Browsing by Subject "Speciation"
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Item Diversification and evolution of treefrogs in the Cerrado savanna of South America : from population structure to biogeographic patterns(2016-05) Vasconcellos, Mariana Mira; Cannatella, David C.; Wilke, C. (Claus); Bolnick, Daniel I.; Simpson, Beryl B.; Young, Kenneth R.; Ryan, Michael J.Historical and ecological factors underlying population structure and speciation of organisms are fundamental to uncover diversification mechanisms that lead to biogeographic patterns. The main goal of this dissertation is to determine the relative roles of geography and climate promoting diversification in a diverse group of treefrogs in the Cerrado savanna of South America, a hotspot of biodiversity. This dissertation approaches diversification at two different time-scales: from a macro-temporal scale of factors that promote species diversification in the Cerrado region, and from a micro-temporal scale of population divergence and recent cryptic speciation. Three main research goals were developed in separate chapters: (1) Phylogenetic and biogeographic analyses of the species in the Hypsiboas pulchellus group were used to quantify dispersal events between the Cerrado and other dry/open or humid/forested neighboring habitats, and to evaluate how this dynamic historical interchange affected diversification. The evolutionary relationships among the species in this group showed a pattern of multiple recent origins of the endemic Cerrado lineages, indicating recent colonization events. These analyses indicate an interesting pattern of recurrent dispersal among open and forest ecoregions accounting for the accelerated diversification in this group. (2) Species delimitation methods using molecular, morphological and mating call characters were used to study the recent speciation of a small clade of Cerrado endemics. This integrative approach allowed for a better resolution to detect species boundaries and the discovery of cryptic species in spite of conserved morphology and mating calls. (3) Population structure in a widespread Cerrado species was investigated using historical species distribution modeling and next generation sequencing data to evaluate the role of recent climatic fluctuations on population differentiation. Divergence among populations seems strongly affected by Pleistocene climatic instability, a pattern we call isolation-by-instability. In conclusion, this study highlights how diversification and biogeographic patterns in the Cerrado savanna can be affected by its historical dynamic climate and landscape.Item Genomic signatures of host-associated differentation in phytophagous insects(2015-12) Bennett, Nichole Lynn; Parmesan, Camille, 1961-; Singer, Michael CAlthough there have been many studies investigating host-associated genomic differentiation in phytophagous insects feeding on different host plants, this review serves to compile the current state of knowledge of the conditions for host-associated genomic differentiation and the patterns and processes of genome-wide divergence. While there are a multitude of theories and expectations for when host-associated genomic differentiation will occur and how, more empirical work is needed on how this operates in natural herbivorous insect systems. In the future, this knowledge of how host-associated genomic differentiation operates may be used to better control better agricultural pests, to manage invasive species, and to develop conservation strategies.Item Impact of bromide, NOM, and prechlorination on haloamine formation, speciation, and decay during chloramination(2009-12) Alsulaili, Abdalrahman D.; Speitel, Gerald E.; Katz, Lynn EllenThe Chlorine-Ammonia Process was developed recently as a preoxidation process to minimize the formation of bromate during ozonation of the waters containing a significant bromide concentration. Chlorine is added first, followed by ammonia 5-10 minutes later, with the goal of sequestering bromide in monobromamine before the subsequent ozonation step. The goal of this research was to improve the Chlorine-Ammonia Process by introducing a very short prechlorination step (i.e., 30 seconds before addition of ammonia) to minimize overall disinfection by-product formation. Also, in this strategy, formation of a powerful halogenating agent, HOBr, is minimized and bromochloramine (NHBrCl) is used predominantly instead of monobromamine to sequester bromide during ozonation. To support this improved approach to bromide sequestration, this study examined the formation and decay of bromochloramine as a function of operating conditions, such as pH and Cl2/N ratio, and refined a chemical kinetic model to predict haloamine concentrations over time. Two natural organic matter (NOM) sources were used in this study (Lake Austin, Texas and Claremore Lake, Oklahoma) to study the effect of NOM on monochloramine and total chlorine decay after 30 seconds of prechlorination. The rate of the reaction between haloamines and fast and slow sites on the NOM was estimated. A kinetics model was developed to model total chlorine decay after a short prechlorination time. The model is based on the Unified Haloamine Kinetic Model developed by Pope (2006). Pope`s model failed to model the initial monochloramine concentration after 30 seconds prechlorination time as well as the monochloramine and total chlorine decay over time. The modified model shows an excellent prediction of monochloramine and total chlorine decay after 30 seconds prechlorination time at pH range of 6.5-8.0 and over a carbonate buffer concentration range of 2-10 mM. The model includes a new bromochloramine decay scheme via the reaction with monochloramine and with itself. In addition, new rate constants for the reaction of HOCl with bromide ion and reaction of HOBr with monochloramine were added. The hypobromous acid formation rate was found to be an acid-catalyzed reaction, which confirms the finding of Kumar et al. (1987). A new value of the acid catalysis effect of hydrogen ion was estimated. New terms were introduced to the hyprobromous acid formation rate including the acid catalysis effect of bicarbonate, carbonic acid, and ammonium ion. In addition, the reaction of HOBr with monochloramine to form bromochloramine was found to be an acid-catalyzed reaction, and a new value of the rate constant was estimated.Item Measurement of arsenic in water and soil based on gas-phase chemiluminescence(Texas Tech University, 2007-05) Idowu, Ademola David; Dasgupta, Purnendu K.; Liu, Shaorong; Quitevis, Edward L.Arsenic occurs widely in nature and is a known human carcinogen. Developmental, immunological, and neurological defects are linked with chronic exposure to arsenic in drinking water. The United States Environmental Protection Agency (US EPA) prescribed safe limit is 10 μg/L. Standard atomic spectrometry based methods are expensive. Field wet techniques require large amounts of acid, other reagents and paper strips impregnated with toxic mercury and lead compounds. This dissertation presents a new, fast, safe, affordable automated system configurable for laboratory or field use. Arsenic in the sample is chemically or electrochemically reduced to arsine that reacts with ozone atop a photomultiplier tube, producing chemiluminescence. Direct chemical, electrochemical, and liquid chromatography methods are described. The first method uses sodium borohydride for the reduction of arsenic. Differential determination of arsenate and arsenite is based on the different pH dependence on their conversion to arsine. At pH ≤1, both arsenate and arsenite are quantitatively converted. At pH 4-5, only arsenite is converted. Under these conditions, limit of detection (LOD) is 0.05 and 0.09 μg/L for total arsenic and arsenite, respectively, with a 3-mL water sample. The relative standard deviation for 3 determinations was 1.2 and 2.1% for 1 μg/L total arsenic and arsenite respectively. The arsenic concentrations in this dissertation are all based on that of elemental arsenic. The Electrochemical method uses a Platinum screen anode and stainless steel cathode in two compartments, separated by a Nafion membrane. Arsenite is selectively reduced on a stainless steel cathode while a cadmium-coated cathode reduces both forms. The limit of detection is 1.5 and 4 μg/L for arsenite and total arsenic respectively with a 2-mL water sample. The relative standard deviation for 3 determinations was 2.6 and 4.5% for 10 μg/L arsenite and total arsenic respectively. This environment-friendly method uses only re-usable sulfuric acid electrolyte, air, water and electricity but requires further development. Arsenite, arsenate, dimethylarsinic acid (DMA) and monomethylarsonic acid (MMA) are separated on anion-exchange column using carbonate and hydroxide eluents. Separated species are photolytically oxidized by UV-light, converting organic species to their respective inorganic forms. Subsequent online reaction with acid and borohydride produces arsine, detected by CL. For arsenite, arsenate, MMA and DMA the LOD is 0.4, 0.2, 0.5 and 0.3 μg/L respectively for a 100-μL injected sample. The relative standard deviation for 3 determinations was 3.5, 2.8, 2.2, and 4.1% for 10 μg/L of each of arsenite, arsenate, MMA, and DMA respectively. The system has been tested successfully on water and soil samples, and can be adapted for matrices such as biological samples and body fluids. There are no significant practical interferencesItem Microbial intervention strategies for Salmonella and Campylobacter reduction in commercial turkey processing(Texas A&M University, 2005-08-29) Stevens, Scott MichaelOne objective of the present investigation was to compare Salmonella and Campylobacter recovery incidence from commercially processed turkeys immediately prior to and following pre-chill and immersion chiller intervention strategies being used in three distinct turkey processing facilities. In each plant, on a single day of processing, 100 carcass rinse samples prior to and following each post-evisceration, pre-chill intervention and following immersion chilling were obtained for Salmonella and Campylobacter recovery. Two of three plants demonstrated a trend of decreased Salmonella on carcasses following the Inside Outside Bird Wash (IOBW), with reductions of 13%, and 11% being observed for Plants 1 and 2, respectively. Results for reductions of Campylobacter contamination were not as straightforward, with only Plant 3 showing decreased levels (11% reduction) following the IOBW. Plant 2 used an additional pre-chill intervention, a low pressure, acetic acid final wash, which was not shown to be effective in causing an additional reduction in either Salmonella or Campylobacter on carcasses. In all three plants, properly managed immersion chilling systems were the most effective microbial intervention for achieving Salmonella andCampylobacter reduction on processed turkey carcasses. While not as effective, the IOBW present in each plant likely contributed to the effectiveness of immersion chiller interventions. If managed properly these intervention points have demonstrated themselves as a viable means to effectively reduce Salmonella and Campylobacter on processed turkeys. Another objective was to modify the scalder environment to an alkaline pH and determine the effects of thermal killing of Salmonella and Campylobacter. In each plant, on a single day of processing, 50 carcass rinse samples prior to and following scald tank immersion and following feather removal were obtained for Salmonella and Campylobacter recovery. Modification of the scald water to alkaline conditions (pH 9- 10) did not result in increased thermal killing of Salmonella or Campylobacter on turkey carcasses, as hypothesized before the investigation. Alkaline conditions are known to facilitate a more efficacious pluck and aid in the detachment of bacteria. Due to this, the bacteria that were recovered at these points on the processing line could have had an impact on the observed data.Item Occurrence, Distribution, And Speciation of Arsenic in the Southern High Plains Aquifer System(2010-12) Venkataraman, Kartik; Rainwater, Ken; Jackson, Andrew W.; Ridley, Moira K.Significant levels of arsenic have been detected in the groundwater of the Southern High Plains. The potential sources include atmospheric deposition, the use of agricultural defoliants and natural subsurface geochemical interactions. To identify the source of arsenic, groundwater and soil samples were collected from sites spread over 18 counties in the Southern High Plains. Total arsenic and its inorganic species were quantified along with commonly occurring and related cations and anions such as iron, manganese and sulfate. Correlation studies were conducted to understand the variation of arsenical species with related parameters. A geochemical modeling tool, MINTEQ was used to predict the speciation of arsenic and compare these results with lab analyses. The distribution of arsenic in the soil profiles tested indicated a positive correlation with depth. The highest concentrations were found close to the water table while the upper soil layers had low to non-detect concentrations. In the groundwater samples, arsenic concentration and speciation varied significantly between sites. As (III) was found to be the dominant species in over 80% of the samples. MINTEQ speciation forecasts compared favorably with a majority of the groundwater analyses. Very little evidence of atmospheric deposition exists and the sources of arsenic are likely anthropogenic land sources in the shallow subsurface and natural geologic processes in the deeper subsurface.Item Speciation in Andean rivers: morphological and genetic divergence in the catfish genus Chaetostoma (Teleostei: Siluriformes)(Texas Tech University, 2007-08) Salcedo, Maurtua NormaDeclining biological diversity and the realization that freshwater is becoming scarce, provide the framework for elevating the priority for taxonomic and biological studies of freshwater organisms. One highly diverse ecosystem, rich in endemic species, is the Andean Montane forest. On the slopes of the Andes the conditions for aquatic life are limited by fast flowing waters and rocky bottoms, which reduce the availability of habitats and resources for many unique forms of live. Nevertheless, the species diversity is high for some fishes such as the catfish genus Chaetostoma. To date there are 45 described species within the genus Chaetostoma, however the type species of the genus has not been used as comparative material in taxonomic studies. Other species are known only from the original description, which all together makes the revision of the genus a model system for studying freshwater montane ecosystems in the Andes. The re-description of two species: Chaetostoma loborhynchos, the type species of the genus, and C. marmorescens, a species with no known type specimen, is suggested after studying their morphology based on available material as the first step towards the revision of the group. Species assigned to the genus Chaetostoma have been considered to have restricted geographic distribution, usually to the basin they inhabit. However, Chaetostoma lineopunctatum was found widely distributed in the Ucayali and Madre de Dios River basins. The presence of cryptic species was tested using morphological divergence, molecular divergence, and phylogenetic structure of samples from both basins. No significant differences were found for morphological divergence (P>0.05) and molecular divergences (1.1%-1.5%) in cytochrome b gene sequences among the localities tested. Phylogenetic structure suggests that the population from the Madre de Dios River basin is more closely related to the Río Tambo population than to the Río Urubamba population. Based on the evidence obtained, these populations are probably the result of recent geographic isolation (~1 Mya) and they should be considered as the same species. Environmental gradients have been suggested as a trigger for speciation. In the mountains of central Peru, two Chaetostoma species live in fast flowing waters of the Río Perené at two different elevation ranges. Chaetostoma lineopunctatum (300-600 m) and C. loborhynhos (1000-1500) were studied to test for phenotype divergence. Geometric morphometric data and interlandmark distances were obtained and analyzed by discriminant analysis. Differences between the phenotypes were significant between the groups (PItem The influence of body size and sexual dimorphism on speciation within Anura(2016-08) Gullett, Taylor Cameron; Cannatella, David C.; Hillis, DavidMany adaptive radiations demonstrate clear relationships between morphological variation and diversity, hinting that trait plasticity leads to increased potential to diversify. This study will examine this pattern within frogs (Anura). Body size is the focal morphological feature of this study due to its ease of collection and close relationship with the niche of an organism. Unlike most large-scale studies, this one takes into account both male and female body size and the extent of sexual size dimorphism (SSD). This allows us to determine not only whether body size relates to diversification rate but also whether body size evolution in one sex is more indicative of changes in diversification rate than the other and what impact SSD has on diversity. The results show that rates of male and female body size evolution as well as extent of sexual size dimorphism were all significantly positively correlated with speciation rate. The relationship between body size and speciation supports the idea that morphological plasticity and enhanced diversification go hand-in-hand. Both sexes rate of body size evolution had a similar relationship with speciation, indicating neither sex is more important for diversification. Increased sexual size dimorphism suggests this selection for extreme variation promotes diversity. Overall, rates of phenotypic evolution and speciation were closely linked across all of Anura.