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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Item INFORMING CONSERVATION OF THREATENED BAT SPECIES USING GENOMICS AND ACOUSTICS(2022) Nagel, Juliet Joy; Nelson, David; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Bats are vital to healthy ecosystems, providing billions of dollars of services in the form of forest and crop pest control. Unfortunately, North American bat populations have faced novel pressures during the past decade that may threaten their persistence. First, several species of tree-roosting bats (primarily hoary [Lasiurus cinereus], eastern red [L. borealis], and silver-haired [Lasionycteris noctivagans] bats) are experiencing large numbers of fatalities at industrial wind-energy facilities. Second, several species of cave-dependent bats have experienced large-scale mortality as the result of infection by a fungal pathogen that causes white-nose syndrome (WNS). As bats are generally long-lived and have low reproductive rates, such increases in mortality can cause significant population declines from which they may be unable to recover. Basic questions about population trends, size and structure remain largely unanswered for these species because of challenges in applying traditional wildlife monitoring approaches to bats. This lack of understanding impedes conservation and management efforts. In my dissertation, I use genomic and acoustic survey techniques to investigate questions related to the threats that wind-energy development and WNS are posing to bat species in North America. In my first chapter, I evaluate range-wide population structure and effective population size (Ne) for hoary, eastern red, and silver-haired bats. Using genotyping-by-sequencing (GBS), I genotyped single-nucleotide polymorphism (SNP) data from 173 hoary, 113 eastern red, and 89 silver-haired bats from multiple locations spread across their geographic distributions. Hoary bats and eastern red bats showed no geographic structure in genetic diversity, whereas silver-haired bats displayed longitudinal population variation. Coalescent modeling suggested that eastern red bats have the largest evolutionary Ne, followed by hoary bats, then silver-haired bats. In my second chapter, I used GBS to assess the population structure of two federally endangered cave bat species: Indiana bats (Myotis sodalis) and gray bats (M. grisescens). Using tissue samples from 45 Indiana bats and 47 gray bats spread across their ranges, I showed that Indiana bats display no geographic genetic structure, whereas gray bats exhibit east–west population variation across the Mississippi River Valley. In my final chapter, I used acoustic surveys across the State of Maryland to investigate bat community changes in the decade following the arrival of WNS. From 2010 through 2019, I conducted annual mobile acoustic routes each summer, for a total of 344 completed routes resulting in 426 hours of recordings and 24,375 identified bat passes. I detected massive (> 92%) declines of little brown bats (M. lucifugus), northern long-eared bats (M. septentrionalis), eastern small-footed bats (M. leibii), and tricolored bats (Perimyotis subflavus), with no evidence of recovery in recent years. Trends in hoary bats and eastern red bats were non-significant during this period. Bat community composition varied among Maryland’s physiographic regions, with eastern red bats comprising a larger percentage in the east. Species composition across the state likely reflects the impact of several factors, including mortality from WNS and wind-energy development, and perhaps reduced interspecific competition. Overall, my results illustrate the unique insights, but also distinct limitations, that genomic and acoustic data can provide regarding the conservation of bats in North America.Item Somatosensory Signaling for Flight Control in the Echolocating Bat Eptesicus fuscus(2014) Chadha, Mohit; Moss, Cynthia F; Neuroscience and Cognitive Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Bats are the only mammals to have evolved powered flight. Their specialized hand-wings with elongated digits and a thin membrane spanning the digits not only enable flight, but give them unrivaled aerial maneuverability. Bat wing membrane is endowed with an array of microscopic hairs that are hypothesized to monitor airflow and provide sensory feedback to guide rapid motor adjustments for flight control. The goal of this thesis is to contribute to a broader understanding of the response properties of wing-associated tactile receptive fields, and the representation of aerodynamic feedback in the bat's nervous system. Using the big brown bat, Eptesicus fuscus, a series of neurophysiological experiments were performed where the primary somatosensory cortical (S1) responses to tactile and airflow stimulation of the wings were analyzed. Results demonstrate that the body surface is organized topographically across the surface of S1, with an overrepresentation of wings, head and foot. The wings have an inverted orientation compared to hand representation of terrestrial mammals, with tactile thresholds that are remarkably close to human fingertips. Airflow stimulation of the wings was achieved by brief puffs of air generated using a portable fluid dispensing system. By changing the intensity, duration and direction, airflow sensitive receptive fields were characterized based on responses of S1 neurons. Results reveal that neuronal responses are rapidly adapting, encompassing relatively large and overlapping receptive fields with well-defined centers. S1 responses are directionally selective, with a majority preferring reversed airflow. The onset latency of evoked activity decreases as a function of airflow intensity, with no effect on response magnitude. Furthermore, when dorsal and ventral wings surfaces are stimulated simultaneously, S1 responses are either inhibited or facilitated compared to either wing surface stimulation alone. This finding suggests that outputs from the two wing surfaces are integrated in a manner that reflects the interplay of aerodynamic forces experienced by the wings. To evaluate the central coding mechanisms of airflow sensing by bat wings, I applied an information theoretic framework to spike train data. Results indicate that the strength and direction of airflow can be encoded by the precise timing of spikes, where first post-stimulus spikes transmit bulk of the information, evidence for a latency code.Item Estimation of Elevation and Azimuth in a Neuromorphic VLSI Bat Echolocation System(2009) Abdalla, Hisham Ahmed Nabil; Horiuchi, Timothy K; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Auditory localization is an interesting and challenging problem; the location of the sound source is not spatially encoded in the peripheral sensory system as it is in the visual or somatosensory systems. Instead it must be computed from the neural representation of the sound reaching both ears. Echolocation is a form of auditory localization, however, an important distinction is that the sound being localized is an echo of the sound emitted by the animal itself. This dissertation presents a neuromorphic VLSI circuit model of a bat echolocation system. The acoustic cues that we use in our system are the binaural interaural level differences (ILDs) and the monaural spectral cues. We have designed an artificial bat head using 3D CAD software and fabricated it using a 3D printer. The artificial bat head is capable of generating the necessary acoustic cues for localization. We have designed and fabricated an ultrasonic cochlea chip with 16 cochlear filters and 128 spiking cochlear neurons (eight neurons per cochlear filter), the cochlear filters and neurons transform the analog input into a spike-based cochlear representation. We have also designed and fabricated two feature extraction chips: a monaural spectral difference chip and a binaural ILD chip, that together can extract the localization cues from the spike-based cochlear representation. The monaural spectral difference chip consists of 240 spiking neurons; each neuron compares the activity of two cochlear filters within the same ear. The binaural ILD chip consists of 32 spiking neurons (two per cochlear filter) that model the processing that takes place in the lateral superior olive (LSO). We demonstrate that the spatiotemporal pattern of spiking outputs from the feature extraction chips can be decoded to estimate the direction (elevation and azimuth) of an ultrasonic chirp.