Genome sequencing reveals inbreeding in extinct Xerces blue butterfly

The Xerces Blue butterfly (Glaucopsyche xerces) was once found in the coastal dunes of San Francisco, USA. However, urban development caused significant destruction of its habitat, and the butterfly’s population was confined to Golden Gate National Park. Known for its stunning deep iridescent blue wings with distinct white spots on the underside, this butterfly became a symbol of human-induced extinction when the last specimens were discovered in 1941 by entomologist W. Harry Lange. In fact, it holds the unfortunate distinction of being the first insect species to become extinct in modern times. Its disappearance inspired the establishment of the Xerces Society, a renowned American conservation organization.

In 2022, a notable study led by Carles Lalueza-Fox, director of the MCNB and researcher at the IBE (CSIC-UPF), and Roger Vila, researcher at the IBE (CSIC-UPF), shed new light on the Xerces Blue butterfly. Mitochondrial DNA extracted from a specimen was compared to that of the Silvery Blue butterfly (Glaucopsyche lygdamus), its closest living relative. The study conclusively established that the two were distinct species, rather than variations within the same population.

Published in eLife, the research team successfully sequenced the genomes of four Xerces Blue butterflies and seven Silvery Blue butterflies. These specimens, aged between 80 and 100 years old, were sourced from the Smithsonian Institution in Washington. The genomic analysis revealed that the Xerces Blue and Silvery Blue butterflies diverged as separate species around one to two million years ago, representing distinct evolutionary lineages.

Furthermore, comparing the genomes provided valuable insights into the decline of the Xerces Blue butterfly population. The DNA analysis indicated a high prevalence of inbreeding, suggesting a decline in population numbers. This finding has significant implications, as it can help identify other insect species facing threats from human activities, which often lack comprehensive extinction data compared to vertebrates. The research may also pave the way for potential de-extinction projects aimed at reviving the Xerces Blue butterfly, a concept that has intrigued the scientific community for years.

The Xerces Blue genome reveals its extinction story

The findings of the research reveal a significant decline in the population of the Xerces Blue butterfly spanning several millennia, likely due to climate fluctuations that did not impact the Silvery Blue butterfly. Nevertheless, it was human-induced habitat destruction that ultimately led to the extinction of the Xerces Blue.

This conclusion was reached by analyzing the butterfly’s genome and identifying specific characteristics associated with small populations. These traits included limited genetic diversity, extended chromosomal segments devoid of genetic variation, and a high occurrence of harmful genetic variants. These factors collectively compromised the survival chances of individuals, rendering the Xerces Blue butterfly highly susceptible to external threats and classifying it as a vulnerable species.

Genomic clues could save other endangered insects

The Xerces Blue butterfly has become an emblematic symbol of insect extinction worldwide. However, there is newfound hope that its genome can play a vital role in preventing the extinction of other endangered insects, especially those whose population declines may not be immediately evident.

According to Roger Vila, a researcher from the Institute of Evolutionary Biology (IBE) at CSIC-UPF and co-leader of the study, detecting endangered mammalian species is relatively simpler since we can often count the number of individuals. In contrast, numerous endangered insect species go unnoticed due to the inherent challenge of accurately assessing their populations. Despite appearing abundant to us, these insects can be highly vulnerable to climate fluctuations and human activities such as pesticide usage.

Thus, the study’s team believes that by identifying genomic traits indicative of the Xerces butterfly’s population decline, they can serve as an early warning system. These traits have the potential to assist future studies in detecting and safeguarding other vulnerable insect species that may be facing similar threats, even if their dwindling populations are not readily apparent.

Knowing the whole genome is the first step towards de-extinction

The decline of insects, particularly pollinators, poses a significant ecological crisis on a global scale. Consequently, the scientific community is highly intrigued by the prospect of using genetic engineering techniques, specifically CRISPR, to de-extinct species like the Xerces Blue butterfly.

The Xerces Blue butterfly stands out as a promising candidate for de-extinction due to several factors. Firstly, its disappearance occurred relatively recently, which means that its reintroduction would have a lesser ecological impact. Additionally, there are no concerns regarding the species becoming pests or experiencing excessive proliferation since the adults only appear for a limited period, typically between March and April. Furthermore, the Xerces Blue butterfly exhibits ecological specialization, further reducing potential risks associated with its reappearance.

Carles Lalueza-Fox, a researcher from the Institute of Evolutionary Biology (IBE) at CSIC-UPF and director of the Natural Sciences Museum in Barcelona, who co-led the study, emphasizes the significance of obtaining the complete genome of the Xerces Blue butterfly. Having this genetic information is anticipated to facilitate future de-extinction endeavors, opening possibilities for conservation and restoration efforts.

Source: Spanish National Research Council

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