SRP405110 PRJNA893229 Population structure of obligate groundwater amphipod crustaceans (Stygobromus sp.) in alluvial aquifers Gravel-bed river floodplains occur in river corridors around the globe. One key habitat of these floodplains are alluvial aquifers that provide habitat for a wide range of obligate groundwater species. Multiple species of the amphipod genus Stygobromus commonly occur in alluvial aquifers, as well as in karstic phreatic systems, but population structure and its relevance to the biogeography of the genus has not been reported in Montana. Using reduced representation genome sequencing, RAD-seq, we investigated the population structure and genetic connectivity of an undescribed Stygobromus species in several alluvial aquifers on floodplains of the Flathead River, Montana (USA).