Date of Graduation

8-2022

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Biology (PhD)

Degree Level

Graduate

Department

Biological Sciences

Advisor/Mentor

Marlis R. Douglas

Committee Member

Michael E. Douglas

Second Committee Member

Jeremy M. Beaulieu

Third Committee Member

Adam M. Siepielski

Keywords

Evolution and development, Genetic Diversity, Genomics, Hybridization, Population Structure, Stream Hierarchy, Trait-based modeling

Abstract

Genetic variation is a crucial component of biodiversity and represents the variability and spatial structure of alleles within and among organisms. Evolution modulates this variability over time through mutation, selection, gene flow, and genetic drift. However, our capacity to test foundational theories of population genetics has always been at the mercy of molecular approaches available to quantify patterns of genetic diversity. Initially, techniques for empirical DNA studies were in their infancy and limited by technologies and the price per unit of genetic information. Because of these constraints, our pursuits have generally been limited to investigations of one or a few species simultaneously, hampering our power to draw broadly applicable conclusions. Advances in molecular technologies, e.g., high-throughput sequencing, now provide so much information at so little cost that a multispecies comparative approach to uncovering generalities about evolution is within reach even for applied studies on non-model organisms. Ultimately, genotyping individuals from all species within a community will be feasible and easily replicated across sampling locations and span entire regions. Variability of genetic diversity, within and among species, can be leveraged to explore the relationship between ecology and evolution and between micro- and macroevolution.For my dissertation research, I employed a multispecies framework to link ecological and evolutionary processes driving spatial patterns of biodiversity through comparative analyses of genotypic variability among sympatric species of freshwater fish that inhabit a large sub-basin of the Mississippi River. First, I quantified the extent of admixed ancestry among species within a community by assessing genomic variability among individuals from many species. My analyses uncovered that fish in nature — particularly minnows — have higher than expected hybridization rates. My data even show evidence of hybrid viability and genetic exchange among species (i.e., introgression). I interpret these findings of widespread admixture among distinct species as an indicator that admixture plays a critical role in ecology and evolution – more so than previously considered. Second, I tested for general mechanisms that define spatial genomic variability within species by comparing models of extrinsic drivers of genetic divergence. The river network, or stream hierarchy model, best explained species' genomic variability, as evidenced by the correspondence between genetic divergence and riverine architecture. This general pattern emerged for all species, but the degree of genetic divergence differed widely, indicating that the intrinsic traits of each species may also play an important role. Finally, I further explored how phenotypic traits may modulate species' genetic diversity and ultimately evolutionary trajectories by comparing relationships between traits and metrics of genetic variability among species within a comparative framework. Significant associations between trait values and genetic patterns emerged, allowing me to develop predictive models of genetic diversity using traits alone, without requiring direct genetic assessments. These trait-based models can be applied to prioritize species for conservation and management. My dissertation research demonstrates that modern molecular approaches are uniquely positioned to help unite ecology and evolution, bridging the long-standing dichotomy between these two disciplines. I provide a comparative framework for conservation biology that integrates various temporal and spatial scales and demonstrate with an empirical example how it can be applied to assess thousands of informative genetic markers across entire communities of non-model organisms. My dissertation research elevates population genomics to the community level and outlines how to explore new dimensions in our long-standing inquiry: What drives variation in genetic diversity among species?

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