More than a century ago, a bluish butterfly fluttered among the sand dunes of San Francisco’s Sunset District, laying its eggs on a plant known as deer weed. When the development of the city overtook the dunes and the deer weed, the butterflies disappeared too. The last Xerces blue butterfly was collected from Lobos Creek in 1941 by an entomologist who would later regret killing one of the last living members of the species.
But was this butterfly really a unique species?
Scientists all agreed that the grim fate of the Xerces blue — the first butterfly known to be extinct in North America due to human activities — was a biodiversity loss. But they were divided on whether Xerces was its own separate species, a subspecies of the widespread silver-blue butterfly Glaucopsyche lygdamus, or even just an isolated population of silver-blue butterflies.
This may seem like a scientific complaint, but if Xerces blue wasn’t, in fact, a genetically distinct lineage, it wouldn’t technically be actually extinct.
Now, researchers have sequenced a nearly complete mitochondrial genome from a 93-year-old museum specimen, suggesting that the Xerces blue was a separate species, which they say could be properly named Glaucopsyche xerces, according to an article published Wednesday. has been published in Biology Letters. .
“It shows how crucial it is to not only collect specimens, but to protect them,” said Corrie Moreau, the director and curator of Cornell University’s insect collection and an author on the paper. “We can’t imagine how they will be used in 100 years.”
Durrell Kapan, a senior research fellow at the California Academy of Sciences who was not involved in the study, said he found the new findings “suggestive and very exciting,” but added that there could be limits to this type of research because “what makes two organisms different species is not always directly addressable with genetic information.”
dr. Kapan is working on a separate genomic project on Xerce’s blue butterflies and close relatives with Revive & Restore, a non-profit initiative to restore extinct and endangered species through genetic engineering and biotechnology.
The researchers started the project several years ago when Dr. Moreau at the Field Museum in Chicago. She and Felix Grewe, now the director of the phylogenomics initiative at the Grainger Bioinformatics Center at the museum, searched the museum archives of Xerce’s blue butterflies to find the least damaged specimen, which theoretically would produce the best-preserved DNA.
“You grind up a piece of an extinct butterfly,” said Dr. Moreau. “You only get one chance.”
dr. Moreau removed a third of the butterfly’s abdomen, a body part full of muscle, fat and other tissues, and sequenced it. DNA this old degrades into short fragments. Historically, researchers would sequence long, uninterrupted stretches of DNA by chopping it up and puzzling it back together. But with new sequencing technology, researchers can work with already chopped, fragmented DNA. “We’re just leaving that step out,” said Dr. Grewe.
After recovering their sequences, the researchers examined publicly available data from other related butterfly specimens.
Their mitochondrial DNA sequences did not resemble each other. They suggested that the Xerces blue was a separate species and that two other butterflies traditionally believed to be subspecies of the silvery blue butterfly – the australis and pseudoxerces clades – may also be different species, and are the closest living relatives of the Xerces – blue.
These results are surprising, as these two butterflies are found in Southern California, far from the Xerces Blue’s original home on the San Francisco Peninsula.
The new paper’s sequencing focused on the mitochondrial gene that codes for the CO1 streak. Mitochondrial DNA is an excellent option for older museum specimens because a single cell contains many more copies of the mitochondrial genome than the nuclear genome, the researchers said. Mitochondrial DNA is inherited from the mother while nuclear DNA is inherited from both parents.
But the CO1 gene represents a “very small sample of the genome,” said Dr. Kapan, adding that he didn’t think the new article finally settled the species debate.
At the California Academy of Sciences, Athena Lam, a genomics researcher, Dr. Kapan and others, clarify where Xerces falls on the evolutionary scale, said Dr. Lamb.
These kinds of genomic studies, said Dr. Kapan, could reveal where to find populations of surviving species in the genus Glaucopsyche that could be well suited for possible reintroduction into the San Francisco sand dunes. According to the new paper, australis or pseudoxerces would be good candidates to investigate, the latter of which has wings reminiscent of Xerces’ brilliant blue hue.
dr. Moreau said she hoped the new study would shed light on blue butterflies that are currently threatened, such as the El Segundo blue, which lives in coastal sand dunes in Southern California, and the Karner blue, which is the most common. occurs in Wisconsin, where wild lupines grow.
And while the Xerces blue is long gone, the deer weed it once needed has recently been replanted in the sand dunes at the Presidio, in anticipation of a somewhat familiar future butterfly.