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 Ground-dwelling beetles as bioindicators in transgenic corn(2009) Lepping, Miles; Shrewsbury, Paula M; Dively, Galen P; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Ecological risk assessment for transgenic crops requires identification of appropriate biological indicator organisms for use in laboratory and field biomonitoring studies. Ground-dwelling predatory beetles in the families Carabidae and Staphylinidae comprise a diverse and abundant group of nontarget organisms in field corn systems where rootworm-resistant transgenic varieties are deployed. First, the utility of two sampling methods (pitfall trapping and suction-based litter extraction) was assessed for estimating ground beetle (Coleoptera: Carabidae) population parameters in Maryland cornfields. Sampling bias was established for pitfall trapping, confirming the limitations of this semi-quantitative method for capturing a representative portion of the epigeal community. Litter extraction data conformed to predictions for abundance in relation to trophic identity, body size and biomass. Litter extraction identified smaller bodied carabid omnivores and carnivores as numerically dominant over larger bodied species that have received focus in risk assessment studies. A small-bodied carabid, Elaphropus xanthopus (Dejean), was identified as the dominant carnivore, and therefore selected for nontarget exposure and toxicity studies. Second, in choice and no-choice experiments, corn pollen was identified as a realistic, direct exposure pathway to transgenic proteins for E. xanthopus. Third, organism-level exposure to Cry34Ab1 rootworm-resistant protein was demonstrated for E. xanthopus in the laboratory and field during corn pollen shed. Field studies also revealed contamination across transgenic and non-transgenic test plots, indicating experimental design must account for the movement of study organisms and/or transgenic plant tissues. Finally, a toxicity study examined the effects of dietary exposure to rootworm-resistant Cry34/35Ab1 corn pollen for two beetle species, a carabid, E. xanthopus, and a staphylinid, Strigota ambigua (Erichson). Transgenic pollen exposure did not affect longevity or sub-lethal behaviors for either species. Small-bodied, predatory ground beetles are recommended as candidate bioindicator organisms in risk assessment studies designed to optimize field monitoring, exposure detection, and bioassay for transgenic pesticides.Item CRITICAL PATCH SIZES AND THE SPATIAL STRUCTURE OF SALT MARSH COMMUNITIES(2009) Martinson, Holly Marie; Fagan, William F; Behavior, Ecology, Evolution and Systematics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The size, connectivity, and quality of habitat patches can have multifaceted impacts on species and communities. In this dissertation, I combined a multi-year field survey, manipulative field experiments, and a literature review to investigate how spatial structure influences species and their trophic interactions in fragmented habitats. For all empirical work, I used as a study system the arthropod assemblage found on patches of the salt marsh grass Spartina patens. In Chapter 1, I conducted seven surveys of habitat patches over three years to examine the effects of patch size, connectivity, and local environmental conditions on a guild of specialist sap-feeding herbivorous insects and their natural enemies. I found striking differences among species in the effects of both patch size and connectivity, which led to differences in species' relative abundances and trophic structure among these patches. In Chapter 2, I manipulated host plant quality and predator density to experimentally examine mechanisms that might structure this arthropod community. I found that positive responses of herbivores to experimentally-elevated patch quality were limited by dispersal constraints and that predation by abundant generalist spiders may constrain the spatial distribution of certain species. Investigating systems beyond the marsh, I conducted a literature review and analysis in Chapter 3 wherein I examined whether the spatial structure of habitats generally influences trophic interactions. From the literature, I identified 171 studies of trophic interactions in fragmented habitats and found that the influence of fragmentation and related variables on the occurrence or strength of trophic interactions was largely predictable based on the habitat affinity of interacting species. With this dataset, I also identified key gaps in the fragmentation literature, including a heavy bias towards the study of two-species interactions. Therefore, in Chapter 4 I took advantage of my data from the salt marsh to identify how, in addition to the two-species interactions of parasitism and egg predation, more complex food web interactions might depend on variation in the size of habitat patches. Overall, my findings show that variation in patch size can have varied, but predictable, effects on patch occupancy, population density, and interactions between species in fragmented habitats.Item GENETIC DIVERSIFICATION, SAPROPHYTIC COMPETENCE AND GENETIC ENHANCEMENT OF THE ENTOMOPATHOGENIC FUNGUS METARHIZIUM(2009) Pava-Ripoll, Monica Patricia; St. Leger, Raymond J; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Entomopathogenic fungi are being investigated as alternatives to chemical insecticides. This study explored the versatility of the entomopathogenic fungus Metarhizium anisopliae by examining its diversification, saprophytic competence and potential for genetic enhancement. M. anisopliae is a radiating species containing both generalist and specialized lineages with broad and narrow host ranges and as such provides an excellent model system to study the evolution of pathogenesis. Using 18S RNA and protease sequences, I demonstrated that strains can be selected representing evolutionary distances ranging from <1 to 8 MY and their natural molecular variation allows analysis of processes of adaptive change. M. anisopliae is particularly abundant in the rhizosphere. Germination of M. anisopliae strain 2575 was >96% in 1 mg/ml root exudate (RE) and growth in RE resulted in 29 (58%) genes being up-regulated and 21 (42%) down-regulated. The identity of these genes is helping to define the physiological requirements for rhizosphere competence. Hypothetical and orphans proteins (41.4%) were also actively expressed indicating that many previously uncharacterized genes may have functions related to survival at the soil-root interphase. Using the fungus as a delivery vehicle for foreign toxins presents a powerful approach for increasing virulence. M. anisopliae was modified to express a scorpion toxin (AaIT) in insect haemolymph and bioassayed against the coffee berry borer Hypothenemus hampei. AaIT increased mortality up to 56.6%, and reduced the medial lethal concentration (LC 50 ) by 15.7-fold and the average survival time (AST) by 20.1%. The AaIT gene and the M. anisopliae esterase gene (Mest1) were inserted into three strains of Beauveria bassiana (ARSEF 252, 8998 and 9184) with high, medium and low mortality, respectively, against the Colorado potato beetle (CPB) Leptinotarsa decemlineata. Mortality rates were strain- and dose- dependant and increased from 16.1 to 36.7% in single transformants (AaIT or Mest1) and from 7.1 to 33.5% in double transformants (AaIT-Mest1). The AST was reduced up to 33% and the LC50 up to 5.9-fold. Although singly both AaIT and Mest1 increased the killing power of B. bassiana against second instar CPB, combining AaIT and Mest1 together did not produce synergistic effects.Item MATING COSTS, MALE CHOICE DISPLACEMENT, AND THE EFFECTS ON HYBRIDIZATION AND SPECIATION IN THE HAWAIIAN CRICKET LAUPALA (SUBFAMILY:TRIGONIDIINAE)(2009) Jadin, Jenna; Shaw, Kerry L; Behavior, Ecology, Evolution and Systematics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Contact zones between two closely-related species provide unique laboratories for studying the processes of speciation. This is because, within these zones, species barriers will be reinforced and speciation will reach completion, or the barriers will break down, causing the two species to become one. Which of these two alternatives will occur depends on the degree of genetic differentiation and behavioral isolation between the species. If there is significant and non-combinable genetic variation between species, but behavioral isolation between the two incipient taxa is incomplete and allows hybrid offspring to be produced, these hybrid offspring will have lower fitness relative to parental types and selection should act directly to eliminate those offspring and indirectly against parents with broad mating preferences or traits. If however the genetic architecture is similar and behavioral isolation is incomplete, the populations would be expected to turn into a hybrid swarm and eventually become one species. Patterns of behavioral isolation and genetic variation in several Laupala species pairs suggest that contact zones between closely related species are marked by conflicting patterns of behavioral isolation and genetic differentiation. Evidence also suggests that the complex courtship system of Laupala may allow male choice to play an important role in sexual selection and speciation. Therefore I tested several hypotheses about the genetic differentiation, sexual selection, and behavioral isolation in a contact zone between the closely-related and morphologically indistinguishable L. tantalus and L. pacifica species pair. First, by using the mitochondrial COI gene and AFLPs as genetic markers, I demonstrated that there appears to be mitochondrial DNA introgression between sympatric, but not allopatric congeners, which suggests contemporary hybridization in the contact zone. Next, I found that males experience post-mating resource-limitation and show a significant tendency to invest less into a second mating, however, their investment is dependent upon female size. Finally, I found that there is apparent displacement of male choice, decreased variation in spermatophore production, and asymmetrical mating isolation within the contact zone. This evidence all suggests that there is increased behavioral isolation in this contact zone, which may be consistent with a hypothesis of speciation by reinforcement. However, this evidence also suggests that male costs may result in male choice conflicting with other isolating mechanisms. If so, this study may be another putative case of reinforcement, or it may be an entirely novel report of conflicting selection pressures within a hybrid zone. I suggest that further studies are needed to measure hybrid fitness as well as to evaluate relative male and female mating costs within the complex mating system of this rapidly-diversifying genus.Item A Computational Study of the Clap and Fling Aerodynamic Mechanism(2009) PANAGAKOS, GRIGORIOS; Balaras, Elias; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Clap and fling is a particular wing kinematic pattern utilized by some insects and birds to produce enhanced aerodynamic forces. It consists of two very distinct phases: i) the leading edges of the two wings are brought together near the upper limit of the upstroke and subsequently the wings are rotated around their leading edges, `'clapping'' like a closing book; ii) at the onset of the downstroke, and while they are still close, the two wings rotate around their trailing edges `'flinging'' apart. Prior theoretical and experimental work suggested that clap-and-fling is responsible for production of unusually high lift coefficients. However, due to limitations of the theoretical models and experimental techniques, detailed quantitative results are yet to be reported. The primary objective of the present work is to provide a concrete description of the underlying physics by means of high-fidelity simulations based on the Navier-Stokes equations for incompressible flow. In particular, the effects of the kinematics and the Reynolds number are discussed in detail in the thesis. Thesis' results verify the lift enhancement trends observed in experiments and identify the particular flow patterns correlated with such increases.Item Predation by eastern mudminnows (Umbra pygmaea) on macroinvertebrates of temporary wetlands(2009) Lombardi, Susan Elizabeth; Lamp, William O.; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Fish play a substantial role in aquatic food webs, yet the effect of feeding activities of small stream fish that enter seasonally-flooded temporary wetlands during periods of hydrologic connectivity is not well understood. In this study, eastern mudminnows (Umbra pygmaea) were introduced to a fishless wetland in Caroline County, Maryland, and the aquatic macroinvertebrate community did not significantly change within two weeks. Gut contents of mudminnows collected from the wetland and a stream consisted primarily of dipteran larvae; ostracods were also a common food source for wetland mudminnows. Common prey not found in gut contents but present in the wetland were tested as food, and all taxa were consumed in a no-choice predation experiment. Mudminnows have the potential to directly affect multiple trophic levels and subsequent ecosystem functioning through predatory interactions with sustained hydrologic connectivity between fish sources and temporary wetlands.Item KINEMATICS OF THE MAYFLY NYMPH GILL ARRAY: AN INTERMEDIATE REYNOLDS NUMBER VENTILATION PUMP(2009) Sensenig, Andrew T.; Shultz, Jeffrey W.; Kiger, Ken T.; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Comparative studies encompassing a wide range of aquatic animals have shown that rowing is exclusively used at low Reynolds numbers (Re <1) while flapping is predominantly used at Re > 100, but few studies have been undertaken to document the transition in individual species that traverse the intermediate Re regime using a single set of appendages. Thus, it is not generally known whether a gradual increase in Re within a system results in a gradual or sudden shift between rowing and flapping. Here I document both the kinematics of the appendages and the surrounding fluid of a nymphal mayfly Centroptilum triangulifer that uses a serial array of seven pairs of abdominal gill plates and operates at Reynolds numbers ranging from 2-22 during ontogeny. I found that some kinematic variables (stroke frequency and metachronal phase lag) did not change during ontogeny but that others changed substantially. Specifically, gills in small instars used strokes with large pitch and stroke-plane deviations, while larger instars used strokes with minimal pitch and minimal stroke-plane deviation. Gills in larger instars also acquired an intrinsic hinge that allowed passive asymmetric movement between half strokes. Net flow in small animals was directed ventrally and essentially parallel to the stroke plane (i.e. rowing), but net flow in large animals was directed dorsally and essentially transverse to the stroke plane (i.e. flapping). The metachronal phasing of the gills produced a time-dependent array of vortices associated with a net ventilatory current, a fluid kinematic pattern here termed a "phased vortex pump". Significantly, absolute vortex size did not change with increasing animal size or Re, indicating that the vortex diameter (Lv) decreased relative to intergill spacing (Lis) during mayfly growth. Given that effective flapping requires organized flow between adjacent appendages, I proposed the hypothesis that rowing should be favored when Lis / Lv < 1 and flapping should be favored when Lis / Lv > 1. Significantly, the rowing-to-flapping transition in Centroptilum triangulifer occurs at Re ~5, when maximum dynamic intergill distance equals vortex diameter. This result suggests that the Re-based rowing-flapping demarcation observed in a wide array of aquatic organisms is determined by the relative size of the propulsive mechanism and its self-generated vortices.Item Nutrient regulation by an omnivore and the effects on performance and distribution(2009) Pearson, Rachel Estelle Goeriz; Gruner, Daniel S; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Omnivores have a unique interaction with their nutritional environment because they have adapted to consume food from different trophic levels. To successfully navigate their variable resources, omnivores must maintain some level of nutrient regulation. To explore the effects of nutrient regulation by an omnivore, I used a salt marsh katydid, Conocephalus spartinae. To first address the ability of Conocephalus to perform on a wide range of diets and to regulate their nutritional intake, I used artificial diets that differed in relative amounts of protein and carbohydrate (Chapter 1). I found that Conocephalus survival decreased on a high protein diet due in part to a decrease in lipid stores but growth was not affected by diet. In a second experiment Conocephalus showed a degree of nutrient regulation as evidenced by the difference in what they actually ate and the predicted consumption if they had been feeding equally on the diets presented in each treatment. However, I did not find evidence for tight macronutrient regulation. Next I explored capacity of Conocephalus to regulate their nutrient intake (nitrogen and lipid) when fed naturally co-occurring prey (Chapter 2). I first established that the prey differed in their protein and lipid content and that these differences were related to the size of the prey species. When Conocephalus were fed different prey species individuals showed no differences in either growth or survival. In the final experiment, I found that Conocephalus did show evidence of a degree of nitrogen and lipid regulation because they did not feed equally on all of the prey species offered. Lastly, I documented the relationship between the ability of Conocephalus to locate plant and prey resources and the effect that these resources have on omnivore performance (Chapter 3). I found that Conocephalus aggregates in areas of high plant quality but that their numbers do not correspond to areas of high prey density. However, I found that katydid growth and survival was enhanced by prey availability but not plant quality. Overall, I documented how an organism like an omnivore relates to its nutritional environment and how nutrient regulation might affect performance and distribution. Last, I documented the relationship between the ability of katydids to locate plant and prey resources and the effect that these resources have on omnivore performance (Chapter 3). I found that katydids aggregate in areas of high plant quality but that their numbers do not correspond to areas of high prey density.Item Soldier neotenics of Zootermopsis nevadensis (Hagen) and Archotermopsis sp. (Isoptera: Termopsidae): Morphology, Development, Behavior, and Evolution(2009) Johnson, Susan Elaine; Thorne, Barbara L; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)I: The relictual reproductive soldier neotenics of primitive Termopsid termites may offer insights into the evolution of eusociality and sterile castes in termites. II: Soldiers and helpers in a new Thai species of Archotermopsis do not display unusually complete gonad development. The first neotenic pair ever reported for this genus is described. III: Morphological differences between soldiers and soldier neotenics in the head and gonads are quantified in Z. nevadensis. There is not necessarily a clear delineation in morphology between soldiers and soldier neotenics. IV: Colony age and size do not significantly influence the differentiation or survival of male replacement reproductives in colonies of Z. nevadensis. Soldier neotenics' development is not significantly influenced by the presence of normal soldiers. V: Soldier neotenics and related female neotenics tend to have greater initial survival after interactions with colonies with only normal neotenics. Mostly helpers are aggressors, never soldier neotenics or neotenics.Item Indirect Effects of Imidacloprid on Natural Enemies of Spider Mites in Two Systems(2009) Creary, Scott; Raupp, Michael J; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)With a growing number of reports showing secondary outbreaks of spider mites following systemic applications of imidacloprid, a study was designed to test the indirect effects of this insecticide on natural enemies of spider mites. We exposed two predators, Chrysoperla rufilabris and Stethorus punctillum, to mites that were reared on boxwoods and elms treated with imidacloprid and examined prey consumption, predator mobility and mortality. Mites reared on treated foliage were extremely toxic to predators, eliciting sharp reductions in feeding, locomotion, and longevity. These findings document that non-target pests feeding on plants treated with imidacloprid cause lethal and sublethal responses in natural enemies. We discuss implications on the compatibility of imidacloprid with IPM practices and infer impacts on generalist and specialist natural enemies.