With a finch and a fish, this scientist changed our understanding of the tree of life

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On the Galápagos Islands, a ground finch that usually nibbled on small, soft seeds was forced during a drought to eat larger, harder ones.

Within a few generations, the bird developed a larger but shorter beak better suited for cracking large seeds.

The ground finch is one of at least 15 species of Galapagos finches descended from a common ancestor that flew on one fateful day about 2 million years ago, possibly carried off to South America or central.

Another finch uses twigs or cactus thorns to dislodge and nibble insects, while another, nicknamed the vampire finch, has developed a particularly sharp beak that allows it to peck seabirds and feed on their blood.

“A bunch of species all descending from one ancestor proliferated, so there are many species now. And they all do different things,” said Dolph Schluter, professor of zoology at Columbia University. Briton in Canada, who began studying finches in the late 1970s.

“Most of them exploit the environment in different ways. There are large beaks and small beaks. There are sharp beaks and dull beaks.

The Royal Swedish Academy of Sciences awarded Schluter the prestigious Crafoord Prize for his work on the mechanics of evolution, which fundamentally changed our understanding of how the tree of life branches. The award is seen as a complement – ​​and for some laureates, a precursor – to a Nobel Prize.

With their isolation and rich biodiversity, the Galapagos Islands have long served as a living laboratory for understanding evolution – and finches have played an illuminating role in the history of life on our planet.

These bird species, along with other island animals, inspired Charles Darwin’s theory of evolution and, 150 years later, enabled Schluter to demonstrate that Darwin’s theories of natural selection are true. In practice.

For Darwin, evolution was largely a thought experiment inspired by what he saw in nature, but Schluter’s work, in the field and in the laboratory, revealed and fleshed out the ecological mechanisms that lead to creation. new species.

In the Galapagos, Schluter found that when two finch species coexist on the same island, the differences in beak size and shape are more dramatic than when the same two species were found separately on different islands.

For Schluter, this phenomenon signaled that the competitive interaction between birds was a mechanism that led to the formation of new species.

An illustration showing the variation in beak size of four of the finch species observed by Chalres Darwin on the Galapagos Islands.  The study of island fauna contributed to Darwin's theory of evolution.

“I was particularly interested in … how competitive interactions — competition for food — made them so much more different than they otherwise would have been,” Schluter said. “And that seems to be a common explanation for the diversity of forms.”

This discovery contradicts the idea received at the time according to which a new species would not arise if the existing population was always in contact and exchanged genes.

Prior to Schluter’s observations of Galapagos finches, evolutionary biologists believed that new species arose primarily through isolation – when one population separated geographically from another and, because of that isolation, accumulated genetic changes. by chance mutations.

“Evolutionary biologists were much more focused and interested in the genetic mechanism. They missed what was happening in nature,” said Kerstin Johannesson, professor of marine ecology at the University of Gothenburg in Sweden and member of the Royal Swedish Academy of Sciences.

“With really elegant experiments and really smart analytical tools, Dolph more or less convinced us all that this (ecology) was really at the center of this process.”

The explosive evolution of a population into a multitude of new species is known as adaptive radiation, and some consider Schluter’s 2000 book, “The Ecology of Adaptive Radiation”, to be one of the most important on evolution since Darwin’s “Origin of Species”.

The Lesser Ground Finch (Geospiza fuliginosa), another of the species studied by Schluter, is pictured on a branch, Urbina Bay, Isabela, Galapagos Islands.

While Schluter launched his scientific career with the famous Galapagos finches, he turned to the humble sticklebacks to further test his ideas.

A relatively young species, this fish lives mainly in the ocean but migrates to freshwater lakes to reproduce. Sometimes it can wash up in lakes and become a permanent freshwater resident.

Schluter has used this feature to its advantage, digging 13 ponds (now 20), each slightly larger than a basketball court, on the University of British Columbia’s South Campus. He and his team used the ponds, acting as island analogues, to study how sticklebacks adapted to a freshwater environment and acquired different traits.

Gradually, differences appeared between fish in the same lake – some lived at the bottom, while others preferred open, open water. After generations of adapting to different habitats for a few years, the differences were such that the two types no longer mated.

With colleagues, he also uncovered the genetic underpinnings of these changes in sticklebacks.

Johannesson said Schluter’s work could help scientists understand how the natural world might change in response to the climate crisis.

“In the ponds, he could see that the evolution was really fast. Of course, this type of evolution does not wait for new mutations but works on the variation already present in the population,” she said in a video produced by the Royal Swedish Academy of Sciences.

“This is relevant, especially now, when the climate is changing. Because we need to know how species can adapt to a changing climate.

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