One definitive way to link ecological changes to evolution would require a time machine. Traveling both backward and forward would allow observers to see how particular animals adapt to changes in climate, environment, or other variables.
Since no such machine exists — except in the movies — a group of researchers leaned on the next best thing: data and experiments. By doing so, this group is the first to link ecological changes to a species’ adaptation — a phenomenon known as “speciation,” according to a report in Science.
The Importance of Darwin’s Finches
The group turned to a well-studied species — the so-called Darwin’s Finches, named because the famous scientist, Charles Darwin, observed them on the Galapagos Islands.
In a study 25 years ago, Jeffrey Podos, a University of Amherst biologist, showed that changes in the beaks of Darwin’s finches affects how they sing. He then speculated that that when the birds would start singing a different tune, they could attract different mates, which could then lead to further evolutionary change. But he had no way then of proving that hypothesis.
Other biologists had studied beak changes in the birds for decades. They found, for instance, that drought tends to select thicker-beaked birds for survival, because those kinds of beaks can crack nuts effectively. Longer, thinner beaks are good for hunting insects, which are rarer in prolonged dry conditions.
Beaks’ shapes then affect the songs the finches sing, which, in turn can attract different potential mates.
“If the beaks are impacting the way that these birds sing, does that impact subsequent species recognition?” says Podos. “It’s actually pretty tricky to test.”
Read More: Here Are Some of Darwin’s Strangest Animal Discoveries
Understanding Finch Evolution Through Time
The tricky part is to determine when, exactly a species changes sufficiently enough to be considered different. In the case of birds, one population descended from a single species might use seeds as its main food source. That population, over time, would develop short, thick beaks, good for crushing seeds.
Another population — again, descended from the same species, might live in a forest and predominantly dine on bugs. Over time, they would develop small, dainty beaks that are good for catching insects.
“But then the real question is, are they different?” says Podos. “And when are they different?”
To answer that question, Podos essentially simulated a time machine. Going backwards was relatively easy, because biologists have accumulated decades of data on finch beaks’ size and shape in relationship to the environment in which they live. They also knew the differences in finch songs as related to beak size and shape.
Going forwards was trickier. It would require an experimental simulation — and that simulation would rely on song.
“Let’s imagine what would happen if you have one subpopulation facing all these droughts and then seeing beak evolution and then songs changing in a certain way and, and that all is based on actual data,” says Podos.
Read More: How Does Speciation Drive Evolution?
Drought Conditions Linked to Beak Size
The researchers knew from earlier work that drought conditions produce birds with thicker beaks, which, in turn results in lower frequencies. So they recorded many finch songs from many generations, as the beaks thickened and the song frequency lowered.
Then they returned to the original population of finches they had been studying and essentially had a bird song listening party. The researchers played successive generations of songs — each with a lower frequency than the one before. The first three generations of change didn’t phase the finches. But after three more, they barely responded to the music at all.
Podos says the study was gratifying, because it demonstrated how data and experimentation support a theory he formed decades earlier. It also represents a solid example of adapting the scientific method to explain an aspect of evolution.
“We can actually collect data, and we find that indeed the ecological differences or the ecological variations can impact the origin of species,” says Podos. “We’re connecting adaptation to speciation.”
Read More: Why Is Darwin Island in the Galapagos Off-Limits to Visitors?
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Before joining Discover Magazine, Paul spent over 20 years as a science journalist, specializing in U.S. life science policy and global scientific career issues. He began his career in newspapers, but switched to scientific magazines. His work has appeared in publications including Science News, Science, Nature, and Scientific American.
