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18 I I I I I I I I I I I I I I I I I I I Douglas, M. E., and M. R Douglas Department of Fishery and Wildlife Biology, Colorado State University, Ft. Collins CO Genetic diversity in suckers (Teleostei, Catostomidae) from the Colorado Plateau. Populations isolated for reasonable periods often diverge quite rapidly from one another at the genetic level. In the Tertiary of western North America, drainage patterns were dramatically shifted due to tectonism and aridity. Headwaters became isolated and fluvial habitats fragmented, thus separating biotas. Later, more pluvial periods, interconnected drainages and optimized potential for stream capture and exchange of fishes. Did this earlier geographic fragmentation promote divergence of fishes? To answer this question, we will invoke a landscape perspective, employ molecular genetic techniques, and use non-TIE species as model organisms, specifically two species of freshwater sucker found on the Colorado Plateau and immediately south, plus a third that is believed distinct but is undescribed. Minckley (Fishes of Arizona, 1973) examined populations offlannelmouth sucker (Catostomus latipinnis) in Grand Canyon and concluded that their morphological variation was greater than expected for a single species. He further argued that a distinct form of the flannelmouth sucker in the upstream Little Colorado River could represent an undescribed species. This form was given a manuscript name (e. "crassicauda") by RR Miller during the early 1960s. We attempt to corroborate and extend the observations of both Minckley and Miller by amplifying and sequencing 1,231 base pairs of three rapidly evolving mitochondrial (mt) DNA genes (ATPase 8, 6, and ND2) in 9 basin-wide populations ofe. latipinnis, 10 widespread populations of the Sonora sucker (c. insignis), and four populations of the Little Colorado River form. Results indicated that the LCR and flannelmouth suckers are virtually identical from the standpoint ofmtDNA. In addition, a haplotype of the Little Colorado River sucker was also found in the Sonora sucker clade. The Sonora sucker also contained an undescribed "Sonora-like" sucker that was found in the Gila River (NM), Virgin River (NY), San Juan River (NM), and mainstem Colorado in Grand Canyon (AZ). These results add more confusion to the already enigmatic status of the LCR form. Its management and distinctness are discussed. Douglas, M. R, and M. E. Douglas Department of Fishery and Wildlife Biology, Colorado State University, Ft. Collins CO Genetic variation in speckled dace (Teleostei, Cyprinidae) from the Colorado River Basin. The speckled dace (Rhinichthys osculus) is widespread throughout western North America. However, it is neither endangered at the national level, nor listed by resource agencies as a "species of concern". Yet, understanding the basin-wide distribution of genetic diversity in this fish is of interest in that it could serve as a model against which other species in the basin could be compared, particularly those now greatly restricted in abundance and distribution. In this sense, it could provide a pre-development perspective on the relationships of drainages, basins, and the biota contained therein. However, such a study requires sampling of numerous populations and individuals throughout western North America. We have elected to complete this task by evaluating drainages and regions separately and in a piecemeal fashion, so that sample sizes of both populations and individuals can be optimized. Last year we reported on levels of genetic variation found in 13 populations of speckled dace from the Virgin River drainage of Arizona, Nevada, and Utah. Here, we coalesce these data with 18 populations from the upper and lower Colorado River basins. We amplified and sequenced three fast-evolving mitochondrial genes