Theses and Dissertations from UMD
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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
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Item Biogeographic, Geochemical, and Paleoceanographic Investigations of Ostracodes in the Bering, Chukchi, and Beaufort Seas(2022) Gemery, Laura; Cooper, Lee W.; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)In this study, I investigated the continental shelf environments of the Bering, Chukchi, and Beaufort Seas using species of Ostracoda and their shell chemistry as indicators of oceanographic conditions and change. Ostracodes are bivalved Crustacea that secrete a calcareous shell commonly preserved in sediments in the Arctic. Because ostracode species have survival limits controlled by temperature, salinity, oxygen, sea ice, food, and other habitat-related factors, they are useful ecological indicators. A primary objective of my dissertation research was to establish how their ecology, biogeography and shell geochemistry is related to ocean variability in water mass properties and productivity at high latitudes. First, I examined community assemblages of ostracodes over several decades (1970-2018) in the northern Bering, Chukchi, and Beaufort Seas, and the main environmental factors that affect their biogeography. Results showed that large-scale south-to-north and small-scale nearshore-offshore gradients in ostracode community structure were tied to changes in water mass properties in combination with food sources and sediment substrate. Although the dominant species did not significantly change over the investigated period, the frequency of two cold-temperate species that are primarily and previously restricted to shallow North Pacific sediments off Asia has increased during the last decade. This suggests that these species are responding to recent increases in coastal and mid-shelf bottom water temperatures and/or carbon flux to the benthos. A second goal was to assess the feasibility of using stable oxygen isotopes (δ18O) of carbonate from ostracode shells as paleoceanographic proxies for water mass identification on Arctic and subarctic continental shelves. Through the use of regression analyses, I established that the δ18O values of carbonates from two species (of five investigated) can be reliable recorders of summer water mass changes in temperature and seawater δ18O content. The third part of the study was to use results from these prior two goals in combination with data on biogenic silica, foraminifera assemblages and stable isotope composition of biogenic carbonates, to reconstruct 2,000 years of paleoceanography from a radiocarbon-dated sediment core on the Mackenzie Shelf of the Beaufort Sea. This high-resolution (sub-centennial) record identified shifts in multiple proxies that are related to climate oscillations such as the Medieval Climate Anomaly, the Little Ice Age, and the modern period of anthropogenic change. The overall findings of my dissertation research support the premise that on complex and dynamic continental shelves, paleoceanographic uncertainties can be addressed by documenting microfossil faunal assemblages, measuring stable isotope variability in microfossil carbonates, as well as relating the distribution of species in time with an understanding of species ecology.Item PLANT–ARTHROPOD ASSOCIATIONS FROM THE WESTERN INTERIOR OF NORTH AMERICA DURING THE LATE CRETACEOUS(2020) Maccracken, Sarah Augusta; Shultz, Jeffrey; Labandeira, Conrad C; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Insects are unparalleled in species diversity and breadth of ecological associations. The most prominent of these ecological associations is insect herbivory on vascular plants, which has shaped terrestrial ecosystems for hundreds of millions of years. Only recently have scientists begun to understand the diversity and intensity of plant–insect associations in the fossil record. The majority of these studies have documented episodes of rapid change in Earth’s history, such as intervals of global warming. However, there are few studies documenting plant–insect associations around longer time intervals, including the radiation of flowering plants (angiosperms) during the Cretaceous Period from 145 to 66 Ma (Mega-annum), which set the stage for many modern plant–insect associations. Herein, I present the results of specimen-based surveys of Campanian Age (83.6–72.1 Ma) macrofossil floras and their associated insect damage from the Kaiparowits Formation of Utah, USA, a fossiliferous deposit within the Western Interior. First, I describe a new genus of fossil laurel (Lauraceae), and analyze the plant–insect associations found on this taxon. After, I describe the diversity and intensity of plant–insect associations from the a single, well-sampled locality. I then describe a new fossil lyonetiid moth leaf mine, which represents the oldest fossil evidence of a cemiostomine leaf-mining moth, as well as the second oldest record of the Yponomeutoidea–Gracillarioidea clade. Then, I describe acarodomatia (mite houses) on fossil leaves, which constitute the oldest evidence for plant–mite mutualisms in the fossil record. Finally, to understand broad-scale and long-term patterns of insect damage in the fossil record, I analyze all available fossil plant–insect associational datasets spanning the Age of Angiosperms (ca. 76–2 Ma). These results indicate that insect preference for plant hosts may have changed through time as local plant diversity increased, but this may stem from differences in sampling regimes and difficulties in identification of fossil angiosperms. My findings collectively indicate that Late Cretaceous plant–insect associations are often novel, diverse, and may be evolutionarily tied to modern plant–insect associations, as well as the acquired insight into the limitations and future directions for this field of research.Item Development and the Early Animal Fossil Record: Evolution and Phylogenetic Applications(2016) Tweedt, Sarah Maureen; Delwiche, Charles F; Erwin, Douglas H; Cell Biology & Molecular Genetics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Although evolutionary developmental biology and paleontology are linked by the study of morphology, the application of development to paleontological questions has only recently become more prominent. The growth of a robust developmental genetic framework for studying the origin and evolution of morphological features, however, holds great promise for understanding ancient animal life. As paleontology provides the historical record as well as the temporal and environmental context of past morphological evolution, uniting knowledge of developmental genetic systems with this historical record will form a key synthetic approach to understanding the early evolution of developmental processes. Ultimately unraveling the sequence of ancient animal developmental evolution will require combining analysis of comparative developmental data, critical assessment of fossil morphology within a developmental framework, and the targeted exploration of specific geologic periods to fill in the missing record of key times in animal developmental evolution. This study addresses each of these three approaches. First, I provide a new compilation and evaluation of recent comparative and experimental developmental biology data to review the nature of developmental ‘toolkits’ at the origin of the most basal animal clades. I reconstruct early animal developmental capacities and integrate these data within a temporal framework to better understand the context of earliest animal development. Second, I assess longstanding evolutionary hypotheses about the origin of the panarthropod clade and the phylogenetic position of Cambrian ‘lobopod’ fossils by examining signal present within current morphological datasets. I apply new methods to fossil panarthropod phylogeny estimation and suggest strategies for developmentally-informed phylogenetic coding of morphological data. Third, I present the discovery of the oldest spicule-bearing fossil sponges in the rock record, which co-occur in latest Ediacaran strata with classic enigmatic Ediacaran fauna. I provide a formal systematic description of fossil material from localities in both Nevada and southern Namibia. The combined approaches presented herein are a first step towards a deeper integration of developmental principles in the study and discovery of ancient animal life, and contribute to our understanding of the evolution of ancient animal developmental processes.Item Using a Combination of Phylogenetic Comparative and Paleobotanical Methods to Elucidate Patterns of Lineage Selection in Rosales (Plantae: Anthophyta)(2016) Simpson, Andrew Gordon; Fenster, Charles B.; Wing, Scott L.; Behavior, Ecology, Evolution and Systematics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)An increasing focus in evolutionary biology is on the interplay between mesoscale ecological and evolutionary processes such as population demographics, habitat tolerance, and especially geographic distribution, as potential drivers responsible for patterns of diversification and extinction over geologic time. However, few studies to date connect organismal processes such as survival and reproduction through mesoscale patterns to long-term macroevolutionary trends. In my dissertation, I investigate how mechanism of seed dispersal, mediated through geographic range size, influences diversification rates in the Rosales (Plantae: Anthophyta). In my first chapter, I validate the phylogenetic comparative methods that I use in my second and third chapters. Available state speciation and extinction (SSE) models assumptions about evolution known to be false through fossil data. I show, however, that as long as net diversification rates remain positive – a condition likely true for the Rosales – these violations of SSE’s assumptions do not cause significantly biased results. With SSE methods validated, my second chapter reconstructs three associations that appear to increase diversification rate for Rosalean genera: (1) herbaceous habit; (2) a three-way interaction combining animal dispersal, high within-genus species richness, and geographic range on multiple continents; (3) a four-way interaction combining woody habit with the other three characteristics of (2). I suggest that the three- and four-way interactions represent colonization ability and resulting extinction resistance in the face of late Cenozoic climate change; however, there are other possibilities as well that I hope to investigate in future research. My third chapter reconstructs the phylogeographic history of the Rosales using both non-fossil-assisted SSE methods as well as fossil-informed traditional phylogeographic analysis. Ancestral state reconstructions indicate that the Rosaceae diversified in North America while the other Rosalean families diversified elsewhere, possibly in Eurasia. SSE is able to successfully identify groups of genera that were likely to have been ancestrally widespread, but has poorer taxonomic resolution than methods that use fossil data. In conclusion, these chapters together suggest several potential causal links between organismal, mesoscale, and geologic scale processes, but further work will be needed to test the hypotheses that I raise here.Item Molecular phylogenetics, biodiversity and life history evolution of Yponomeutoidea (Lepidoptera: Ditrysia), with a catalog and an overview of the lepidopteran fossils(2013) Sohn, Jae-Cheon; Mitter, Charles; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Yponomeutoidea, one of the earliest-branching superfamilies of advanced (ditrysian) Lepidoptera, comprise about 1,800 species worldwide, including notable pests and models of insect-plant interaction. Yponomeutoids were one of the earliest lepidopteran clades to evolve external feeding and to colonize extensively herbaceous angiosperms. Despite the group's economic importance, and its value for tracing early lepidopteran evolution, the biodiversity and phylogeny of Yponomeutoidea have been relatively little studied. Even the monophyly and composition of the superfamily have been in doubt. In this dissertation, the most detailed molecular phylogeny to date for Yponomeutoidea is presented (Chapter 1). The resulting phylogeny is compared to previous morphological evidence, and its implications for evolutionary trends in yponomeutoid host association and biogeography are explored. As a prerequisite to divergence dating in the Yponomeutoidea, which is necessarily based on outgroup fossils as none are known for yponomeutoids, a general summary and overview of the lepidopteran fossil record (Chapter 2) is provided, based a recent, comprehensive catalog of known fossils. For chapter 2, all known lepidopteran fossils have been catalogued with annotations of their preservation, specimen deposition, fossil localities and ages (Chapter 3). As a contribution toward better characterization of yponomeutoid biodiversity, taxonomic reviews are provided for the New World genera Eucalantica and Atemelia (Chapter 4). The molecular phylogeny estimate (Chapter 1) is based on 8-27 protein coding nuclear genes sequenced in 86 Yponomeutoidea and 53 outgroups. Monophyly for Yponomeutoidea is corroborated. Results from different analyses are highly congruent and relationships within Yponomeutoidea are well supported overall. There is strong support overall for monophyly of families (or major parts thereof) previously recognized on morphological grounds, including Yponomeutidae, Ypsolophidae, Plutellidae, Glyphipterigidae, Argyresthiidae, Attevidae, Praydidae, Heliodinidae, and Bedelliidae. The formerly yponomeutid subfamily Scythropiinae are elevated to family rank (Scythropiidae stat. rev.). Host plant family associations of yponomeutoid subfamilies and families are non-random, but show no trends suggesting parallel phylogenesis, and are less conserved than is mode of feeding (e.g. internal versus external). My analyses reveal previously unrecognized tropical clades in several families, and suggest that previous characterization of yponomeutoids as predominantly Palearctic/ Holarctic was based on insufficient sampling.Item A carbon and nitrogen isotopic analysis of Pleistocene food webs in North America: implications for paleoecology and extinction(2008-05-05) France, Christine Ann Missell; Kaufman, Alan J; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Carbon and nitrogen isotopic reconstructions of North American Pleistocene trophic relationships were used to examine the extinction within terrestrial mammals ~10,000 years ago and distinguish between two potential causal mechanisms - human over-hunting and climate change. Additionally, individual animals were examined for unique isotopic signatures associated with feeding specializations, digestive strategies, and juveniles. Bones representing a comprehensive set of Pleistocene mammalian genera were obtained from three fossil localities: McKittrick Brea, California; Saltville, Virginia; and several sites in Florida. Collagen, a durable bone protein whose carbon and nitrogen isotopic composition reflects dietary input, was extracted from specimens and analyzed for delta-13C, delta-15N, % collagen, %C, %N, and C:N. Radiocarbon dating and amino acid analyses were performed on select sample sets. Results indicated that several specimens contained well preserved collagen, the isotopic values of which indicated both trophic position and vegetation preference. Those samples that contained residual diagenetic proteinaceous material exhibited increased hydrolysis of collagen with time and leaching of disassociated amino acids. Trophic relationships were reconstructed from well preserved specimens for Aucilla River, Florida and the herbivores of Saltville, Virginia, with a less complete reconstruction established for McKittrick Brea, California. The following notable trends emerged: 1) absence of nitrogen isotopic distinction between ruminants and non-ruminants, 2) enriched juvenile nitrogen isotopic signature, 3) distinction of giant ground sloths as omnivores, 4) C4 grass grazers and open C4 grasslands restricted to southern North American latitudes, 5) generalized and opportunistic feeding habits of herbivores, 6) potential prey specializations of carnivores. A noticeable lack of competition and feeding specialists among herbivores suggested a stable base to these late Pleistocene ecosystems, which argues against climatically induced stress on plants. While carnivore specimens were fewer, the apex trophic levels appeared to exhibit a similar lack of competition, which would be expected in a human-driven extinction where carnivores were stressed due to rapidly over-hunted herbivores. The ultimate cause of the late Pleistocene mammalian extinction in North America can not be exclusively attributed to either of these two mechanisms at this point in time; rather, a combination of factors should be considered.Item "SCIENTIFIC TRUTH, RIGHTLY UNDERSTOOD, IS RELIGIOUS TRUTH": THE LIFE AND WORKS OF REVEREND EDWARD HITCHCOCK, 1793-1864(2005-12-13) Segal, Ariel Jacob; Gilbert, James B; History/Library & Information Systems; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Reverend Edward Hitchcock (1793-1864) was an important figure in 19th century American science. He contributed to the fields of geology and paleontology, and was the founder of paleoichnology. The overriding passion of Hitchcock's life was the reconciliation of science with evangelical Protestant Christianity. For most of his career, he located all of geological time in a "gap" between the first two verses of Genesis, but later tended to view the Creation days themselves as symbolic. Hitchcock also dealt intensively with the scientific understanding of Noah's flood. At first, he advocated a Deluge covering the entire planet. Subsequently, he held that the Deluge only affected the portion of the planet inhabited by humanity during the time of Noah. Hitchcock used evidence from science to support both natural and revealed religion. He combined this synthesizing with an increasingly extravagant romanticism, and confidently looked forward to continuing his scientific investigations in Heaven.