the ecological factor, which typically favors finches with thicker beaks. He also recognized that he could predict and simulate the songs of the finches as they might evolve through repeated drought episodes.
“Essentially, we designed the calls for future finches,” Podos states.
Generally, thicker beaks correlate with slower songs and a narrower frequency range. Each drought event is expected to result in progressively thicker beaks, which in turn would lead to even slower songs and a further narrowing of frequency bandwidths.
Ultimately, Podos and his team returned to the specific population of medium ground finches and played them the altered calls representative of future finches.
“We observed no change in the finches’ responses to our adjusted calls, even when the simulated songs shifted as if they had experienced three droughts,” explains Katie M. Schroeder, a co-author who undertook this research as part of her doctoral training with Podos at UMass Amherst. “However, after six drought events, the songs had changed sufficiently that the finches hardly responded at all.”
This suggests that due to the association between beak shape and song, an entirely new species of Darwin’s medium ground finches could potentially emerge in response to six significant droughts in the Galápagos.
“Our research isn’t a dramatic shift in perspective,” states Podos, “but it provides empirical, experimental validation of ecological speciation and its feasibility.”
This study received support from the Charles Darwin Research Station, the Galápagos National Park Service, and the U.S. National Science Foundation.
