Life Sciences Commons^™

Genetic Structuring And Community Assembly In Neotropical Birds, Oscar Johnson

LSU Doctoral Dissertations

The factors that influence how species form is of fundamental interest to biology. Under the framework of the speciation cycle, the process begins by population subdivision creating structured populations that then diverge until two new species form. Following speciation, however, continued divergence is necessary for these new species to be able to coexist without adverse interactions, known as the transition to secondary sympatry. At this point the speciation cycle is complete and the process can begin anew. Many of the factors influencing these processes remain poorly understood. Here, I explore the factors that influence speciation and community assembly in Neotropical …

Quantifying Structure And Variation In Complex Phylogenetic Data, Genevieve Geraldine Mount

LSU Doctoral Dissertations

Identifying the source and structure of variation in nature is crucial to understanding fundamental aspects of evolution. Despite a recent plethora of genetic and morphological data, many interesting questions about the relationships between different groups remain unresolved. My dissertation evaluates three approaches for identifying and quantifying the variation within phylogenetic datasets. Characterizing variation within datasets and across analytical methods gives insight into biologically interesting characters, unusual evolutionary processes, and areas for model improvement.

Network-based community detection approaches offer a powerful tool to describe variation in phylogenetic signal across the genome (i.e., gene tree variation). In Chapter 2, I investigate the …

Evolution Of Green Blood In New Guinea Lizards: Phylogenomics, Biogeography, And Comparative Genomics, Zachary Rodriguez

LSU Doctoral Dissertations

Non-model organisms with evolutionary novelties and complex distributions can provide valuable insight into the mechanisms underlying biological diversity. Green blood is one of the most unusual vertebrate physiologies and has repeatedly evolved in lizards from the megadiverse island of New Guinea. An unusually high concentration of the toxic green bile pigment biliverdin causes the green coloration of these lizards' blood, muscles, and bones. This dissertation uncovered the complex history of this novel trait (Chapter 2), identified protein-coding sequences that underlie green blood in lizards (Chapter 3), and explored evolutionary processes that drive genetic diversity in high-elevation lizards. To accurately trace …

Phylogeny And Evolution Of Swallows (Hirundinidae) With A Transcriptomic Perspective On Seasonal Migration, Clare Elisabeth Brown

LSU Doctoral Dissertations

Evolutionary biology seeks to understand the forces that have generated and shaped patterns of diversity. In this dissertation, I investigated phylogenetic relationships and the evolution of three traits—migration, nest-type, and geographic distribution—in the swallow family (Hirundinidae), a globally distributed group of about 85 species of aerial insectivorous birds. I first applied a dataset of several thousand ultraconserved element (UCE) loci to reconstructing the phylogeny of the New World genus Tachycineta. Three methods of phylogenetic inference produced topologically discordant trees, but post-inference analyses provided evidence that the tree produced by maximum likelihood analysis of a concatenated data matrix is the most …

Evolutionary History Of A Large-Genome Salamander Across Five Disjunct Regions Of The Southeastern United States, Catherine Elizabeth Newman

LSU Doctoral Dissertations

The southeastern United States has a dynamic geologic history. Mountain range uplift, sea level fluctuations, and river basin evolution have shaped species geographic distributions in the region. My dissertation objectively identifies amphibian species with highly fragmented distributions in the Southeast (Chapter 2) and examines the phylogeographic history of one of those species, Plethodon serratus. This salamander species has a widely disjunct range across five regions: the Appalachians, the Ozarks, the Ouachitas, and two allopatric sites in Louisiana. Analyses of mitochondrial and nuclear loci (Chapter 3) showed that P. serratus is comprised of multiple genetic lineages, and the five regions are …

Evolutionary Relationships Among Fungal Soybean Pathogens And Molecular Marker Development In The Genus Cercospora, Sebastian Albu

LSU Doctoral Dissertations

Cercospora leaf blight (CLB) and purple seed stain (PSS) are common soybean diseases in the Gulf South of the United States (USA). For nearly a century, Cercospora kikuchii has been considered as the only pathogen causing these diseases. However, previous reports of genetic diversity among isolates collected throughout Louisiana suggested the presence of multiple lineages or species. Recent systematic studies classified species of Cercospora using a taxonomic system based on phylogenetic analysis of five nuclear loci (legacy genes). Using a similar approach, cercosporoid fungi tentatively identified as C. kikuchii were evaluated along with 53 other species of Cercospora. No …