(CN) — The Xerces blue butterfly was last seen in the early 1940s in San Francisco. The small, iridescent blue insect, originally discovered in 1852, was endemic to and once plentiful among the coastal sand dunes of the upper San Francisco Peninsula, then abruptly disappeared amid habitat loss caused by urban development.
Though the Xerces blue is typically recognized as the first American insect species destroyed by urban development, questions persisted over whether it was really its own species to begin with or simply a subpopulation of another common butterfly.
Now, an analysis of the DNA of a 93-year-old Xerces blue specimen in museum collections has confirmed that its DNA is indeed unique enough to merit consideration as its own species. The findings were published Tuesday in the journal Biology Letters.
“It’s interesting to reaffirm that what people have been thinking for nearly 100 years is true, that this was a species driven to extinction by human activities,” Felix Grewe, co-director of the Chicago Field Museum’s Grainger Bioinformatics Center and lead author of the study, said in a statement.
Scientists had debated whether the Xerces blue was really a distinct species or just a population of a plentiful species called the silvery blue butterfly that is common across the west coast of North America, according to Corrie Moreau, director of the Cornell University Insect Collections, who began work on the study as a researcher at the Field Museum.
“The widespread silvery blue species has a lot of the same traits. But we have multiple specimens in the Field Museum’s collection, and we have the Pritzker DNA lab and the Grainger Bioinformatics Center that has the capacity to sequence and analyze lots of DNA, so we decided to see if we could finally solve this question,” Moreau said in a statement.
To settle the debate, Moreau and her colleagues used forceps to extract a tiny sample from the abdomen of a Xerces blue collected in 1928 from pinned butterfly specimens stored in the drawers of the Field Museum’s insect collections.
“It was nerve-wracking,” Moreau recalled, “because you want to protect as much of it as you can. Taking the first steps and pulling off part of the abdomen was very stressful, but it was also kind of exhilarating to know that we might be able to address a question that has been unanswered for almost 100 years that can’t be answered any other way.”
The sample went to the Field Museum’s Pritzker DNA Laboratory, where the tissues were treated with chemicals to isolate the remaining DNA.
“DNA is a very stable molecule, it can last a long time after the cells it’s stored in have died,” Grewe said.
Even still, DNA degrades over time. But by comparing multiple threads of DNA code, scientists can piece together what the original version of a strand of DNA looked like.
“It’s like if you made a bunch of identical structures out of Legos, and then dropped them,” Moreau explained. “The individual structures would be broken, but if you looked at all of them together, you could figure out the shape of the original structure.”
Together with their colleagues, Grewe and Moreau compared the genetic sequence of the Xerces blue butterfly with the DNA of the silvery blue and found that the Xerces blue’s DNA was different, indicating it is a distinct species.
The findings of the study have profound implications.
“The Xerces blue butterfly is the most iconic insect for conservation because it’s the first insect in North America we know of that humans drove to extinction. There’s an insect conservation society named after it,” Moreau said.
The Xerces Society – whose tagline is “conserving the diversity of invertebrates is the biggest job in the world” – focuses on protecting pollinators, conserving endangered species and reducing pesticide use and impacts, among other efforts, according to its website.
“It’s really terrible that we drove something to extinction, but at the same time what we’re saying is, okay, everything we thought does in fact align with the DNA evidence. If we’d found that the Xerces blue wasn’t really an extinct species, it could potentially undermine conservation efforts,” Moreau said.
Grewe and Moreau’s paper highlights that there is an urgent need to protect insects.
“We’re in the middle of what’s being called the insect apocalypse,” Moreau noted. “Massive insect declines are being detected all over the world. And while not all insects are as charismatic as the Xerces blue butterfly, they have huge implications for how ecosystems function.”
She continued, “Many insects are really at the base of what keeps many of these ecosystems healthy. They aerate the soil, which allows the plants to grow, and which then feeds the herbivores, which then feed the carnivores. Every loss of an insect has a massive ripple effect across ecosystems.”
Grewe said the study also shows the importance of museum collections.
“When this butterfly was collected 93 years ago, nobody that thinking about sequencing its DNA,” he said. “That’s why we have to keep collecting, for researchers 100 years in the future.”
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