UMD Theses and Dissertations
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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 given thesis/dissertation in DRUM.
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Item NEURAL BASIS OF VIBRATION DETECTION IN LEPIDOSAURIAN REPTILES(2024) Han, Dawei; Carr, Catherine E.; Neuroscience and Cognitive Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)There are three potential pathways for detection of substrate vibration: cochlear, otolithic and somatosensory, reviewed in chapter one. How different lepidosaurian reptiles detect substrate vibration from these three pathways was explored from neuroanatomical and physiological perspectives. In chapter two, I described vibration sensitivity and the organization of the brainstem cochlear nuclei in the western snake (Pantherophis obsoletus). The western ratsnake is sensitive to low-frequency vibrations, comparable to other snakes. It has two first-order cochlear nuclei, nucleus magnocellularis (NM) and nucleus angularis (NA), similar to other reptiles. NM is small, while NA is relatively robust. In chapter three, I examined the connections and response properties of nucleus vestibularis ovalis (VeO) in the hindbrain of the tokay gecko (Gekko gecko). VeO receives input from the saccule, and connections of VeO mirror those of the cochlear nuclei, including an ascending projection to the central nucleus of the torus semicircularis. VeO neurons are sensitive to low-frequency vibration. In chapter four, I revisited a classic study to determine the connections and response properties of the snake torus semicircularis. In the western ratsnake, the torus can be divided into a central nucleus and a paratorus, the latter receiving input from the spinal cord, nucleus myelencephali dorsalis in the spinomedullary junction, as well as auditory nuclei. Toral neurons are sensitive to low frequency vibration and have heterogenous response characteristics. In chapter five, I discuss future directions based on findings in my dissertation and highlight the importance of vibration detection for lepidosaurs.Item SPATIOTEMPORAL DISTRIBUTION OF CHESAPEAKE BAY MYSIDS IN THE CHOPTANK AND PATUXENT RIVERS, MARYLAND(2024) Quill, Danielle; Woodland, Ryan; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The importance of mysids as trophic links in key Chesapeake Bay food webs has been well documented. However, their abundance, distribution, and demographics haven’t been examined in Chesapeake Bay since 1930. The goal of this study was to examine patterns of mysid abundances and demographic dynamics between and within two key Chesapeake Bay tributaries (the Choptank and Patuxent rivers). I hypothesized that mysid abundances would be greater in the Choptank River due to its historically better water quality (particularly dissolved oxygen saturation) than the Patuxent River. Secondarily, I hypothesized that Neomysis americana (hereafter, Neomysis) would be the most abundant mysid species in both the Chopank and Patuxent rivers. Six stations in each river were sampled monthly from May to September of 2018. Numerical dominance of the mysid assemblage in both rivers shifted from Neomysis in the early summer to a mixed-species group belonging to the genus Americamysis (Americamysis spp.) between August and September. Total abundance across genera and abundance of Neomysis were significantly greater in the Choptank River in early summer, then did not differ from Americamysis spp. abundance thereafter. Neomysis abundance was greater than Americamysis spp. from May through June, did not differ from Americamysis spp. abundance in July, and was less abundant than Americamysis spp. from August through September in the Patuxent River. The Patuxent River displayed overall lower dissolved oxygen saturation in the summer, which correlated with lower mysid abundances, providing support for my hypothesis. Understanding the intricacies of mysid population dynamics within nursery areas for ecologically and economically important predators should strengthen ecosystem-based management strategies for those areas.Item Assessing vertebrate biodiversity across the Chesapeake Bay using environmental DNA metabarcoding(2023) Rodriguez, Lauren Kelly; Bailey, Helen; Woodland, Ryan J; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Through the collection and sequencing of trace genomic evidence from environmental samples (e.g., water, air, and soil), environmental DNA (eDNA) metabarcoding can detect a range of vertebrates. Despite the dynamic characteristics of estuarine environments, which often hinder the persistence of genomic material, this project successfully employed metabarcoding to assess the distribution of vertebrates in the Chesapeake Bay. Primarily, the study evaluated the effects of using various eDNA sampling, laboratory, and post-hoc analysis techniques when investigating species presence and biodiversity of an area. This study also identified spatially-explicit fish communities along salinity gradients as described by a Generalized Additive Mixed Model (GAMM) and a Permutational Multivariate Analysis of Variance (PERMANOVA). Community compositions were similar to previous findings by traditional trawling and seining methods. This research supports the usefulness of eDNA metabarcoding to assess species presence across spatiotemporal extents, making it a promising tool for future biomonitoring efforts in the Chesapeake Bay.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 ECOLOGICAL CAUSES AND CONSEQUENCES OF NON-BREEDING MOVEMENTS IN A DECLINING MIGRATORY SONGBIRD, WOOD THRUSH (HYLOCICHLA MUSTELINA)(2019) Stanley, Calandra Quinn; Dudash, Michele R; Marra, Peter P; Behavior, Ecology, Evolution and Systematics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)In this dissertation I evaluate the ecological correlates of non-breeding space-use strategies and how these drive within and between season movement dynamics in a declining migratory songbird, wood thrush (Hylocichla mustelina). In Chapter 1, I deployed high-resolution GPS transmitters across 5 breeding populations to quantify habitat selection as wood thrush moved across the annual cycle. I found seasonal variation in habitat selection at the regional, landscape and local scales which suggests the factors driving the evolution of habitat selection preferences vary across seasons and environmental conditions. In Chapter 2, I combined radio telemetry and GPS tracking to examine how environmental conditions drove space-use strategies during the non-breeding stationary period. I found evidence that both small- and large-scale movement dynamics were dependent on moisture levels on tropical non-breeding grounds. At small spatial scales, dry conditions drove low food availability, reduced individual body condition and these individuals had larger home ranges. In this same chapter I integrated archival GPS tag data to demonstrate that wood thrush from across the breeding range engaged in permanent large-scale mid-winter shifts in home ranges and, similar to radio-tagged birds, that individuals from wetter, higher quality habitats were more likely to use this strategy. I suggest that the facultative movements are a condition-dependent strategy allowing wood thrush to find alternative habitats as conditions deteriorate across the dry season in their non-breeding grounds. Finally, to determine how food availability may influence timing of spring migration, I performed a food manipulation experiment with captive wood thrush in Chapter 3. I found that food availability and body condition modulated the intensity, but not onset, of migratory restlessness (Zugunruhe), an index of migratory disposition in captive birds. These results suggest that non-breeding food limitations could constrain migration preparation in wood thrush. Low food availability also advanced the onset of migratory fattening. I suggest that advancing migratory fattening when food availability is low may provide a mechanism to flexibly adjust migration timing under poor environmental conditions. Together these findings suggest that wood thrush exhibit a diversity of behavioural mechanisms to handle environmental heterogeneity across the annual cycle.Item Multi-locus phylogenetic analysis of Amphipoda indicates a single origin of the pelagic suborder Hyperiidea(2019) Biancani, Leann M; Cummings, Michael P; Osborn, Karen J; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Hyperiidea is an exclusively pelagic suborder of amphipod crustaceans, exhibiting a wide array of unique adaptations to life in the dark, open expanse of the oceanic midwater. No common morphological synapomorphy unites approximately 350 described species. Instead, hyperiid amphipods are defined only by their pelagic existence. Hyperiidea exhibits many of the characteristics of an adaptive radiation and could represent a midwater example of this phenomenon. Previous morphological and molecular analyses have led to uncertainty in the shared ancestry of Hyperiidea. The evolutionary history of their diverse adaptations, as well as their relationship to other amphipods, remains unknown. Here we present results of a multi-locus phylogenetic analysis of publicly available amphipod sequences for three nuclear loci (18S, 28S, and H3) and two mitochondrial loci (COI and 16S) from over 300 amphipod genera, 40 of which are hyperiids. We recover strong support for a monophyletic Hyperiidea as well as reciprocally monophyletic hyperiid infraorders Physocephalata and Physosomata (with enigmatic genera Cystisoma and Paraphronima more closely related to Physosomata). We also identify several benthic, commensal amphipods representing potential sister groups for Hyperiidea. These taxa have not previously been considered close hyperiid relatives and include the genera Amphilochus, Colomastix, Anamixis, Paranamixis, and Leucothoe. Our results support the current definition of Hyperiidea and inform the phylogenetic placement of the suborder within Amphipoda.Item NOVEL ADAPTATIONS IN MORPHOLOGY, DEVELOPMENT, AND NUTRIENT AQUISITION FOR HOST EXPLOITATION IN THE MESOSTIGMATID HONEY BEE PARASITE VARROA DESTRUCTOR(2018) Ramsey, Samuel David; vanEngelsdorp, Dennis; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The parasitic mite Varroa destructor is the most significant single driver of the global honey bee health decline. Better understanding of the association of this parasite and its host is critical to developing sustainable management practices. This work shows that Varroa is not consuming hemolymph as has been the accepted view, but damages host bees by consuming fat body. Feeding wounds in adult bees were imaged for the first time showing that Varroa feed on the underside of the abdomen where fat body is the immediate underlying tissue. Fat body at the wound site showed evidence of external digestion. Hemolymph and fat body in honey bees were then marked with fluorescent biostains. Fluorescence associated with the fat body was consistently detected in the gut of mites fed on these bees while comparatively little fluorescence was detected from the hemolymph biostain. Mites were then fed a diet composed of one or both tissues. Mites fed fat body tissue survived longer and produced more eggs than those fed hemolymph. Mites fed hemolymph showed fitness metrics no different from the starved control group. Collectively, these findings show that Varroa are exploiting the fat body as their primary source of sustenance; a tissue integral to proper immune function, pesticide detoxification, overwinter survival and several other essential processes in healthy adult and immature bees. Additional study was undertaken to better understand how the Varroa accelerates its reproductive rate. Via gel electrophoresis and immunodetection, undigested honey bee vitellogenin was found in Varroa eggs. The presence and identity of these host proteins was confirmed via HPLC MS/MS. This particular cleavage of vitellogenin is found only in the fat body. These findings fundamentally alter our understanding of the etiology of varroosis and underscore a need to revisit our understanding of this parasite and its impacts, both direct and indirect, on honey bee health. Further study of Varroa adaptations focused on expanding knowledge of Varroa morphology with the aim of determining features that can distinguish between Varroa species. Using low temperature scanning electron microscopy, we were able to provide better resolution of key morphological features, detail variability within traits, and provide novel descriptions of certain characters.Item Phylogenomics, Systematics, and Evolution within the Nudibranch Group Cladobranchia (Mollusca: Gastropoda)(2017) Goodheart, Jessica Ann Marie; Cummings, Michael P; Collins, Allen G; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)To truly understand evolution, we must document patterns of variation in traits – ranging from anatomical features of individuals to geographic ranges of species – to gain insights into the mechanisms that lead to changes in diversity through time. This type of work requires a robust historical context of evolutionary relationships in order to make comparisons across taxa and inferences about past events. My dissertation provides a thorough phylogenetic analysis of the marine gastropod group Cladobranchia (Mollusca) to better understand the evolution of defensive capabilities within the clade. In the absence of a protective shell, lineages within Cladobranchia have evolved a diverse array of alternative defense mechanisms, including the use of stinging organelles (nematocysts) acquired from their cnidarian prey. It has been hypothesized that incorporation of nematocysts as a defensive strategy may have been an evolutionarily important event that led to large-scale diversification within this group. As such, understanding the steps involved in the evolution of this ability is necessary for evaluating this hypothesis. A major objective for my dissertation has been to use transcriptome (RNA-Seq) data from 37 species in Cladobranchia in order to generate a well-supported phylogenetic hypothesis of Cladobranchia. This research has produced the most highly supported phylogenetic tree of Cladobranchia thus far and contributes to confidence in the efficacy of genomic data to resolve relationships among gastropod lineages. As I have been able to expand this phylogenetic hypothesis with additional taxon sampling, including molecular data from a further 60 species, I have been able to provide context for understanding the evolutionary steps that led to the ability to sequester nematocysts. This phylogeny was then combined with morphological data from 50 nematocyst sequestering species within Cladobranchia to allow for a more detailed reconstruction of the evolution of nematocyst sequestration and prey preference within this clade. Overall, this work builds knowledge of the relationships among major lineages within Cladobranchia, and has substantially increased understanding of the evolution of morphological and ecological characters in this group.Item UNRAVELING THE EVOLUTIONARY HISTORY OF NOCTURNALITY IN THE STRISORES(2017) White, Noor; Carleton, Karen L; Braun, Michael J; Behavior, Ecology, Evolution and Systematics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Tracing the processes of adaptation is a fundamental practice in the study of evolutionary biology. By combining multiple lines of evidence, we can elucidate the processes of diversification, speciation, and ultimately, evolution. For my doctoral dissertation, I studied the evolutionary history of a superorder of birds (Strisores) that have undergone a dramatic life history transition, the shift from a day-living (diurnal) to a night-living (nocturnal) lifestyle. Previous study found that the diurnal Apodiformes (swifts and hummingbirds) are nested deep within the clade of nocturnal or crepuscular Caprimulgiformes (nightbirds). However, resolution of the other major lineages eluded previous efforts, precluding analysis of the evolution of nocturnality in this group. To resolve the phylogeny of Strisores, I utilized a novel class of genome-scale markers, ultraconserved elements (UCEs). UCEs are operationally defined regions of extreme conservation between two or more genomes. I collected and sequenced ~4,000 UCEs from each of 191 species of birds representing every major extant lineage, plus two crocodilian outgroups—a greater number of elements than had ever been collected or studied before. With this data, I have resolved the phylogeny of the largest and oldest (Caprimulgidae and Nyctibiidae, respectively) lineages of nightbirds, as well as the superorder Strisores, and have shed light on best practices for the use of UCEs in phylogenomics. With a phylogeny representing the evolutionary history of Strisores I then ask when, and where, potential adaptations to nocturnality occurred. To this end, I have developed a molecular tool to efficiently enrich 47 genes comprising the phototransduction cascade, a network of genes that converts the absorption of a photon by an opsin into a neural signal. I demonstrated that this tool is effective in 33 bird species chosen to cover extant avian diversity. The data captured using this array will facilitate the identification of potential molecular adaptations to nocturnality, enable the improvement of models predicting opsin sensitivity from sequence data, and allow strong inference about the perception of color across birds and other vertebrates.Item The neuro-humoral control of circulation, or the morphology and physiology of the vascular changes involved in gill reduction in salamanders(1934) Figge, Frank H. J.; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)