Molecular ecology and evolution of intertidal sculpins

It is critical to understand the factors influencing species evolution and diversification in terrestrial and freshwater systems. Some of the well-known studies done on fish that address species formation and adaptive radiation have mostly been done on freshwater fishes (i.e. cichlids and sticklebacks). However, patterns from freshwater systems seem to be of limited applicability to marine organisms because many environmental (upwelling, El Nino), ecological (competition for space) and life history traits (juvenile recruitment, larval dispersal) that influence speciation in the marine realm are markedly different, and therefore cannot be addressed by freshwater studies. Thus the degree to which genetic drift, selection, historical biogeography, gene flow and local adaptation each contributes to the speciation between closely related marine fish species is still at best poorly understood.; This study examined aspects of some of these evolutionary forces, specifically, genetic drift, historical biogeography and gene flow. I focused on a group of sculpins (Family: Cottidae) off the Pacific west coast. Sculpins serve as good candidates to study the speciation process because there are approximately twenty genera found in the north Pacific, they are found intertidally and subtidally, and have several closely related genera whose relationships are controversial. A phylogeny was constructed to examine historical biogeographic factors that have contributed to the speciation of cottids as well as determine the timing of speciation radiations. Second, the evolution of a mitochondrial gene rearrangement discovery in several genera was used to evaluate the speciation of sculpins. Lastly, a phylogeographic study explored the process of gene flow and population structure for intertidal fish.; A phylogeny was constructed from DNA sequences for mitochondrial gene fragments Cytochrome B and nitrogen-dehydrogenase subunit one (ND1), along with one nuclear intron (S7 ribosomal protein). Maximum parsimony, maximum likelihood, and Bayesian algorithms were employed to reconstruct phylogenetic trees. I found that several genera are not monophyletic and that there is an overall trend of subtidal fishes invading the intertidal. Furthermore, work on C. analis (Cottidae) revealed that the tRNA for Proline resides within the 3' end of the control region. Subsequent sequencing efforts also revealed that there is a second and almost identical control region between 16S and ND1. This novel mtDNA rearrangement was found in other sculpins. Using a molecular clock for Cytochrome B suggest that the majority of the species split and the gene rearrangement occurred during the Pliocene-Pleistocene.; Several different species (Oligocottus snyderi, O. maculosus, C. globiceps and C. analis) were used for preliminary analysis of the phylogeographic study. I found similar results of no population structure, therefore I only focused on the intertidal wooly sculpin ( C. analis) because previous studies indicated that there might be a subspecies. Two hundred and forty-five individuals were collected throughout its range from Northern California to Baja California. The 5' end of the mitochondrial control region (274bp), considered the most variable portion of the mitochondrial genome, was used to determine how much larval movement (estimated using gene flow levels) occurs between populations. I also sequenced the mitochondrial genes ATPase6 and ATPase8 to confirm that the control region was not behaving oddly because of the discovery of two control regions for this fish. The results indicate the control region when compared to ATPase 6 and 8 markers was not in concordance and that there is high migration between most populations, which results in very little population structure between populations when the data is combined. In fact the control region was far less variable than ATPase 6 and 8. The discrepancy found between the genes is discussed.