BIO Theses

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    The temporal response of a generalist soil-borne fungal plant pathogen in native grassland communities
    (Wichita State University, 2023-07) Houchen, Barrett Brad; Houseman, Gregory R.
    Soil-borne fungal plant pathogens (SFPP) occupy the soils of ecosystems globally, but the ecology of individual species is often not well understood. One approach to help better understand a SFPP is to examine its temporal variation and response to its environment. Research on SFPP is biased towards agriculture, but many agriculturally important SFPP inhabit adjacent untilled, native systems. One such case is the SFPP Macrophomina phaseolina. Past research has shown that M. phaseolina thrives in soil with high temperatures and low moisture. In untilled grasslands, the presence of this SFPP and its response to seasonal fluctuations in soil temperature and moisture remains unclear. To determine the dynamics of M. phaseolina in untilled systems, I established nine plots within distinct soil types and quantified the monthly response of M. phaseolina to shifting soil temperature and moisture conditions from May 2022 to May 2023. I hypothesized that M. phaseolina density would increase across the growing season, reaching its highest densities in the month of August 2022 when high soil temperatures and low soil moisture would be most favorable. Macrophomina phaseolina density was highly variable among the nine plots during the growing season and seldom reached its highest density during August 2022. During the dormant season, M. phaseolina density markedly decreased to its lowest densities before sharply increasing to unexpectedly high densities in April 2023. These findings suggest that the sporadic variation of M. phaseolina in untilled systems during the growing season contrasts with frequent assertions that soil temperature and moisture will heavily influence this SFPP’s density throughout the year. The results suggest that soil temperature and moisture play a reduced role in untilled systems, as plant community phenology and competing soil antagonists may more strongly impact M. phaseolina growth and disease development.
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    Investigating the impacts of drought-related drying events following pond refill on the growth, survival, and postmetamorphic fitness of lithobates blairi tadpoles
    (Wichita State University, 2023-05) Skerlec, Samantha Marie; Luhring, Thomas M.
    The incomplete recovery following drying events can have long-lasting impacts on aquatic ecosystems through altered resource availability, changes to water quality and temperature, microhabitat suitability, and community structure. Dynamic impacts of drying events can have detrimental effects on numerous aquatic organisms, but amphibians are particularly susceptible due to their reliance on aquatic environments for reproduction. This study aims to understand how drying events affect amphibian larval communities that recolonize a pond post-refill by investigating the impacts of incomplete recovery on their growth and development. While similar studies have investigated larval amphibian responses to active drying, few have directly assessed the carryover effects of drying events on organisms that recolonize a previously dried pond. Using a 64-mesocosm array, we examined the effects of drying (non-dry vs. dry-rewet) and tadpole density (10, 20, 40, or 80 individuals per tank) on larval amphibian growth, development, and survivorship. We hypothesized that drying and rewetting would decrease growth and development of tadpoles by reducing food resources, and that high larval densities would decrease growth and development through competition. Our results demonstrate strong effects of past drying on larval amphibian growth, time to metamorphosis, and survivorship. Additionally, we observed carryover effects of larval treatments on juvenile jumping performance, which was influenced by body mass at metamorphosis. Larger juveniles were found to jump further distances on average than smaller individuals, which has implications for the terrestrial fitness of these organisms, including predator evasion, foraging, and mating success. These findings emphasize the importance of drying events for amphibian survivorship and developmental plasticity, and that larval history can determine post-metamorphic fitness.
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    Exploring the effects of cranberry extract on the growth of sinorhizobium meliloti (ensifer meliloti) when paired with known antimicrobial compounds
    (Wichita State University, 2023-05) Denner, Abraham Verschelden; McDonald, David
    Huanglongbing disease (HLB), also known as citrus greening disease, is devastating the citrus industry. It is caused by three species of Candidatus Liberibacter. The presentation of this disease in North America is primarily caused by the asiaticus species. Ca. L. asiaticus is spread by the Asian Citrus Psyllid Diaphorina citri during feeding. Current treatments include broad-spectrum antibiotics, and targeting of the insect vector, both having thus far demonstrated little effectiveness. This has led to our effort to find more suitable antimicrobial substances for this purpose. Finding novel antimicrobials that are effective against Ca. L. asiaticus is essential to combat the spread and severity of HLB. Sometimes, when using antimicrobials together, they can produce a powerful effect that is greater than the sum of the parts; this is known as synergy. By focusing on using candidate antimicrobials in combination in hopes of finding synergistic reactions, one can minimize the potential of antimicrobial resistance forming. As Ca. L. asiaticus cannot be readily cultured in labs, an alternative model must be used. For this research, we used Sinorhizobium meliloti (S. meliloti) as the target bacterium due to its being closely related as well as being more robust due to its free-living capabilities. Cranberries contain phenolic compounds such as proanthocyanidins that can interfere with and repress biofilm formation and alter selective membrane permeability and multidrug efflux pumps. Plant-derived antimicrobials such as methylglyoxal, oregano oil, and clove oil have a variety of antimicrobial mechanisms. This project sought to test these plant-derived antimicrobials in combination with cranberry extract to see if they demonstrated inhibition of growth against the target bacteria. Serial dilutions of cranberry extracts paired with plant-derived antimicrobials were assessed in a checkerboard assay in the presence of S. meliloti. By finding the minimum inhibitory concentrations (MICs) and the fractional inhibitory concentrations (FICs), the level of synergy was determined. While synergy was not demonstrated in this study, two of the plant-derived antimicrobials, methylglyoxal and oregano oil, combined with cranberry extract did prove to be additive. These additive combinations are still beneficial and could be further studied as potential treatment sources or as a basis for further research regarding effective antimicrobial candidates to combat Ca. L. asiaticus based on their mechanisms and efficacy together.
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    Effects of temperature, predation risk, and resource availability on larval amphibian phenotypic plasticity and terrestrial performance
    (Wichita State University, 2023-05) Bristow, Stephanie Allison; Luhring, Thomas M.
    Aquatic ectotherms show an immense capacity to adapt to their environment in early life stages with plastic development. For example, larval amphibian development and growth rates are highly responsive to predation risk. However, growth and development rates are simultaneously constrained by resource availability and temperature. Although there is considerable work on how these factors singly alter growth and development, they are commonly experienced simultaneously within natural systems. Here, we investigate phenotypic plasticity in the face of predation risk and resource limitation across thermal regimes. Using Lithobates blairi, we conducted a 2 x 3 x 6 factorial experiment with 2 predation treatments (control & Procambarus gracilis cues), 3 resource levels (low, medium, & high), and 6 temperatures (15, 20, 22, 24, 26, 28°C). For 38 weeks, we calculated the proportion of individuals successfully reaching metamorphosis in each treatment combination, and individual development and growth rates. Additionally, we measured pre- & post-metamorphosis body length, and juvenile jumping performance to describe whether larval history has lasting effects across life stages. We found that rates of metamorphosis were highest in intermediate temperatures and observed minor interactions with predation risk and resource availability. Development and growth rates of tadpoles were temperature-dependent under high resource conditions. Predation risk and limited resources reduced the range of development and growth rates seen across temperature. Further, development and growth rates increased simultaneously with temperature, and differences in body size were only found post-metamorphosis between predation treatments. Juvenile size and performance decreased with added predation risk, and performance increased with resource availability in the absence of predator cues. Our results suggest that successful metamorphosis is largely temperature-dependent, but the breadth of plastic traits is constrained by resource availability, and consequences of predation risk may not be observed until terrestrial life stages.
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    Vascular flora of the Flint Hills Tallgrass Prairie Preserve
    (Wichita State University, 2022-12) Hawkinson, Barnabas Paul; Beck, James B.
    The Flint Hills Tallgrass Prairie Preserve (FHTPP) comprises 3 parcels of land owned and protected by The Nature Conservancy of Kansas. It sits approximately 8 km (5 miles) east of Cassoday, Kansas in Butler and Greenwood counties. The preserve totals 885 hectares (2,188 acres), and this study was performed on a portion of the preserve that is 130 hectares (321 acres) in size. The FHTPP has not been grazed since its acquisition, providing a unique opportunity for comparison to similar preserves. Though the flora of Butler County is relatively well documented, no floristic checklist has been published for the county or a site within. The goals of this study were to document all vascular plant species present on the site, compare the floristic composition of the FHTPP to that of two comparable properties, and assess potential vegetation differences between previously tilled and untilled portions of the FHTPP. Over three seasons 542 collections were made from which 274 taxa (176 genera and 59 families) were identified. Native taxa comprised 89% of observed taxa. Of the 29 non-native taxa, one taxon (Lespedeza cuneata) is classified as a category C noxious weed in Kansas. Seven species are county records. Comparisons with unpublished checklists from the nearby Youngmeyer Ranch and Tallgrass Prairie National Preserve establish that the FHTPP contains comparable levels of overall species conservatism, although riparian and woodland areas at the FHTPP host fewer conservative taxa. This suggests that the lack of recent grazing history at the FHTPP has not notably increased or decreased basic levels of floristic quality relative to similar sites with grazing. Although measures of taxonomic richness and floristic quality did not differ between tilled and untilled plots, the relative abundance of native taxa was significantly higher on plots that were untilled. Seven native taxa were significantly correlated with untilled plots, while two exotic taxa and three native taxa were significantly associated with previously tilled plots. This suggests that a comparable plant community has re-established following tillage at the FHTPP, although these areas might be more vulnerable to invasion by non-native species.
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