DNA Hybridization Comparison of Mitochondrial Versus NuclearDNA Evolution in Birds

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By virtue of its simplicity and fast rate of evolution, mitochondrial DNA (mtDNA) is playing an increasingly important role in avian systematics. Yet despite its great potential, the application of mtDNA to avian problems depends heavily upon evolutionary assumptions extrapolated from mammal mtDNAs. While initial rates of bird mtDNA evolution appear to be fast, it is unknown whether they are the same as in mammals. Further, evidence is accruing that the mtDNA saturation plateau in birds may be lower than in mammals, which implies a difference between bird and mammal rates at some levels of divergence. The upshot is that we are producing data on avian genetic divergences without knowing how rate patterns are influencing those estimates. In this project, mtDNA and single-copy nuclear (scn) DNA hybridization will be employed to estimate phylogenies of the Hirundinidae (swallows) and Paridae (chickadees and titmice) and divergences among selected non-passerine taxa. DNA hybridization is especially appropriate for such analyses because it can measure overall divergence among taxa for both the small mt and huge scn genomes, and present them in a single data form. These data can then be plotted, without conversion or reference to fossil datings, to depict relative rates and saturation levels. DNA-hybridization phylogenies will also be compared to one another and to results of extensive restriction fragment analyses to assess the various types of phylogenetic data.