Theses and Dissertations from UMD
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New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM
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Item Physiological dynamics of injury and regeneration in the clonal freshwater annelid Pristina leidyi(2022) Rennolds, Corey William; Bely, Alexandra E; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The threat that mechanical injury poses to homeostasis and survival has spurred the evolution of diverse processes to mitigate these effects. The most dramatic of these is regeneration, a process that restores the form and function of lost body parts. The apparent benefits of regeneration may come at considerable cost, however, and these may substantially diminish regeneration’s adaptive value in certain contexts, potentially contributing to evolutionary losses of regeneration. The costs and benefits of regeneration are poorly understood in most animals, precluding more than speculation of the evolutionary drivers of regeneration. Naids are a group of small, clonally reproducing freshwater annelids that feature great diversity of regenerative ability and are well suited to experimental studies. I used the species Pristina leidyi to determine how injury and regeneration affect organismal function and fitness, integrating physiological and molecular approaches. I first investigated how injury and regeneration differentially affect an individual’s ability to tolerate environmental stress, an ecologically relevant and energetically demanding task. I found that stress tolerance is reduced by regeneration in a stressor- and tissue-specific manner while, unexpectedly, tolerance is temporarily improved shortly after injury. These effects are unrelated to whole-organism metabolic rate, which surprisingly does not differ between early and late injury recovery. Using 3’ TagSeq, I found that, while injury and heat stress elicit largely distinct responses, both upregulate certain shared damage control pathways. I then tested whether the physiological cost of regeneration has potential to translate into fitness costs by examining the interaction between regeneration and reproduction, which occurs by asexual fission in this species. By modulating resource availability, I found evidence for an energetic trade-off between regeneration and reproduction that is masked when food is abundant. This tradeoff is manifested through a reduction in per-offspring allocation rather than reproductive rate. Overall, my results demonstrate that injury and regeneration costs are highly context dependent in P. leidyi. More broadly, these findings contrast in key ways from evolutionarily distant animals with very different life history traits, illustrating the importance of investigating the physiological mechanisms that may mediate selection on regeneration in diverse lineages.Item Evaluating white perch (Morone americana) fecundity in select Chesapeake Bay tributaries in repsonse to pathology and fitness(2020) Shaner, Jacob; Harrell, Reginal M; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Fecundity studies have emerged as a complement to generalized stock assessment methods in an effort to more accurately determine reproductive potential, as well as explain a lack of stock recovery in some cases. The Chesapeake Bay presents an interesting case study, in that widespread anthropogenic influence has created the potential to reduce reproductive fitness among resident species, including white perch (Morone americana). This study seeks to investigate white perch population fecundity in response to habitat quality, as well as disease and nutrition, through the use of stereological and automated counting methods to assess agreement between stock assessments and reproductive potential. Results indicate lack of impact on fecundity from degraded habitat, limited impact of individual nutrition, and no conclusive effect from disease. These findings, coupled with stable recruitment, indicate that white perch reproduction in the Chesapeake Bay is unaffected by increased population stress.Item Resisting Reproductive Regulation in Early Twentieth Century American Women's Fiction(2017) DePriest, Elizabeth Ann; Mallios, Peter L; English Language and Literature; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Resisting Reproductive Regulation contributes to a growing body of criticism about how women participated in early twentieth century debates about reproduction in the United States. While the mainstream American birth control movement led to the legalization of contraception, it gained popular support by prioritizing the desires of married white women who were able-bodied, born in the United States, and members of the middle and upper classes. Because birth control advocates embraced eugenics and condemned abortion, their campaigns resulted in greater reproductive regulation for many women deemed “unfit” for reproduction by eugenicists, including unmarried, poor, non-white, immigrant, and disabled women. Resisting Reproductive Regulation examines the fiction written by American women during this period that challenges this limited agenda. These writers insist that women should be able to control the reproductive potential of their own bodies, regardless of their circumstances or forms of embodiment, and they examine the negative consequences that reproductive regulation enacts in American women’s lives. As a result, their texts depict women’s reproductive struggles in ways that anticipate late twentieth and early twenty-first century intersectional campaigns for reproductive justice. Though Mary Hunter Austin, Josephine Herbst, and Katherine Anne Porter each enjoyed relative privilege as white, American-born, and generally able-bodied women, each experienced reproductive difficulties in her own life. Each subsequently challenged mainstream birth control advocacy from this period in her fiction by grappling with those difficulties and examining the conditions that caused them. In so doing, these writers expose the prejudices encoded in the arguments upon which early twentieth century American eugenicists and birth control advocates relied. Resisting Reproductive Regulation argues that their fiction reveals inextricable relationships between the reproductive regulations American women faced and American prejudices about (dis)ability, sexuality, class, race, and/or country of origin. By addressing these connections, these writers explore the ways that reproductive regulations secure and perpetuate existing patriarchal, nationalist, white supremacist, heteronormative, capitalistic, and ableist systems of power. By advocating for women to be able to control the reproductive potential of their own bodies, these writers also attempt to interrupt the reproduction of these systems of power. Further, American women writing about contraception, abortion, and reproduction in the early decades of the twentieth century knew their depictions of these topics were subject to censorship, suppression, and marginalization. This dissertation argues that these writers resisted this form of reproductive regulation as well, developing innovative narrative and aesthetic techniques in order to communicate with readers about reproductive issues. While some of their concerns and experiences were successfully suppressed and marginalized during their lives, Austin, Herbst, and Porter each preserved illuminating materials in their personal archives. This dissertation recovers many of those materials, which provide new context within which to examine their published fiction and to recognize their literary and feminist contributions.Item Probing the 3D Structure and Function of a Cation/H+ Exchanger in Plant Reproduction(2015) Czerny, Daniel; Sze, Heven; Cell Biology & Molecular Genetics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Maintaining intracellular pH and K+ homeostasis are necessary for a cell to divide, grow, and communicate with other cell types. How a cell responds to stimuli and subsequently regulates intracellular pH and K+ content are largely unknown. Ion transporters, including cation/H+ exchangers are one potential determinant of intracellular pH and K+ content. A novel family of CHX transporters, predicted to exchange a cation for a H+, is found in all land plants, though their functions in the plant and the mode of transport are mostly unknown. What is the mode of transport of Arabidopsis thaliana CHX17? Model structures of the CHX17 transmembrane domain were built from two crystallized bacterial Na+/H+ antiporters. Based on protein architecture and homology, residues were selected for mutagenesis and CHX17 activity was tested in yeast. Thr170 and Lys383 in the discontinuous α-helices of transmembrane 4 and 11, and Asp201 and Lys355 in the middle of transmembranes 5 and 10 are necessary for CHX17 activity. Results suggest these are core residues that participate in cation binding and/or catalysis. Glu111 near the cytosolic surface of CHX17 was necessary for activity, suggesting CHX17 could be regulated by cytosolic pH. Thus the protein fold and mode of transport of Arabidopsis CHX17 resemble a K+/H+ exchanger. What roles do K+/H+ exchangers play in plant reproduction? chx17/18/19 mutant plants showed a 56%-77% reduction in seed set though the biological basis was unknown. Reciprocal crosses showed reduced seed set was primarily caused by defects in the male gametophyte. Mutant chx17/18/19 pollen grains developed normally and pollen tubes grew and reached most ovules. However, half the ovules receiving a mutant pollen tube failed to develop. Wild-type pistils that received chx17/18/19 pollen showed unfertilized ovules, ovules with single fertilizations, and some embryos that developed similarly to wild-type. Thus, some triple mutant pollen showed failure to complete fertilization. When fertilization was successful, embryos from self-fertilized chx17/18/19 pods showed delays in development. Our findings suggest maintenance of pH and K+ homeostasis in endomembrane compartments by CHX17 and its homologs could regulate membrane trafficking events necessary for pollen tube growth, male gamete fusion, and embryo development.Item Lifestyle Sex Selection: Reproduction, Transnational Flows, and Inequality(2012) Bhatia, Rajani; Thornton Dill, Bonnie; Women's Studies; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This dissertation examines new practices and technologies of sex selection with a particular focus on the interrelationship between the scientific products that enable these practices; the discursive production of these practices through news media, promotional literature and self-help communication; and the institutional operations of U.S. clinics both within and across national borders. In the late 1990s mass print and television media began heralding the emergence of new technologies as the answer to a long quest for scientifically proven methods for selecting the sex of a child. MicroSort and preimplantation genetic diagnosis gained considerable attention as methods of sex selection that diverged from earlier technologies because they do not require an abortion. Instead, both methods are applied before pregnancy and must be used in conjunction with assisted reproduction such as in-vitro fertilization. Along with the technologies appeared new discourses that make-meaning of these practices and new institutional mechanisms that embed them within a larger phenomenon of cross-(national) border reproductive practices. Using a genealogical approach, I trace how these three processes (material, discursive and institutional) configure a new form of sex selection at the same time as they construct a stratified system of global sex selection practices, contrasting reasonable, lifestyle motivations in the West with gender-biased forms in the East. The research uses qualitative, multi-sited modes of analysis and extends feminist STS scholarship on reproductive technologies by shifting focus to a transnational realm as manifested in what is currently conceptualized as "cross-border" reproductive practices. Against a shifting terrain of transnational reproductive practices, the study aims to displace a dichotomous framing of global sex selection practices that polarizes western from eastern practices with the more varied and complex movements that take place in cross -bordered sex selection. The study examines an emerging form of sex selection as an optic through which to theorize and reframe the meanings and interconnections among reproduction, transnational, and inequality, thereby generating new directions in feminist theorizing on reproduction.Item ASSESSMENT OF MALE GIANT PANDA SEASONAL REPRODUCTION, SEXUAL MATURITY AND COMPARATIVE SPERM CRYOTOLERANCE(2010) Aitken-Palmer, Copper; Ottinger, Mary Ann; Howard, JoGayle; Animal Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The giant panda is unique as one of the most studied endangered species. Interestingly, despite this, little is known about basic male reproductive physiology. Behavioral problems have posed challenges for reproductive success in the captive population, while geographical isolation and habitat fragmentation threaten the wild population. Techniques such as sperm cryopreservation can improve genetic management and reproductive success within captive populations. But without comparative freeze-thawing studies, diverse methods used for cryopreservation result in inconsistent post-thaw quality, potentially compromising sperm quality and fertility for artificial insemination. This, compounded by limited knowledge of male reproductive physiology, has challenged conservation goals for the giant panda. Specific objectives of this study include: 1) assess the influence of season on male giant panda reproduction by determining annual changes in testis size, body size, testosterone production, sperm quality and production, and reproductive behaviors throughout the year; 2) characterize the onset of sexual maturity in the male giant panda by documenting the timing of initial sperm production, increasing testicular size and body weight, rising androgen production and initiation of reproductive behaviors; and 3) identify factors influencing giant panda sperm cryopreservation by comparing the effect of freeze-thawing on sperm motility, acrosomal integrity, forward progressive movement and longevity. Results provide evidence that 1) reproductive seasonality in the male giant panda is more protracted than the female, with coordinated increases in testes size, androgen production, sperm density, and sexual behaviors; thereby maintaining reproductive competence to prepare for, and accommodate, a brief unpredictable female estrus; 2) sexual maturity in the male giant panda is first observed with consistent sperm production at 5.5 yr, then accompanied by increasing body weight, fecal androgen concentrations, and culminating with the onset of reproductive behaviors, such as scent marking between 7.5 - 8.5 yr; and 3) the giant panda spermatozoon has the capacity to withstand cold stress applied by multiple means, specifically after freezing and thawing using a unique field friendly dry shipper approach. These data greatly improve our understanding of male giant panda reproductive physiology, specifically seasonal rhythms, the cascade of changes associated with sexual maturation, and insights into improved comparative approaches for sperm cryopreservation.Item Understanding the Reproductive Biology of the Przewalski's Horse (Equus ferus przewalskii)(2010) Collins, Christina Wynne; Keefer, Carol ` L; Animal Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The Przewalski's horse (Equus ferus przewalskii) once roamed the Eurasian Steppe but is now considered Critically Endangered with only 1872 individuals remaining in the world, representing progeny from only 14 founder animals (Lee and Boyd, 2008). Genetic diversity needs to be optimal for long term survival of this species. Unfortunately, increasing genetic diversity of the captive population in North America has been hindered by a decrease in fertility. Therefore, the main focus of this research was to characterize reproductive parameters in Przewalski's horse, including estrus cycle in mares and seminal traits in stallions, and determining whether age or inbreeding had an impact on these traits. A secondary focus was to determine whether hormone manipulation of the estrous cycle in mares could be utilized for the long-term goal of using artificial insemination as a breeding management tool for this species. To facilitate these studies, a technique for palpation of Przewalski's mares was developed; the first application of such a procedure in a wild equid. Subsequently, we were able to describe follicular changes in relation to urinary hormone patterns. Fifty percent of the mares had either irregular or acyclic hormonal and follicular patterns. These patterns were directly correlated with inbreeding which is the first time such a correlation has been described in this species. Estrous manipulation was possible using an injectable biorelease form of the progestagen, altrenogest. In stallions, we developed a reliable method of semen collection for Przewalski's stallions and, as a result, describe seminal traits from 98 semen collections from 14 stallions. Based on these collections, we were able to show that sub-fertility in this population could be due to the low percentage of normal spermatozoa. Based on variable analysis, seminal traits total concentration, volume and morphology showed variable changes through the year. Traits also varied on an individual stallion basis. Together, these studies demonstrated that inbreeding is detrimentally affecting the reproductive fitness of this species and that aggressive management is needed for long term sustainability of the captive population.Item Sex, Dispersal, and Deep Divergence: the Population Genetics of the Protistan Parasite Perkinsus marinus(2010) Thompson, Peter Christian; Hare, Matthew P; Rosenthal, Benjamin M; Behavior, Ecology, Evolution and Systematics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The protistan parasite Perkinsus marinus causes Dermo disease in the eastern oyster, Crassostrea virginica. This parasite causes reduced growth and fecundity in its ecologically and economically important host, and as such has become a focal point for shellfish research. Though much is known regarding the seasonal dynamics and interactions between host and parasite, little research has focused on the basic biology of this parasite. In the research presented here, I used population genetic approaches to investigate the reproduction, dispersal, and origins of extant populations of P. marinus. First, I determined the extent of clonality in P. marinus populations. Repeated sampling of the same multilocus genotypes and extensive multilocus linkage disequilibrium indicated that clonal reproduction is prevalent. However, genotypic diversity was great and recombination occurred between genetic loci, supporting sexual reproduction as an important source of new genetic variation in P. marinus. An interesting consequence of sexual reproduction is that genotypic correlations may be maintained through inbreeding when sex occurs. Next, I investigated the genetic connectivity among locations. Clustering analyses revealed that local geographic samples are collections of independent clonal lineages rather than freely interbreeding populations. Some lineages were widespread while others were found at high frequencies only in specific locations indicating that P. marinus has a high capacity for dispersal, but local conditions may determine the success of certain lineages. Finally, I examined an interesting pattern of di-allelism observed in P. marinus DNA sequences. Two allelic classes were discovered at six out of seven nuclear loci where large divergences indicated the alleles had been independent for possibly millions of years. Balancing selection may be responsible for the retention of ancient diversity in this parasite, but it seems more likely that a recent hybridization event has occurred between two formerly allopatric lineages. These results underscore risks in the anthropogenic movement of protistan parasites as there may be no reproductive barriers between ancient lineages. Resulting hybrids could result in increased parasite virulence with increased disease in host populations.Item A comparative analysis of sperm storage in six brachyuran superfamilies: mating behavior, ecological variation and phylogenetic patterns(2010) Rodgers, Paula Jane; Reaka, Marjorie L; Hines, Anson H; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)While life history traits are shaped by allometric, phylogenetic, environmental and behavioral factors, few comparative studies of brachyuran life history patterns have considered sperm storage traits as important components of reproductive strategies. To understand the evolutionary forces selecting for sperm storage and their interactions with other life history traits, I (1) used controlled laboratory experiments and field mating observations to examine variation in male sperm transfer patterns, (2) sampled variation in female reproductive output and sperm storage for two species across a latitudinal gradient, (3) conducted a survey of life history traits across a broad range of brachyuran taxa, and (4) used phylogenetic analyses to identify patterns in the evolution of life history traits in brachyurans. From mating experiments and observations on five species, I found that males transfer more sperm with longer than shorter copulation durations and that variation in copulation duration was shaped by differences in the species' ecologies. Latitudinal surveys of two species with contrasting mating systems identified seasonal and geographical variation in female reproductive output. While the variation in most reproductive traits could best be explained at smaller spatial scales, a sperm storing species, Callinectes sapidus became sperm limited at low latitudes. From a comparative survey of male and female life history traits across 61 species of brachyurans, I found that allometry, phylogeny and mating strategies explained much of the variation in life history traits. Using rigorous phylogenetic techniques, male life history traits showed more plasticity across the phylogeny than female traits suggesting male traits may be influenced more by behavioral and environmental factors. After correcting for phylogenetic signals, species with larger male sperm stores had larger amounts of sperm stored by the female. In summary this dissertation illustrates the importance of partitioning variation in mating behavior, phylogeny, environmental factors and allometry when examining the evolution of life history traits in brachyurans.Item The effect of sperm mobility phenotype on fertility persistence in layer and broiler hens(2008) Baczynski, Kathleen; Estevez, Inmaculada; Animal Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Domestic fowl (Gallus gallus domesticus) were studied to identify accurate predictors of potential fertility in two lines of broiler breeder males along with fertility persistency in layer and broiler hens. Sixty-four Hy-Line layer and thirty-seven broiler breeder hens were AI with identical amounts of high or low mobility sperm from FG males. Morphological measurements were taken to determine relationships of these with semen volume, concentration, and mobility. We hypothesized that 1) semen quality would decline as males aged, 2) morphology would be positively correlated with semen quality, and 3) females AI with high mobility sperm would have a longer duration of fertility. Results revealed a significant age*line interaction for semen volume (p=0.0307), sperm concentration (p=0.0003), and sperm mobility (p=0.0405). Morphological measurements were correlated with different semen parameters in both lines. Fertility was positively correlated with semen quality. Sperm mobility influenced fertility in layer hens but not in broiler breeders.