Biology Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2749
Browse
3 results
Search Results
Item Patterns of oyster natural mortality in Chesapeake Bay, Maryland during 1991-2017 and its relationships with environmental factors and disease(2019) Doering, Kathryn Leah; Wilberg, Michael J; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)A common method of estimating natural mortality in bivalves includes several assumptions that are likely violated for oysters Crassostrea virginica in Chesapeake Bay, Maryland. In addition, while oyster disease dynamics are well studied spatially and temporally in the mid-Atlantic region, changes in disease-related relationships have not been investigated in Maryland. We developed a Bayesian estimator for natural mortality and applied it to oysters in Maryland. We then used the model output along with environmental factors and disease data to explore changes in the disease system over time. We found the largest differences in natural mortality estimates between the box count method and Bayesian model 1-3 years after a high mortality event. Some relationships changed over time in the disease system, most notably those associated with MSX, suggesting resistance to MSX has potentially developed. This work improves our estimates of natural mortality and understanding of oyster disease dynamics in Maryland.Item The skin microbiome of woodland salamanders and its association with hosts' taxonomy, environment and health status(2016) Muletz Wolz, Carly Rae; Lips, Karen R.; Behavior, Ecology, Evolution and Systematics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Microbial communities play central roles in animal health. Host species, environmental conditions and presence of pathogens can affect the diversity and composition of animal-associated microbiomes. Amphibians form integral and functionally important symbioses with microbes. The amphibian microbiome interacts with pathogens, and can protect hosts from disease, including the disease chytridiomycosis, caused by skin infection by Batrachochytrium dendrobatidis (Bd). The implications of amphibian-microbiome associations are difficult to predict because little is known about the factors shaping bacterial communities or their functional traits, such as anti-Bd properties. I used culture-dependent and culture-independent methods to characterize the skin microbiome of Plethodon salamanders in field and laboratory studies. I hypothesized that the evolutionary history, environmental conditions, and health status of the hosts shape skin bacterial community assemblages. In a field study, I sampled sympatric, congeneric salamander species (Plethodon cinereus, P. glutinosus, P. cylindraceus) across three localities to quantify the distribution of both anti-Bd bacteria and the entire bacterial community. I identified 50 anti-Bd bacterial OTUs and 480 bacterial OTUs overall on the salamander skin, with high prevalence and abundance of anti-Bd bacterial genera Pseudomonas, Acinetobacter and Stenotrophomonas. Within a locality, co-occurring salamanders generally had similar microbiome diversity and composition patterns, but these differed among sites. This indicates that environment is more influential in shaping skin microbiome patterns than differences in host properties in these species. I sampled P. cinereus along an elevational gradient, as a proxy for environmental variables that co-vary with elevation. Microbiome diversity and composition changed with elevation, in which compositional changes were related to soil pH. In a laboratory experiment, I quantified the responses of P. cinereus and the skin microbiome to temperature (13, 17, 21 °C) and pathogen (Bd+, Bd-) exposure to determine whether the native microbiome affected survival at natural temperatures. Temperature changed the microbiome, but this did not prevent host mortality from Bd. Instead, Bd exposure changed the microbiome and caused 78% mortality. My results demonstrate that environmental conditions and pathogen presence are important factors determining skin microbiome structure in Plethodon salamanders. These findings contribute to our understanding of animal-microbial symbioses, microbial community ecology, and amphibian disease ecology.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.