Milton, Sarah L.

Antibiotic resistance is a growing concern due to the improper use of antibiotics. Not only is antibiotic resistance increasingly occurring in human populations, but it appears to be spreading in wildlife populations too due to drug overuse and misuse in medicine, farming, and industrial settings, and the subsequent release into watersheds. This project examined the prevalence of antibiotic resistant bacteria in the hindgut microbiome of green (Chelonia mydas) (n=60) and loggerhead (Caretta caretta) (n=57) sea turtles. Hindgut swabs were cultured for gram negative bacteria and exposed to 6 antibiotics. 83.3% of samples were resistant or intermediately resistant to at least one antibiotic, and 27.7% of samples were resistant or intermediately resistant to three antibiotics. This study provides more information regarding the relationship between turtle characteristics and the presence of antibiotic resistance in the hindgut of Florida sea turtles, as well as examine the types of bacteria found in the hindgut.

High nest incubation temperatures can result in numerous physiological and behavioral outcomes in sea turtle hatchlings, including body characteristics for efficient swimming. This project examined the effects of incubation temperature on yolk metabolization, body morphology, buoyancy, swimming kinematics, and blood chemistry to better understand variations in locomotor performance in loggerhead (Caretta caretta) sea turtle hatchlings of South Florida. Nest temperatures, body measurements, and blood samples were collected in conjunction with swim-trial force measurements and video recordings. Data suggest hatchlings from nests with higher incubation temperatures tend to be significantly smaller in size, less buoyant, and display lower power stroke frequencies. These variations between hatchling morphology and performance indicate hatchlings from high temperature nests (i.e., >33°C) may exhibit weaker swimming abilities. The results of this study provide a further understanding of the effect of incubation temperatures on hatchling physiology and early survival in their important frenzy period.

Sea level rise threatens loggerhead sea turtle (Caretta caretta) nests laid close to the high tide line (HTL) with inundation from washover. Boca Raton, Florida is a relatively steep, dynamic beach with changes in beach morphology even during nonactive hurricane seasons. One potential solution to conserve sea turtle nests is to relocate nests laid at or below the HTL closer to the dune. In this study, I examined reproductive success for in situ vs relocated nests. Relocation did not decrease reproductive success, while nests left near the HTL were at risk of washout. During a dry season, nests that experienced one to three days of washover had significantly higher reproductive success than nests that experienced no washover. Relocation can be a useful method to preserve nests against sea level rise, but nonrelocated nests near the HTL may sometimes benefit from washover to cool the nests during hot and dry years.

Sea turtle hatchlings face a variety of obstacles as they crawl down the beach to the ocean after emergence. One of these obstacles is Sargassum, a floating brown macroalgae, that washes up in large quantities on beaches from Florida to South America. This study examined the physiological response and physical performance of three species of sea turtle hatchlings (D. coriacea, C. caretta, and C. mydas) after crawling over various heights of Sargassum. In all three species, the addition of Sargassum significantly increased the amount of time it took to crawl down the pathway. There was no significant difference in righting response, blood glucose levels, or plasma corticosterone concentrations between different crawling treatments. During periods of high Sargassum accumulation, hatchlings will spend more time on the beach trying to navigate through the algae, leaving them vulnerable to predation for longer periods of time.

Urbanization and land development, climate change, pollution, the spread of invasive species, and sea level rise are unprecedented challenges that have led to 25% of avian species worldwide facing an elevated risk of extinction. Under rapidly changing environmental conditions, traditional population models are not ideal because they typically assume that demographic parameters are static in order to estimate the probability of species extinction over a chosen timeframe. This assumption disregards species’ potential to adapt to environmental change; adaptations which could alter not only a species’ extinction outlook but also its legal protection status. The goal of my PhD research is to re-evaluate the risk of extinction of one threatened species, the Wood Stork (Mycteria americana), by accounting for potential adaptation in the context of planned and predicted changes in the southeastern United States. Since the 1970s, Wood Storks have shifted the timing of their breeding season, expanded their range northward and into novel habitats in urban areas, and begun consuming non-native fishes. I investigate these observations by comparing the physiology and diet of Wood Storks nesting in the historical core of their U.S. range (tree islands in the flooded Everglades marsh) with storks occupying novel habitats in urban and temperate locations. Faster growth rate, improved body condition, and increased survival by nestlings in urban areas would be evidence that colonies on the leading edge of the species’ range may be capable of sustaining growth of the whole population. In a third and final chapter, I forecast nest abundance and distribution patterns in the entirety of the U.S. range given various hydrological scenarios. Increased Wood Stork population size and stability are recovery criteria which must be met before the species can qualify for removal from the federal Endangered Species List. More broadly, understanding Wood Stork response to human development in the Everglades illuminates general patterns in avian species response to extreme changes in landscape, and could serve as a framework for proactively incorporating evolutionary potential into the framework of Endangered Species Act recovery in other species which have a high adaptive capacity.

Green sea turtles (Chelonia mydas) are an endangered species prone to a debilitating disease called fibropapillomatosis (FP). The aim of this study was to determine the influence of UV light on vitamin D levels and immune function in juvenile green sea turtles with FP. Phagocytosis, plasma vitamin D levels and viral load of ChHV5 were measured for FP- and FP+ turtles kept at the Gumbo Limbo Nature Center (GLNC) and for turtles caught at the St. Lucie power plant. Turtles kept at GLNC were housed in tanks exposed to varying amounts of UV light. Turtles brought into GLNC had lower phagocytosis compared to turtles at the St. Lucie power plant. Individuals exposed to greater UV light had higher plasma vitamin D levels and a more successful recovery. The results of this project will provide rehabilitation facilities with a mechanism to improve the recovery of animals with this disease.

Stroke is one of the leading causes of human death in the United States. The debilitating effects of an ischemic stroke are due to the fact that mammalian neurons are highly susceptible to hypoxia and subsequent oxygen reperfusion. From studies in Drosophila melanogaster, cGMP-dependent Protein Kinase (PKG) enzyme is thought to affect anoxia tolerance by modifying the electrical current through potassium ion channels. In this research, two animal models were employed: Drosophila melanogaster and mammalian neurons exposed to stroke-like conditions. First, in vivo studies using Drosophila were performed to further our knowledge about the differences between the naturally occurring variants of the Drosophila foraging gene, which shows different protein levels of PKG. Mitochondrial density and metabolic activity between two fly genotypes exposed to anoxia and reoxygenation were compared. It was found that flies with less enzyme potentially showed mitochondrial biogenesis and higher metabolic rates upon reoxygenation. Next, in vivo studies where PKG enzyme was activated pharmacologically were performed; it was found that the activation of the cGMP/PKG pathway led to neuroprotection upon anoxia and reoxygenation. Furthermore, this model was translated into the in vitro model using Drosophila cells. Instead of anoxia and reoxygenation, hypoxia mimetics and hydrogen peroxide were used to induce cellular injury. After showing the cGMP/PKG pathway activation-induced cell protection, the potential downstream targets of the molecular signaling as well as underlying biochemical changes were assessed. It was found that mitochondrial potassium ion channels were involved in the protective signaling and the signaling modulated metabolic function. Furthermore, it was found that acidosis protected Drosophila cells from cell death, metabolic disruption, and oxidative stress. Finally, this research was translated to a mammalian in vitro model of neuronal damage upon stroke-like conditions; there, it was demonstrated that the cGMP/PKG pathway activation in rat primary cortical neurons and human cortical neurons was protective from low oxygen and acute oxidative stress. The results of this study lead to a better understanding of molecular mechanisms taking place during low oxygen and oxidative stresses. Consequently, this knowledge may be used to identify potential therapeutic targets and treatments that may prevent detrimental neurological effects of an ischemic stroke in humans.

Climate change will expose sea turtle nests to higher temperatures and more
storms; both may negatively impact sea turtle nest success. In this study, unhatched eggs
were collected from the Boca Raton, Florida beach and developmental stage at
embryonic death determined. Elevated nest temperatures increased embryonic mortality,
and the most significant relationship was between mortality and the percent of time
embryos were exposed to temperatures above 34°C. Loggerhead turtles exhibited higher
rates of mortality compared to green turtles at temperatures above 34°C. Only loggerhead
nests were exposed to inundation, but embryonic mortality did not differ from noninundated
nests. Beach profiles across the nesting season were also determined. A major
storm altered the beach more in areas of coastal development; however, this was
impacted by a nourishment project and the presence of a structured inlet. Future management strategies may need to protect sea turtle nests from extended periods at
elevated temperatures.

Ischemic stroke is one of the leading causes of human death worldwide. It occurs due to
high susceptibility of neurons to anoxia and reoxygenation. Unlike mammals, invertebrate
Drosophila melanogaster withstands low oxygen levels without showing pathology. In the
present study, Drosophila Schneider (S2) cells were employed to investigate the role of the
cGMP-dependent Protein Kinase (PKG) signaling pathway in Drosophila anoxia-tolerance in
vitro. This was accomplished by subjecting cells to chemical anoxia and oxidative stress
concurrently with treatments by pharmacological agents affecting specific targets of the PKG
pathway and assessing cytotoxicity. In this study, activation of the PKG pathway protected S2
cells from the aforementioned stresses. The results of this study may lead to a better
understanding of fruit fly’s innate anoxia-tolerance strategies. Consequently, this knowledge may
be used to identify potential therapeutic targets to prevent detrimental neurological effects of an
ischemic stroke in humans.