In this study, I sequenced the mitochondrial cytochrome b gene to elucidate the extent and pattern of genetic variations among and within populations of Rhinichthys osculus (Santa Ana Speckled Dace) found in the different watersheds in Southern California, Central California Coast and Eastern California Desert. I described and analyzed the structural characteristics and pattern of base sequence substitutions in the cytochrome b gene to understand the molecular evolution of the gene. The Phylogenetic analyses showed that the Southern California Santa Ana Speckled dace is a distinct population from the Central California Coast dace population and Eastern California Desert dace population, and is more closely related to the Colorado River speckled dace population. There is a high degree of genetic variation among all populations including a significant genetic structure associated with watersheds, mountain ranges, and geographic grouping based on locations. The SWISS-Model automated protein structure homology elucidated the conserved and invariant residues within the cytochrome b gene where the amino acid substitutions are located in the trans-membrane of the protein sequence. The implication for conservation and management of the Southern California Santa Ana Speckled dace is high because of habitat lost for this distinct dace population. The data from this study will contribute to preserving the genetic variability of the Santa Ana Speckled Dace as a separate taxa and species, as well as to help maintain intact the population in the different Southern California creeks.

Rhinichthys osculus (Cyprinidae), the speckled dace, is the most widely distributed freshwater fish in the western United States. The southern California populations of R. osculus are identified as the Santa Ana speckled dace (SASD), though the SASD has not yet been formally recognized as a distinct taxon. Current mtDNA analysis performed in the Metcalf Lab has shown a reciprocally monophyletic relationship among three California regions; southern, central coast, and Owens Valley. Similarly, microsatellite genotyping has shown significant levels of geographic population structure. The purpose of this study was to provide nuclear DNA sequence data to determine the taxonomic status of the SASD to elucidate their evolutionary history and the relationships among the three regions, and to further define their evolutionary trajectory by comparing SASD sequence data to that of speckled dace from the Colorado River of Arizona. To examine this, three EPIC intron markers were sequenced on 54 samples representing all four regions. Based on the mtDNA and microsatellite data alone, there is strong support that the southern California populations of R. osculus are a reproductively isolated taxon at the species level. My study confirms this by showing the SASD to be reciprocally monophyletic for nuclear DNA markers, in conjunction with the mitochondrial DNA marker analyses. Because they are evolutionarily independent and face increased incidence of drought, fire, and flood, endangered species status should be considered.

Microhabitat use by adult speckled dace (Rhinichthys osculus), adult longnose dace (R. cataractae), and juvenile dace (R. spp.) was investigated during the summer of 1992 in an Oregon Cascades stream. Selected areas were snorkeled day and night in order to evaluate differential use of habitat resources both temporally and spatially. Speckled dace were active both day and night but longnose dace were only observed at night when they were found primarily in fast flowing midstream areas. Small speckled dace (<8 cm TL) shifted from relatively fast flowing midstream daytime habitats to slower inshore areas at night. Large speckled dace (8-14 cm TL) used slower areas during the day and faster water at night. Potential competition between large speckled dace and longnose dace (8-20 cm TL) at night may be deflected by spatial microhabitat segregation. Within the fast water habitat at night, longnose dace used the fastest, shallowest areas with large substrates and were usually on the bottom. Large speckled dace used relatively slower, deeper water with smaller substrates and were near, but not on, the bottom. / Graduation date: 1994