It’s been nearly 80 years since the Xersis blue butterfly was last seen flying on pastel wings across the coastal sand dunes of California. 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. Moreover, this discovery means that the blue butterfly Xerces (Zerzat Glucophage) is the first insect species in the United States known to be extinct by humans, researchers report July 21 in Biology Letters.
The butterfly lived only on the San Francisco Peninsula. But by the early 1940s, less than a century after its official scientific description in the 1850s, the evil-winged butterfly had disappeared. Its rapid disappearance is attributed to the loss of habitat and local plant food as a result of urban development, and possibly the spread of an influx of invading ants despite cargo shipping.
It’s not yet clear if the Xersis blue butterfly is its own species, or just an isolated group of another, more widespread species of blue butterfly, says Cory Morrow, an entomologist at Cornell University.
To find out, Morrow and his colleagues turned to a 93-year-old sample of Xerces housed at the Field Museum in Chicago, to extract DNA from a small portion of the insect’s tissue. Although the DNA deteriorates with age, the team can compare identified Xerces genes with those of other closely related blue butterflies. The researchers also compared the genomes, or genetic instruction books, to the insects’ mitochondria — cellular structures involved in energy production and which have their own set of DNA.
Using genes and “myogenomes,” the researchers created an evolutionary tree, showing how all species of butterflies are related to each other. The team found that the extinct Zerses blue butterfly was genetically distinct, warranting classification as a species.
“We kind of lost a piece of the biodiversity puzzle that was the fabric of the San Francisco Bay Area when this species was driven by extinction,” Morrow says.
Akito Kuwahara, a wing-thermal specialist at the Florida Museum of Natural History in Gainesville, thinks the results are “fairly convincing” that the Zerses blue butterfly is its own species.
The butterfly is considered a candidate for resurrection, says Moreau, in which extinct species are brought back by cloning or other genetic manipulation (SN: 10/20/17). But she warns against it. “Maybe we should spend that time, energy and money ensuring that the already threatened blues we know about are protected,” she says.
One of these insects is the endangered El Segundo blue (Euphilotes battoides allyni), is native to the Los Angeles area. She and other butterfly populations are increasingly endangered by many threats, such as climate change, changes in land use and the use of pesticides (SN: 8/17/16).
For Felix Grewe, an evolutionary biologist at the Field Museum, the new discovery explains why long-term museum collections are important: The usefulness of real specimens may not be clear for many years. After all, the genetic techniques used in the study to shed light on the true identity of the Xerces blue butterfly were not there when the insect became extinct.
“You don’t know what technology is there [will be] 100 years from now,” says Grewe.