UMD Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/3
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 DEVELOPMENT OF A NUCLEIC ACID-BASED SPECIFIC GROWTH MODEL FOR JUVENILE BLUE CRAB, CALLINECTES SAPIDUS(2016) Zaveta, Danielle Rae; Miller, Thomas J; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The evaluation and identification of habitats that function as nurseries for marine species has the potential to improve conservation and management. A key assessment of nursery habitat is estimating individual growth. However, the discrete growth of crustaceans presents a challenge for many traditional in situ techniques to accurately estimate growth over a short temporal scale. To evaluate the use of nucleic acid ratios (R:D) for juvenile blue crab (Callinectes sapidus), I developed and validated an R:D-based index of growth in the laboratory. R:D based growth estimates of crabs collected in the Patuxent River, MD indicated growth ranged from 0.8-25.9 (mg·g-1·d-1). Overall, there was no effect of size on growth, whereas there was a weak, but significant effect of date. These data provide insight into patterns of habitat-specific growth. These results highlight the complexity of the biological and physical factors which regulate growth of juvenile blue crabs in the field.Item Influence of environmental conditions on the age, hatch dates, and growth of juvenile Atlantic menhaden in the Choptank River, MD(2016) Atkinson, Alexandra Nicole; Secor, David H; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Since 1993 Atlantic menhaden has experienced sustained low juvenile production (recruitment) in the Chesapeake Bay. Factors controlling growth, abundance, and mortality of larval and juvenile menhaden change throughout ontogeny such that larval growth rates could carry over to juvenile growth and survival. The effects of winter thermal conditions on the hatch dates and growth of larval and juvenile Atlantic menhaden in Atlantic shelf and Chesapeake Bay habitats were examined using otolith (ear-stone) increment analyses and growth models. For 2010-2013, truncated hatch-date distributions provided evidence for a winter recruitment bottleneck in Atlantic menhaden caused by cold temperatures. Hatch-dates of surviving juveniles were skewed towards warmer months for years characterized by colder temperatures. Reduced larval growth rates, influenced by reduced temperature and food availability, carried over to juvenile growth rates. A growing degree-day model performed well in simulating observed juvenile growth rates in the Choptank River tributary of Chesapeake Bay.Item Dispersal and Population Ecology of the Red-backed Salamander (Plethodon cinereus)(2015) Hesed, Kyle Miller; Wilkinson, Gerald S; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Terrestrial salamanders are major components of ecosystems in eastern North America. One species, the Red-backed Salamander (Plethodon cinereus), may be the most abundant vertebrate throughout its range. Red-backed Salamanders are commonly monitored as indicators of ecosystem health and to assess the effects of forest management practices. In order to address poorly understood aspects of the ecology of Red-backed Salamanders, I conducted a 4-y mark-recapture study of a population in Maryland, resulting in 2,745 records of 752 marked salamanders, along with a complementary genetic analysis of six microsatellite loci. I estimated growth rates and age at sexual maturity using a hierarchical Bayesian model fitted by mark-recapture measurements, then measured home range size and seasonal and annual movement distances by immatures and adults, before and after the experimental removal of 98 conspecifics. Males grow and mature more slowly than females, despite reaching slightly larger asymptotic sizes; they may also face greater competition for space: adult males occupy the largest home ranges and show the largest increase in home range size after the removal of conspecifics. The largest between-year movements were made by individuals as they transitioned from immaturity to maturity. Using mark-recapture population models, I found that estimates of survival, detection, and abundance varied temporally along with the age and sex of the individuals present, both within and among seasons. Encounter probability varied among weekly sampling occasions, and models with separate parameters for each sex were strongly preferred. Survival was approximately the same over winters and summers, and lower for males than for females; this may be an artifact of sex-biased dispersal, as the majority of encountered immature individuals were estimated to be males, with models indicating a pulse of emigration in the fall and an influx of immature males onto the study site in the spring. An FST randomization test of multilocus genotypes showed a significant male bias in dispersal. Of salamanders captured repeatedly as both immatures and adults, males moved significantly farther before maturity than females did. Together, these results provide a comprehensive assessment of sex-biased dispersal at fine spatial and temporal scales in a terrestrial ectothermic vertebrate.Item The effects of co-varying diel-cycling hypoxia and pH on disease susceptibility, growth, and feeding in Crassostrea virginica(2014) Keppel, Andrew George; Breitburg, Denise L; North, Elizabeth W; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Diel-cycling hypoxia and pH co-occur in shallow waters world-wide. Eutrophication tends to increase the occurrence and severity of diel cycles. We used laboratory experiments to investigate effects of diel-cycling DO and pH on acquisition and progression of infections by Perkinsus marinus, the protistan parasite which causes Dermo disease, as well as hemocyte activity, growth, and feeding in the eastern oyster, Crassostrea virginica, an important estuarine species. Diel-cycling DO increased P. marinus infection and cycling DO and pH stimulated hemocyte activity and reduced oyster growth. However, ambient environmental conditions and oyster age modulated some of these effects. Co-varying DO and pH cycles sometimes had less severe effects than either cycle independently. Oysters may acclimate to, or compensate for, effects of cycling conditions on growth. Variation in magnitude and spatial extent of cycling conditions is an important consideration when choosing restoration sites, as severe cycling conditions may hinder re-establishment of estuarine populations.Item Insights into the Control of Growth and Axon Guidance by the Drosophila Insulin Receptor(2011) Li, Caroline Rita; Pick, Leslie; Molecular and Cell Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The Drosophila insulin receptor (DInR) regulates a diverse array of biological processes, including growth, axon guidance, and sugar homeostasis. Growth regulation by DInR is mediated by the adaptor protein Chico, the Drosophila homolog of vertebrate Insulin-Receptor-Substrate (IRS) proteins. In contrast, DInR regulation of photoreceptor axon guidance in the developing visual system is mediated by the SH2/SH3 domain adaptor protein Dreadlocks (Dock). In vitro studies by others suggested that different parts of DInR interact with different adaptor proteins: five NPXY motifs, one situated in the juxtamembrane region and four in the signaling C-terminal tail (C-tail), were important for interaction with Chico. Yeast two-hybrid assays suggested that a different region in the DInR C-tail interacts with Dock. To test whether these sites are required for growth or axon guidance in the animal, in vivo add-back type experiments were conducted. A panel of DInR proteins, in which the putative Chico and Dock interaction sites had been mutated individually or in combination, were tested for their ability to rescue viability, growth, and axon guidance defects of dinr mutant flies. Sites important for viability were identified. In addition, mutation of all five NPXY motifs drastically decreased growth in both male and female adult flies, but did not affect photoreceptor axon guidance, showing that different binding sites on DInR control growth and axon guidance. Unexpectedly, mutation of both putative Dock binding sites, either individually or in combination, did not lead to defects in photoreceptor axon guidance. Finally, none of the seven putative ligands for DInR, the Drosophila insulin-like peptides (dilps), was required for directing photoreceptor axon guidance, although we found that dilp1, -2, -3, -4, and/or -5 are required for controlling whole animal allometry. Importantly, we showed that the developmental delay exhibited by dinr mutants is not a factor underlying their photoreceptor axon guidance defects. Together, these studies confirmed the role of Chico-interacting regions of DInR in regulation of growth in vivo. They demonstrated that DInR is necessary to control axon guidance in vivo and showed that this role is not simply a function of developmental timing. However, they leave open the mechanisms activating DInR in regulating axon targeting.Item An RNA:DNA-based index of growth in juvenile Atlantic menhaden (Brevoortia tyrannus): laboratory calibration and field assessment(2009) Edwards, Jason Lee; Miller, Thomas J; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Atlantic menhaden (Brevoortia tyrannus) is an ecologically and economically important species in the mid-Atlantic coastal ecosystem. Its population dynamics are influenced by growth and survival during juvenile occupancy in estuarine nursery habitats. Therefore, quantifying production of potential nursery areas is important to understanding population processes and defining essential fish habitat for this species. Based on laboratory growth experiments, an RNA:DNA-based growth model was developed for young-of-the-year menhaden. The temporal response of RNA:DNA to changes in feeding condition was also quantified in the laboratory. Results of these investigations indicate RNA:DNA as a reliable tool for estimating recent growth and condition in relation to habitat residency. RNA:DNA-based estimates of growth were combined with site-specific abundance estimates to evaluate the spatiotemporal variability in production of potential menhaden nursery habitats. Site-specific production estimates exhibited high spatiotemporal variability suggesting menhaden utilize a mosaic of habitats to promote production, rather than specific sites consistently generating high levels of production.Item An Integrated Item Response Model for Evaluating Individual Students' Growth in Educational Achievement(2009) Koran, Jennifer; Hancock, Gregory R.; Measurement, Statistics and Evaluation; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Measuring continuous change or growth in individual students' academic abilities over time currently uses several statistical models or transformations to move from data representing a student's correct or incorrect responses on individual test items to inferences about the form and quantity of changes in the student's underlying ability. This study proposed and investigated a single integrated model of underlying growth within an Item Response Theory framework as a potential alternative to this approach. A Monte Carlo investigation explored parameter recovery for marginal maximum likelihood estimates via the Expectation-Maximization algorithm under variations of several conditions, including the form of the underlying growth trajectory, the amount of inter-individual variation in the rate(s) of growth, the sample size, the number of items at each time point, and the selection of items administered across time points. A real data illustration with mathematics assessment data from the Early Childhood Longitudinal Study showed the practical use of this integrated model for measuring gains in academic achievement. Overall, this exploration of an integrated model approach contributed to a better understanding of the appropriate use of growth models to draw valid inferences about students' academic growth over time.Item Empirical Essays in Comparative Institutional Economics(2007-05-02) Mukashev, Yerzhan Bulatovich; Murrell, Peter; Economics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Essay 1 investigates an empirical link between institutional variables and the performance of firms based on cross-country firm-level survey data. Current empirical evidence based on this type of data is unsatisfactory because employing survey responses as direct measures of institutional concepts and using those to analyze the effects of institutions at the firm level would limit the researcher to findings only within countries effects. This happens at the expense of losing inherent cross-country variation in institutions. Essay 1 offers a simple conceptual framework that decomposes survey responses for each firm into the average of their country and a residual firm-specific component. Importantly, the estimation results indicate that both variations have clearly different effects on growth of sales of firms. Essay 2 estimates the causal effects of economic shocks on the incidence of politically destabilizing events. The estimation is difficult due to the joint endogeneity between economic growth and events related to the political environment, which is addressed by the instrumental variable method. The variation in oil prices is used as an instrument for economic growth in the sample of small oil importing economies during 1960 - 1999. In contrast to a common belief and OLS estimates, the most striking finding of the IV estimation is that higher economic growth has a strong and robust positive effect on the incidence of relatively peaceful unrest such as demonstrations, strikes and riots. Essay 3 studies the question of differences in economic growth rates between Democratic and Republican governorships in the United States. The question is difficult to answer by simply comparing growth rates because the party affiliation is not randomly selected during elections. The empirical analysis employs the Regression Discontinuity Method to address the endogeneity in the party control variable. Focusing on very close elections permits the generation of quasi-experimental estimates of the impact of a "randomized" change in party control at the 50 percent threshold. When comparing Democratic with Republican governorships, the results are suggestive about the possibility of slightly worse performance of Democratic governors but the lack of statistical significance does not fully support this evidence.Item Ecology of Juvenile Bluefish, Pomatomus saltatrix, in Maryland Coastal Waters and Chesapeake Bay(2005-12-12) Callihan, Jody; Secor, David; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Shallow coastal ocean environments may function as important nursery habitats for juvenile bluefish, yet little ecological research has been conducted in ocean habitats. This thesis examines seasonal production, growth rates, and diet composition of juveniles in Maryland's coastal ocean environment and the Chesapeake Bay estuary. Summer-spawned juveniles dominated in ocean habitats and exhibited rapid growth rates, 2.0 - 2.4 mm d-1, which were likely fueled by an abundant forage base of young-of-the-year bay anchovy present in ocean environments during late summer/early fall. This summer cohort was rare in the Chesapeake Bay, where spring-spawned juveniles dominated. These results suggest ocean habitats provide principal nurseries for summer-spawned bluefish, and that the Chesapeake Bay and other estuaries are principal nurseries for spring-spawned juveniles. Accordingly, year class strength is likely shaped by contributions of juveniles from both oceanic and estuarine nursery habitats.