Theses and Dissertations from UMD
Permanent URI for this communityhttp://hdl.handle.net/1903/2
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
More information is available at Theses and Dissertations at University of Maryland Libraries.
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Item Extratympanic hearing in salamanders: A comparative assessment of structural variation and terrestrial function of an atympanic ear(2021) Capshaw, Grace; Carr, Catherine E; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The auditory system mediates the detection of acoustic cues and enhances survival within complex environments by enabling organisms to construct an auditory scene of their surroundings. The tympanic middle ear evolved multiple times in all terrestrial tetrapod lineages to overcome the impedance mismatch encountered by sound pressure at the air-skin boundary, indicating its significance for aerial hearing; however, fossil evidence demonstrates that the earliest terrestrial tetrapods retained aquatically-adapted ears that were unspecialized for detecting airborne sound. How did these unspecialized ears function on land? Comparative study of extant atympanate vertebrates can provide key insights into the ancestral state and early evolution of the terrestrial tetrapod auditory system following the water-to-land transition. In this dissertation, I use atympanate salamanders as a model to investigate the structural and functional parameters underlying terrestrial hearing with unspecialized ears. In chapter one, I review the biology of the salamander auditory system. In chapter two, I characterized morphological variation of the salamander ear and found evidence for habitat-related specialization, suggesting underlying physiological variation. In chapter three, I measured auditory sensitivity to sound pressure and seismic vibration, and observed variation in sensitivity that corroborates the ecomorphological trends reported in chapter two. I assessed the contributions of hypothesized extratympanic pathways for hearing, including seismic sensitivity, cavity resonance, and bone conduction. I determined that aerial auditory sensitivity is mediated by bone conduction of sound as head vibrations that are detectable to the inner ear. In chapter four, I evaluated the sound localization capabilities of an atympanic ear. I found that bone conduction hearing in salamanders supports a figure-eight pattern of directional sensitivity to airborne sound. I contextualize my findings with other studies of tympanate and atympanate taxa and suggest that bone conduction may represent a general mechanism enabling aerial sound detection and localization in terrestrial species with atympanic ears.Item Thermal Physiology in a Widespread Lungless Salamander(2018) Novarro, Alexander Joseph; Bely, Alexandra E; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Understanding species responses to climate change has become a top priority for conservation biologists. Unfortunately, current models often treat species as a single entity, ignoring population-level variation. This approach may result in major oversights when managing widespread species, which generally exhibit physiological variation across their geographic range. The eastern red-backed salamander (Plethodon cinereus) is the most widely distributed Plethodon species, extending farther north than any other lungless salamander. This species’ geographic distribution raises two major questions: How does P. cinereus thrive across a wide range of temperatures, and does it possess thermal adaptations that will buffer the ecological consequences of climate change? To explore these questions, I first examined the effects of elevated temperature on metabolic hormone release rates and physiological performance (i.e., ingestion rate and mass gain) across a latitudinal population gradient. I found that physiological traits and populations differ in their thermal flexibility, and that salamanders from warmer localities are more resilient to elevated temperatures. Second, I performed a study to disentangle the environmental and evolutionary drivers of thermal limits across the geographic range of P. cinereus. I found strong support for evolutionary constraints on lower thermal limits, though there was some degree of plasticity in relation to local environmental temperatures. By contrast, upper thermal limits showed little variation across the species’ geographic range and among clades, and far exceeded survival requirements. Third, I combined laboratory experiments, field observations, and population models to explore the role of behavioral thermoregulation in shaping physiological performance in P. cinereus. I found that individuals are likely to exploit moist conditions at the cost of reduced performance, and that populations living in poor thermal quality habitats have greater thermoregulatory accuracy. Overall, my work demonstrates significant variation in thermal physiology across the geographic range and among lineages of P. cinereus and shows that thermal traits differ in their responsiveness to thermal variability. Together, these results highlight the importance of considering multiple physiological metrics and sampling large geographic areas to understand species’ abundance and distributions, and to assess species’ vulnerability to climate change.Item EPIDEMIOLOGIC ANALYSIS OF RISK FACTORS FOR LOCAL DISAPPEARANCES OF NATIVE RANID FROGS IN ARIZONA(2005-08-11) Witte, Carmel Lee; Kane, Andrew S.; Animal Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This study used epidemiologic case-control methodology to examine habitat and environmental factors contributing to amphibian declines in Arizona. Risk factors were compared between sites where frogs disappeared (cases) and persisted (controls) using univariate and multivariable logistic regression analyses. Thirty-six percent (117/324) of all sites became cases during the study period. Elevation, non-native predators, hydrologic characteristics, aspect, and effects of nearby sites were significantly associated with frog persistence or disappearance. In the final multivariable model, risk for disappearance increased with increasing elevation (OR=2.7 for every 500 meters, P<0.01). Sites where disappearances occurred were 4.3 times more likely to have other nearby sites that also experienced disappearances (P<0.01), while having an extant population nearby decreased risk of disappearance by 85% (OR=0.15, P<0.01). Sites experiencing disappearances were 2.6 times more likely to have crayfish than control sites (P=0.04). Identification of risk factors associated with frog disappearances will guide future research and conservation efforts.