Population structure of Plains Sucker Pantosteus jordani (Evermann 1893) in Canada

Freshwater fishes are declining globally due to habitat loss, climate change, and other anthropogenic pressures. The Plains Sucker (Pantosteus jordani), recently recognised as a distinct species due to genetic and biogeographical factors, occurs east of the Rocky Mountains in Canada and the northern United States. Canadian populations are divided into the Missouri Basin and the Saskatchewan-Nelson Basin, but their genetic structure remains poorly understood. To assess population differentiation and connectivity, we analyzed mitochondrial DNA (7,770 bp) and eight microsatellite markers from 371 individuals across 21 sites in Alberta, Saskatchewan (Canada); and Montana (USA). Mitochondrial analyses revealed high haplotype diversity with significant regional clustering, particularly in the Frenchman River population, which was strongly differentiated from all other sites. Microsatellite analyses further supported basin-level structuring, with clear genetic separation between the Missouri and Saskatchewan-Nelson basins and strong differentiation among Missouri tributaries. In contrast, Saskatchewan-Nelson populations showed little genetic differentiation, consistent with recent or ongoing connectivity. The Frenchman River exhibited reduced genetic diversity, suggesting a history of drought-driven isolation and potential population bottlenecks. Together, these results highlight the influence of both historical colonization and contemporary fragmentation on the genetic structure of P. jordani. The Missouri Basin populations, with their restricted distributions and lower genetic diversity, may be particularly vulnerable to climate change and anthropogenic barriers, while Saskatchewan-Nelson populations appear more resilient but face ongoing threats from habitat alteration and pollution. By identifying distinct population units, this study provides critical insights for conservation planning and management of P. jordani.