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.
Browse
5 results
Search Results
Item Echolocation, high frequency hearing, and gene expression in the inner ear of bats(2017) Mao, Beatrice; Wilkinson, Gerald S; Moss, Cynthia F; Behavior, Ecology, Evolution and Systematics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Bats are the only mammals capable of true flight, and are the second-most speciose mammalian radiation, represented by over 1200 extant species. Key to their evolutionary success was echolocation, which is a complex trait requiring specializations for vocalization, hearing, and echo processing. Because they rely on detecting and analyzing echoes that may return greatly attenuated relative to their outgoing calls, interference from non-target ‘clutter’ echoes poses a challenge for echolocating bats. Here, I demonstrate that the echolocating bat Eptesicus fuscus alters its echolocation behavior to ameliorate the impact of clutter echoes when tracking a moving target, and that the magnitude of its behavioral adjustments depended on the distance and angular offset of two symmetrically placed ‘distracter’ objects. Furthermore, I found that individual bats make different adjustments to their calls, call timing, or head movements, suggesting that multiple strategies for echolocating in clutter may exist. In my second chapter, I examined the expression patterns of hearing-related genes in juvenile bats. Biomedical research establishing the functional roles of hearing genes rarely examines gene expression beyond the early post-natal stage, even though high frequency hearing does not mature until late in development. I show that several key hearing genes implicated in human deafness are upregulated in juvenile bats relative to adults, or exhibit sustained upregulation through the developmental period corresponding to the maturation of echolocation behavior. In my third chapter, I review the evolution of high frequency hearing in mammals, focusing on echolocating bats and whales, which have independently evolved this complex trait. I provide an overview of recent studies that have reported molecular convergence in hearing genes among distantly related echolocators, and assert that the contribution of gene expression to hearing deserves further investigation. Finally, I argue that echolocators provide a unique opportunity to investigate the basis of high frequency amplification, and may possess mechanisms of hearing protection which enable them to prolong the use of echolocation throughout their long lives.Item ADAPTIVE FLIGHT AND ECHOLOCATION BEHAVIOR IN BATS(2015) Falk, Ben; Moss, Cynthia F; Neuroscience and Cognitive Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Bats use sonar to identify and localize objects as they fly and navigate in the dark. They actively adjust the timing, intensity, and frequency content of their sonar signals in response to task demands. They also control the directional characteristics of their sonar vocalizations with respect to objects in the environment. Bats demonstrate highly maneuverable and agile flight, producing high turn rates and abrupt changes in speed, as they travel through the air to capture insects and avoid obstacles. Bats face the challenge of coordinating flight kinematics with sonar behavior, as they adapt to meet the varied demands of their environment. This thesis includes three studies, one on the comparison of flight and echolocation behavior between an open space and a complex environment, one on the coordination of flight and echolocation behavior during climbing and turning, and one on the flight kinematic changes that occur under wind gust conditions. In the first study, we found that bats adapt the structure of the sonar signals, temporal patterning, and flight speed in response to a change in their environment. We also found that flight stereotypy developed over time in the more complex environment, but not to the extent expected from previous studies of non-foraging bats. We found that the sonar beam aim of the bats predicted flight turn rate, and that the relationship changed as the bats reacted to the obstacles. In the second study, we characterized the coordination of flight and sonar behavior as bats made a steep climb and sharp turns while they navigated a net obstacle. We found the coordinated production of sonar pulses with the wingbeat phase became altered during navigation of tight turns. In the third study, we found that bats adapt wing kinematics to perform under wind gust conditions. By characterizing flight and sonar behaviors in an insectivorous bat species, we find evidence for tight coordination of sensory and motor systems for obstacle navigation and insect capture. Through these studies, we learn about the mechanisms by which mammals and other organisms process sensory information to adapt their behaviors.Item Communication and Social Influences on Foraging in Bats(2012) Wright, Genevieve Spanjer; Wilkinson, Gerald S; Moss, Cynthia F; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Using social information can be an efficient way to respond to changing situations or to learn skills. Other benefits of foraging in a group, such as social facilitation, have also been reported. Furthermore, individuals foraging near conspecifics may use acoustic communication to mediate interactions. Many bat species (Order Chiroptera) are gregarious, and many tropical frugivorous bats rely on seasonally-abundant foods such that following conspecifics to a food source could benefit "followers" without harming "leaders." Animal-eating bats do not typically share food, but information obtained from experienced foragers could help facilitate development of prey acquisition skills in young bats. Additionally, communicative vocalizations serving various social functions have been reported in diverse bat species. Despite the opportunities for social learning and information transfer that many bats experience, few studies have attempted to determine if these phenomena occur in bats. Similarly, despite research on echolocation and some communicative calls, the context and function of social calls emitted by flying, foraging bats have received relatively little study. In this dissertation, I examine interactions between individuals in a foraging context and the impact of these interactions on the individuals' behavior. Specifically, I used pairs of big brown bats (Eptesicus fuscus) to test whether insectivorous bats can acquire a new foraging skill via social learning and what social cues might facilitate learning. I then describe the context of and attribute function to social calls emitted by bats in pairs. Finally, I examine the effects of social context on the foraging behavior of the frugivorous short-tailed fruit bat (Carollia perspicillata) presented with a food-finding task. My results provide the first evidence of the role of social learning (via attention to feeding buzzes and interaction with experienced individuals) in the development of foraging skills in young insectivorous bats. I also report a repertoire of social calls produced by foraging big brown bats and present evidence that males use social calls to defend food and increase their foraging success. Finally, I present evidence that social facilitation increases foraging performance in short-tailed fruit bats. These findings contribute to our knowledge of the social aspects of foraging in group-living animals.Item Sound Localization by Echolocating Bats(2007-05-14) Aytekin, Murat; Moss, Cynthia F.; Psychology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Echolocating bats emit ultrasonic vocalizations and listen to echoes reflected back from objects in the path of the sound beam to build a spatial representation of their surroundings. Important to understanding the representation of space through echolocation are detailed studies of the cues used for localization, the sonar emission patterns and how this information is assembled. This thesis includes three studies, one on the directional properties of the sonar receiver, one on the directional properties of the sonar transmitter, and a model that demonstrates the role of action in building a representation of auditory space. The general importance of this work to a broader understanding of spatial localization is discussed. Investigations of the directional properties of the sonar receiver reveal that interaural level difference and monaural spectral notch cues are both dependent on sound source azimuth and elevation. This redundancy allows flexibility that an echolocating bat may need when coping with complex computational demands for sound localization. Using a novel method to measure bat sonar emission patterns from freely behaving bats, I show that the sonar beam shape varies between vocalizations. Consequently, the auditory system of a bat may need to adapt its computations to accurately localize objects using changing acoustic inputs. Extra-auditory signals that carry information about pinna position and beam shape are required for auditory localization of sound sources. The auditory system must learn associations between extra-auditory signals and acoustic spatial cues. Furthermore, the auditory system must adapt to changes in acoustic input that occur with changes in pinna position and vocalization parameters. These demands on the nervous system suggest that sound localization is achieved through the interaction of behavioral control and acoustic inputs. A sensorimotor model demonstrates how an organism can learn space through auditory-motor contingencies. The model also reveals how different aspects of sound localization, such as experience-dependent acquisition, adaptation, and extra-auditory influences, can be brought together under a comprehensive framework. This thesis presents a foundation for understanding the representation of auditory space that builds upon acoustic cues, motor control, and learning dynamic associations between action and auditory inputs.Item Parent-Offspring Recognition and Alloparental Care in Greater Spear-Nosed Bats(2005-12-02) Bohn, Kirsten M; Wilkinson, Gerald S; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Selection should insure that parents selectively care for their own offspring. Thus, alloparental care, or care of other's young, seems counterintuitive to evolutionary theory. Alloparental care is often attributed to: 1) mistaken identity, when individuals confuse their young with others or 2) cooperation, when the alloparent and young mutually benefit. Cooperative care, in turn, is often explained by kin selection, where animals selectively care for genetic relatives. In this dissertation, I examine these alternative explanations for alloparental care in greater spear-nosed bats (Phyllostomus hastatus). In this species, females form stable social groups of relatively unrelated individuals. Females give birth once a year to nonvolant pups that frequently fall from roost sites in cave ceilings and likely perish unless retrieved by an adult. In this context, pups emit vocalizations, termed isolation calls, that are used in parent-offspring recognition. I examine parent-offspring recognition in P. hastatus by examining isolation call variability and both detection and perception of isolation calls by adults. I found that pups emit individually distinctive calls but that pups from the same social group have more similar calls than pups from different social groups. Psychoacoustic experiments in the laboratory showed that greatest hearing sensitivity and frequency selectivity in adult P. hastatus is at the fundamental frequency of isolation calls. I found that this is a common phenomenon in bats using comparative phylogenetic methods. Finally, using psychoacoustic experiments I demonstrated that P. hastatus females could discriminate between pups' isolation calls regardless of the pups' social groups. Next, I examine parental care in the natural habitat of P. hastatus. I found that females respond more frequently and spend more time visiting group mates' pups than non-group mates pups, even though many of these females are not missing pups of their own. These results, combined with the results from psychoacoustic studies, indicate that mistaken identity cannot explain this visiting behavior. By visiting group mates' pups, females protect them from non-group mates who attack and sometimes kill them. However, kin selection cannot explain this behavior because females are unrelated to group mates' pups that they visit.