| Summary: | Rivers transport sediment, nutrients and life throughout a continent, all-the while shaping the landscapes they flow through. My thesis investigates the processes that govern the dynamics of river basins and the ways in which these processes may influence the evolution of aquatic life. In Chapters 1-3 of my thesis I investigate river network reorganization, a phenomenon that occurs when some river basins erode faster than their neighbors, growing at their expense. The exchange of drainage area across drainage basin divides can influence the relative size of drainage basins, the route in which rivers flow across a landscape, and the dispersal corridors available to aquatic organisms. If a channel is abruptly rerouted into a neighboring basin, a process called river capture, populations of organisms may be separated and undergo genetic divergence and eventual speciation. In Chapter 1 of this thesis, I use geomorphic observations to describe an ongoing river capture occurring between the Rio Orinoco and Amazon River, two of the largest rivers in the world. However, very few river captures are observed, and are instead almost always inferred from topographic evidence, the accuracy of which is unknown. Therefore, in Chapter 2, I use erosion rates to test the accuracy of topographic evidence for divide motion along the Blue Ridge Escarpment in the Appalachian Mountains. In Chapters 3-4 I investigate the connections between geomorphic processes and biological evolution. In Chapter 3, I build a coupled model that simulates river network reorganization in addition to speciation, extinction and dispersal of organisms within the simulated landscape. I find that river network reorganization can increase diversification rates, especially when river captures are frequent and the organisms disperse slowly throughout the landscape. In Chapter 4, I use genomic data to investigate mechanisms driving speciation within, as opposed to between, drainage basins. I connect spatial and temporal patterns of the diversification of an endemic fish species to fluvial erosion into spatially varied rocks in the Tennessee River, USA. Altogether, this work illustrates the rich connections between rivers, landscapes, and the evolution of aquatic life.
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