Biology Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2749
Browse
7 results
Search Results
Item INSIGHTS IN ECOLOGY, BEHAVIOR, AND REPRODUCTION FROM VISUAL MODELS OF AFRICAN CICHLIDS(2024) Gonzalez, Zeke Martin; Carleton, Karen L; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Sexual selection has long been proposed to have played an important role in the explosive speciation of east African cichlids. Further, it is known that visual signals are the most salient ones to cichlids when it comes to reproduction. However, studies examining visual signals such as egg spots and size have been historically difficult to conduct due to the relationship between such phenotypes and confounding variables like age. In addition, the results from such studies often conflict and do not highlight clear patterns and hypotheses. In this dissertation, I use a receptor noise limited (RNL) visual model of increasing complexity to examine the discriminability of important visual signals in cichlid ecology, behavior, and evolution. In determining whether cichlid egg spots are truly mimics of cichlids eggs, I quantified fish and egg reflectance and found that two cichlid species are unable to distinguish the colors of eggs and egg spots in the lighting of their natural habitat. In order to bring together these quantitative methodologies with behavioral data, I tested the viability of using virtual stimuli displayed on a monitor to robustly examine how various visual signals affect conspecific male aggression. I found that although the cichlid Metriaclima zebra responds to virtual stimuli with equal aggression as towards live fish, it also responds with equal aggression towards virtual stimuli that differ in egg spot presence, body color, movement, and size. This suggests that virtual stimuli are not useful for behavioral tests in this species. Finally, in order to examine the salience of egg spots and body color in the wild, I calculated chromatic distance as a function of viewing distance for cichlid body colors against biologically-relevant backgrounds, conspecific body colors, and heterospecific body colors. The study shows that M. zebra body colors are discriminable from the space light at up to 5 m, but from the rocks at shorter distance, though distances that are comparable to the spacing of male territories. This suggests that males should be able to discriminate potential conspecific rivals on their breeding territories. Additionally, the visual model shows that M. zebra is highly discriminable from yellow heterospecifics but not so from blue heterospecifics. This dissertation emphasizes the importance of avoiding human biases in studies of cichlid color vision and behavior.Item CORTICAL AND STRIATAL MECHANISMS OF VALUE-BASED DECISION-MAKING AND THEIR DISRUPTION IN ADDICTION(2022) Hadfield, Heather; Roesch, Matthew R; Neuroscience and Cognitive Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)For decisions both great and small, the brain utilizes an extensive network that integrates value assessment, reward prediction, and motivation to quickly and efficiently select the most beneficial option while minimizing aversive consequences for ourselves. Numerous psychiatric conditions, in particular drug addiction, can disrupt this network and impair decision-making behavior. It is therefore important to understand the neural underpinnings of decision-making and how neural activity and its associated behavior are disrupted by drugs of abuse. My dissertation will expand on current studies of this circuitry by examining epigenetic and neurophysiological mechanisms of value-based decision-making within two regions of the brain. In my final aim, I explore a new behavioral assay that may be used to study these and other regions relevant for value-based decision-making in the context of another complex behavior.In my first aim, I have recorded from single neurons in the rat dorsal lateral striatum (DLS) after overexpressing histone deacetylase 5 (HDAC5), an epigenetic enzyme implicated in incubation of craving, in the dorsal striatum (DS). In my second aim I used pharmacological lesion and single-neuron recording combined with cocaine self-administration techniques to study anterior insula, a region well-known for combining internal and external experience but largely under-studied in the context of higher cognitive processes. These studies were conducted while rats performed an odor-guided decision-making task in which the value of rewards were manipulated by either the delay to or the size of the reward across a series of trial blocks. I have found overexpression of HDAC5 in DS promoted inflexible, faster, and automatic behavior in the decision-making task while increasing DLS’s response to reward cues- similar to previous studies examining DLS activity and behavior after cocaine self-administration. In my studies of insula, I found recording from this region novel, global signals of reward value that seemed to reflect the overall structure of the behavioral task. Following cocaine-exposure, these signals were diminished while immediate rewards were over-represented on a trial-by-trial basis, leading to steeper discounting of delayed rewards. Additional studies lesioning this region promoted faster reaction times and increased goal-directed behavior. Together, these results provide insights into how drugs of abuse may impair behavioral flexibility and the tracking of long-term changes in reward from multiple mechanisms. However, it is still unknown how these changes in value assessment give rise to complex impairments of behavior. As a first step to addressing this issue, I used a new task to examine how chronic drug use- which disrupts both neural signals in the corticostriatal circuit and epigenetic enzymes- also impairs the complex ability to delay gratification. This final study replicated well-established findings of drug-induced reversal-learning impairment, but surprisingly did not alter decision-making. This collection of work demonstrates the complexity with which drug exposure alters neural circuitry and value-based decision-making, and additionally shows the importance of utilizing complex behavioral assays to explore the relationship between brain and behavior.Item SURVIVING THE DEAD ZONE: INTERACTIONS AMONG JELLYFISH, COPEPODS, AND FISH IN THE CHESAPEAKE BAY(2020) slater, wencheng katherine; Pierson, James J; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The oxygen-deficient areas (dissolved oxygen < 2 mg L-1) in oceans and estuaries have been increasing worldwide in recent decades and are especially common in populated and developed areas due to eutrophication and warming. The objectives of this dissertation were to understand the effects of hypoxia on zooplankton and the plankton foodweb in the Chesapeake Bay. The study focused on copepod (Acartia tonsa) and its major predators bay anchovy (Anchoa mitchilli), comb jellyfish (Mnemiopsis leidyi), and bay nettle (Chrysaora chesapeakii) with data collected during six cruises in 2010 and 2011 and an individual-based model. Oxygen deficiency was evaluated with both dissolved oxygen concentration (DO < 2 mg L-1) and the oxygen supply and demand of the copepod (pO2 < Pcrit). The effects of hypoxia on zooplankton concentrations were estimated with net tows, and the impact of hypoxia on the plankton foodweb were quantified by comparing copepods’ nonpredatory mortality (estimated with neutral red experiments) and predatory mortality (estimated with gut contents of comb jellyfish and bay anchovy). A copepod behavior model was also built to examine how stress-induced behavior affected copepod vertical distributions and the tradeoffs between avoiding both hypoxia and predation. The results indicated the impact of oxygen deficiency could be underestimated using solely the metric of dissolved oxygen, especially under warm and saline conditions. Both copepod and planktivorous fish concentrations were lower under hypoxic conditions, but gelatinous zooplankton concentrations were higher. Both nonpredatory and predatory mortality of copepods were higher under hypoxic conditions, suggesting a direct linkage between hypoxia and decreasing copepod abundance. Most importantly, the source of copepod mortality changed with both hypoxic severity and season: the relative importance shifted from nonpredatory in spring to a combination of predatory and nonpredatory in summer and autumn, and the dominant predators shifted from juvenile bay anchovies under moderate hypoxia to comb jellyfish under warm and severely hypoxic conditions. The model demonstrated how enhancing stress avoidance would result in aggregating at a shallower depth and thus increasing predation risk, supporting the hypothesis that behavior change under hypoxia may increase predatory mortality. Overall my research has shown that hypoxia directly decreases zooplankton abundance and increases predation impact, and avoiding hypoxia could contribute to higher predation impact.Item Neuromodulation in the Olfactory Bulb(2015) Smith, Richard Scott; Araneda, Ricardo C; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Neuromodulation of olfactory circuits by acetylcholine (ACh) plays an important role in odor discrimination and learning. Early processing of chemosensory signals occurs in two functionally and anatomically distinct regions, the main and accessory olfactory bulbs (MOB and AOB), which receive significant cholinergic input from the basal forebrain. Here we explore the regulation of AOB and MOB circuits by ACh, and how this modulation influences olfactory mediated behaviors. Surprisingly, despite the presence of a conserved circuit, activation of muscarinic ACh receptors revealed marked differences in cholinergic modulation of output neurons: excitation in the AOB and inhibition in the MOB. Granule cells (GCs), the most abundant intrinsic neuron in the OB, also exhibited a complex muscarinic response. While GCs in the AOB were excited, MOB GCs exhibited a dual muscarinic action, a hyperpolarization and an increase in excitability uncovered by cell depolarization. Furthermore, ACh had a different effect on the input/output relationship of MCs in the AOB and MOB, showing a net effect on gain in MCs of the MOB, but not in the AOB. Interestingly, despite the striking differences in neuromodulatory actions on output neurons, chemogenetic inhibition of ACh release produced similar perturbations in olfactory behaviors mediated by these two regions. Decreasing ACh in the OB disrupted the natural discrimination of molecularly related odors and the natural investigation of odors associated with social behaviors. Thus, the distinct neuromodulation by ACh in these circuits could underlie different solutions to the processing of general odors and semiochemicals, and the diverse olfactory behaviors they trigger.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 FROM GENES TO BEHAVIOR: VARIATION IN THE VISUAL SYSTEMS OF LAKE MALAWI CICHLID FISHES(2011) Smith, Adam Ray; Carleton, Karen L; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Visual systems are ideal models for the study of sensory evolution. The cichlids of Lake Malawi possess an elaborated complex of genes (opsins) that encode chromatic visual pigments, which allows us to study the evolution and diversification of chromatic vision in great detail. In this dissertation, we investigated the molecular and behavioral properties of cichlid visual systems in order to more thoroughly understand the diversification of visual systems and the behavioral consequences of these changes. The work is organized into three research projects, with the following results: (1) Opsin gene sequence variation, with corresponding functional sensitivity changes, were found for the SWS1 (ultraviolet-sensitive), SWS2B (violet-sensitive), RH2Aβ (green-sensitive), and LWS (red-sensitive) opsin genes. Of the two genera profiled, each had two variable genes, suggesting that diversifying selection acts on different opsins in each genus. Furthermore, our data suggest that the variation in the SWS1 gene has arisen recently in Lake Malawi and is under rapid selection. (2) Intraspecific cone opsin gene expression variation was found in wild populations of multiple species. Expression variation was found primarily for the LWS and SWS1 genes, while the other genes were relatively consistent within species. This finding suggests that expression can be modulated by adding genes to what may otherwise be considered a species-specific expression pattern. Quantitative models suggested that this expression variation was not the result of environmental constraint. (3) Fish raised in different ambient developmental light environments had different cone opsin gene expression, primarily in the LWS opsin gene. These expression differences caused an increase in behavioral sensitivity in the optomotor response. Furthermore, analyses indicated that the OMR response is determined solely by the LWS cone pigment, rather than a complement of different cone types. Taken together, these findings shed new light on how visual systems diversify over short evolutionary time-scales, and the possible linkage of early determinants of visual sensitivities (opsin genes) and processes that directly influence speciation (behavior).Item THE BEHAVIOR OF THE SCYPHOMEDUSAE CHRYSAORA QUINQUECIRRHA AND AURELIA AURITA AND ITS ECOLOGICAL IMPORTANCE(2004-11-23) Matanoski, Joseph Carroll; Hood, Raleigh R; Purcell, Jennifer E; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Scyphomedusae are important components in trophic and community structures of marine and estuarine systems worldwide. Behavior likely has a significant influence on medusa population dynamics and growing evidence points to the disproportionate effect individual behavior has on population responses, yet there are few quantitative studies of medusa behavior and no method for quantifying the behavior of individual pelagic organisms. A numerical model of medusa swimming behavior would be an important tool for assessing its effect on spatial patterns and foraging efficiency. An approach was developed that uses a suite of statistical techniques to quantitatively describe time-dependent changes in behavior of pelagic organisms and tested on the swimming behavior of Aurelia aurita and the foraging behavior of Chrysaora quinquecirrha. An individual-based model of medusa swimming behavior was formulated as a correlated random walk of velocity vectors in three dimensions. Each A. aurita medusa exhibited a unique swimming behavior, including varying swimming bell pulsations, speed, and turning at characteristic frequencies. C. quinquecirrha swam in mostly linear trajectories that alternated between periods of slow and fast swimming while searching for prey, but swam at a constant moderate rate with increased anisotropic turning while feeding. Foraging behavior by medusa groups depended on interindividual and intraindividual variability in medusa behavior, including deterministic changes in swimming pulsation strength and turning. Empirical and model results showed that variability of behavior among medusae and by individual medusae over time are integral components determining the aggregated population response. Medusa foraging behavior appears adapted for patchily distributed prey. Alternating between slow and fast swimming while searching for prey may minimize energy expended while periodically generating prey-entraining currents. Increased turning in the presence of prey increases the likelihood of remaining in prey patches. Anisotropic turning created vertically spiraling paths, well suited to horizontally compressed prey patches. Model results demonstrated that medusae tend to swim toward and accumulate at the surface, avoid direct contact with the bottom, orient search patterns to long-range stimuli (e.g. gravity) and feeding patterns to local stimuli (e.g. prey contact), and exhibit periodicities of velocity outside prey patches and turning within patches that result from deterministic behavior.