Doctor of Philosophy (PhD)


Biological Sciences

Document Type



The northern Neotropics (NN) represents one of the most geologically-complex regions on the planet, composed of island-like geological blocks that have undergone multiple episodes of isolation and connectivity at various geological times. The riverscapes of the NN harbor a unique assemblage of freshwater fishes. In contrast to the freshwaters systems of South America, which are dominated by ostariophysan lineages, the aquatic systems of the NN are dominated by lineages of two families: Cichlidae (cichlids) and Poeciliidae (livebearers). It has been suggested that the geologically complex nature of the region allowed ancestors of cichlids and livebearers to colonize and radiate within these island-like geological blocks in the absence of competitors (i.e., ostariophysan lineages). The unique assemblage of freshwater fishes and complex paleographic history of the NN has sparked a wealth of large-scale biogeographic investigations. These biogeographic studies have shed light regarding the timing and routes from which Neotropical elements have arrived and diversified in the region. In contrast, our understanding of the patterns and processes that have promoted the diversification of freshwater fishes within the riverscape of the NN is less understood. Thus, the objective of this dissertation is to investigate fine-scale biogeographic patterns in the riverscape of the NN. First, we investigate fine-scale biogeographic patterns of freshwater fishes within a large-scale area of endemism. We provide evidence that present-day river basins are not single biogeographic units and instead comprise up to five nested areas. Next, we evaluate the biogeographic history of the Herichthyine cichlids, which are considered an adaptive radiation but for which the role of the geographic arena in driving diversification is not well understood. This investigation highlights the role of allopatric speciation (e.g., via river capture) in promoting diversification within Herichthyines in the region. Third, we investigate the systematics and biogeographic history of the diverse ostariophysan genus Hyphessobrycon (Characidae) in Middle America. Our robust phylogenomic hypothesis allow us to uncover a novel biogeographic pattern of colonization of Central America by ostariophysan fishes. This pattern suggests an early colonization of each geological block followed by in-situ diversification after colonization. These results underscore the importance of fine-scale investigations to better understand the patterns and processes that make up the evolutionary history of this unique assemblage of freshwater fishes in the northern Neotropics.



Committee Chair

Chakrabarty, Prosanta