Genomic and ecological divergence support recognition of a new species of endangered Satyrium butterfly (Lepidoptera, Lycaenidae)

We describe a highly isolated population of hairstreak butterfly from Waterton Lakes National Park, Alberta, Canada, as a new species, <i>Satyriumcuriosolus</i> <b>sp. nov.</b>, previously recognized as <i>Satyriumsemiluna</i> (Half-moon Hairstreak). We propose "Curiously Isolated Hairstreak" as the common name due to its disjunct and unusual distribution. Previous whole-genome analyses revealed <i>S.curiosolus</i> has extremely low genomic diversity and is highly divergent from the nearest <i>S.semiluna</i> populations in British Columbia and Montana, more than 400 km distant. Further analysis suggested prolonged inbreeding and isolation for up to ~40,000 years BP. Ecological niche modeling indicated that <i>S.curiosolus</i> occupies environmental conditions that are distinct from <i>S.semiluna</i>, suggesting niche divergence driven by long-term geographical and ecological separation. While host plant and ant associations have not been definitively resolved, they likely differ between <i>S.curiosolus</i> and <i>S.semiluna</i>. As part of this description, we provide whole-genome consensus sequences for each individual of the type series and identify 21,985 single nucleotide polymorphisms (SNPs) that are divergently fixed between <i>S.curiosolus</i> and <i>S.semiluna</i>, including 117 unlinked SNPs distributed across the genome as putative diagnostic markers. Previously listed as Endangered in Canada as the Waterton population of <i>S.semiluna</i>, <i>S.curiosolus</i> should retain this conservation status due to its extreme isolation, small population size, and flatlined genomic diversity. We propose species recognition as a testable hypothesis under the General Lineage Concept and recommend further research to explore the taxonomy, ecological relationships, and conservation of the greater species complex, including <i>S.curiosolus</i>, <i>S.semiluna</i>, and <i>S.fuliginosa</i>.