Image of a female and a male Xerces Blues on Acmispon glaber or deerweed, the plant they ate.
Newswise — The Xerces Blue moth (Glaucopsyche xerces) thrived in the sandy shores of San Francisco, USA. Urban growth wrecked much of its dwelling, leaving Golden Gate National Park as its sole refuge. Its wings bore a vibrant azure hue, adorned with distinctive white marks underneath. In 1941, entomologist W. Harry Lange discovered the final surviving individuals of this species. Its demise marks the first recorded insect extinction. The loss of this species has elevated it to an emblem of human-caused extinction, so much so that a renowned American conservation group, the Xerces Society, bears its name.
In 2022, a prior investigation successfully extracted mitochondrial DNA from a specimen of the Xerces Blue butterfly. This genetic material was then compared to that of the Silvery Blue butterfly (Glaucopsyche lygdamus), which is its nearest living kin. The study's findings unequivocally established that these two butterflies were genuinely separate species and not merely diverse populations.
Led by Carles Lalueza-Fox, the director of MCNB and a researcher at IBE (CSIC-UPF), and Roger Vila, a researcher at IBE (CSIC-UPF), a research endeavor involving the participation of Tomàs Marquès-Bonet, an ICREA researcher at the Department of Medicine and Sciences of Life (MELIS) of Pompeu Fabra University and IBE, and a professor at the same institution, has accomplished the successful sequencing of the genomes of four Xerces Blue butterflies and seven Silvery Blue butterflies. These specimens, aging between 80 and 100 years, were sourced from the Smithsonian Institution in Washington. The study, published in eLife, has enabled researchers to deduce that the divergence between the two species occurred approximately one to two million years ago, signifying their distinct evolutionary lineages.
Analyzing the genomes of both species uncovered a significant occurrence of inbreeding within the DNA of the Xerces Blue butterfly. This observation indicates a decline in population and presents an opportunity to identify other insect species at risk due to human activities. Unlike vertebrates, the extinction patterns of insects remain relatively unknown. This discovery may provide valuable insights into the conservation efforts for threatened insect species. Additionally, this breakthrough could potentially pave the way for the de-extinction of the beloved Xerces Blue butterfly—an aspiration that has captivated the scientific community for numerous years.
The Xerces Blue genome reveals its extinction story
The research findings suggest that the Xerces Blue butterfly underwent a significant decline in population spanning tens of thousands of years. This decline was likely influenced by climate changes that did not impact the Silvery Blue butterfly. Nevertheless, it was ultimately the destruction of its habitat by human activities that served as the catalyst for the eventual extinction of the Xerces Blue butterfly.
Based on the analysis of the Xerces Blue butterfly's genome, the study concluded that the species exhibited genetic characteristics commonly associated with small populations. These traits included low genetic diversity, extended chromosomal segments devoid of genetic variation, and a notable presence of detrimental alleles. These factors collectively contributed to the diminished viability of individuals and rendered the Xerces Blue butterfly a vulnerable species by today's standards.
Genomic clues could save other endangered insects
The Xerces Blue butterfly serves as a symbol of insect extinction worldwide. Presently, its genome may aid in averting the demise of additional imperiled insects, whose rapid population declines may not be readily apparent.
Roger Vila, the co-leading researcher from IBE (CSIC-UPF), explains that detecting endangered mammalian species is simpler due to the possibility of individual counting. However, numerous endangered insects remain unnoticed as their populations are exceptionally challenging to census, despite appearing abundant to us. Yet, they can be profoundly affected by climate fluctuations and human activities, such as pesticide usage. Therefore, we believe that the genomic characteristics indicating the decline of the Xerces butterfly population could serve as an alert, aiding us in identifying vulnerable insects in subsequent studies.
Knowing the whole genome is the first step towards de-extinction
The vanishing of insects, notably pollinators, poses a highly significant ecological issue on a global scale. Hence, the revival of species like the Xerces Blue butterfly through CRISPR-based genetic engineering methods holds immense fascination for the scientific community.
Carles Lalueza-Fox, a co-leading researcher from IBE (CSIC-UPF) and director of the Natural Sciences Museum in Barcelona, highlights that the Xerces Blue butterfly is an ideal candidate for de-extinction. This is attributed to its recent disappearance, which reduces the ecological impact of its reappearance, and the limited risk of pests or excessive proliferation due to the short adult appearance period (between March and April) and ecological specialization. With the complete genome of the Xerces Blue butterfly, we anticipate its potential contribution to future de-extinction endeavors.
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