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Description
In an effort to address the lack of literature in on-campus active travel, this study aims to investigate the following primary questions:<br/>• What are the modes that students use to travel on campus?<br/>• What are the motivations that underlie the mode choice of students on campus?<br/>My first stage of research involved a series of qualitative investigations. I held one-on-one virtual interviews with students in which I asked them questions about the mode they use and why they feel that their chosen mode works best for them. These interviews served two functions. First, they provided me with insight into the various motivations underlying student mode choice. Second, they provided me with an indication of what explanatory variables should be included in a model of mode choice on campus.<br/>The first half of the research project informed a quantitative survey that was released via the Honors Digest to attract student respondents. Data was gathered on travel behavior as well as relevant explanatory variables.<br/>My analysis involved developing a logit model to predict student mode choice on campus and presenting the model estimation in conjunction with a discussion of student travel motivations based on the qualitative interviews. I use this information to make a recommendation on how campus infrastructure could be modified to better support the needs of the student population.
ContributorsMirtich, Laura Christine (Author) / Salon, Deborah (Thesis director) / Fang, Kevin (Committee member) / School of Public Affairs (Contributor) / School of Life Sciences (Contributor) / Barrett, The Honors College (Contributor)
Created2021-05
Description
Natural history is, and was, dependent upon the collection of specimens. In the nineteenth century, American naturalists and institutions of natural history cultivated and maintained extensive collection networks comprised of numerous collectors that provided objects of natural history for study. Effective networks were collaborative in nature, with naturalists such as Spencer Baird of the Smithsonian trading their time and expertise for specimens. The incorporation of Darwinian and Neo-Lamarckian evolutionary theory into natural history in the middle of the century led to dramatic changes in the relationship between naturalists and collectors, as naturalists sought to reconcile their observations within the new evolutionary context. This dissertation uses the careers of collectors Robert Kennicott, Frank Stephens, Edward W. Nelson, E.A. Goldman, and Edmund Heller as case studies in order to evaluate how the changes in the theoretical framework of late nineteenth century natural history led to advances in field practice by assessing how naturalists trained their collectors to meet new demands within the field. Research focused on the correspondence between naturalists and collectors, along with the field notes and applicable publications by collectors. I argue that the changes in natural history necessitated naturalists training their collectors in the basics of biogeography - the study of geographic distribution of organisms, and systematics - the study of the diversity of life - leading to a collaborative relationship in which collectors played an active role in the formation of new biological knowledge. The project concludes that the changes in natural history with regard to theory and practice gradually necessitated a more professional cadre of collectors. Collectors became active agents in the formation of biological knowledge, and instrumental in the formation of a truly systematic natural history. As a result, collectors became de facto field naturalists, the forerunners of the field biologists that dominated the practice of natural history in the early and middle twentieth century.
ContributorsLaubacher, Matthew (Author) / Green, Monica (Thesis advisor) / Laubichler, Manfred (Thesis advisor) / Wright, Johnson Kent (Committee member) / Arizona State University (Publisher)
Created2011
Description
The oceans play an essential role in global biogeochemical cycles and in regulating climate. The biological carbon pump, the photosynthetic fixation of carbon dioxide by phytoplankton and subsequent sequestration of organic carbon into deep water, combined with the physical carbon pump, make the oceans the only long-term net sink for anthropogenic carbon dioxide. A full understanding of the workings of the biological carbon pump requires a knowledge of the role of different taxonomic groups of phytoplankton (protists and cyanobacteria) to organic carbon export. However, this has been difficult due to the degraded nature of particles sinking into particle traps, the main tools employed by oceanographers to collect sinking particulate matter in the ocean. In this study DNA-based molecular methods, including denaturing gradient gel electrophoresis, cloning and sequencing, and taxon-specific quantitative PCR, allowed for the first time for the identification of which protists and cyanobacteria contributed to the material collected by the traps in relation to their presence in the euphotic zone. I conducted this study at two time-series stations in the subtropical North Atlantic Ocean, one north of the Canary Islands, and one located south of Bermuda. The Bermuda study allowed me to investigate seasonal and interannual changes in the contribution of the plankton community to particle flux. I could also show that small unarmored taxa, including representatives of prasinophytes and cyanobacteria, constituted a significant fraction of sequences recovered from sediment trap material. Prasinophyte sequences alone could account for up to 13% of the clone library sequences of trap material during bloom periods. These observations contradict a long-standing paradigm in biological oceanography that only large taxa with mineral shells are capable of sinking while smaller, unarmored cells are recycled in the euphotic zone through the microbial loop. Climate change and a subsequent warming of the surface ocean may lead to a shift in the protist community toward smaller cell size in the future, but in light of these findings these changes may not necessarily lead to a reduction in the strength of the biological carbon pump.
ContributorsAmacher, Jessica (Author) / Neuer, Susanne (Thesis advisor) / Garcia-Pichel, Ferran (Committee member) / Lomas, Michael (Committee member) / Wojciechowski, Martin (Committee member) / Stout, Valerie (Committee member) / Arizona State University (Publisher)
Created2011
Description
Microbial electrochemical cells (MXCs) are promising platforms for bioenergy production from renewable resources. In these systems, specialized anode-respiring bacteria (ARB) deliver electrons from oxidation of organic substrates to the anode of an MXC. While much progress has been made in understanding the microbiology, physiology, and electrochemistry of well-studied model ARB such as Geobacter and Shewanella, tremendous potential exists for MXCs as microbiological platforms for exploring novel ARB. This dissertation introduces approaches for selective enrichment and characterization of phototrophic, halophilic, and alkaliphilic ARB. An enrichment scheme based on manipulation of poised anode potential, light, and nutrient availability led to current generation that responded negatively to light. Analysis of phototrophically enriched communities suggested essential roles for green sulfur bacteria and halophilic ARB in electricity generation. Reconstruction of light-responsive current generation could be successfully achieved using cocultures of anode-respiring Geobacter and phototrophic Chlorobium isolated from the MXC enrichments. Experiments lacking exogenously supplied organic electron donors indicated that Geobacter could produce a measurable current from stored photosynthate in the dark. Community analysis of phototrophic enrichments also identified members of the novel genus Geoalkalibacter as potential ARB. Electrochemical characterization of two haloalkaliphilic, non-phototrophic Geoalkalibacter spp. showed that these bacteria were in fact capable of producing high current densities (4-8 A/m2) and using higher organic substrates under saline or alkaline conditions. The success of these selective enrichment approaches and community analyses in identifying and understanding novel ARB capabilities invites further use of MXCs as robust platforms for fundamental microbiological investigations.
ContributorsBadalamenti, Jonathan P (Author) / Krajmalnik-Brown, Rosa (Thesis advisor) / Garcia-Pichel, Ferran (Committee member) / Rittmann, Bruce E. (Committee member) / Torres, César I (Committee member) / Vermaas, Willem (Committee member) / Arizona State University (Publisher)
Created2013
Description
Human activity has increased loading of reactive nitrogen (N) in the environment, with important and often deleterious impacts on biodiversity, climate, and human health. Since the fate of N in the ecosystem is mainly controlled by microorganisms, understanding the factors that shape microbial communities becomes relevant and urgent. In arid land soils, these microbial communities and factors are not well understood. I aimed to study the role of N cycling microbes, such as the ammonia-oxidizing bacteria (AOB), the recently discovered ammonia-oxidizing archaea (AOA), and various fungal groups, in soils of arid lands. I also tested if niche differentiation among microbial populations is a driver of differential biogeochemical outcomes. I found that N cycling microbial communities in arid lands are structured by environmental factors to a stronger degree than what is generally observed in mesic systems. For example, in biological soil crusts, temperature selected for AOA in warmer deserts and for AOB in colder deserts. Land-use change also affects niche differentiation, with fungi being the major agents of N2O production in natural arid lands, whereas emissions could be attributed to bacteria in mesic urban lawns. By contrast, NO3- production in the native desert and managed soils was mainly controlled by autotrophic microbes (i.e., AOB and AOA) rather than by heterotrophic fungi. I could also determine that AOA surprisingly responded positively to inorganic N availability in both short (one month) and long-term (seven years) experimental manipulations in an arid land soil, while environmental N enrichment in other ecosystem types is known to favor AOB over AOA. This work improves our predictions of ecosystem response to anthropogenic N increase and shows that paradigms derived from mesic systems are not always applicable to arid lands. My dissertation also highlights the unique ecology of ammonia oxidizers and draws attention to the importance of N cycling in desert soils.
ContributorsMarusenko, Yevgeniy (Author) / Hall, Sharon J (Thesis advisor) / Garcia-Pichel, Ferran (Thesis advisor) / Mclain, Jean E (Committee member) / Schwartz, Egbert (Committee member) / Arizona State University (Publisher)
Created2013
Description
Once perceived as an unimportant occurrence in living organisms, cell degeneration was reconfigured as an important biological phenomenon in development, aging, health, and diseases in the twentieth century. This dissertation tells a twentieth-century history of scientific investigations on cell degeneration, including cell death and aging. By describing four central developments in cell degeneration research with the four major chapters, I trace the emergence of the degenerating cell as a scientific object, describe the generations of a variety of concepts, interpretations and usages associated with cell death and aging, and analyze the transforming influences of the rising cell degeneration research. Particularly, the four chapters show how the changing scientific practices about cellular life in embryology, cell culture, aging research, and molecular biology of Caenorhabditis elegans shaped the interpretations about cell degeneration in the twentieth-century as life-shaping, limit-setting, complex, yet regulated. These events created and consolidated important concepts in life sciences such as programmed cell death, the Hayflick limit, apoptosis, and death genes. These cases also transformed the material and epistemic practices about the end of cellular life subsequently and led to the formations of new research communities. The four cases together show the ways cell degeneration became a shared subject between molecular cell biology, developmental biology, gerontology, oncology, and pathology of degenerative diseases. These practices and perspectives created a special kind of interconnectivity between different fields and led to a level of interdisciplinarity within cell degeneration research by the early 1990s.
ContributorsJiang, Lijing (Author) / Maienschein, Jane (Thesis advisor) / Laubichler, Manfred (Thesis advisor) / Hurlbut, James (Committee member) / Creath, Richard (Committee member) / White, Michael (Committee member) / Arizona State University (Publisher)
Created2013
Description
Biological soil crusts (BSCs), topsoil microbial assemblages typical of arid land ecosystems, provide essential ecosystem services such as soil fertilization and stabilization against erosion. Cyanobacteria and lichens, sometimes mosses, drive BSC as primary producers, but metabolic activity is restricted to periods of hydration associated with precipitation. Climate models for the SW United States predict changes in precipitation frequency as a major outcome of global warming, even if models differ on the sign and magnitude of the change. BSC organisms are clearly well adapted to withstand desiccation and prolonged drought, but it is unknown if and how an alteration of the precipitation frequency may impact community composition, diversity, and ecosystem functions. To test this, we set up a BSC microcosm experiment with variable precipitation frequency treatments using a local, cyanobacteria-dominated, early-succession BSC maintained under controlled conditions in a greenhouse. Precipitation pulse size was kept constant but 11 different drought intervals were imposed, ranging between 416 to 3 days, during a period of 416 days. At the end of the experiments, bacterial community composition was analyzed by pyrosequencing of the 16s rRNA genes in the community, and a battery of functional assays were used to evaluate carbon and nitrogen cycling potentials. While changes in community composition were neither marked nor consistent at the Phylum level, there was a significant trend of decreased diversity with increasing precipitation frequency, and we detected particular bacterial phylotypes that responded to the frequency of precipitation in a consistent manner (either positively or negatively). A significant trend of increased respiration with increasingly long drought period was detected, but BSC could recover quickly from this effect. Gross photosynthesis, nitrification and denitrification remained essentially impervious to treatment. These results are consistent with the notion that BSC community structure adjustments sufficed to provide significant functional resilience, and allow us to predict that future alterations in precipitation frequency are unlikely to result in severe impacts to BSC biology or ecological relevance.
ContributorsMyers, Natalie Kristine (Author) / Garcia-Pichel, Ferran (Thesis advisor) / Hall, Sharon (Committee member) / Turner, Benjamin (Committee member) / Krajmalnik-Brown, Rosa (Committee member) / Arizona State University (Publisher)
Created2013
Improving cyanobacterial hydrogen production through bioprospecting of natural microbial communities
Description
Some cyanobacteria can generate hydrogen (H2) under certain physiological conditions and are considered potential agents for biohydrogen production. However, they also present low amounts of H2 production, a reaction reversal towards H2 consumption, and O2 sensitivity. Most attempts to improve H2 production have involved genetic or metabolic engineering approaches. I used a bio-prospecting approach instead to find novel strains that are naturally more apt for biohydrogen production. A set of 36, phylogenetically diverse strains isolated from terrestrial, freshwater and marine environments were probed for their potential to produce H2 from excess reductant. Two distinct patterns in H2 production were detected. Strains displaying Pattern 1, as previously known from Synechocystis sp. PCC 6803, produced H2 only temporarily, reverting to H2 consumption within a short time and after reaching only moderately high H2 concentrations. By contrast, Pattern 2 cyanobacteria, in the genera Lyngbya and Microcoleus, displayed high production rates, did not reverse the direction of the reaction and reached much higher steady-state H2 concentrations. L. aestuarii BL J, an isolate from marine intertidal mats, had the fastest production rates and reached the highest steady-state concentrations, 15-fold higher than that observed in Synechocystis sp. PCC 6803. Because all Pattern 2 strains originated in intertidal microbial mats that become anoxic in dark, it was hypothesized that their strong hydrogenogenic capacity may have evolved to aid in fermentation of the photosynthate. When forced to ferment, these cyanobacteria display similarly desirable characteristics of physiological H2 production. Again, L. aestuarii BL J had the fastest specific rates and attained the highest H2 concentrations during fermentation, which proceeded via a mixed-acid pathway to yield acetate, ethanol, lactate, H2, CO2 and pyruvate. The genome of L. aestuarii BL J was sequenced and bioinformatically compared to other cyanobacterial genomes to ascertain any potential genetic or structural basis for powerful H2 production. The association hcp exclusively in Pattern 2 strains suggests its possible role in increased H2 production. This study demonstrates the value of bioprospecting approaches to biotechnology, pointing to the strain L. aestuarii BL J as a source of useful genetic information or as a potential platform for biohydrogen production.
ContributorsKothari, Ankita (Author) / Garcia-Pichel, Ferran (Thesis advisor) / Vermaas, Willem F J (Committee member) / Rittmann, Bruce (Committee member) / Torres, Cesar (Committee member) / Arizona State University (Publisher)
Created2013
Description
Gene-centric theories of evolution by natural selection have been popularized and remain generally accepted in both scientific and public paradigms. While gene-centrism is certainly parsimonious, its explanations fall short of describing two patterns of evolutionary and social phenomena: the evolution of sex and the evolution of social altruism. I review and analyze current theories on the evolution of sex. I then introduce the conflict presented to gene-centric evolution by social phenomena such as altruism and caste sterility in eusocial insects. I review gene-centric models of inclusive fitness and kin selection proposed by Hamilton and Maynard Smith. Based their assumptions, that relatedness should be equal between sterile workers and reproductives, I present several empirical examples that conflict with their models. Following that, I introduce a unique system of genetic caste determination (GCD) observed in hybrid populations of two sister-species of seed harvester ants, Pogonomyrmex rugosus and Pogonomyrmex barbatus. I review the evidence for GCD in those species, followed by a critique of the current gene-centric models used to explain it. In chapter two I present my own theoretical model that is both simple and extricable in nature to explain the origin, evolution, and maintenance of GCD in Pogonomyrmex. Furthermore, I use that model to fill in the gaps left behind by the contributing authors of the other GCD models. As both populations in my study system formed from inter-specific hybridization, I review modern discussions of heterosis (also called hybrid vigor) and use those to help explain the ecological competitiveness of GCD. I empirically address the inbreeding depression the lineages of GCD must overcome in order to remain ecologically stable, demonstrating that as a result of their unique system of caste determination, GCD lineages have elevated recombination frequencies. I summarize and conclude with an argument for why GCD evolved under selective mechanisms which cannot be considered gene-centric, providing evidence that natural selection can effectively operate on non-heritable genotypes appearing in groups and other social contexts.
ContributorsJacobson, Neal (Author) / Gadau, Juergen (Thesis advisor) / Laubichler, Manfred (Committee member) / Pratt, Stephen (Committee member) / Arizona State University (Publisher)
Created2012
Description
Future robotic and human missions to the Moon and Mars will need in situ capabilities to characterize the mineralogy of rocks and soils within a microtextural context. Such spatially-correlated information is considered crucial for correct petrogenetic interpretations and will be key observations for assessing the potential for past habitability on Mars. These data will also enable the selection of the highest value samples for further analysis and potential caching for return to Earth. The Multispectral Microscopic Imager (MMI), similar to a geologist's hand lens, advances the capabilities of current microimagers by providing multispectral, microscale reflectance images of geological samples, where each image pixel is comprised of a 21-band spectrum ranging from 463 to 1735 nm. To better understand the capabilities of the MMI in future surface missions to the Moon and Mars, geological samples comprising a range of Mars-relevant analog environments as well as 18 lunar rocks and four soils, from the Apollo collection were analyzed with the MMI. Results indicate that the MMI images resolve the fine-scale microtextural features of samples, and provide important information to help constrain mineral composition. Spectral end-member mapping revealed the distribution of Fe-bearing minerals (silicates and oxides), along with the presence of hydrated minerals. In the case of the lunar samples, the MMI observations also revealed the presence of opaques, glasses, and in some cases, the effects of space weathering in samples. MMI-based petrogenetic interpretations compare favorably with laboratory observations (including VNIR spectroscopy, XRD, and thin section petrography) and previously published analyses in the literature (for the lunar samples). The MMI was also deployed as part of the 2010 ILSO-ISRU field test on the slopes of Mauna Kea, Hawaii and inside the GeoLab as part of the 2011 Desert RATS field test at the Black Point Lava Flow in northern Arizona to better assess the performance of the MMI under realistic field conditions (including daylight illumination) and mission constraints to support human exploration. The MMI successfully imaged rocks and soils in outcrops and samples under field conditions and mission operation scenarios, revealing the value of the MMI to support future rover and astronaut exploration of planetary surfaces.
ContributorsNúñez Sánchez, Jorge Iván (Author) / Farmer, Jack D. (Thesis advisor) / Christensen, Philip R. (Committee member) / Garcia-Pichel, Ferran (Committee member) / Robinson, Mark S. (Committee member) / Sellar, R. Glenn (Committee member) / Williams, Lynda B. (Committee member) / Arizona State University (Publisher)
Created2012