Playing songs to Darwin’s finches helps confirm link between environmental change and emergence of new species

Date:


The beaks of Darwin’s medium ground finches can evolve to crush the shells of hard seeds. Credit: Andrew Hendry

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 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 Galapagos 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.

The new study shows that beak-driven changes to songs themselves can impact species recognition, and thus drive the separation of species.

“I started working with these birds 25 years ago,” says Jeffrey Podos, professor of biology at UMass Amherst and the paper’s senior author. “In my very first publication on the finches, back in 2001, I showed that changes in the beaks of Darwin’s finches lead to changes in the songs they sing, and I speculated that, because Darwin’s finches use songs to attract mates, then song changes related to beak evolution could perhaps catalyze ecological speciation.”

But, at the time, Podos had no smoking-gun experimental evidence with which to prove his hypothesis that environmentally-driven changes to beak shapes were driving the emergence of new finch species.

Part of the difficulty is that speciation is an historical process, which makes it tricky to document. Being able to watch it unfold as it happens would be like catching lightning in a bottle. As a workaround, Podos devised an experimental study that built on simulations, and he had some helpful leads to work with.







The mating song of a male Darwin’s medium ground finch. Credit: Jeff Podos

He knew, for instance, that beaks can either evolve powerfully to crush hard seeds or they can remain more delicate, thereby enabling the faster movements necessary for more elaborate singing. “It takes serious motor performance to sing an intricate song, like that of the swamp sparrow,” says Podos, “and a big, powerful beak is just too clunky to manage the movements required.”

Thanks to decades’ worth of quantitative research that the wider biology community has conducted on the exact changes that the beaks of Darwin’s finches undergo due to different environmental changes, Podos realized that he could model how beaks would change into the future.

In this case, he chose drought as the ecological driver, which tends to select for thicker-beaked finches. And he also knew that he could both predict, and then simulate, the songs of the finches as they would change through successive future episodes of drought.

“Essentially, we engineered the calls of future finches,” says Podos.

In general, the thicker the beak, the slower the songs and the narrower the bandwidth of the frequencies. Each subsequent drought event is predicted to render beaks that are increasingly thicker, which should further slow the rate and decrease the bandwidth of the songs.

How playing songs to Darwin's finches helped UMass Amherst biologists confirm link between environment and the emergence of new species
Each drought event should increase the beak depth, which should in turn drive changes to the Darwin’s medium ground finch song (l). The right panel gives a graphical representation of simulated beak changes and a spectrogram showing the corresponding projected changes in vocal performance. Credit: Podos et al. 2024.

Finally, Podos and his team returned to the specific population of Darwin’s medium ground finches and played them the calls of the future finches.

“We found that there were no changes in the finches’ responses to our modified calls even when the simulated songs had changed by the equivalent of three drought events,” says Katie M. Schroeder, the paper’s co-author who participated in this research during her doctoral training under Podos at UMass Amherst. “But by six drought events, they had changed so much that the finches barely responded at all.”

These findings suggest that, because of the links between beaks and song, an entirely new species of Darwin’s medium ground finches could evolve in response to six major Galapagos droughts.

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

More information:
Jeffrey Podos, Ecological speciation in Darwin’s finches: Ghosts of finches future, Science (2024). DOI: 10.1126/science.adj4478. www.science.org/doi/10.1126/science.adj4478

Citation:
Playing songs to Darwin’s finches helps confirm link between environmental change and emergence of new species (2024, October 10)
retrieved 10 October 2024
from https://phys.org/news/2024-10-playing-songs-darwin-finches-link.html

This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no
part may be reproduced without the written permission. The content is provided for information purposes only.



Share post:

Subscribe

Popular

More like this
Related