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.

More information is available at Theses and Dissertations at University of Maryland Libraries.

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    Feeding behavior and distribution of Varroa destructor on adult bees of Apis mellifera
    (2022) Lamas, Zachary Siqueira; Hawthorne, David J; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Varroa destructor is a competent vector of honey bee viruses and the leading cause of colony losses worldwide. Much about its feeding behavior and distribution on adult bees remains unknown. This work shows that Varroa are promiscuous feeders of adult bees, actively switching from one host to another. Laboratory trials showed there is a large heterogeneity in the host switching rate with some Varroa switching infrequently while others switched at high rates. The consequences of Varroa feeding on adult bees is largely unknown because adult feeding has largely been overlooked. This work shows that there is a high relative risk of death from Varroa feedings. Adult workers die quickly without developing high levels of infection after being fed upon by an infectious Varroa, and confer lower risk to their non-parasitized nestmates than counterparts which were nestmates to longer lived parasitized bees. Further experiments showed communicable routes of virus transmission may explain these findings. Trophallaxis between adult workers allowed for the movement of the pathogen to naïve nestmates. These nestmates act as an infectious reservoir to naïve Varroa showing communicable transmission between hosts can influence the acquisition and subsequent vectoring of the same pathogen by the vector. Another social behavior, cannibalization, was shown to have the same influence on Varroa vectoring. Varroa were also shown to be susceptible to viral acquisition through shared feedings on adult bee and brood hosts. Naïve Varroa readily acquired and then transmitted deformed wing virus when sharing the same host with an infectious Varroa. Collectively this work exemplifies how host social behavior and Varroa-Varroa transmission routes can increase the risk of vectors becoming infectious. Varroa feedings and virus transmission on adult workers cannot describe one of the most glaring features of Varroa infestations. For a portion of the year Varroa aggregate predominantly on adult drones, largely ignoring the worker cohort. Parasite burden only shifts onto workers when drone production ceases.
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    Analyzing the Wikisphere: Tools and Methods for Wiki Research
    (2010) Stuckman, Jeffrey Charles; Purtilo, James; Computer Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    We present tools and techniques that facilitate wiki research and an analysis of wikis found on the internet. We developed WikiCrawler, a tool that downloads and analyzes wikis. With this tool, we built a corpus of 151 Mediawiki wikis. We also developed a wiki analysis toolkit in R, which, among other tasks, fits probability distributions to discrete data, and uses a Monte Carlo method to test the fit. From the corpus we determined that, like Wikipedia, most wikis were authored collaboratively, but users contributed at unequal rates. We proposed a distribution-based method for measuring wiki inequality and compared it to the Gini coefficient. We also analyzed distributions of edits across pages and users, producing data which can motivate or verify future mathematical models of behavior on wikis. Future research could also analyze user behavior and establish measurement baselines, facilitating evaluation, or generalize Wikipedia research by testing hypotheses across many wikis.
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    Zooplankton ecology in the Chesapeake Bay estuarine turbidity maximum, with emphasis on the calanoid copepod Eurytemora affinis
    (2006-04-27) Lloyd, Scott Steven; Roman, Michael R; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The estuarine turbidity maximum (ETM) region of Chesapeake Bay, located near the limit of saltwater intrusion, is characterized by high total suspended solid (TSS) concentrations, high light attenuation, and high densities of zooplankton. Due to high light attenuation, primary production is generally low in ETMs, yet the Chesapeake Bay ETM region is often considered a 'hot spot' of zooplankton abundance within the Bay. The omnivorous copepod Eurytemora affinis is especially prevalent in the ETMs of Chesapeake Bay and its tributaries and in ETM regions worldwide. In order to determine the factors influencing 1) zooplankton distribution and abundance in the Chesapeake Bay ETM, 2) E. affinis reproduction in the Chesapeake Bay and Choptank River ETMs, and 3) zooplankton position maintenance, cruises in the Chesapeake Bay and Choptank River ETMs were conducted in 1996 and 2001-2003. Laboratory experiments examining the egg production cycle of E. affinis were also performed. The cruise results show that zooplankton taxa within the Chesapeake Bay ETM region tend to be distributed along a salinity gradient from up-estuary to down-estuary, with cladocerans being most common in low salinity/freshwater regions, E. affinis found in slightly higher salinities than cladocerans, and mysids and the copepod Acartia tonsa found in more mesohaline conditions. Eurytemora affinis appears to be contained in the ETM by freshwater limiting its up-estuary extent and biological interactions with A. tonsa and salinity tolerances limiting its down-estuary abundance. Grazing and egg production results indicate that E. affinis production is not food-limited in the ETM region and that this copepod's particle selection ability favors its success in the ETM over that of A. tonsa. Laboratory egg production experiments also suggest that the most accurate estimates of E. affinis egg production (and of all brooding copepods in general) are achieved by incorporating both a temperature-based estimate of interclutch duration (the time between successive clutches) with a temperature-based estimate of egg hatching time.