Small Fish in a Large Landscape: Diversification of Rhinichthys osculus (Cyprinidae) in Western North America

We mapped 112 restriction sites in the mitochondrial DNA genome of the Speckled Dace (Rhinichthys osculus), a small cyprinid fish broadly distributed in western North America. These data were used to derive a molecular phylogeny that was contrasted against the hydrographic evolution of the region. Although haplotypic variation was extensive among our 59 sampled populations and 104 individuals, their fidelity to current drainage basins was a hallmark of the study. Two large clades, representing the Colorado and Snake Rivers, were prominent in our results. The Colorado River clade was divided into four cohesive and well-defined subbasins that arose in profound isolation as an apparent response to regional aridity and tectonism. The Lower and Little Colorado River subbasins are sister to one another and (with the Upper Colorado River) form a large clade of higher-elevation populations that seemingly reflect postglacial recolonization from refugia in the Middle Colorado River. The latter subbasin is ...