Influences of Historical and Contemporary Environmental Conditions on Threatened and Endemic Aquatic Organisms
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Historical and contemporary environmental conditions affect the distribution of aquatic species. The following three chapters seek to assess the degree to which conditions have impacted current distribution and population structure of fishes and mussels. The first chapter assesses genomic hybridization dynamics between the endemic and threatened Macrhybopsis australis and the widespread M. hyostoma in the Red River basin of Texas. This work found hybridization in a reach of the river upstream from Lake Texoma, and the distribution of hybrid and pure organisms is associated with several water quality parameters. The second chapter is a biogeographical assessment of the Macrhybopsis species complex within Texas. I used genomic techniques, and found a complex history of dispersal and vicariance, which likely occurred during the Pliocene and Pleistocene, that influenced current distributions. This work supports a stepping-stone model of dispersal, suggesting coastal drainages acted as islands, where species were able to transfer via connections during low sea levels. The third chapter assessed the effects of major floods on mussel populations using a closed robust mark-capture design to account for imperfect detection at two sites on the Colorado River. There were significant decreases in estimated abundances and apparent survival at one site, but not the other. The differential effects observed in estimated abundance and apparent survival among species were attributed to flood magnitude differences, substrate differences, and life-history traits of each species. These three chapters ultimately provide valuable information about the effects of historical and contemporary environmental conditions on threatened and endemic aquatic organisms. I show that hybridization dynamics of fishes are significantly associated with water quality parameters, the evolutionary history of fishes in Texas shows patterns indicative of a stepping-stone model of dispersal, and population dynamics of freshwater mussels have a complex relationship with flood magnitude, substrate, and life-history traits. In summary, this work provides evidence that historical and contemporary environmental conditions shape the biology and ecology of aquatic organisms.