<p>The seasonal response patterns of net photosynthesis and respiration (and nitrogenase activity in Nostoc) are described within a multivariate framework of temperature, moisture and light for the alpine and grassland crustaceous lichens Rhizocarpon superficiale and Caloplaca trachyphylla respectively and for the grassland surface cyanophyte Nostoc commune. These physiological responses are discussed in context of each species' boundary layer environment, with particular emphasis placed on interactions between environmental constancy and adoption of acclimation strategies.</p> <p>For R. superficiale the high frequency of thermal fluctuations experienced by hydrated thalli, sometimes on an hourly basis, precluded any strategy of seasonal acclimation. Instead, photosynthetic rates exhibited a broad temperature response, remaining near 1 mg CO₂ h⁻¹g⁻¹ from 1 up to 21°C, with no changes evident between seasonal responses. In marked contrast C. trachyphylla shows a distinct winter/summer pattern of photosynthetic acclimation. In winter months rates are optimal near 7°C, while in summer the temperature optima of net photosynthesis shift to 21°C. These changes correlate well with predictable seasonal microclimate events, particularly those associated with winter Chinook snowmelt periods. A third pattern of response was seen in N. commune, where no seasonal changes in response patterns were evident and both nitrogenase activity and net photosynthesis were maximal near 35°C. This response pattern allows maximum carbon gain and nitrogen fixation during spring and summer periods following precipitation events, while its more sheltered aspect reduces the importance of winter snowmelt periods.</p> / Doctor of Philosophy (PhD)

Antibiotic resistance is a problem of significant and growing international concern, in part due to the rapid evolution of new resistances. One potentially important factor in the emergence of resistance is concentrated antibiotic use in environments such as hospitals. Such high use creates a strong selective pressure for pathogens to evolve resistance. We analyze some strategies hospitals can use to slow the evolution of resistance, and estimate the length of the delay between evolution and outbreak of resistance.

Methane hydrates are frozen deposits of methane and water found in high pressure or low temperature sediments. When these deposits destabilize, large quantities of methane can be emitted into the atmosphere. This is significant to climate change because methane has 25 times more greenhouse gas potential than Carbon Dioxide. Worldwide, it is estimated there are between 2500 and 10000 gigatons of methane stored in hydrate deposits. This represents more carbon than all fossil fuels on Earth. It is estimated that between 200 and 2000 gigatons of methane are stored in hydrates in Arctic waters acutely vulnerable to greenhouse warming. Over the last decade, researchers have identified instances of hydrate destabilization that have already begun. To gain insight into the potential climatic effects widespread hydrate dissociation would have, researchers have examined hydrate dissociation during the Paleocene Eocene Thermal Maximum 55 million years ago as a geologic precedent. In this period, large-scale hydrate dissociation contributed to 5-8 degree Celsius warming worldwide. If such a climatic shift were to transpire today, impacts on society would be enormous. There is currently a debate in the scientific community as to whether the risk of methane hydrate dissociation is relevant to the present generation. One side argues that not enough methane could be emitted into the atmosphere from today’s hydrate sources to have a meaningful impact on climate warming, where the other side contends that more than enough methane could be emitted from present day hydrate deposits to cause significant impacts to the global greenhouse effect. Given the information currently known about hydrates, it is reasonable to conclude there is a moderate risk of widespread destabilization that could impact global climate change in the coming decades. Significant acceleration of the conversion to alternative energies and implementation of geoengineering strategies should be considered.

Estuarine marshes are generally considered to be productive but not necessarily diverse ecosystems. During 24 consecutive months, I collected 65,000 fishes and decapods comprising over 65 species from the New Orleans Land Bridge, an estuarine salt marsh. My research details the distribution of nekton across five contiguous but geomorphically different regions, which I defined as “Areas”. This factor “Area” was significant in explaining community composition differences in 11 of the 24 months I evaluated. That is, during those 11 months community structure was different among the Areas. Specific “month” was also found to be a significant factor as community structure was found to differ among the months. No consistent abiotic factors were associated with community structure. These observations imply that a different set of factors are associated with community structure at the Area level than at the microhabitat level. Sampling of nekton in shallow estuarine salt marsh habitats was difficult. The cast net is a useful gear type for this type of sampling and can be readily standardized for each operator. Standardization of the area covered by the net allows density of collected nekton to be calculated. Little is known about the life cycle of one important estuarine dependent sport fish, tarpon (Megalops atlanticus), in southeastern Louisiana. This research details the presence of the major life stages of the species in Louisiana and suggests that it is capable of completing its life cycle in State waters. The presence of a spawning capable female and male tarpon is documented.

Teratospermia (ejaculation of ≥ 60% structurally abnormal spermatozoa) is prevalent among felids facing extinction risk, including the cheetah. This trait also occurs in certain domestic cat populations, providing a valuable research model. Multiple components of sperm function are disrupted in teratospermic cats, and even structurally normal spermatozoa from these ejaculates may be functionally compromised. Teratospermic ejaculates are highly sensitive to damage during cryopreservation, limiting the success of genome resource banking programs for species conservation. Although both teratospermia and cryopreservation are linked to disruptions in multiple energy-dependent sperm processes, the metabolism of these cells has not been investigated. This project explored how cellular metabolism of domestic cat and cheetah spermatozoa is influenced by species physiology, teratospermia, and sperm cryopreservation. The project scope was divided into four studies that collectively examined the two main energy-producing pathways in spermatozoa, i.e., glycolysis and oxidative phosphorylation. Each study compared three animal populations: normospermic cat, teratospermic cat, and cheetah. First, rates of glycolytic and oxidative substrate utilization were correlated to standard metrics of sperm function. Second, the influence of exogenous substrate availability and glycolytic enzyme activity was investigated. Third, mitochondrial activity and the role of oxidative metabolism were assessed. Lastly, sperm metabolic function was examined after cryopreservation and postthaw processing.enzyme activity was essential for sperm function, but, unexpectedly, the importance of this pathway appeared to be linked to glycerol rather than glucose metabolism. Sperm oxidative metabolism was severely compromised in the cheetah, and comparison with the teratospermic cat proved this defect to be species-specific. Spermatozoa from both species experienced metabolic damage during cryopreservation. Post-thaw processing recovered a metabolicallynormal sperm subpopulation in the cat, but cheetah spermatozoa remained functionally compromised. Collectively, these studies provided key insight into metabolism and cryosensitivity of felid spermatozoa and highlighted the importance of domestic animal models for wildlife research. Patterns of substrate utilization were similar in spermatozoa of the cat and cheetah, including an unexpected lack of glucose uptake. However, rates of sperm pyruvate uptake and lactate production were reduced in the teratospermic cat and cheetah compared to the normospermic cat. Lactate production predicted ejaculate quality in each study. Glycolytic

The objective of this study is to determine whether changes in arthropod community structure in restored longleaf pine savannas corresponds to differences in vegetation structure often associated with burn frequency. Longleaf pine savannas are fire-maintained ecosystems characteristic of the southeastern United States and have experienced severe declines (around 97%) since European settlement. Changes in fire regime have been instrumental in the declines. Restoration of these ecosystems has involved reinstitution of periodic burnings to promote and maintain vegetative characteristics of the savannas. This study investigates trends in arthropod communities from areas heavily invaded by hardwood shrubs against those dominated by longleaf pines and associated vegetation. These data suggest that herb-dominated sites have higher overall diversity. While overall abundance differences were not found, significant differences have been detected at the order and family level, indicating that vegetation structure and periodic burning are important factors in maintaining arthropod communities characteristic of these savannas.

The well-known symbol for conservation, the giant panda bear, and the original red panda have been forced into remote habitats due to anthropogenic disturbance, making ecological study difficult. Therefore the first known species distribution model was created to predict the most likely areas of occurrence within the known range of these elusive animals. These models were then projected onto North America and evaluated against existing breeding programs. Additionally, the close proximity of the Gray Fossil Site and the discovery of the most complete fossil red panda specimens in the world allowed ecomorphological comparisons between the modern red panda, Ailurus fulgens and the fossil red panda, Pristinailurus bristoli. Spatial data and morphometric results from this study will aid conservation work and breeding programs globally.

Papilio dardanus displays female-limited polymorphic mimicry of multiple model species. Butterfly wing shape is species-specific and can influence mimetic signaling, but has not been characterized in this species. We used elliptical fourier analysis to investigate whether mimetic P. dardanus female forms have converged on the wing shape of their respective models. Although both models and mimics varied in forewing and hind wing shape, we found no evidence of forewing shape convergence between them. Overall, forewings did not differ in shape between sexes in P. dardanus, nor in four non-mimetic Papilio used for comparison. Similarly, there were no hind wing differences between the sexes in the four non-mimetic Papilio. However, P. dardanus hind wings varied significantly between mimetic females and non-mimetic individuals suggesting that, in addition to wing color pattern, the evolution of mimicry has led to changes in hind wing shape in P. dardanus.

Phenotypic plasticity is favored in heterogeneous environments in which alternative phenotypes can exploit alternative resources. However, it’s not clear whether phenotypic plasticity is useful in environments that become more homogenous over an organism’s life cycle. I studied a population of grasshopper Melanoplus differentialis that experiences high resource diversity as nymphs but low resource diversity as adults to determine if individuals can undergo diet-induced morphological plasticity in head shape to increase biting ability and ingestion of hard diets. Insects on a soft diet were larger and had greater bite force than those on a hard diet. Head structures related to chewing ability changed shape with mass, heads became taller and narrower. Scaling relationships among body parts suggested that there wasn’t evidence for tradeoff in allocation to chewing vs. locomotor performance. Results are consistent with the idea that essential adult feeding morphology constrains the advantage of plasticity in feeding structures among nymphs.

In this study, I sequenced the mitochondrial cytochrome b gene to elucidate the extent and pattern of genetic variations among and within populations of Rhinichthys osculus (Santa Ana Speckled Dace) found in the different watersheds in Southern California, Central California Coast and Eastern California Desert. I described and analyzed the structural characteristics and pattern of base sequence substitutions in the cytochrome b gene to understand the molecular evolution of the gene. The Phylogenetic analyses showed that the Southern California Santa Ana Speckled dace is a distinct population from the Central California Coast dace population and Eastern California Desert dace population, and is more closely related to the Colorado River speckled dace population. There is a high degree of genetic variation among all populations including a significant genetic structure associated with watersheds, mountain ranges, and geographic grouping based on locations. The SWISS-Model automated protein structure homology elucidated the conserved and invariant residues within the cytochrome b gene where the amino acid substitutions are located in the trans-membrane of the protein sequence. The implication for conservation and management of the Southern California Santa Ana Speckled dace is high because of habitat lost for this distinct dace population. The data from this study will contribute to preserving the genetic variability of the Santa Ana Speckled Dace as a separate taxa and species, as well as to help maintain intact the population in the different Southern California creeks.