Inconsistent reproductive isolation revealed by interactions between Catostomus fish species

Interactions between species are central to evolution and ecology, but we do not know enough about how outcomes of interactions between species vary across geographic locations, in heterogeneous environments, or over time. Ecological interactions between species are known to vary, but evolutionary interactions such as reproductive isolation are often assumed to be consistent. Hybridization among Catostomus fish species occurs over a large and heterogeneous geographic area and across taxa with distinct evolutionary histories, and allows us to assess consistency in species interactions. We analyzed hybridization among six Catostomus species and found extreme variation in hybridization across locations. Variation in hybridization outcomes might result from uneven fitness of hybrids across locations, polymorphism in genetic incompatibilities, chance, unidentified historical contingencies, or some combination thereof. Our results suggest caution in assuming that one or a few instances of hyb...