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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    GENOME-WIDE ANALYSIS OF DIVERGENCE AND INTROGRESSION IN TOWHEE HYBRID ZONES
    (2012) Kingston, Sarah Elizabeth; Fagan, William F; Braun, Michael J; Behavior, Ecology, Evolution and Systematics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    ABSTRACT Title of Dissertation: GENOME-WIDE ANALYSIS OF DIVERGENCE AND INTROGRESSION IN TOWHEE HYBRID ZONES Sarah Elizabeth Kingston, Doctor of Philosophy, 2012 Dissertation directed by: William F. Fagan, PhD, Department of Biology Michael J. Braun, PhD, Smithsonian Institution Hybrid zones offer a natural laboratory in which investigation of the evolutionary forces involved with reproductive isolation and differentiation is possible. Highly multilocus population genomics is a powerful and feasible new tool with which to address such questions of evolutionary interest. I utilize a unique spatial setting that incorporates two hybrid gradients of the towhess Pipilo maculatus and P. ocai. These species likely diverged in allopatry and are in secondary contact. I utilize genome-scale multilocus techniques to address questions regarding the architecture of differentiation and introgression across these hybrid gradients and the influence of location specific environmental factors on isolation. The multilocus analysis reveals cross-genomic variation in selective constraints on gene flow and locus-specific flexibility in the permeability of the interspecies membrane. Maintenance of historical divergence is acting in a cohesive manner, but local environmental and stochastic factors are also important driving forces. Habitat corridors for dispersal potential indicate hotspots of connectivity where the two transects meet. Both habitat connectivity and genetic differentiation between geographically disparate parental types appear to influence the dynamics of gene flow across the hybrid gradient. Environmentally-mediated gene flow in the context of secondary contact and hybridization is an important force influencing evolutionary trajectory.
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    Isolation and characterization of antimicrobial resistant Staphylococcus aureus in retail ground meats
    (2010) Li, Yi; Meng, Jianghong; Food Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Staphylococcus aureus is commonly present in humans and animals. It can cause a variety of suppurative infections, food intoxication and toxic shock syndrome. Antimicrobial resistant S. aureus, especially methicillin-resistant S. aureus (MRSA), have emerged and are a major public health concern. There is an increasing risk of food production animals serving as a reservoir and transmitting S. aureus and MRSA in community environments. Due to the increased food safety risk posed by MRSA in addition to its multidrug resistance, we were interested in determining the prevalence of S. aureus and MRSA in retail meat and investing the multidrug resistance of the S. aureus isolates. A survey study was conducted, involving 480 retail ground meat samples (231 ground pork and 249 ground beef) collected in the Washington DC area from March 2009 to March 2010. Approximately 42.08% (n = 202) of the samples were identified as S. aureus positive and one MRSA isolate was recovered from a ground beef sample. Antimicrobial resistance testing showed 53.34% of recovered S. aureus isolates exhibited different levels of antimicrobial resistance to CLI, CHL, GEN, LEVO, CIP, SYN and TGC. The MRSA isolate was resistant to 8 of 22 antimicrobials tested. PFGE fingerprinting identified the MRSA isolate as USA300 subtype, which also carried genes of virulence factors PVL and protein A. Our findings indicated that antimicrobial resistant S. aureus strains were common in retail ground beef and port, and that MRSA could also be present in such products that could potentially serve as a reservoir.