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I I I I I I I I I I I I I I I I I I I A genetic evaluation of hybridization among indigenous and non-native Yampa River suckers (Catostomidae). Douglas, MarIis R. l. and Michael E. Douglas l. I Department of Fishery and Wildl~fe Biology. Colorado State University. Ft. Collins CO Numerous factors contribute to the decline of indigenous fishes in western North America. While habitat alteration is a major concern for indigenous fish communities, impromptu introduction of alien species is probably a more serious threat to their long- term survival. Impacts of the latter are less immediate, and often go unnoticed by the general public. Introgression of alien genes gradually erodes the genetic integrity of native species, and irreversibly alters the local genetic adaptation that has evolved over millions of years. As a result, indigenous genes become replaced and the endemic fauna is effectively eliminated. We applied a molecular genetic approach to define the extent and magnitude of hybridization between the introduced White Sucker (Catostomlis eommersoni) and endemic suckers of the Colorado River Basin, the Flannelmouth Sucker (C. latipinnis) and the Bluehead Sucker (c. discobollis). These three hybridize in a 50- mile reach of river between Lily Park and Craig. Species-specific nuclear markers were developed to assess the status (i.e., pure or hybrid) of over 500 specimens. Results demonstrated that morphological and genotypic identifications were congruent with over 95% of the individuals. A small fish in a large landscape: Phylogeography of Rhinichthys osculus, the Speckled Dace. Douglas, Michael E.l, David D. Oakey, and .\ilarIis R. Douglasl I Department of Fishery and Wildlife Biology. Colorado State University, Ft. Collins CO; 2 Dept. of Biology. Arizona State University. Tempe. AZ We mapped 114 restriction sites in the mitochondrial (mt) DNA genome of the Speckled Dace (Rhiniehthys oseullis), a small cyprinid tlsh broadly distributed in western North America. These data were used to derive a molecular phylogeny for the species 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 sub-basins that arose in profound isolation as an apparent response to regional aridity and tectonism. The Lower, and Little Colorado River sub-basins are sister to one another, and (with the Upper Colorado River), form a large clade of higher-elevation populations that reflect post- glacial re-colonization from refugia in the Middle Colorado River. The latter sub-basin is sister to the L.)S Angeles Basin, and thus supports the hypothesis of an ancient connection between the two. A haplotype from the Northern Bonneville was sister to the entire J"'