Theses/Dissertations - Biology
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Item Alder cover drives nitrogen availability and decomposition of grass litter in salmon-rearing headwater streams, Kenai Peninsula, Alaska.(2010-10-08T16:26:59Z) Shaftel, Rebecca S.; King, Ryan Steven, 1972-; Biology.; Baylor University. Dept. of Biology.Terrestrial sources of nitrogen (N), such as N fixed by alder, may be important for sustaining production in headwater streams that typically lack subsidies of nutrients from spawning salmon. High nutrient concentrations in streams increase litter decomposition and can offset the low nutrient quality of grass litter. Alder cover was compared to watershed physiographic variables as predictors of stream N and contrasted over the growing season among 25 headwater streams. Leaf packs of bluejoint grass were deployed for two months across a nutrient gradient of 6 headwater streams. Alder cover explained over 75 – 96% of the variance in stream N. Bluejoint breakdown rates were related to dissolved stream nutrient concentrations and litter quality. A diversity of macroinvertebrate consumers utilized bluejoint for habitat and food. Alder drives stream N concentrations and the breakdown rate of bluejoint, which is an important consumer resource during the summer months when deciduous litter inputs are low.Item Analysis of Escherichia coli populations in a large watershed.(2008-06-10T20:44:35Z) Nemec, Michelle D.; Drummond Massengale, Andrea Rene.; Biology.; Baylor University. Dept. of Biology.Escherichia coli are one of the most common model organisms used today. This organism has played an integral role in our understanding of bacterial conjugation, phage genetics, and gene structure, and it is also responsible for many of the advances in the areas of proteomics and biotechnology. However, very little is known about the characteristics of E. coli populations in their natural habitats. In this study, three characteristics of E. coli populations isolated from nine different sources were investigated, including: 1) antibiotic resistance, 2) carbon–substrate usage, and 3) genetic diversity. Antibiotic resistance was examined using eight antibiotics. Overall, the incidence of amoxicillin resistance was high in all of the E. coli populations, and multi-drug resistance was common. Antibiotic resistance was prevalent across populations, and the highest level of resistance was found in isolates obtained from sewage and dairy cattle. The carbon–substrate utilization of the E. coli populations was examined using Biolog GN2 microplates. The fundamental metabolic capabilities of the E. coli isolates were relatively stable across populations; however, variation did occur in the extent to which some isolates in the populations could utilize the various carbon substrates. Metabolic similarities were greatest between E. coli isolates from the same population. Rep–PCR was implemented to assess the genetic diversity present in the various E. coli populations. Overall, the genetic diversity of the E. coli isolates appeared to be large. Unfortunately, there are very few other studies available with which to compare these data. The level of genetic diversity varied between each population of isolates; although, isolates from the same population tended to be more genetically similar than isolates from different populations. Finally, Jackknife analysis demonstrated that the various E. coli populations were more distinct from each other genetically than they were based on antibiotic resistance or carbon–utilization. When all three characteristics were combined, relatively clear distinctions could be made between most populations. When the characteristics of E. coli isolated from water were compared with the characteristics of the isolates from the other sources, the majority of the water isolates were most similar to E. coli obtained from cattle.Item Bacterial dynamics at the sediment-water interface of a stratified, eutrophic reservoir.(2007-03-08T15:35:55Z) Christian, Bradley W.; Lind, Owen T., 1934-; Biology.; Baylor University. Dept. of Biology.Sediment-water interfaces (SWIs) are loci of dynamic physical, chemical, and biological interactions in stratified, eutrophic reservoirs. Seasonal reservoir mixing and stratification affects SWI physicochemical processes as well as bacterial abundance, diversity, biomass, and metabolism. Because SWI bacteria transform chemicals and release nutrients that affect water quality and eutrophication, seasonal changes in these bacterial dynamics help define reservoir carbon and nutrient cycles and trophic interactions. Four studies were conducted to assess SWI bacterial dynamics in Belton Reservoir, a eutrophic, monomictic impoundment. The first utilized [3H]-L-serine to measure SWI bacterial activity and biomass production. Highest activity and production occurred during summer stratification under anoxic conditions. Lowest activity and production occurred under oxic conditions during autumnal overturn and winter mixing. The second study consisted of two parts, both utilizing Biolog EcoPlates to measure SWI carbon substrate utilization rates (CSURs). The first part tested the effectiveness and interpretability of EcoPlates. Optimal use was dependent upon inoculum density, incubation temperature, and aerobic/anaerobic incubation techniques. The second part concluded that CSURs for carbohydrates were highest during onset of stratification and winter mixing, CSURs for amino acids were highest during winter mixing, and CSURs for carboxylic acids were highest during late season stratification. The third study analyzed quantities and sources of SWI carbon, nitrogen, and bulk organic matter (OM). OM concentration did not differ among seasons. Inorganic carbon and nitrogen differed seasonally. OM C/N ratios and stable isotopes (13C and 15N) were significantly different at the SWI of the shallowest depths, indicating that OM at this site was of allochthonous origin. The last study utilized automated ribosomal intergenic spacer analysis (ARISA) and denaturing gradient gel electrophoresis (DGGE) to elucidate total and sulfate-reducing (SRB) SWI bacterial diversity and similarity. Total SWI bacterial diversity did not significantly differ. During stratification, high similarity occurred among sites on individual dates. During mixing, high similarity occurred through time. Although SRB are functionally strict anaerobes, they exhibited higher richness during oxic rather than anoxic conditions.Item Basking dynamics among sympatric turtle species (Trachemys scripta elegans, Pseudemys texana, and Graptemys pseudogeographica kohnii) in Waco Creek, Texas.(2013-09-24) Bardwell, Jeff H.; Duhrkopf, Richard.; Biology.; Baylor University. Dept. of Biology.The premise of this manuscript condenses into three words: turtles on logs. Turtles splaying their limbs and sunning themselves on emergent deadwood is commonly known as basking. Basking involves ectotherms taking advantage of solar radiation to boost their core temperature and fuel metabolic processes. This study examines a community assemblage of three turtle species within the Family Emydidae—Trachemys scripta elegans: Red-eared Slider, Pseudemys texana: Texas River Cooter, and Graptemys pseudogeographica kohnii: False Map Turtle—in Waco Creek, Texas, a tributary of the Brazos River, from 2010-2012. Turtles were collected daily via specialized traps which take advantage of repetitive basking habits, individually marked, measured, identified, and then released from June to October 2010, April to October 2011, and April to October 2012. Multiple recaptures allowed for observation of individual, population, and community progression over time. This manuscript asks three fundamental questions about the role of basking behavior in the Waco Creek emydid turtles: 1) What is the significance of the basking community assemblage composition in Waco Creek, 2) How do basking trap modifications and population demographic selection affect group trap response, and 3) How do polynomial and k-growth mixed models describe juvenile turtle logistic growth? Trachemys scripta elegans comprise 46%, Pseudemys texana 32%, and Graptemys pseudogeographica kohnii 23% sample composition within the Waco Creek basking turtle assemblage. All mature populations were significantly male skewed and turtle demographics exhibited several expected seasonal behavior patterns. The community has a large abundance of juveniles, young males, and immature females regardless of species. In addition, juvenile T. scripta appear to be the most actively basking demographic. Between individual demographic behavior and trap design as predictors for trap response, demographic behavior was significant across most response variables whereas trap design variables were not. This study pioneered a new technique for comparing turtle logistic growth models using a polynomial mixed model as a control. With an adequate sample size and consistent seasonal dispersal, results from this technique agree with reports from the literature and look promising.Item Bat activity in forest margins : canopies, edges, seasonality, and competition.(2011-12-19) Pettit, Thomas W.; Wilkins, Kenneth T., 1953-; Biology.; Baylor University. Dept. of Biology.Forest edges provide open space that bats often use to travel and forage. As another type of margin, forest canopies provide similar structural space for bat activities. Such margins may supply bats in forests with the structural resources they require, such that some species could compete over edge space as a preferred habitat type. This project examined the role of forest canopies and edges as an important habitat type for bats through the observation and examination of bat activity levels. Bat communities in the Rocky Mountains of northern Utah (summers 2008-2009) and the pineywoods of eastern Texas (fall 2009 and spring 2010) were observed through the use of Anabat SD1 bat detectors. Activity levels of bats in Utah were much higher in forest edges than in canopies. This phenomenon appears to have a strong seasonal component, during which period competition over edge resources intensifies between high and low frequency guild bats. In the pineywoods of eastern Texas, bat activity levels also differ between canopies and edges, but bats in this habitat seem to shift seasonally between margin types. These shifts may coincide with seasonal migrations of some bat species. Future research would further investigate seasonality in bat activity, and better define the role of clutter in bat activity in forest margins.Item Chemical toxicity distributions in aquatic toxicology : relative sensitivities of estrogenicity assays and ecotoxicity of parabens in model freshwater organisms.(2008-12) Dobbins, Laura L.; Brooks, Bryan W.; Biology.; Baylor University. Dept. of Biology.A probabilistic ecological hazard assessment technique, chemical toxicity distributions, was used to examine the relative sensitivities of in vitro and in vivo assays for detecting estrogenicity, and to assess the hazards associated with parabens to model aquatic organisms, Pimephales promelas and Daphnia magna. Parabens represent a class of understudied personal care products with estrogenic activity that have been detected in surface waters. MCF-7 and rainbow trout vitellogenin induction were found to be the most sensitive in vitro and in vivo assays of estrogenicity, respectively. Parabens were determined to not pose a hazard to aquatic organisms at levels that are environmentally relevant, based on the bioassay endpoints evaluated. A screening level assessment further identified estrogenic activity of select parabens to adult male P. promelas. This thesis demonstrated the utility of chemical toxicity distributions for determining sensitivities among toxicological models and for assessing those compounds for which environmental exposure data are limited.Item Comparing the genetic diversity of late Pleistocene Bison with Modern Bison bison using ancient DNA techniques and the mitochondrial DNA control region.(2007-01-22T18:45:33Z) Douglas, Kory C.; Baker, Lori; Adams, Robert P.; Biology.; Baylor University. Dept. of Biology.The transition between the Pleistocene and Holocene Epochs brought about a mass extinction of many large mammals. The genetic consequences of such widespread extinctions have not been well studied. Using ancient DNA and phylogenetic techniques, we compared the genetic diversity and phylogenetic relatedness of extinct Pleistocene Bison ranging from Siberia to mid-latitude North America (10,000 ybp to 50,000 ybp) to extant Bison bison. The mitochondrial DNA control region was sequenced from 10 Bison priscus skulls obtained from the Kolyma Region of Siberia, Russia. Control region sequences from other Pleistocene Bison and Bison bison were obtained from Genbank. Our analysis indicates a measurable loss of genetic diversity in Bison bison compared to Pleistocene Bison. Furthermore, the Pleistocene Bison population was strongest in North America from a time period of 30,000 ybp to 10,000 ybp, and the genetic diversity present in this population is not represented in the Bison bison population.Item CTR2 and the nonsense-mediated mRNA decay pathway in Saccharomyces cerevisiae.(2012-11-29) Wang, Xuya.; Kebaara, Bessie W.; Biology.; Baylor University. Dept. of Biology.The nonsense-mediated mRNA decay (NMD) pathway recognizes and degrades mRNA with premature termination codon and some natural mRNA as well. CTR2 is a natural mRNA degraded by NMD in Saccharomyces cerevisiae. The goals of this research were to identify the sequence features that target the CTR2 mRNA for NMD and the physiological consequences resulting from this degradation. These goals were addressed by making fusion constructs and determining total cellular, cytoplasmic and vacuolar copper levels in wild-type and nmd mutant yeast cells. Features contribute to the NMD-mediated degradation of CTR2 were identified. When cultured in medium with excess copper, nmd mutants accumulated significantly higher vacuolar copper levels than wild-type yeast cells, however nmd mutants accumulated significantly less cytoplasmic copper levels than that in wild-type yeast cells. These results are consistent with the inference that nmd mutants tolerate excess copper as a result of ctr2p transporting excessive copper from cytoplasm into vacuole.Item Diving physiology in marine mammals : significant findings in pinniped muscle physiology and trachea morphology.(2014-09-05) Moore, Colby D.; Trumble, Stephen John.; Biology.; Baylor University. Dept. of Biology.The muscular biochemistry and respiratory morphology of diving mammals are closely intertwined through the utilization and allocation of inspired oxygen for metabolism. Marine mammal physiological mechanisms and adaptations are of great intrigue due to the heightened environmental pressures that these animals are routinely subjected. These species also experience varying degrees of ischemia, hypoxemia and gas tissue saturation, which are pathological in terrestrial mammals. Data included in this dissertation suggest a unique skeletal muscle fiber type profile for the deep-diving Northern elephant seal; a profile predominately comprised of enlarged aerobic type I myofibers. In addition, enzymatic data suggest that diving mammals maintain higher levels of aerobic enzymes in primary locomotory muscle and that muscle-based enzymes degrade rapidly and variably with temperature and time. Histological analysis of harbor seal tracheal rings microscopically describes a unique continuity of cartilage that correlates with lung compression, depth at which lungs collapse, as well as maximum dive depth. Cumulatively, biochemical and structural adaptations allow diving mammals to reach extensive depth, while maintaining homeostatic levels of on-board gasses and avoiding dive-related injury. Ultimately, this research highlights the relationship between morphology, physiology and life history of these animals.Item Early periderm development in the shoots of Ulmus alata michx.(2007-02-14T21:52:29Z) Fowler, Tiffany B.; Rushing, Ann E.; Biology.; Baylor University. Dept. of Biology.Periderm is a protective tissue that replaces the epidermis in woody plants and consists of three layers: phellogen, phellem, and phelloderm with cells in discrete radial files. Lenticels and cork wings deviate from this arrangement. Stems of Ulmus alata were examined using scanning and transmission electron microscopy to determine the site of phellogen initiation, lenticel initiation, cork wing initiation and their development. Phellogen is initiated in the subepidermal parenchyma which is consistent with other members of Ulmus. Phellogen initiation does not appear to be associated with structures of the epidermis or underlying stem. Lenticels are initiated by irregular divisions of the lenticel phellogen and the radial expansion and lateral separation of the cells produced. Mature lenticels have alternating layers of complementary cells and closing layers. Cork wings are initiated by the radial expansion of phellem followed by increased divisions of cork wing phellogen compared to the rest of the periderm.Item The effect of suspended bentonite and kaolinite clay on phosphorus uptake and release by lotic periphyton.(Springer., 2009) Wolfe, June Elmer, 1961-; Lind, Owen T., 1934-; Biology.; Baylor University. Dept. of Biology.Lotic systems act as nutrient buffers to receiving lentic systems. As streams transport allochthonous phosphorus through a watershed, the loads are modified in quantity and quality through biotic and abiotic mechanisms. Lotic systems are frequently dominated by periphyton, the attached benthic community consisting mainly of algae and bacteria. This community exhibits the ability to buffer phosphorus loads to receiving waters through several mechanisms including: biotic uptake, chemical precipitation, and mechanical filtration. Stream sediments, including clays, influence dissolved phosphorus concentrations primarily through equilibrium-driven sorption/desorption reactions. Additionally, suspended clays in aquatic environments are known to: modify food webs, influence species composition, and affect biotic integrity by altering the physical and chemical conditions. Given the influence that suspended clays exert upon aquatic systems, it was hypothesized that suspended clays would modify, either positively or negatively, phosphorus uptake and/or release by lotic periphyton. Experiments were conducted using two clay minerals, dissolved reactive phosphorus, and cultivated periphyton communities. Bentonite and kaolinite were selected to represent two clay types commonly found in aquatic systems. Standardized laboratory procedures were utilized to describe the physical characteristics and phosphorus sorption behavior of the clays. An artificial stream system was designed, tested, and operated to control water conditions necessary to cultivate periphyton communities, support suspend clays, and conduct clay-phosphorus-periphyton interaction studies. Periphyton communities were subjected to different clay and phosphorus concentrations under controlled conditions in artificial streams and laboratory microcosms. Phosphorus uptake rates were unaffected by the presence of clays at several different concentrations in artificial stream settings. Periphyton exposure to heavy clay loads in lotic microcosms, under laboratory conditions, had no effect on the ability of the periphyton to uptake or release phosphorus. The results may be helpful to water resource managers working with water quality issues and researchers interested in basic ecosystem function.Item Effects of chiral contaminants to aquatic organisms: pharmaceuticals as model compounds for enantiomer specific ecological hazard assessment.(Houston, Texas : SETAC Press., 2006-07) Stanley, Jacob K.; Brooks, Bryan W.; Biology.; Baylor University. Dept. of Biology.In the present study, enantiospecific effects of chiral contaminants were explored using two chiral pharmaceutical contaminants as model compounds. These compounds are the selective serotonin reuptake inhibitor antidepressant fluoxetine and the [beta]-adrenergic receptor blocking agent propranolol. An aquatic invertebrate, Daphnia magna, and an aquatic vertebrate, Pimephales promelas, were used as model organisms. In addition to commonly used standardized bioassay endpoints, effects of these compounds were also assessed using nontraditional sublethal endpoints that were specifically chosen to target the known modes of action of the model pharmaceuticals. These include D. magna heart rate and grazing rate and P. promelas feeding rate, swimming performance, and swimming behavior. Known enantiospecific differences in activity of propranolol and fluoxetine in mammals were compared with enantiospecific differences in their toxicity to aquatic organisms. Results indicate that mammalian pharmacology data on enantiospecific effects are more predictive of enantiospecific toxicity in aquatic vertebrates than invertebrates for the two drugs tested. The results presented here also demonstrate that mode-of-action-targeted endpoints should be considered for pharmaceuticals as they can be more sensitive than traditional endpoints, show enantiospecific and sex-specific effects, and provide information on highly ecologically relevant biological processes such as feeding. A summary of the current regulatory provisions for chiral contaminants is made along with the author’s recommendations for the improvement of the assessment of environmental risk for chiral contaminants.Item Effects of habitat affinities and resource needs on edge responses by small mammals.(2012-11-29) Green, Nicholas Scott.; Wilkins, Kenneth T., 1953-; Biology.; Baylor University. Dept. of Biology.Edge effects are the responses of organisms to ecological boundaries. I studied edge responses by small mammals in two prairie communities to test two models: 1) edge responses reflect and map to simple habitat associations, and 2) edge responses reflect differences in resource availability on either side of an edge. I also investigated how edge contrast, the degree of difference between habitats at an edge, could modify edge responses. Pilot sampling in 2009 and 2010 at a Blackland prairie preserve revealed that hispid cotton rats (Sigmodon hispidus Say and Ord 1825) responded negatively to edges of wooded patches and weakly positively to edges between tallgrass and dicot forbs. Deer mice (Peromyscus maniculatus (Wagner 1845)) and fulvous harvest mice (Reithrodontomys fulvescens Allen 1894) did not respond to habitat edges, although this may have been an artifact of low capture rate (especially in 2010). Sampling in 2011 at the Lyndon B. Johnson National Grasslands (LBJNG), a mixed grass preserve, found that S. hispidus responded negatively to edges where dense grass abutted dicot forbs or wooded patches. These edge effects reflected the strong association of S. hispidus with grassland habitat. Sampling of leptin, a hormone secreted by adipose tissue and associated with energy intake in many species, revealed that serum leptin concentration (SLC) was limited by body mass and not associated with any other organismal characteristic. Among male S. hispidus SLC was limited by food availability and among females the lower limit of SLC decreased with increasing grass cover. This suggests that if S. hispidus edge responses are caused by resource mapping, the critical resource is not nutrition. Other species at LBJNG, P. maniculatus and hispid pocket mice (Chaetodipus hispidus (Baird 1858)) were associated with habitats with intermediate ground cover and did not show clear edge responses. I concluded that 1) when prairie dwelling small mammals respond to edges, they are more likely to show matrix effects (response to nonhabitat) than ecotonal effects (emergent properties at boundaries); and 2) small mammal abundances and edge responses are driven by resources other than nutrition.Item Effects of stream nutrient enrichment on aquatic insect stoichiometry : importance of life-history traits, sex, and ontogeny.(2014-01-28) Back, Jeffrey Alan.; King, Ryan Steven, 1972-; Biology.; Baylor University. Dept. of Biology.I investigated the effects of stream nutrient enrichment on aquatic insect stoichiometry, particularly in the context of species life-history traits, sex, and ontogeny. The majority of studies investigating nutrient content of organisms preceding this research had assumed that aquatic insect species maintain a homeostatic concentration of carbon, (C) nitrogen (N) and phosphorus (P) content with respect to developmental stage and nutrient enrichment of their food resources. However, P content was shown not to be homeostatic across the ontogeny of 19 species of aquatic insects and C and N were quasihomeostatic. Growth rates for Caenis mayflies were higher on P enriched foods, and smaller individuals grew faster than larger individuals. Further, female mayflies were equal to or larger than males and had equal or higher body P content than males, depending upon species. A phylogenetic pattern in body P content was found for baetid and leptophlebiid mayflies. Male and female baetids declined in % P across their ontogeny, whereas leptophlebiid females increased in the 3 species studied. Finally, a study of streams spanning a steep nutrient enrichment gradient revealed that females of Baetis sp. and Neochoroterpes nanita attained a much larger size than males and were more enriched in P. Body P content of both mayfly species was higher at low P sites, and body size was much larger at high P sites. In insects, P content is a good indicator of growth rate (higher P, faster growth), and body size is a good predictor of fecundity (bigger body, more fecund). Nutrients not only play a role in determining an organism’s reproductive success, growth rate and size. The effects of nutrients are seen in organism nutrient recycling rates, food web organization, and community structure and function.Item Effects of suburban development on lizard and snake assemblies in central Texas.(2013-09-16) Kuhlman, Stefan G.; Gehlbach, Frederick R., 1935-; Biology.; Baylor University. Dept. of Biology.A common threat to biological communities is habitat degradation, particularly in urban areas. Snakes and lizards (squamates) play significant roles in many ecosystems and may be limited by a variety of thermal conditions, habitat structures, and predator/prey abundance, which can all be altered by increased urbanization. The goal of this study is to compare variation in abundance, morphology, and habitat-use among various squamate species and locations with varying degrees of urbanization. I will use a multivariate regression and quantile regression to analyze morphology data, canonical correspondence analysis to establish relationships between species abundance and environmental variables, and a dissimilarity matrix and cluster analysis to compare study sites. I will demonstrate that morphology is significantly affected by degree of urbanization, show relationships between species abundance, ground cover, soil composition, and several vegetation measures, and establish several meaningful relationships between study sites.Item Evolutionary forces driving population differentiation in Lake Malawi rock-dwelling cichlids (Pisces: Cichlidae)(2014-01-28) Husemann, Martin, 1982-; Danley, Patrick D.; Biology.; Baylor University. Dept. of Biology.The East African cichlids with more than 2000 species represent the most diverse vertebrate radiation known. Lake Malawi harbors the most species rich flock with more than 700 endemic cichlids. In this work I use a population based approach to study the forces driving the divergence of populations and the factors contributing to the maintenance of species diversity. I examine the effect of genetic drift on population divergence through time and space using an analysis of effective population sizes. This study indicates that populations of the widespread Maylandia zebra are over 550 individuals in size and are at an equilibrium state. The microendemic Maylandia benetos has a relatively small population size (~500 individuals) and evidence for drift is found. I also examine the phenotypic divergence in ecological and sexual characters in M. zebra. This study reveals that ecological selection plays an important role in the divergence of body shape and length in M. zebra. Divergence in male color pattern shows weaker evidence for selection. Furthermore, the divergence estimates for body shape and melanophore count are slightly correlated. This correlation between an ecological and a sexual trait may indicate that both phenotypes might be under correlational selection. Correlational selection on ecological and sexual traits is further supported by the correlation of body shape and male coloration in replicated sympatric species pairs of Maylandia. A common garden experiment using the sympatric M. zebra and M. benetos, representing a sympatric species pair with divergent coloration, shows that body shape had a strong genetic component but also exhibited phenotypic plasticity. Hybrid crosses of the two species reveal a complicated mode of inheritance for body shape differences and demonstrated high degrees of transgressive segregation. Overall, selection appears to be the driving force of phenotypic evolution in rock-dwelling cichlids. However, small population sizes of microendemics expose them to the effects of drift. Evidence for correlational selection suggests that specific combinations of reproductive and ecological traits might be favored. Finally, phenotypic plasticity and transgressive segregation are two mechanisms generating new phenotypic diversity contributing to the diversification of cichlids.Item Factors affecting blue catfish populations in Texas reservoirs.(2011-01-05T19:36:40Z) Bartram, Brian L.; Danley, Patrick D.; Biology.; Baylor University. Dept. of Biology.While some blue catfish Ictalurus furcatus populations are native in Texas reservoirs, many are the result of introductions through stocking programs. Some of these stockings result in established populations while others do not. Blue catfish populations were sampled in 30 Texas reservoirs and population metrics were compared with multiple physicochemical and biological variables collected at each reservoir to examine the key factors that influence their establishment and survival. Factor analysis indicated that both gill net catch rates and low-frequency electrofishing catch rates were positively correlated to measures of primary productivity. The analysis also showed that gill net catch rates increased with increasing reservoir surface area. The occurrence of natural reproduction showed a weak negative correlation to length of growing season. This study provides further insight into the biology of blue catfish and provides managers with information that can be used to prioritize future stocking efforts.Item The functional analysis of NPXY motif in β integrin in vivo.(2009-03-31T15:39:15Z) Ahn, Jeong H.; Lee, Myeongwoo.; Biology.; Baylor University. Dept. of Biology.NPXY (Asn-Pro-X-Tyr) is a conserved tyrosine phosphorylation motif that binds to PTB (phospho-tyrosine binding) domain of other protein. Integrins, a heterodimeric cell surface receptor for extracellular matrix (ECM), include two NPXY motifs in tandem on the cytoplasmic tails of β subunits. I generated a tyrosine to glutamate mutation mimicking constitutive phosphorylation of NPXY in βpat-3 integrin of Caenorhabditis elegans. The transgenic animals displayed disorganized muscle actin and abnormal gonad migration and tail morphology, suggesting that the phosphorylation of tyrosine causes defective phenotypes. In addition, the transgenic animals produced the high number of males, implying that the transgenic animals are similar to him-4/hemicentin alleles and that the lack of him-4 may cause the phosphorylation of NPXY. Genetic analyses revealed that tyrosine to phenylalanine mutations in both positions, βpat-3(YYFF), was able to suppress high incidence in male, mating ability, and egg-laying phenotypes of him-4 mutant, suggesting that a function of him-4 is to prevent the phosphorylation of βpat-3 NPXY. Taken together, our data suggest that changes in the ECM regulate the phosphorylation of the integrin NPXY.Item Gregarine parasitism in dragonfly populations of Central Texas with an assessment of fitness costs in Erythemis simplicicollis.(2010-10-08T16:21:43Z) Locklin, Jason L.; Vodopich, Darrell S.; Biology.; Baylor University. Dept. of Biology.Dragonfly parasites are widespread and frequently include gregarines (Phylum Apicomplexa) in the gut of the host. Gregarines are ubiquitous protozoan parasites that infect arthropods worldwide. More than 1,600 gregarine species have been described, but only a small percentage of invertebrates have been surveyed for these apicomplexan parasites. Some consider gregarines rather harmless, but recent studies suggest otherwise. Odonate-gregarine studies have more commonly involved damselflies, and some have considered gregarines to rarely infect dragonflies. In this study, dragonfly populations were surveyed for gregarines and an assessment of fitness costs was made in a common and widespread host species, Erythemis simplicicollis. Adult dragonfly populations were surveyed weekly at two reservoirs in close proximity to one another and at a flow-through wetland system. Gregarine prevalences and intensities were compared within host populations between genders, among locations, among wing loads, and through time. Host fitness parameters measured included wing load, egg size, clutch size, and total egg count. Of the 37 dragonfly species surveyed, 14 species (38%) hosted gregarines. Thirteen of those species were previously unreported as hosts. Gregarine prevalences ranged from 2% – 52%. Intensities ranged from 1 – 201. Parasites were aggregated among their hosts. Gregarines were found only in individuals exceeding a minimum wing load, indicating that gregarines are likely not transferred from the naiad to adult during emergence. Prevalence and intensity exhibited strong seasonality during both years at one of the reservoirs, but no seasonal trend was detected at the wetland. The seasonal trend at the reservoir suggests that gregarine oocyst viability parallels increasing host population densities and may be short-lived. Prevalence and intensity also differed between dragonfly populations at the locations. Regression analyses revealed that host species, host gender, month, and year were significant explanatory variables related to gregarine prevalence and intensity. The fitness parameters measured were not correlated with presence or intensity of gregarines, suggesting that either gregarines do not affect wing loading and egg production in E. simplicicollis, or that virulence depends on parasite intensity and/or the specific gregarine species infecting the hosts. Our results emphasize the importance of considering season, hosts, and habitat when studying gregarine-dragonfly ecology.Item Identification of germline and somatic cell specific genes essential for ovulation in Caenorhabditis elegans.(2011-05-12T15:49:31Z) Rongali, Sharath C.; Lee, Myeongwoo.; Biology.; Baylor University. Dept. of Biology.The process of ovulation is an integral part of sexual reproduction in Caenorhabditis elegans. Various genes and signaling pathways are responsible for the successful process of ovulation to occur. Identification of these key mechanisms will help us gain knowledge into the mechanisms underlying the process of ovulation. C. elegans, a free living soil nematode, was used to identify and study the genes that are essential for ovulation. To facilitate this study we have used RNA interference (RNAi), a reverse genetics process, to restrict the function of the genes. RNAi causes degradation of the target gene by introduction of a double stranded RNA which has sequence specificity to the gene of interest. I have analyzed data pertaining to sterile (Ste) phenotype from the previous genome-wide RNAi screens. This search yielded 259 genes which caused Ste phenotype in the wild type background. In this screen, we analyzed 259 genes by RNAi in the wild type and various RNAi resistant mutant backgrounds. A detailed study of the gonad morphology was done to analyze the effect of the depletion of each gene on ovulation. Based on the ability of the mutants to suppress sterility, the genes were categorized as germline or somatic cell specific. In order to study the morphological changes related to gonad arm, we have conducted nomarski microscopy and nuclear staining techniques. Based on our study, 20 genes were categorized as germline specific for ovulation and 9 genes somatic cell specific. Genes that have been identified as germline specific belong to functional classes which code for protein synthesis, gene expression regulation, protein transport and modification, protein degradation, ATP synthesis and RNA specific functional classes. The somatic cell specific genes mainly constitute cell architecture, signaling and other functional groups.
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