Heterogeneity in Genomic Outcomes of Hybridization Among River Drainages and Species Pairs Calls for Tailored Management Strategies

Interspecific hybridization between native and introduced species may constitute a threat to the persistence of native fishes. Historically, most fisheries management practices have treated hybridization as a single, homogenous process across the geographic range of an interaction between species. However, we know from evolutionary studies that outcomes of hybridization may vary geographically and across species pairs within a genus. In this study, we compared outcomes of contact between native bluehead and flannelmouth suckers (Catostomus discobolus and C. latipinnis) and introduced white suckers (C. commersoni) across a large geographic area. We generated genomic data for approximately 3,000 fish from >20 locations, resulting in one of the most geographically and genomically comprehensive studies of fish hybridization to date. We observed variation in outcomes of hybridization both across species pairs (flannelmouth×white and bluehead×white sucker hybrids) and across rivers. These results suggest that reproductive isolation is polymorphic both within and among species pairs in the Catostomidae. This means that the threat to native species through introgressive hybridization with introduced species is also heterogeneous, and more complex than initially recognized. Thus, our analyses suggest that successful conservation of native bluehead and flannelmouth suckers might require species-specific and river-specific strategies.