Biological Sciences electronic theses and disserations (MU)
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The items in this collection are the theses and dissertations written by students of the Division of Biological Sciences. Some items may be viewed only by members of the University of Missouri System and/or University of Missouri-Columbia. Click on one of the browse buttons above for a complete listing of the works.
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Item Behavioral ecology, ecophysiology, and social dynamics in miniaturized Puerto Rican geckos (Sphaerodactylus)(University of Missouri--Columbia, 2025) Perez-Martinez, Christian Alessandro; Leal, Manuel[EMBARGOED UNTIL 05/01/2026] The impact of body size on organismal biology continues to fascinate biologists, particularly when considering miniaturized animals at the smallest extremes. Geckos of the genus Sphaerodactylus are characterized by their diminutive size, species richness, and the diverse habitats they occupy across the Caribbean. First, I contextualized Sphaerodactylus within the squamate phylogeny, demonstrating the repeated evolution of miniaturization across 11 families, corroborating brain size as a limiting factor for body size (along with a relative increase in telencephalic volume), and revealing an ecological shift to terrestrial microhabitats [Chapter II]. These findings were used as a springboard to evaluate the potential consequences of miniaturization in Sphaerodactylus with respect to activity patterns [Chapter III], thermal physiology [Chapter IV], and social behavior [Chapter V]. Under natural conditions, I implemented a vibrational monitoring system to characterize activity patterns across leaf litter strata in S. grandisquamis and S. townsendi. Vibrational data revealed that Sphaerodactylus exploit their niche in a threedimensional manner, a pattern thus far underappreciated, and that behavior is used as a mechanism to buffer climatic changes in xeric habitats [Chapter III]. Physiological traits are expected to evolve to favor homeostasis under a species' preferred habitat conditions, regardless of body size, yet few studies have tested whether this pattern extends to miniaturized taxa. I measured standard metabolic rate (SMR) and evaporative water loss (EWL) via open-flow respirometry in five Sphaerodactylus species from three distinct habitat types. Physiological traits exhibited divergence mediated by habitat type -- xeric, mesic, and submontane -- and between sympatric species, indicating that the evolutionary potential of physiological traits was not limited by miniaturization in Sphaerodactylus [Chapter IV]. Lastly, I used S. grandisquamis to study social dynamics, further elucidating the behavioral ecology of a miniaturized leaf litter species. Specifically, I evaluated the possibility of social recognition and the effect of the social environment on individual behavior. Through behavioral assays, I introduced familiar individuals to their own groups and unfamiliar individuals to existing groups. Increased rates of exploratory and agonistic behaviors were performed by group members toward unfamiliar individuals, supporting recognition of familiarity. Furthermore, geckos from multi-male groups showed reduced rates of behaviors toward unfamiliar individuals, including agonistic behaviors, in concert with male-male agonism and potentially increased intersexual conflict within their groups. Social recognition and the effect of the social environment as a modifier of individual behavior are perhaps unexpected for a putatively solitary, miniaturized species. The cognitive processes underlying social behavior may be related to the ecology of Sphaerodactylus, particularly their high population densities, facilitated by miniaturized body size [Chapter V].Item Molecular mechanisms that regulate the amino acid composition in Arabidopsis seeds(University of Missouri--Columbia, 2025) Bagaza, Clement; Angelovici, Ruthie[EMBARGOED UNTIL 05/01/2026] Amino acids (AA) are the building blocks of proteins, which makes them extremely important for growth and development. Crop seeds, such as legumes and cereals, play an essential role as a key food source in the diet of humans and livestock but do not meet the dietary requirements of essential amino acids (EAA), which are the AA that humans and vertebrates cannot synthesize and must obtain from the diet. Lacking sufficient levels of EAA in the diet can lead to protein-energy malnutrition, which adversely affects the immune, gastrointestinal, nervous, and cardiovascular systems. Efforts to fortify AA composition in crop seeds have had a very limited success because plants respond to induced protein composition alterations by activating a regulatory mechanism that "resets" it back to the original state. This phenomenon is known as proteome re-balancing, and, while beneficial for plants' growth and development, has been a major hurdle to biofortification. A good understanding of the regulation and rebalancing mechanism of AA in seeds would improve the biofortification of AA composition. Chapter One of this dissertation provides a comprehensive introduction from previous studies of what is known about amino acid composition in seeds, the challenges identified in previous experimentation, and how the content of the other chapters builds upon and adds value to the area of seed amino acid research and to the understanding of proteome rebalancing. Chapter Two uncovers the genes and biological processes that underly proteome relancing using mutants of the most abundant seed storage proteins (SSPs), the cruciferins also known as 12S. To better understand how proteome rebalancing is achieved in seeds, we conducted a comprehensive analysis on Arabidopsis mutants lacking the three most abundant SSPs, the cruciferins (CRUs). The multi-omics analysis such as transcriptome, proteome, metabolome, and measurement of physiology parameters was conducted on single mutants (crua, crub, and cruc) and the triple knock out (cruabc) mutants compared to the wild type (Col-0). All major seeds storage compounds remained unchanged in these mutants suggesting rebalanced seeds. Further analysis showed that translation and oxidative stress responses are the two key biological processes that dominated proteome rebalancing. Chapter Three focuses on how proteome rebalancing is achieved in the second most abundant seed storage proteins known as the Napins or 2S. In this chapter, I used one napin-RNAi (RNA interference) to target all 5 members of this gene family. Using the multi-omics analyses, all reserve compounds remained the same compared to Col-0 except the sulfur. Only oxidative stress response dominated the biological processes involved in proteome rebalancing in the Napin seed storage proteins. Chapter Four covers the remaining seed storage protein mutants from the cruciferins, these were the double mutants (cruab, cruac, and crubc). In this chapter, all analyses performed compared the doubles (cruab, cruac, and crubc) to Col-0; genes and key pathways involved in proteome rebalancing were revealed. Lastly, Chapter Five, the conclusion, reiterates the contributions of this dissertation to the field of seed amino acid proteome rebalancing and provides future directions and research projects that can be done to bring much more insight into this field.Item Cell envelope integrity in the polar-growing bacterium Agrobacterium tumefaciens(University of Missouri--Columbia, 2025) Amstutz, Jennifer; Brown, Pamela[EMBARGOED UNTIL 05/01/2026] Peptidoglycan (PG), the primary structural component of the bacterial cell wall, is essential for maintaining cell integrity and shape. While most bacteria rely on penicillin-binding proteins (PBPs) to generate crosslinks in PG, some species also use LD-transpeptidases (LDTs). Members of the Hyphomicrobiales order within the Alphaproteobacteria, which are characterized by polar growth, possess PG enriched in LD-crosslinks—suggesting an expanded role for LDTs. This work investigates the roles of LDTs and their interaction with outer membrane proteins (OMPs) in maintaining envelope integrity and supporting growth, particularly under stress conditions in the plant pathogen Agrobacterium tumefaciens. In Chapter 2, a structural and phenotypic analysis identified a conserved set of Hyphomicrobiales-specific LDTs (Group 3) that play essential roles in cell elongation and polar growth. Despite a high degree of functional redundancy among these enzymes phenotypic differences suggest some LDTs have specialized functions, such as tethering OMPs to the cell wall. Chapter 3 builds on this by showing that a subset of these LDTs, along with the β-barrel OMP AopB, are transcriptionally regulated by the ChvG-ChvI two-component system—a regulatory pathway activated by cell envelope stress. LDT-mediated crosslinking of AopB to the peptidoglycan enhances envelope stability under heat, osmotic, and cell wall stress, with both ΔaopB and Δgr3 mutants exhibiting similar stress sensitivity profiles. These findings highlight an expanded role for the ChvG-ChvI regulon in envelope remodeling during stress. Finally, Chapter 4 explores the potential modulation of the outer membrane proteome by the ChvG-ChvI regulatory network response to envelope damage. Activation of ChvG-ChvI likely promotes cell envelope integrity by enhancing structural reinforcement of the envelope through β-barrel OMP-PG crosslinking mediated by LDTs and increased production of EipA a periplasmic, β-barrel protein. Together, these studies define a critical role for the LDTs and their substrates in the adaptive envelope remodeling of A. tumefaciens and position the ChvG-ChvI pathway as a central regulator of envelope integrity and environmental resilience.Item Characterization of cell fate determination in oocyte differentiation and oocyte development in the mouse ovary(University of Missouri--Columbia, 2025) Wilson, Faith; Lei, LeiThe production of the oocyte in mammals begins in the fetal stage with the formation of primordial germ cells (PGCs). PGCs differentiate through the process of oocyte differentiation to become primary oocytes. After the emergence of primary oocytes, the oocytes become quiescent and enclosed by somatic follicle cells to form the ovarian reserve. The ovarian reserve forms through a highly conserved process in mammals and serves as the only resource to sustain and prolong female reproductive life. Primary oocytes are activated periodically from the ovarian reserve when puberty occurs. Once a primary oocyte is activated in the ovary, it has two fates available to it, continue through oocyte development and potentially be ovulated or face cell death. In my master's thesis I explore the cellular mechanisms of the mouse ovary spanning oocyte differentiation to oocyte development. In chapter one, I investigate oocyte differentiation, specifically cell fate determination in fetal gametogenesis. During mammalian fetal gametogenesis, both male and female germ cells are connected via intercellular bridges yet experience major differences in cell fate determination. In mouse fetal testes, male germ cells arrest in G0/G1 after embryonic day (E)14.5 and differentiate into gonocytes postnatally. In contrast mouse female germ cells enter meiosis after E14.5 and initiate oocyte differentiation. During oocyte differentiation, two fates are possible, ~80 percent of the germ cells donate organelles and undergo cell death; ~20 percent of the germ cells collect organelles from sister germ cells and become primary oocytes. Due to the small percentage of germ cells that become primary oocytes, this led us to investigate the differences in cell fates between female and male germ cells using single cell RNA sequencing. The findings highlight key features in female and male germ cell transcriptomics. This data helps us understand cellular mechanism differences in female and male germ cell populations and how it relates to differential cell fates. In chapter two, I investigate oocyte development, specifically whether quiescent primary oocytes experience cellular senescence and non-apoptosis cell death in the mouse ovary, a process that may lead to primary ovarian insufficiency (POI) and physiological ovarian aging. Cellular senescence is characterized by cell cycle arrest and production of the senescence associated secretory phenotype (SASP) associated with tissue aging. The activation of primary oocytes from the ovarian reserve is an irreversible process that forces the oocytes to develop via folliculogenesis or undergo cell death. In this project we used a mouse model with POI phenotypes caused by Pten depletion specifically in the oocyte. We examined quantitatively cellular senescence and cell death (apoptosis and ferroptosis) in 2 weeks and 4 weeks old mutant mouse ovaries, when primary oocyte loss take place. Our data demonstrated that overactivation of primary oocytes contributes to a reduction in the ovarian reserve in mutant ovaries; and an increased number of senescent primary oocytes were found in mutant ovaries as well. Although it appeared in a low number, it was found that all primary oocytes that undergo ferroptosis were senescent. This data drives what is known about cellular mechanisms in oocytes further by providing quantitative results of follicle loss, cellular senescence, and cell death markers in the primary oocyte.Item The evolutionary history and impact of polyploidy in mustard crops and their relatives(University of Missouri--Columbia, 2025) Thomas, Shawn Kodiattu; Pires, J. Chris||Washburn, Jacob D.Gene duplications provide raw material for the emergence of novel traits. The two primary mechanisms for gene duplication are polyploidy events, which result in whole genome duplications or triplications (WGD, WGT), and small-scale duplications (SSD). Together, these processes play a crucial role in plant evolution. Mustard crops (Brassica) such as bok choy, broccoli, cabbage, and canola belong to the tribe Brassiceae within the mustard family (Brassicaceae), nested in the larger order Brassicales. These crops share a relatively recent Br-[alpha] WGT, which has influenced their domestication, phenotypic plasticity, and secondary metabolism. However, the precise timing and placement of this event on the mustard phylogeny remain unclear. To resolve this, sequence and fossil data are used to determine when and where the Br-[alpha] WGT occurred in Chapter 2. These findings have important implications for understanding the evolution and taxonomy of this group. While extensive research has explored gene duplications in mustard crop species, their wild relatives within tribe Brassiceae remain largely unstudied. A combination of ionomics, metabolomics, and comparative genomics is applied in Chapter 3 to investigate salt and heavy metal stress responses in the mustard crop wild relative Cakile maritima. These analyses identify retained duplicate genes likely contributing to stress adaptation, highlighting the roles of both WGT- and SSD-derived duplications in environmental resilience. These findings highlight the value of crop wild relatives in understanding adaptation and identifying genetic targets for improving stress tolerance in crops. Beyond tribe Brassiceae, the Br-[alpha] WGT is only one of several ancient polyploidies in Brassicales. The At-[beta] WGD is shared by most Brassicales species, but its exact placement remains uncertain. To address this, the first haplotype-resolved genome assembly of Moringa oleifera is generated in Chapter 4, providing a foundation for studying trait evolution following ancient polyploidy. This genome, in combination with other genomic resources, also supports future crop improvement efforts in the species. Overall, this research advances the understanding of mustard crop evolution and their wild relatives. Studying the evolution of crops and their wild relatives provides valuable insights into agronomically important traits, contributing to the development of sustainable agriculture.