Population genomics of a culturally important amphibian on a remote archipelago reveals a distinct and depauperate population

Amphibian populations are at risk globally and understanding their evolutionary history is critical to their future conservation. The Western Toad ( Anaxyrus boreas ) is widely distributed across western North America, but is the only native amphibian on Haida Gwaii, a large and remote archipelago off the northwest coast of British Columbia (BC), Canada. Hlk’yáan Ḵ’ust’áan/Hlk'yan ḵ'uust'an (Western Toad) is a culturally important species for the Haida Nation, with recent concerns of possible extirpations of breeding sites. To examine genetic diversity and differentiation within populations on Haida Gwaii as compared to elsewhere in coastal BC, we sampled 1,370 individuals from 47 breeding sites across Haida Gwaii, Vancouver Island to the south, the southwest Lower Mainland, and the Northwest BC mainland. Genotyping-by-sequencing generated ~ 1,368 single nucleotide polymorphisms (SNPs) for the full dataset after quality control filtering. Haida Gwaii toads are strongly differentiated from other coastal BC populations (pairwise F _ST = 0.363). Genetic connectivity between breeding sites is higher within Haida Gwaii ( F _ST = 0.080) than within other regions ( F _ST = 0.105). Genetic diversity is also lower in Haida Gwaii (nucleotide diversity π = 0.0004) than elsewhere (0.0007). The site frequency spectrum suggests a founder event or bottleneck may have caused this reduced diversity in Haida Gwaii. Our results suggest that Haida Gwaii toads should be treated as a distinct population for management, targeting protection of breeding habitats and connectivity between breeding sites to promote persistent populations and prevent declines of this culturally and ecologically important species.