CM – DNA from a 93-year-old butterfly confirms the first US case of human-made insect death


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July 20, 2021

from Field Museum

The blue Xerces butterfly was last seen flapping its iridescent evergreen wings in San Francisco in the early 1940s. It is generally accepted that it was extinct, the first American insect species to be destroyed by urban development, but the question remains whether it was really a species or just a subpopulation of another common butterfly. In a new study in Biology Letters, researchers analyzed the DNA of a 93-year-old blue specimen of Xerces in museum collections and found that its DNA was unique enough to be considered a species. The study confirms that the Xerces blue was indeed extinct and that insect repellent is something we need to take seriously.

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« It is interesting to reiterate that what people have been thinking for almost 100 years is true, that this was a species that was driven to extinction by human activity, » says Felix Grewe, co-director of the Grainger Bioinformatics Center des Field and lead author of the Biology Letters paper on the project.

“For a long time the question was whether the blue Xerces butterfly is really its own species or just a population of a very widespread species called silver blue, the found all over the west coast of North America, ”said Corrie Moreau, director of Cornell University Insect Collections, who began working on the study as a researcher at the Field Museum in Chicago. “The widespread silvery-blue species has many of the same characteristics. But we have several specimens in the Field Museum collections, and we have the Pritzker DNA Laboratory and the Grainger Bioinformatics Center, which has the capacity to sequence and analyze a lot of DNA, so we decided to see if we could answer that question can finally solve. « 

To see if the Xerces blue was really a species of its own, Moreau and her colleagues turned to butterfly specimens stuck in drawers in the field’s insect collections with tweezers she cut a tiny piece off a belly she had collected in 1928. « It was nerve-wracking because you want to protect as much of it as possible, » she recalls. « Taking the first steps and peeling off part of the belly was very exhausting, but it was also kind of intoxicating to know that we may be able to answer a question that has been unanswered for almost 100 years and to which no other one can be answered. « 

After the butterfly’s body piece was recovered, the sample was sent to the Field Museum’s Pritzker DNA Laboratory, where the tissue was treated with chemicals to isolate the remaining DNA. « DNA is a very stable molecule; it can survive long after the cells in which it is stored have died, » says Grewe.

Although DNA is a stable molecule, it is broken down over time. There is DNA in every cell, however, and by comparing multiple strands of DNA code, scientists can piece together what the original version looked like. “It’s like making a series of identical structures out of Legos and then dropping them. The individual structures would be broken, but if you look at them all together, you could find out the shape of the original structure, ”says Moreau.

Grewe, Moreau and their colleagues compared the genetic sequence of the blue Xerces butterfly with the DNA of the spread the silvery blue butterfly and found that the DNA of the blue Xerces butterfly was different, meaning it was a species of its own.

The study’s results have far-reaching implications. “The Xerces blue butterfly is the most iconic insect for conservation because it is the first insect in North America that we know has been eradicated by humans. There is an insect protection society named after him, ”says Moreau. « It’s really horrible that we made something extinct, but at the same time we’re saying, okay, everything we thought actually matches the DNA evidence that it is an extinct species, it could potentially undermine conservation efforts. »

DNA analysis of extinct species sometimes raises questions about bringing the species back, à la Jurassic Park, but Grewe and Moreau state in their paper that these efforts could better be used to protect species that still exist. « Before we If we start to put a lot of effort into the resurrection, we should strive to protect what is there and learn from our past mistakes, « says Grewe.

Moreau agrees, pointing out the urgent need to protect insects. « We are in the middle of the so-called insect apocalypse – a massive decline in insects is being noted worldwide, » says Moreau. « And although not all insects are so charismatic are like the blue Xerces butterfly, they have a huge impact on the functioning of ecosystems. Many insects are the basis of what keeps many of these ecosystems healthy and which then feeds the herbivores who then feed the carnivores. Every loss of an insect has a massive impact on ecosystems. « 

In addition to the effects of the study on conservation, Grewe shows that the project shows the importance of museum collections. » When this butterfly was collected 93 years ago, nobody thought of it to sequence his DNA. That is why we have to keep collecting, for researchers 100 years in the future.  »

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