Muller, Tyler2024-01-052024-01-052023-07https://hdl.handle.net/11299/259572University of Minnesota M.S. thesis.July 2023. Major: Conservation Biology. Advisor: Andrew Simons. 1 computer file (PDF); iv, 46 pages.The Southeastern United States is home to exceptionally high fish diversity among temperate latitudes. Species richness and endemism in this region is commonly attributed to historic biogeographic processes dating back to the Pliocene or earlier, and influences of sea levels through a relatively old though stochastic landscape and drainage basins. Specific and subspecific differentiation within the Southeastern United States occurs over a small geographic area and is well documented, though several species of lowland fishes seemingly defy biogeographic and phylogeographic models and expand well beyond other species ranges without any hypotheses for dispersal. Pirate Perches, Aphredoderus, are a widespread lowland freshwater fish native to the Eastern half of the United States. Aphredoderus was thought to contain a single species divided into an Eastern and Western subspecies on either side of the Appalachian Mountains with a widespread intergrade zone through much of the Eastern Gulf of Mexico and Southern Atlantic drainages. I use morphology and ddRADseq from specimens spanning the entire range of the genus to determine species limits within Aphredoderus. I find evidence of five species, four of which exhibit widespread sympatry in the Southeastern United States. I elevate A. sayanus sayanus and A. sayanus gibbosus to species, supplement previous descriptions, and describe three new species, A breviopercularis sp. nov., A. retrodorsalis sp. nov., and A. ornatus sp. nov. This research suggests that expansion through the Pliocene and Pleistocene was differential and several different historic refugia existed to facilitate allopatric speciation similar to what is proposed in earlier biogeographic and phylogeographic studies.enBiogeographyIchthyologyPhylogeographyThesis or Dissertation