It’s been roughly 80 years since the Xerces blue butterfly was last spotted flitting about on pastel wings across coastal California sand dunes. But scientists are still learning about the insect.
New research on DNA from a nearly century-old museum specimen shows that the butterfly was a distinct species. That finding means that the Xerces blue butterfly (Glaucopsyche xerces) is the first U.S. insect species that scientists recognized went extinct because of humans, researchers report July 21 in Biology Letters. There are insects that went extinct earlier, like the Rocky Mountain locust (Melanoplus spretus), that scientists have strong suspicions that humans were to blame for the extinction. But for this butterfly, there was no question at the time.
The butterfly used to live only on the San Francisco Peninsula. But by the early 1940s, less than a century after its formal scientific description in the 1850s, the gossamer-winged butterfly had vanished. Its rapid disappearance is attributed to the loss of habitat and native plant food as a result of urban development and, possibly, an influx of invasive ants likely spread though the shipment of goods.
But it’s long been unclear if the Xerces blue butterfly was its own species, or simply an isolated population of another, more widespread species of blue butterfly, says Corrie Moreau, an entomologist at Cornell University.
To find out, Moreau and colleagues turned to a 93-year-old Xerces specimen housed at Chicago’s Field Museum, extracting DNA from a tiny bit of the insect’s tissue. Despite the DNA being degraded from age, the team could compare selected Xerces genes with those of other closely related blue butterflies. The researchers also compared the genomes, or genetic instruction books, of the insects’ mitochondria — cellular structures involved in energy production that have their own set of DNA.
Using the genes and the “mitogenomes,” the researchers crafted an evolutionary tree, showing how all of the butterfly species are related to each other. The extinct Xerces blue butterfly was genetically distinct, thus warranting classification as a species, the team found.
“We sort of lost a piece of the biodiversity puzzle that made up the tapestry of the San Francisco Bay area when this species was driven to extinction,” Moreau says.
Akito Kawahara, a lepidopterist at the Florida Museum of Natural History in Gainesville not involved with the study, thinks the results are “fairly convincing” that the Xerces blue butterfly was its own species.
The butterfly is considered a candidate for resurrection, Moreau says, where extinct species are brought back via cloning or other genetic manipulations (SN: 10/20/17). But she cautions against it. “Maybe we should spend that time and energy and money on ensuring that we protect the blues that are already endangered that we know about,” she says.
One of these insects is the endangered El Segundo blue (Euphilotes battoides allyni), native to the Los Angeles area. It and other butterfly populations are increasingly imperiled by numerous threats, such as climate change, land-use changes and pesticide use (SN: 8/17/16).
For Felix Grewe, an evolutionary biologist at the Field Museum, the new finding illustrates why long-term museum collections are so important: Specimens’ true utility may not be clear for many years. After all, the genetic techniques used in the study to illuminate the Xerces blue butterfly’s true identity didn’t exist when the insect went extinct.
“You don’t know what technology there [will be] 100 years from now,” Grewe says.
