Mutations affecting the mitochondrial electron transport chain cause numerous neurodegenerative disorders in humans and affect longevity in other organisms. A natural model system to study the relationship between mitochondrial function and aging within an evolutionary or population genetic context has been lacking. Natural populations of Caenorhabditis briggsae nematodes were recently found to harbor mitochondrial genetic variation with likely functional consequences for aging. Specifically, C. briggsae isolates containing high frequencies of a deletion mutation affecting the mitochondrial NADH dehydrogenase 5 (ND5) gene were found to have reduced reproductive fitness and lifespan and elevated levels of mutagenic superoxide. Here, rates of growth and aging and aerobic respiratory capacity were evaluated in several isolates spanning the range of mitochondrial genetic variation in this species. There is considerable variation among isolates for all measured traits, although the observed relationships between isolate-specific trait means and ND5 deletion frequency did not always conform to my expectations. In an effort to determine whether the among-isolate phenotypic variation is due to mitochondrial rather than to nuclear genetic variation, inter-population hybrids of C. briggsae were created and compared to the progenitor isolates. Surprisingly, evidence for paternal mitochondrial inheritance was detected in many of these hybrid lines. Where mitochondrial genomes were maternally inherited as expected, intergenomic epistasis appears to contribute to fitness, longevity, and aging in this species.

Cementitious materials obtained from different sources, while evaluated and classified by the same methods and criteria, often produce concrete with compressive strength variance despite other inputs remaining constant. The focus of this thesis was to enumerate and illustrate the possible compressive strength variation when cementitious material sources are interchanged, and investigate the influence that aggregate can have on this variation. This was accomplished by compiling and analyzing compressive strength data from previous research initiatives, and concluded that coefficient of variation (COV) and range values at the 14-, 28-, and 56-day timeframes due to a cement source change varied between 15.3% and 18.1% and 1,988 psi and 2,728 psi in concrete, and 16.1% and 22.9% and 3,406 psi and 5,884 psi in paste or mortar. Concrete that included supplementary cementitious material (SCM) displayed up to 4.1% higher COV values versus non-SCM mixtures, and specific aggregate/cementitious material combinations influenced compressive strength variability.

The pet overpopulation problem is a multiactorial problem that many organizations such as animal shelters attempt to manage. Many studies have focused on the reasons animals are relinquished by their owners but few have also looked at the characteristics that may influence adoption. Identifying which characteristics that influence adoption may help shelters provide more detailed adoption programs based on their dog and cat profile. Increases in the number of dogs and cats entering animal shelters during the spring and summer month is a perception among shelter staff. Investigating the seasonal trends in the number of animals entering a shelter may help the facility prepare to provide additional space and resources. The focus of this study was to identify any seasonal variation in the number of dogs and cats entering animal shelters in Mississippi and to determine the characteristics of dogs and cats that influenced their adoption.

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No description available.

No description available.

Understanding the changes undergone during the life of an organism is often crucial to properly interpreting the evolutionary history of a group. For extinct organisms, this process can only be directly studied through growth series of fossils representing individuals at different stages of maturity. The growth patterns of the earliest dinosaurs (230–190 million years ago), in particular the morphological changes undergone during the life history of an individual (i.e., ontogeny) is poorly understood. To tackle this problem, I studied the changes undergone during growth of two early theropod dinosaurs, Coelophysis bauri and Megapnosaurus rhodesiensis. To reconstruct the growth of these dinosaurs I used ontogenetic sequence analysis (OSA). I found that, unlike living birds, early dinosaurs possessed an extremely high amount of intraspecific variation in growth. This variation had been previously interpreted as sexual difference; however, I found no evidence of this. Because this variation is widespread among early dinosaurs and their relatives, I hypothesize that this is the ancestral condition of dinosaurian growth, and that this was lost along the evolution to birds. These ontogenetic events are conserved through evolution, and I used this to assess the maturity of large Triassic theropods: I suggest that all known large-bodied Triassic theropods were still growing rapidly at death, and that the maximum body size of Triassic theropods was higher than previously supposed. Theropods were large before the end Triassic mass extinction, unlike what has been previously hypothesized. / Master of Science

Les régions arctiques et subarctiques constituent un défi pour la recherche sur la biodiversité en raison de leur éloignement et des conditions environnementales extrêmes. Cependant, il est essentiel d'acquérir une compréhension fondamentale du biote polaire. Les bryophytes sont une composante importante des écosystèmes polaires à cause de leur abondance et de leurs rôles écologiques, tels que la production primaire, la stabilisation des sols et le cycle des nutriments par le biais d'interactions bactériennes. Malgré leur rôle vital dans les écosystèmes polaires, l'écologie des bryophytes est loin d'être comprise. Cette thèse contribue à la connaissance des bryophytes de l'Arctique et du Subarctique, en mettant l'accent sur les populations de mousses. Je me suis concentré sur trois sujets principaux : l'histoire évolutive, la diversité génétique locale et les interactions microbiennes en utilisant la mousse *Racomitrium lanuginosum* comme espèce modèle. Une approche intégrative a été utilisée pour étudier ces sujets, englobant le séquençage Sanger, le génotypage par séquençage (GBS), des modèles de répartition des espèces, le séquençage des amplicons, les essais de réduction de l'acétylène (ARA) et la spectrométrie de masse à plasma inductif (ICP-MS). Le premier chapitre dévoile l'histoire évolutive de la mousse dans l'hémisphère nord, en découvrant quatre groupes génétiques cryptiques repartis dans des environnements subarctiques et arctiques et en montrant l'impact des dernières glaciations sur la diversité génétique des populations. Le deuxième chapitre illustre comment la reconnaissance de lignées cryptiques peut avoir un impact sur les évaluations de la diversité génétique dans les habitats et peux aider à comprendre la répartition de la variation génétique dans des populations clonales de *R. lanuginosum*. Le troisième chapitre étudie les communautés microbiennes associées à la mousses et leurs capacités de fixation d'azote dans l'écotone forêt-toundra, en mettant en évidence le microbiote central des mousses, les différences de communautés bactériennes entre les habitats et les bactéries diazotrophes qui façonnent la fixation d'azote. En résumé, cette thèse contribue de manière significative à la connaissance des aspects évolutifs et écologiques des plantes de la région subarctique, en se concentrant sur un organisme clé de la toundra. L'étude souligne l'importance des bryophytes et de leurs relations symbiotiques dans les écosystèmes polaires, et met en évidence la nécessité de poursuivre les recherches sur ces systèmes complexes. Afin d'assurer la préservation à long terme de ces écosystèmes vulnérables, il est essentiel d'acquérir une compréhension approfondie de leur dynamique et de développer des stratégies de conservation efficaces, tout en évaluant la manière dont les organismes réagissent aux changements environnementaux. / The Arctic and subarctic regions pose a challenge to biodiversity research due to their remote location and harsh environmental conditions. However, gaining a fundamental understanding of the polar biota is crucial. Bryophytes are significant components of polar ecosystems due to their abundance and ecological roles, such as primary producers, soil stabilization, and nutrient cycling through bacterial interactions. Despite their vital role in polar ecosystems, bryophyte ecology remains far from being understood. This thesis contributes to the knowledge of Artic and Subarctic bryophytes, with a focus on mosses. I covered three main topics: evolutionary history, local genetic diversity and microbial interactions using the moss *Racomitrium lanuginosum* as a model species. An integrative approach was used to study these topics, encompassing Sanger sequencing, genotyping-by-sequencing (GBS), species distribution modeling, amplicon sequencing, acetylene reduction assays (ARA), and inductively coupled plasma mass spectrometry (ICP-MS). The first chapter unveils the evolutionary history of the moss in the Northern Hemisphere, uncovering four cryptic genetic groups scattered across subarctic and arctic environments and showing the impact of the last glaciations on the population's genetic diversity. The second chapter illustrates how recognizing cryptic lineages can impact genetic diversity assessments in habitats and help to understand the partition of genetic variation in clonal populations of *R. lanuginosum*. The third chapter delves into the moss-associated microbial communities and their N₂ fixation capabilities in the forest-tundra ecotone, highlighting the moss core microbiome, the bacterial community differences between habitats and the diazotrophic bacteria influencing this process. In summary, this thesis significantly contributes to the knowledge of the evolutionary and ecological aspects of plants in the subarctic region, focusing on a key tundra organism. The study emphasizes the importance of bryophytes and their symbiotic relationships in polar ecosystems, highlighting the need for further investigations into these intricate systems. A deep understanding of plant dynamics in Arctic and Subarctic environments will be crucial to ensure the long-term preservation of these vulnerable ecosystems

Abiotic and biotic variation has been shown to be important in regulating nutrient cycling and belowground communities in natural systems. However, genetic variation in dominant plants as a driver of rates of nutrient cycling is still poorly understood and few studies have looked at genotype interactions across multiple environments. Using Populus angustifolia and a common garden approach, we hypothesized that all three factors: tree genetic variation, environmental conditions and genetic by environment (G x E) interactions would affect soil carbon (C) storage and nitrogen (N) cycling. Replicated copies of five different reciprocally planted Populus genotypes were studied in three separate 18-21 year old common gardens at different elevations (1300m, 1384m and 1587m) in northern Utah, to measure the genotype and environmental effects on pools of soil C and N as well as rates of soil net N nitrification and net mineralization. Our results indicate that genotypes influence pools of soil C, total N and C:N, but genotype did not influence net rates of nitrogen mineralization. Environmental variation significantly influenced pools of soil C, total N, soil C:N and rates of net nitrification and net N mineralization. As predicted, G x E interactions significantly influenced both pools and processes of soil C and N cycling. Overall, we found that genetic variation in plant traits (tree diameter and leaf/root chemistry) as well as soil texture across gardens were significant predictors of soil C and N pools and fluxes across seasons. These data help us understand the relative role of genotypic variation on above- and belowground interactions in different environments and the consequences of these interactions on ecosystem processes. The results from this study show that across an environmental gradient Populus angustifolia genotypes can influence nitrogen mineralization through feedbacks between environmental variation, tree phenotype and soils.

Abiotic and biotic variation has been shown to be important in regulating nutrient cycling and belowground communities in natural systems. However, genetic variation in dominant plants as a driver of rates of nutrient cycling is still poorly understood and few studies have looked at genotype interactions across multiple environments. Using Populus angustifolia and a common garden approach, we hypothesized that all three factors: tree genetic variation, environmental conditions and genetic by environment (G x E) interactions would affect soil carbon (C) storage and nitrogen (N) cycling. Replicated copies of five different reciprocally planted Populus genotypes were studied in three separate 18-21 year old common gardens at different elevations (1300m, 1384m and 1587m) in northern Utah, to measure the genotype and environmental effects on pools of soil C and N as well as rates of soil net N nitrification and net mineralization. Our results indicate that genotypes influence pools of soil C, total N and C:N, but genotype did not influence net rates of nitrogen mineralization. Environmental variation significantly influenced pools of soil C, total N, soil C:N and rates of net nitrification and net N mineralization. As predicted, G x E interactions significantly influenced both pools and processes of soil C and N cycling. Overall, we found that genetic variation in plant traits (tree diameter and leaf/root chemistry) as well as soil texture across gardens were significant predictors of soil C and N pools and fluxes across seasons. These data help us understand the relative role of genotypic variation on above- and belowground interactions in different environments and the consequences of these interactions on ecosystem processes. The results from this study show that across an environmental gradient Populus angustifolia genotypes can influence nitrogen mineralization through feedbacks between environmental variation, tree phenotype and soils.