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How Ecotypes Harbor the Genetic Memory of a Species’ Past
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genomics
How Ecotypes Harbor the Genetic Memory of a Species’ Past
By
Marlowe Starling
May 21, 2026
Evolutionary biologists are uncovering genomic mechanisms that allow populations to adapt quickly to different, hyperlocal habitats without splitting into new species.
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The green ecotype of Cristina’s timema, a species of stick insect, blends in with broad leaves. Other ecotypes of the same species are colored to blend in with narrower leaves. With genomics, scientists are answering century-old questions about how a single species can manifest such distinct traits.
Aaron Comeault
Introduction
By Marlowe Starling
Science Writing Fellow
May 21, 2026
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biology
DNA
ecology
evolutionary biology
genome
genomics
memory
natural selection
species
All topics
When she was a graduate student in the 1970s, the evolutionary biologist Kerstin Johannesson regularly walked the shores of a Swedish archipelago, scanning the ground for pebbles that moved: marine snails. Her adviser, a taxonomist, had tasked her with describing the species present there by documenting their traits. She noticed that snails with thicker shells stayed on the shore, while those with thinner shells seemed to prefer wave-battered rocks, and in between the two habitats were snails with intermediate shell thickness. While they seemed like distinct species, Johannesson couldn’t help but wonder whether these snails might instead be different types of the same one.
Around 50 years earlier, the botanist Göte Turesson had had a similar revelation in a similar setting. As he walked Sweden’s shores, he noticed that saltbush plants from different stretches of coastline had distinct traits — earlier or later flowering times, or shorter or longer stalks — and between habitats, those traits fell somewhere in the middle. He bred the plants in his home garden and found that these distinct traits had a genetic basis even though they arose from the same species. In 1922, he published his results and coined the term “ecotype” to describe a subpopulation of a species adapted to a hyperlocal habitat.
At that time, the definition of a species was even less clear than it is today. Genes were still theoretical, and the structure of DNA wouldn’t be discovered for another 30 years. Turesson “struggled to be accepted,” said Johannesson, now the director of Tjärnö Marine Laboratory at the University of Gothenberg. How can a species contain multiple distinct phenotypes — or sets of traits — without separating into two species? “He had quite a job to try to convince his colleagues that there were inherited differences and local adaptation within species,” she said.
It wasn’t until the early 2000s, when whole-genome sequencing became accessible to evolutionary biologists, that Turesson’s ideas about ecotypes could be tested. By comparing the DNA sequences of ecotypes across the tree of life — from marine snails to stickleback fish to stick insects and more — scientists can study adaptation and speciation, the process by which new species form, at a molecular level.
Since the 1970s, the evolutionary biologist Kerstin Johannesson has tried to understand how various forms of marine snail could possibly represent the same species.
Bo Johannesson
“It’s by far the most exciting time to be a biologist, ever, in my opinion — maybe with the exception of going right back to Darwin,” said Sean Stankowski, an evolutionary geneticist at University College London. “Even when we understood that organisms were programmed by genetic code, we could really never access that. Now, we’re looking at every single [nucleotide molecule] — A, T, G, and C [adenine, thymine, guanine, and cytosine] — in the genome.”
An analysis of genomic ecotypes by Johannesson, Stankowski, and other researchers explains how some species can maintain the DNA sequences for multiple adaptations, allowing evolutionary processes to effectively select among ecotypes as environmental conditions change — sometimes within only a few generations. The data also suggests that some canonically diverse groups of species, including Darwin’s finches, may not be separate species at all, but rather different ecotypes of the same species.
Ecotypes represent a kind of “genetic memory,” Stankowski said, that reflects a species’ history of...