Intercontinental dispersal, biogeography, and speciation in a freshwater zooplankter: Investigations of the Daphnia of Argentina

This thesis investigates the interactions among long-distance dispersal, environmental conditions, and phylogenetic constraints in shaping the evolutionary diversification of a freshwater zooplankton assemblage. The initial section of the thesis focuses on the use of genetic analyses to resolve species boundaries in the Daphnia fauna of Argentina. New and published DNA sequences from Daphnia from four continents were subsequently used to construct a phylogenetic framework for the genus in order to examine the factors influencing the distribution of polyploid taxa, the role of intercontinental allopatric divergence in the diversification of the genus, and the relative importance of geographic, genetic, and ecological modes of speciation in the evolution of the group. In addressing each of these topics, this study highlighted the importance of long-distance dispersal in promoting speciation and in structuring large-scale biogeographic patterns. While chance historical events have played a fundamental role in the evolution of daphniid diversity, this study revealed that clade-specific properties are also important in determining overall patterns of diversity.