Date of Award


Document Type


Degree Name

Master of Science in Biology



First Reader/Committee Chair

Metcalf, Anthony


The purpose of this genetic study of the Santa Ana Speckled Dace Rhinichthys osculus was three-fold. The first goal was to characterize the molecular structure of the mtDNA control region of R. osculus. An 1143 base-pair region of the mitochondrial DNA genome, which included the complete control region was sequenced for all individuals. Analysis of the sequence data revealed that the molecular structure of the speckled dace control region was similar to the molecular structure described for other vertebrate taxa. The speckled dace control region contains three major domains, which vary in base frequency as well as in the frequency of nucleotide polymorphisms. Domain II was observed to be the most conserved, and Domain I was the most variable domain of the control region, in agreement with studies of other vertebrate control regions. The second goal of this study was to ascertain the phylogeny of R. osculus in Southern California in relation to other speckled dace in California. Seventy-four specimens of R. osculus were collected from five different watersheds located in three geographic regions of California: Southern California, the Central California Coast, and the Eastern Desert of the Owens River valley. Phylogenetic analysis of sequence data revealed that the Santa Ana Speckled Dace is a genetically distinct population from R. osculus inhabiting the Central Coast or Eastern Desert regions, which both differ from the Santa Ana Speckled Dace by a genetic distance of more than 7 percent. The Santa Ana Speckled Dace inhabiting the watersheds of Southern California form a reciprocally monophyletic clade with respect to the Central Coast dace and the Eastern Desert dace, which are sister clades to one another. The third goal of this study was to describe the population genetics of R. osculus in Southern California. Population genetic analysis demonstrated that a high degree of geographic population structure exists for the Speckled Dace in California, with 96% of molecular variance attributable to regional differences through isolation by distance. A high degree of population structure also exists among populations within the Southern California region as well. It was found that 45% of molecular variance in the Santa Ana Speckled Dace is attributable to differences among tributaries. This study finds that the distribution of speckled dace in Southern California best fits a model of population structure by individual tributary, with episodes of localized population bottlenecks followed by sudden population expansion, most likely linked to climatic variation. It is proposed the Santa Ana Speckled Dace constitutes an Evolutionarily Significant Unit (ESU) that qualifies it as a separate subspecies on the basis that it is geographically separated from other populations, genetically distinct from other dace populations due to restricted gene flow, and possesses unique phenotypic characteristics. This information suggests conservation and management strategies for the speckled dace populations which remain in existence in Southern California.