Theses/Dissertations - Biology

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    Bacteroides fragilis outer membrane vesicles are used for secretion of a discrete subset of bacterial RNAs that stimulate an immune response in colonic epithelial cells.
    (May 2023) Sheikh, Aadil, 1996-; Greathouse, K. Leigh.
    Alterations in the diversity and function of the gut microbiome are associated with changes in the host physiology, including inflammation. A critical component of the inflammatory response system are receptors capable of sensing foreign nucleic acids (e.g. small RNAs) that are carried as cargo in bacterial outer membrane vesicles (OMVs). The mechanisms by which human extracellular RNAs elicit immune responses have been well established, while the contribution of bacterial sRNA to host physiology remain unclear. We hypothesize that pathogenic and commensal microbes use OMV-associated small RNA species to differentially affect host inflammatory responses. First, we profiled the small RNA contents of purified OMVs from a commensal strain (NTBF) and a pathogenic strain (ETBF) of Bacteroides fragilis. To distinguish the differences in the sRNA profiles of both strains and their OMVs, we conducted small RNA-seq and identified enrichment of discrete sRNA species in OMVs that were also differentially expressed between the two strains. This evidence led us to investigate the differential effects of these OMVs upon intestinal epithelial cells. To understand the effects of OMVs on pattern recognition receptors, we treated Toll-like receptor (TLR) reporter cells with NTBF and ETBF vesicles. We observed activation of TLR2 in a dose-dependent manner, and activation of TLRs 3 and 7 at high doses of OMVs. Using Caco-2 and HT29 cells exposed to OMVs from each strain, we ran qPCR to test several pro- and anti-inflammatory cytokines. We observed that both strains upregulate the expression of IL-1β and TGFβ, but NTBF stimulates a greater IL-8 response compared to ETBF. These results indicate that bacteria may preferentially load small RNAs into vesicles that target host cells, which differentially affect host immune responses through RNA-sensing pathways. Overall, our data suggest a key function of bacterial small RNAs and their OMV vehicles in controlling host immune system.
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    Intraspecific variation in fatty acids in a deep diving marine mammal, the northern elephant seal.
    (December 2022) Kirkpatrick, Aaron W., 1988-; Trumble, Stephen John.
    The northern elephant seal (Mirounga angustirostris) is one of the most studied semi-aquatic mammals; recovering from the brink of extinction in the early 1900’s. For over 60 years, research on this species has been continuous since the formation of the Año Nuevo colony in California. Like all large ocean predators, northern elephant seals face uncertainty as the aquatic environment they inhabit responds to the impacts of anthropogenic climate change, over-exploitation of prey, and marine pollution. Northern elephant seals spend up to 8 months of the year foraging between two terrestrial fasts for breeding and molting. Lipids, and more specifically, fatty acids, deposited during foraging trips are used to fuel up to 98% of metabolic needs in fasting northern elephant seals. Each life history stage experiences age specific demands and sex specific demands driven by the evolution of extreme sexual dimorphism characteristic of this species. The goal of this dissertation was to characterize the fatty acid profiles in two metabolically active tissues, blubber and skeletal muscle, that are fundamental for surviving fasting periods and powering long foraging migrations. To gain an understanding of how fatty acids change across ontogeny, I collected blubber samples from fasting northern elephant seals across age groups and sexes to assess the compositions of the main energy substrate of this species and how it changes with the demands of each life history stage. In addition, skeletal muscle samples were also collected to identify skeletal muscle fatty acid profiles for the first time in northern elephant seals and assess changes in fatty acids across ontogeny and within sexes of this sexually dimorphic species. Lastly, blubber and muscle fatty acids were collected from translocated juveniles to better understand short-term diving behaviors on fatty acid metabolism in these tissues. I found fatty acids of blubber and skeletal muscle varied across ontogeny, highlighting the specific demands of each life history stage, the youngest age group of northern elephant seals were found to be the most dependent on one of the highest fat content milks found in nature to fuel their development and survival during their first foraging trip. Interspecific differences in skeletal muscle fatty acid profiles were driven by varying proportions of five major fatty acids, weaned pups and juveniles had significantly more abundant saturated fatty acids, influenced by the post-weaning development period in pups and limited foraging ability during juveniles first trip to sea. We observed contrasting proportional changes in skeletal muscle fatty acid classes of diving seals that had transit times <20 hours in comparison to seals that transited for >47 hours, while monounsaturated fatty acids decreased in the blubber of all translocated seals and blubber polyunsaturated fatty acids increased in the three younger seals. Northern elephant seals become more efficient divers as they develop over successive foraging trips during the first two years of life, influencing the fatty acid profiles of both fasting and diving seals.
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    Developing a fieldable viral detection toolkit and identifying invasive species and bloodmeal preference in Texas mosquitoes.
    (December 2022) Mann, James Gerard, 1996-; Pitts, R. Jason.
    Mosquitoes are arguably responsible for more human deaths than any other single cause in human history. They have had a tremendous impact on human existence and have influenced the rise and fall of societies. They exist as a highly diverse group of organisms across six continents comprised of over thirty-five hundred species. Only a tenth are known to disseminate pathogens that cause debilitating diseases, which include Zika virus, Dengue fever, yellow fever, and malaria. Despite so few species acting as disease vectors, mosquitoes continue to exert significant negative impacts on public health, especially in low and middle income countries. Therefore, continuing efforts to understand their distributions and factors that affect disease transmission cycles are greatly needed. Accurate identification of species is paramount due to the sparse number of species implicit in pathogen transmission. Morphological identification, a cheap and highly portable technique, allows for discernment without the need for taxonomical expertise. Differences in fourth instar and adult morphology allow for identification of specimen to the species level. For more similar species, or damaged specimens, researchers can shift to barcoding. Barcoding, or using molecular sequence polymorphisms, provide species level identification. This method is efficient in elucidating vector host interactions as they can determine from what species a bloodmeal may be from. By understanding and recognizing interactions between species and bloodmeal host, we can tailor response strategies to have more profound impacts. Pathogen transmission is a consequence of vector host interactions. Rapid detection and a rapid response to threats is critical for successful mosquito surveillance and abatement programs. Knowledge and capability gaps exist, with the most critical being the availability of portable and effective diagnostic tools for individual use. CRISPR-Cas12 detection assays have high ease of use, high on-target specificity, and portability. This technique could prove paramount because it has demonstrated the ability to detect HIV and COVID-19. Guided by target specific crRNA, enzymes are able detect minuscule amounts of complementary target sequences. Packaged with isothermal amplification and lateral flow detection, these assays can facilitate future improvements in surveillance and controlled efforts to disrupt the transmission of mosquito-borne illnesses in a fielded format.
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    Longitudinal biomarker and chemical analyses in marine vertebrates.
    (August 2022) Charapata, Patrick M., 1989-; Trumble, Stephen John.
    Oceans covers over 70% of the Earth’s surface and regulates climate, provides food, energy, and transportation, as well as being important for religious or cultural traditions. Currently, approximately 40% of the global population lives within 200 km of the ocean. Over the past century, the oceans and their inhabitants have been subjected to an increase in the scope, magnitude, and footprint of anthropogenic activities (shipping, noise, toxins, temperature, over-fishing), which threaten the productivity and health of the oceans. Researchers have employed periodic sampling (blubber, skin, blood, muscle) to address issues regarding the impacts of anthropogenic or environmental perturbations on animals and ecosystems. However, these sampling methods provide a “snapshot” of the health of an individual or the targeted ecosystem and cannot consider baseline differences in targeted analytes among individuals. Obtaining longitudinal analyte data from an individual animal provides a time-series of data to assess change over time and/or can baseline correct differences among individuals. The fundamental questions to be addressed in this dissertation include examining time-specific longitudinal data obtained from incrementally grown tissues in long-lived fish (rockfish; ~100 years) and pinniped (leopard seal) species to 1A) determine/validate steroid hormone concentrations (progesterone, estradiol, and cortisol) in annual growth increments obtained from a teleost operculum 1B) estimate reproductive parameters implemented in fish population models (e.g., age of sexual maturity and spawning frequency) and quantify stress events; 2) correlate lifetime reproductive and stress data with environmental variables; 3A) develop temporal records of trace elements with paired stable isotope analysis for information on diet from whiskers; and 3B) determine trace element changes in whiskers over time with diet. Key findings include validating novel methods to obtain lifetime longitudinal reproductive and stress data in a long-lived teleost that may help improve fish population models and assess physiological resiliency to environmental change. Additionally, contaminant with paired diet time-series data were reconstructed in the leopard seal, which provides critical physiological and ecological data for a remote and elusive apex Antarctic predator. This dissertation provides a suite of methods for obtaining longitudinal records of biological data to examine the resilience of elusive marine vertebrates to climate change.
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    Resolving the evolutionary history of multiple groups of freshwater mussels (Bivalvia: Unionidae).
    (2020-07-02) Smith, Chase H., 1992-; Doyle, Robert D. (Robert Donald)
    Freshwater mussels are a group of aquatic invertebrates comprised of approximately one thousand species worldwide, and the greatest diversity of freshwater mussels lies within North America with at least three hundred species. The high level of biodiversity in this group is strongly shaped by a life history strategy that includes an obligate parasitic larval stage. Alarmingly, anthropogenic alterations to freshwater ecosystems have disproportionately impacted mussels as a group, resulting in freshwater mussels being one of the most imperiled groups of organisms on Earth, and global collaboration is needed to understand the factors contributing to their demise. Although considerable progress has been made in understanding ecology and evolution of freshwater mussels, the biology of many species is poorly understood and there remains a critical need for robust phylogenetic evaluation to understand the evolutionary history of many freshwater mussels. Genetic techniques have emerged as one of the most promising tools in understanding of the basic biological processes and dynamics of species; however, it is evident that integrating molecular data with multiple lines of evidence should be used to resolve evolutionary relationships. My dissertation research focuses on integrating robust phylogenetic evaluations with independent data types to resolve the evolutionary history and systematic relationships in multiple groups of North American freshwater mussels. My approach helped resolve numerous enigmatic questions pertaining to multiple groups of mussels, including accurately defining systematic placement, resolving species boundaries, and identifying functional traits that have driven lineage diversification. My findings have profound implications on the understanding of evolution and taxonomy, as well as illustrating the importance in incorporating multiple lines of evidence into phylogenetic assessments of freshwater mussels. As the scientific community continues to resolve the ecology and evolution of freshwater mussels globally, a firm understanding of species-specific traits will be critical toward determining conservation priorities and predicting species-specific responses in these highly imperiled organisms.
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    Blubber fatty acid signature analysis of harbor seals in Alaska, 1997-2010.
    (2022-03-21) Neises, Victoria M., 1985-; Trumble, Stephen John.
    The projected course and rate of global climate change presents major challenges to the wellbeing and survival of Arctic and subarctic marine mammals. In Alaska, the harbor seals (Phoca vitulina richardii) broad range and severe population decline within certain regions led to increased research efforts to investigate the potential influence of diet changes on their lack of recovery. While these studies provide the foundation of knowledge regarding Alaskan harbor seal foraging ecology, detailed temporal and spatial changes in the harbor seals diet and possible impacts of diet overlap with other Alaskan pinnipeds has yet to be investigated. To date, the majority of harbor seal diet studies have used traditional diet determination methods. Due to the inherent limitations and sampling biases associated with these traditional techniques, blubber fatty acid (FA) analysis has emerged as one of the best methods of investigating diet in marine mammals. The goal of this dissertation was to characterize blubber FAs of Alaskan harbor seals through the evaluation of 15-years of blubber FA signatures. To gain an understanding of spatial and temporal differences, harbor seal blubber FA profiles were qualitatively investigated for regional, seasonal, and age class differences. In addition, to examine possible prey resource partitioning between different species populations, we compared regional and seasonal FA profiles of harbor seals and Steller sea lions within Prince William Sound and Southeast, Alaska. Lastly, differences between harbor seal reproductive state (pregnant, lactating, non-lactating-non-pregnant females), mother-pup pairs, and pinniped families were investigated to explore harbor seal blubber FA distribution during lactation. Key findings demonstrate the large degree of diet variability among harbor seal stocks within Alaska and shed light on how diet differences among Alaskan pinniped populations, and the physiological and behavioral limitations of the harbor seal lactation strategy, may be impairing population recovery in certain areas. As a sentinel species in Alaska, the ability to survey blubber FAs of harbor seals provides a way to not only monitor diet changes that could lead to population level impacts, but also provides a means to oversee prey community changes and ecosystem health within the regions they inhabit.
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    Functional characterization of olfactory receptors and molecular species identification of vector mosquitoes.
    (2022-02-28) Huff, Robert Mark, 1992-; Pitts, R. Jason.
    Mosquitoes are responsible for the transmission of hundreds of etiological agents. Many of these are emerging infectious diseases including, dengue, malaria, yellow fever, and Zika. Not all species of mosquitoes are responsible for vectoring these pathogens however, so accurate identification and surveillance are extremely important and directly impact human health. DNA barcoding allows for a rapid, accurate, and reliable species identification and does not rely on morphological features. Our method utilizes a highly conserved mitochondrial gene cytochrome oxidase 1 (CO1) to determine species identity based on single nucleotide polymorphisms (SNPs). Molecular species identification allows for discrimination between morphologically similar specimens without the need for taxonomical expertise and dramatically decreases hands on time spent identifying individual samples. Timely surveillance of species-specific vector introductions can help mitigate the impact vector disease contributes to public health. Mosquitoes can detect environmental cues by utilizing sensory appendages such as antennae, maxillary palps, and labella. These structures are covered in small hair-like sensilla. Within sensilla reside dendritic extensions of olfactory sensory neurons that are embedded with ligand gated olfactory receptors. Mosquito sensory receptors consist of three main families comprising odorant receptors (Ors), ionotropic receptors (Irs), and gustatory receptors (Grs). Detection of semiochemicals via olfactory receptors modulates behaviors including nectar seeking, host seeking, oviposition site selection, mate selection, and resting place selection, all of which have direct impacts on vector fitness. The discovery of behaviorally relevant odorants and their corresponding receptors has the potential to impact vector surveillance and control by leading to the development of novel deterrents, personal protective compounds, and implementation of push-pull vector management. As the efficacy of current control strategies erodes in the wake of insecticide resistance and behavioral adaptations in mosquito populations, new approaches will become increasingly more important to vector management programs. Deepening our understanding of the chemosensory abilities of vector species may facilitate future improvements in surveillance technologies and may aid in the development of novel methods for disrupting arbovirus transmission.
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    Toward re-scaffolding the Phanerozoic : an improved representation of plants in the Late Paleozoic Ice Age.
    (2022-03-04) Matthaeus, William J., 1984-; White, Joseph Daniel.
    Plants have served as the scaffolding of terrestrial ecosystems for hundreds of millions of years. Era-appropriate vegetation function and distribution are critical to resolve Earth’s natural history and potential future climates. However, plants have evolved and functioned differently across the Phanerozoic. This work aims to clarify plant function and ecosystem impacts in the Late Paleozoic Ice Age (LPIA, Pennsylvanian Subperiod), a representative time period and the most recent Icehouse before the present one. Pursuant to this aim I present: (Chapter Two) the first process-based global vegetation cover estimate for the LPIA, (Chapter Three) the first fossil-derived simulations of sapwood dysfunction in a paleo-ecosystem model, and (Chapter Four) an approach to stomatal pore measurement to allow resolution of lineage functional differences. In Chapter Two, I use GENESIS v3 global climate model data, and fossil-derived plant traits to parameterize the paleo-ecosystem model Paleo-BGC. Simulation results corroborate near-global vegetation cover based on leaf water balance. However, vegetation cover was limited by freezing temperatures, affecting surface runoff and mineral transport. Stem properties likely also limited Pennsylvanian plants. In Chapter Three, I expand Paleo-BGC to explore the importance of stem hydraulic properties of plants to ecosystem processes as an intersection of climate and natural selection associated with anatomical constraints on water supply. The limited ability of ancient plant stems to tolerate water stress suggests that even subhumid conditions certain plant types may have been water limited. These modeling approaches are based on incomplete plant physiological information due to open topics in that field regarding differences in stomatal function, which may have distinguished plant groups and their role in ecosystems for hundreds of millions of years. Toward the resolution of functional differences, I present (Chapter Four), an improved method for measuring stomatal pores in vivo that: 1) allows the characterization of additional pore dimensions (i.e., pore depth), 2) avoids artifacts of previously described methods, and 3) is applicable across a range of experimental conditions. Reconciling the details of extinct plant function by combining inferences from models, natural history, and Plant Physiology will allow improved predictions of future climate change impacts on ecosystems.
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    Epigenetic modulation of epithelial-mesenchymal plasticity through chromatin modifiers KDM6A and CTCF.
    (2022-04-22) Johnson, Kelsey S., 1993-; Taube, Joseph H.
    Epithelial-mesenchymal transition (EMT) and its reversal, mesenchymal-epithelial transition (MET) drive tissue reorganization critical for early development. In carcinomas, processing through EMT promotes migration, invasion, dormancy, and metastatic colonization. As a reversible process, EMT is inherently regulated at epigenetic and epigenomic levels. To understand the epigenomic nature of EMT, we characterized chromatin accessibility dynamics, transcriptomic output, protein expression, and cellular phenotypes during stepwise reversible EMT. We find that KDM6A and CTCF are suppressed and re-expressed, coincident with dynamic H3K27me3 and broad alterations in chromatin accessibility, during EMT/MET. These two factors are also lower in triple-negative breast cancer cell lines with EMT features. Through analysis of chromatin accessibility we identify that early EMT is characterized by enrichment for AP-1 family member binding motifs but also by diminished enrichment for CTCF binding motifs. Through loss-of-function analysis we demonstrate that suppression of CTCF strengthens the epithelial phenotype via upregulation of epithelial markers E-cadherin/CDH1, and downregulation of N-cadherin/CDH2. Conversely, upregulation of CTCF leads to upregulation of EMT gene expression and an increase in mesenchymal traits. These findings are indicative of a role of CTCF in regulating epithelial-mesenchymal gene expression.
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    Design and delivery of novel antimicrobial peptides (AMPs) targeted towards specific microbial pathogens.
    (2021-10-22) Choudhury, Ankan, 1990-; Kearney, Christopher Michel, 1958-
    Targeted therapies selectively eliminate a pathogen without disrupting the native microbiota. Traditional antibiotics, in contrast, destroy the native microbiota along with pathogens, causing adverse health outcomes for the patient. In my research, antimicrobial peptides (AMPs) were synthesized by fusing a guide-peptide that makes them selective towards a target pathogen. Staphylococcus aureus was chosen as a preliminary pathogen and a previously published guiding peptide (A12C) was selected. A12C was fused to AMPs, eurocin and plectasin, and the guided-AMPs (gAMPs) were expressed in E. coli. The gAMPs showed strong selective inhibition of S. aureus in vitro but were significantly less toxic towards several off-target bacteria. This selective bactericidal effect was observed in both planktonic culture and bacterial film formations. To optimize the in vivo delivery of gAMPs through oral route, I used engineered Lactococcus lactis, a probiotic bacterium and native resident of the human stomach flora. Helicobacter pylori, a main causal factor for peptic ulcers and gastric cancer, was the target pathogen. I targeted the VacA protein, an important virulence factor of H. pylori, with a guide peptide from a portion of Multimerin-1 (MM1), a human receptor for VacA. Three different AMPs, each fused to the MM1 guide, were tested. In vitro, co-culture of the engineered probiotic expressing gAMPs strongly inhibited H. pylori while being significantly less toxic to off-target bacteria. In vivo tests in mice were completed by introducing the H. pylori and engineered probiotic by oral gavage. Probiotics delivering gAMPs as a therapy reduced the H. pylori stomach titer by 1860-fold compared to untreated infected mice. As a prophylactic, gAMP probiotics effectively inhibited H. pylori colonization of the stomach. Microbiome analysis showed that the recovery or preservation of taxonomic diversity of the stomach microbiota was much greater with the use of gAMP probiotics than with AMP probiotics or antibiotics. My research shows that guided AMPs can be a novel and useful approach for combating pathogens without endangering the natural microbial flora and that bioengineered probiotics can be used to secrete gAMPs at the site of infection. Given the wealth of AMPs and potential guide peptides, both natural and synthetic, this approach can be adapted to develop a diverse array of chimeric guided AMPs and can be cloned into probiotics to create a safe and effective alternative to conventional chemical antibiotics.
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    Effects of nutrient stoichiometry and environmental conditions on the growth, toxin concentration, and nitrogen uptake of cyanobacteria.
    (2021-10-27) Osburn, Felicia S., 1993-; Scott, J. Thad (Jefferson Thad)
    Anthropogenic influences are negatively affecting water bodies by both increasing the concentrations of nutrients as well as contributing to increased temperatures from climate change. Nitrogen (N) and phosphorus (P) are the main nutrient contributors to eutrophication, and as such have become nutrients of high interest with many studies devoted to further understanding their influence. One issue seen with eutrophication is the proliferation of harmful algal blooms (HABs). One of the main phytoplankton groups responsible for HAB events in inland waters are cyanobacteria, of which some members are capable of both N fixation as well as cyanotoxin production. A method to better understand the effects N and P have on N fixation, cyanotoxin production and cyanobacteria prevalence is that of ecological stoichiometry. Ecological stoichiometry utilizes ratios to better understand how elements move through the abiotic and biotic environment, based on organisms' optimum N:P demands. In this dissertation, nutrient stoichiometry is used to determine how the diazotroph Dolichospermum’s cellular N:P changes through time when grown under various N:P levels, as well how N acclimation affects N fixation. We then examine the effects both N:P and salinity have on particulate and dissolved cyanotoxins in a non-diazotroph (Microcystis) and diazotroph (Aphanizomenon). Both genera were grown in N:P 4 and 50 (by mol) media, and when found to reach N limitation in the N:P 4 they were exposed to salinities varying from 0-10 g L.1. Lastly, Lake Waco, Waco, TX USA was sampled spatiotemporally to investigate if phytoplankton community composition and nutrient limitation differed between sites within the lake, as well as how environmental variables influenced different phytoplankton groups. Together, these chapters utilize N:P stoichiometry and other environmental variable to better understand how cyanobacteria respond to environmental changes.
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    The production, nitrogen, and phosphorus dynamics of Elodea sp., Potamogeton sp., and Nitella sp. in Sam Rayburn reservoir, Texas.
    (1978) Neely, Robert Kyle; Lind, Owen T., 1934-; Baylor University.
    The 1977 annual maximum biomass of Elodea sp., Fota- — 2 mogeton sp., and Nitella sp. was found to be 1013.6 g m~ , 168.4 g m **, and 32?.6 g m~'', respectively. Combined, these plants produce 80,528.16 kg dry wt lake”* year”*. However, this value is only 0.289?5 of phytoplankton production. Production of the macrophytes may have been greater had a a severe draw-down not occurred. The seasonal changes in ash weight and nutrient concentrations did not conform to the typical curves» nor did the seasonal change in biomass conform to the expected sigmoid curve (Westlake, 1965b)* The atypical patterns were due to the effects suffered from the water level change. Nitrogen and phosphorus concentrations in the plant tissues were not found to be indicative of environmental concentrations of nitrogen and phosphorus. This occurrence may have been due to neither nitrogen nor phosphorus of waters or sediments being limiting. Evidence for secretion of phosphorus by Elodea sp. was found. Diffusion gradients of phosphorus were found between the interior and exterior of the Elodea sp. stands.
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    Variation in benthic community structure: the role of the macroenvironment along a downstream gradient.
    (1984) Meyerhoff, Richard D.; Lind, Owen T., 1934-; Baylor University.
    McKittrick Creek, a discontinuous mountain-desert stream in Guadalupe Mountains National Park, Texas, was sampled at discrete 1 ocations(pools ) to test for differences among biomass, density, species diversity, equitability, and species richness in the benthic macroinvertebrate community. Significant differences occurred among pools for the biotic characteristics of the benthic community along the downstream gradient. Connected pools were more similar to each other than pools separated by dry reaches. The greatest biomass (700-1200 mg dry weight /m ) and species diversity (2.5-3*2) values occurred at the two furthest downstream pools and two furthest upstream pools, while the least biomass (150-600 mg dry weight/m ) and species diversity (2.2-2.14) values occurred at two midstream pools. Equitability (0.65-0.80) and species richness (11.0-7.6) values varied considerably among pools, but were generally greatest in downstream pools. Density values also varied considerably among pools (2500-14000 organisms/m ) with the greatest density at the furthest downstream pool. Variation in macroenvironmental characterist i cs associated with food availability was more important than substrate size and fish predation in determining the benthic community structure of McKittrick Creek. Variance in biomass and density of the benthic community was explained best by differences in quantities of coarse detritus. Pools with greater quantities of coarse detritus had less invertebrate biomass and density. Variance in species diversity and species richness values was explained best by changes in periphyton biomass. Variance in equitability values was not associated with any macroenvironmental characteristics. Although the type of food available (e.g., coarse detritus or periphyton) explained most of the variance among pools for benthic community characteristics, interaction among available food type, substrate size, and predation by fish may actually determine the benthic community structure of some pools.
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    Age and growth of the white crappie, Pomoxis Annularis Rafinesque, in Lake Waco, Texas.
    (1969) Chen, Terry Huei-Hsiung; Lind, Owen T., 1934-; Baylor University.
    The major collection of white crappie was from 17 July 1967, to 10 April 1968, by traps and gill nets. Other fish were taken by anglers and seines in June 1968. A total of 1142 fish were included in this study. Spawning season for Lake Waco crappie was from late February to early May and was at its peak in March and April. White crappie in Lake Waco may spawn after one year. Growth rate of Lake Waco white crappie was rapid. The average back-calculated total lengths(TL) for Lake Waco crappie for the last 4 years were as follows: 145mm for the first year’s growth, 216mm for the second age group, 271mm for the third age group, and 309mm for the fourth age group. In the white crappie scales started to develop on the caudal peduncle in fish 16mmTL. The first fully scaled fish observed was 31mmTL. The region between the dorsal fin and pectoral fin was the last place to develop scales. The mathematical expression of the length-weight relationship for the white crappie of Lake Waco is: log W = -5.6131 + 3.2954 log L where W= body weight in grams L=total length in millimeters. The body-scale relationship demonstrated a parabolar curve. The equation L=35.506219 + 1.215665 S + 0.000931 s2 fitted the body-scale relationship of Lake Waco white crappie well. Principal food items of white crappie were small fishes (mainly shads, Dorosoma cepedianum and D. petenense), aquatic insects, and small crustaceans. Lymphocystis was only found in the spring, and about 1.7 percent of the fish were infected. Infection by nematode parasites, Camallanus oxycephalus, was observed in the spring and summer, but infected fish showed no signs of weakness.
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    The ostracode Cypridopsis vidua: physiological response due to thermal stress.
    (1973) Wysong, Mark Lee; Lind, Owen T., 1934-; Baylor University.
    Upper temperature effects were measured on the mean oxygen consumption, carbon dioxide production, ingestion, assimilation, and egestion rates of the ostracode Cypridopsis vidua. to determine positive or negative effects of temperature stress. Oxygen consumption and carbon dioxide production were near the literature reportings of the Class Ostracoda, with a linear increase with increasing temperatures. Respiratory Quotients were very low. Ingestion and assimilation rates were positively linearly related with temperature to 30C and 25C. respectively, above which each was negatively affected. Assimilation efficiency dropped from 70 percent at 15C to 16 percent at 35C. Ingestion and assimilation rates increased per mg biomass with decreasing size of organism. Active avoidance of 30 and 35C temperatures was observed.
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    Some effects of thermal history on the largemouth black bass, Micropterus salmoides (Lacepede), of two central Texas reservoirs receiving power plant effluents.
    (1972) Venables, Barney James; Lind, Owen T., 1934-; Baylor University.
    Mean annual growth of the first three age classes of largemouth black bass from Tradinghouse Reservoir was near the average growth reported in the literature for southern waters. Largemouth black bass collected from the discharge canals of Tradinghouse Reservoir (which has received power plant effluent for only 2 years) and Lake Creek Reservoir (which has received power plant effluent for 20 years) showed no difference in male or female gonadal development, condition factor, or thyroid activity; however, the largemouth black bass collected from the Tradinghouse Reservoir discharge canal showed signs of decreased physiological activity with respect to the Lake Creek sample. No significant detrimental effects of the power plant effluents were detected.
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    Structure and photosynthetic response to abrupt thermal stress of a periphyton algal community colonized in a power plant discharge canal.
    (1976) Lukins, David Alan; Lind, Owen T., 1934-; Baylor University.
    Tremendous increases in energy needs have led to construction of many new power plants. Effects of heated power plant effluents on aquatic organisms have not been clearly established, Periphyton community structure was used to assess these effects. Species diversity (H") was used to monitor changes in periphyton algal community structure in the discharge canal of a fossil fuel power plant near Waco, Texas. Diversity decreased closer to the power plant discharge. Minimum diversity was 0,96 in June at the sampling station closest the power plant and maximum diversity was 2.89 at the station farthest from the discharge in March. Diatoms dominated the attached algal flora at all stations in the January and March samples. By May diatoms were being replaced by bluegreens at the sampling station closest the power plant, yet diatoms were still the major group at all stations. By June bluegreens were dominant at the station closest the power plant and were increasing at the other' stations but were not dominant. Primary periphyton production per unit biomass was measured following exposure to abrupt thermal change as encountered during shutdown and startup of a power plant. Production was greatest for samples colonized near the power plant discharge for both 10 C and 30 C experimental temperatures. Maximum primary periphyton production using methods was 0.61 ug C organic matter * hr“*.
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    Pond succession on the Kaibab Plateau, Arizona.
    (1969) Kimmel, James Ross; Lind, Owen T., 1934-; Baylor University.
    Quantitative data were obtained for a serai comparison of five sinkhole ponds on the Kaibab Plateau, Arizona. Species diversity, community metabolism, primary production, and relative serai rank were assayed. Information theory and non-information theory species diversity indices were used to compare the phyto- and zooplankton, benthos, and emergent vegetation both within and among ponds. Species diversity of these four pond features showed large fluctuations, hence diversity indices afford distinction only between early versus late serai stages. The ponds were divided into early versus late categories based on community metabolism estimates, as calculated by the diel oxygen curve method. Primary production values, derived from diel oxygen curve values, indicate that primary production increases during succession to a certain point, then decreases as the aquatic ecosystem approaches senescence. Methods of estimating serai stage based on measurements of individual characteristics were ineffective, so a systems analysis approach was developed. Species diversity, photosynthesis-respiration ratio, and mean depth wer*e related mathematically to produce a serai ranking value which varies directly with serai stage. Values calculated with this formula correspond well with presumed serai stages of the ponds.
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    Phytoplankton production in a central Texas reservoir.
    (1969) Kimmel, Bruce Lee; Lind, Owen T., 1934-; Baylor University.
    Phytoplankton production and other environmental variables were measured from June to November, 1968 to determine factors affecting production and trophic status of the producer community in a shallow, polymictic, central Texas reservoir. The reservoir was highly productive and eutrophic. Net phytoplankton production estimates, derived from data, averaged 390 mg C m“3 day“^, 857 mg C m“2 day”^, and 300 g C m"^ yr~for the impoundment. Light extinction by organic and inorganic turbidity limited phytoplankton production by decreasing the photic depth. Nutrient limitation was of minor importance, although greater production occurred near points of nutrient inflow than in other reservoir areas. Wind-mixing of the reservoir is believed to accelerate its eutrophication by promoting rapid nutrient recirculation, and thus maintaining nutrient availability for primary production. The impoundment is expected to age more rapidly with time as its basin shallows and phytoplankters spend an increasingly larger fraction of their lives in the productive zone.
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    Phytoplankton productivity of tropical Lake Chapala, Mexico.
    (1985) Doyle, Robert D. (Robert Donald); Lind, Owen T., 1934-; Baylor University.
    Phytoplankton productivity and other environmental variables were measured for one year (June 1983 - June 1984) at five stations on Lake Chapala, Mexico. Contrary to expectations, productivity in this shallow, tropical lake 14 was low. Phytoplankton productivity, estimated from C data, was 76.4 g C m”^ year”'*' (209 mg C m”^ day”'*'). Phytoplankton productivity at the depth of optimum light intensity averaged 320 mg C m”^ day”'*', and always occured within the top 70 cm of the water column. Light extinction due to' inorganic turbidity was the principal limiting factor of areal phytoplankton productivity. Nutrient limitation was less important, although nitrogen may have become limiting during the dry season. Among stations, areal phytoplankton productivity varied inversely with turbidity and was decidedly seasonal. It was highest during the rainy season (June - September), when the water was most transparent.