Ecological Context for Variable Genomic Outcomes of Hybridization in Catostomus Fish Species

Reproductive isolation between related species in natural populations is likely to include spatial, temporal, genetic, and ecological components. If components of reproductive isolation vary geographically, repeated contact between a pair of species is likely to result in variable outcomes, from extensive hybridization to coexistence with continued reproductive isolation. This is empirically demonstrated by our work in native and introduced Catostomus fish species in the Upper Colorado River basin. Genomic data from approximately 2,800 individual fish representing six hybridizing Catostomus species from >20 rivers suggest that genomic outcomes of hybridization vary substantially among rivers and across species pairs. To better understand the ecology of hybrids, we combined genomic and isotopic data to compare how fish of different ancestry feed. We used fish body condition to understand relative ecological success conferred by different feeding phenotypes. From these analyses, we conclude that ecology and ecological success of Catostomus hybrids also vary across rivers and species pairs. Maladaptive or ecologically mismatched phenotypes in hybrids might act to constrain hybridization in some locations, while adaptive phenotypes might facilitate hybridization in other locations. Hybrid phenotypes that influence ecological success might therefore play a major role in determining outcomes of secondary contact between related species.