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Extinct Butterfly Sequences Provide Look at Relationships, Waning Population Warning Signs

A team from Spain, Estonia, Denmark, and the US describes genetic features found in the Xerces Blue butterfly (Glaucopsyche xerces), an extinct species last collected in the wild in the western US in the early 1940s. As they report in eLife, the researchers performed whole-genome sequencing on four Xerces Blue samples going back 80 to 100 years, comparing the sequences to genomes for seven related species in available historical sample collections and to a new genome assembly extending more than 619.5 million base pairs from a related butterfly, the Silvery Blue (G. alexis), that was collected in Spain. With phylogenetic analyses based on mitochondrial and nuclear sequences, the authors placed the split between the extinct Xerces Blue species and the Silvery Blue species at more than 850,000 years ago, while uncovering signs of shrinking population size, increased inbreeding, an uptick in deleterious mutation loads, and rising runs of homozygosity in the Xerces Blue butterfly prior to its extinction. "Our analyses indicate that the Xerces Blue had experienced a severe demographic decline for tens of thousands of years, likely associated with changing climatic factors," they report, noting that "the destruction of the Xerces Blue habitat by humans was likely the final blow in the extinction process.