Society requires better insights into how disturbances will alter the global carbon cycle. Ecosystem models help us understand the carbon cycle and make predictions about how the terrestrial land sink will change under future climate regimes. Disturbances drive ecosystem cycling, but modeling disturbances has unique challenges, particularly in incorporating heterogeneity and parameter uncertainty. In this dissertation, I explore two questions. 1) How can we capture disturbance ecology in models?, which I explore in my first and second chapters, and 2) How can we use those models to make projections for the Southeastern US?, which I explore in my third and fourth chapters. Both my first and second chapters point to the practical trade-offs in model structure and realism. In my first chapter, I found that representing spatially implicit contagious disturbances in terms of shape and frequency accurately captured structural changes over time and separated the disturbance regimes of different regions. Representing spatially implicit disturbances in terms of shape and frequency sacrificed the specificity of a space-based approach but may be more computationally efficient. In my second chapter, I developed a framework for calibrating models based on an iterative cycle between uncertainty analysis and literature synthesis, targeted field campaigns, and statistical constraint. I found that targeted field work and statistical constraint reduced parameter uncertainty until structural uncertainty began to dominate. Models that capture disturbance dynamics can help us anticipate effects of global change factors like climate change and invasive species. In my third chapter, I found that elevated temperatures reduce cogongrass biomass, and that cogongrass facilitates pine dominance over oaks in a mixed pine-oak stand. This suggests that cogongrass mediates inter-species competition at an ecosystem scale. Prescribed burns are a management technique used to suppress cogongrass and has an add-on benefit of reducing tick populations. However, climate change may threaten how frequently prescribed fires can be safely deployed. In my fourth chapter, I found that tick populations are most sensitive to leaf litter and humidity, which allows for management strategies as an alternative to prescribed burns.

Viruses in the Flavivirus genus (e.g., Zika, yellow fever, dengue, West Nile, and Japanese encephalitis viruses) are arthropod-borne, globally distributed, and can cause a range of neurological or hemorrhagic diseases. The ongoing epidemics of flaviviral disease consistently demonstrate the need for new vaccines capable of outbreak control. However, safe, effective, and easy-to-produce vaccines remain relatively elusive due to limitations of conventional vaccine development that make it difficult to balance safety and efficacy. Insect-specific flaviviruses (ISFVs) are emerging as a novel method to overcome this challenge. Herein, we develop a new flavivirus vaccine platform based on the novel insect-specific flavivirus called Aripo virus, which we used to create a preclinical Zika virus (ZIKV) vaccine named Aripo/Zika virus (ARPV/ZIKV). ARPV/ZIKV is a live recombinant virus consisting of the ZIKV pre-membrane and envelope protein genes expressed on an Aripo virus backbone. In this work, we quantify the safety and efficacy of ARPV/ZIKV in multiple murine models, and begin to elucidate the mechanisms of humoral and cell-mediated immune induction for this new platform. Overall, the vaccine showed no evidence of pathogenicity in immunocompromised or suckling mice, and demonstrated a complete inability to replicate in various vertebrate cell lines. Despite this lack of replication, a single dose of live, unadjuvanted ARPV/ZIKV completely prevented ZIKV disease in mice and prevented in utero ZIKV transmission in gravid mice. Direct protection post-ZIKV challenge appears to be primarily mediated by neutralizing antibodies based on passive transfer, adoptive transfer, and T-cell depletion studies. However, vaccination studies in Rag1 KO, Tcra KO, and muMt- mice demonstrate the critical role of T-cell responses in developing immunity post-vaccination. In summary, ARPV/ZIKV is a promising vaccine candidate that induces robust adaptive immune responses, and this success is a positive indication of ARPV's potential as a new resource for flavivirus vaccine development. This body of work contributes to the rapidly expanding field of insect-specific virus-based vaccines and generates new insights into their optimization. Ultimately, this work may help protect the health of millions of people worldwide that are currently at risk of flavivirus infection. / MPH / Arthropod-borne viruses (especially flaviviruses such as Zika virus (ZIKV), yellow fever virus, West Nile virus) represent a major global health threat and a significant burden on human life. Vaccination is a critical tool for controlling the often unpredictable outbreaks of flavivirus diseases. However, licensed flavivirus vaccines remain relatively elusive. This is, in part, because the same characteristics of traditional live-attenuated vaccines that make them highly effective can also reduce their safety. Insect-specific flaviviruses (ISFVs) are emerging as a novel method to overcome this challenge. ISFVs only replicate in insects and thus are safe in humans. They do not cause disease in vertebrates, eliminating the need for the chemical or physical inactivation methods required by traditional whole inactivated vaccines and which can result in reduced efficacy. Herein, we develop a new flavivirus vaccine platform based on a novel ISFV called Aripo virus (ARPV). As proof of concept, we used ARPV to create a preclinical ZIKV vaccine named Aripo/Zika virus (ARPV/ZIKV). ARPV/ZIKV expresses immune system-stimulating ZIKV structural proteins on its virus particle. However, it remains highly safe because the genetic material from ARPV makes it incompatible for replication in human cells. Here, we demonstrate the safety and protective ability of ARPV/ZIKV, and begin to elucidate its mechanisms of protection. Overall, ARPV/ZIKV shows promise as a ZIKV vaccine candidate, which supports the potential of ARPV as a platform for new flavivirus vaccines and the potential to protect the health of the millions of people currently at risk of flavivirus infection.

The intent of this thesis is to develop ordinary differential equation models to better understand the mosquito population. We first develop a framework model, where we determine the condition under which a natural mosquito population can persist in the environment. Wolbachia is a bacterium which limits the replication of viruses inside the mosquito which it infects. As a result, infecting a mosquito population with Wolbachia can decrease the transmission of viral mosquito-borne diseases, such as dengue. We develop another ODE model to investigate the invasion of Wolbachia in a mosquito population. In a biologically feasible situation, we determine three coexisting equilibria: a stable Wolbachia-free equilibrium, an unstable coexistence equilibrium, and a complete invasion equilibrium. We establish the conditions under which a population of Wolbachia infected mosquitoes may persist in the environment via the next generation number and determine when a natural mosquito population may experience a complete invasion of Wolbachia.

Aedes aegypti mosquitoes, vectors for many human diseases, begin life as larvae developing in water, potentially exposed to runoff with herbicides and pesticides. This study serves as a novel investigation into the transstadial effects of exposure to Roundup on A. aegypti life history, immunity, and stress response and aims to account for these effects in an R0 model for vectorborne disease transmission. Prior work has shown that Roundup negatively affects mosquito life history. I hypothesized that larval exposure to the maximum sublethal dose of Roundup (7189µg/L) would negatively impact A. aegypti life history, immunity (candidate gene approach), and stress response (heat shock protein expression and fluctuating asymmetry). No significant differences were found for survival from the larval to adult stages, body size, size or shape fluctuating asymmetry, or sex ratio. However, the Roundup treatment group developed significantly slower for both time to pupation and to adult eclosion (both p < 0.0001). Adult immune gene expression showed no difference between groups, but the larval immune genes Dome (JAK-STAT pathway) and Spatzle (TOLL pathway) were downregulated in the Roundup treatment (p=0.0383 and p=0.0035, respectively), suggesting the larvae have reduced immunity. This study suggests that Roundup may have off-target effects on A. aegypti mosquitoes that are unaccounted for by current models, and these effects may potentially alter disease transmission to human hosts.

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京都大学 / 新制・課程博士 / 博士(農学) / 甲第23949号 / 農博第2498号 / 新制||農||1091(附属図書館) / 学位論文||R4||N5384(農学部図書室) / 京都大学大学院農学研究科森林科学専攻 / (主査)教授 北島 薫, 教授 神﨑 護, 教授 北山 兼弘 / 学位規則第4条第1項該当 / Doctor of Agricultural Science / Kyoto University / DGAM

Tick-borne diseases represent major public and animal health issues worldwide. Ixodes ricinus, primarily associated with deciduous and mixed forests, is the principal vector of causative agents of viral, bacterial, and protozoan zoonotic diseases in Europe. Recently, abundant tick populations have been observed in European urban green areas, which are of public health relevance due to the exposure of humans and domesticated animals to potentially infected ticks. In urban habitats, small and medium-sized mammals, birds, companion animals (dogs and cats), and larger mammals (roe deer and wild boar) play a role in maintenance of tick populations and as reservoirs of tick-borne pathogens. Presence of ticks infected with tick-borne encephalitis virus and high prevalence of ticks infected with Borrelia burgdorferi s.l., causing Lyme borreliosis, have been reported from urbanized areas in Europe. Emerging pathogens, including bacteria of the order Rickettsiales (Anaplasma phagocytophilum, “Candidatus Neoehrlichia mikurensis,” Rickettsia helvetica, and R. monacensis), Borrelia miyamotoi, and protozoans (Babesia divergens, B. venatorum, and B. microti) have also been detected in urban tick populations. Understanding the ecology of ticks and their associations with hosts in a European urbanized environment is crucial to quantify parameters necessary for risk pre-assessment and identification of public health strategies for control and prevention of tick-borne diseases.

The recent discovery of Amblyomma maculatum sensu lato (s. l.) ticks in southern Arizona has renewed discussions around species designations for members of the Amblyomma maculatum tick group. Amblyomma maculatum s. l. from Arizona appear to be morphologically intermediate between A. maculatum sensu stricto (s. s.) and A. triste s. s. At present there is no conclusive species designation for the ticks from Arizona. My research focused on analyzing the systematics of both A. maculatum s. l. and Rickettsia parkeri, a common bacterial pathogen transmitted by these ticks. In the laboratory, A. maculatum s. l. from Arizona and A. maculatum s. s. from Georgia readily mated on experimental animals to produce F1 hybrid ticks; there was no difference in fertility with these two populations when compared with homologous populations. However, the F1 hybrids produced during these experiments exhibited diminished fitness and did not produce a viable F2 generation. These results suggest that A. maculatum s. l. and A. maculatum s. s. represent separate biological species. Results of the crossbreeding experiment conflict with recent genetic analyses of A. maculatum s. l. and A. maculatum s. s. suggesting they are a single species. Thus, I developed and optimized 14 microsatellite loci that amplify both A. maculatum s. s. and A. maculatum s. l. These novel microsatellite markers can be used in future analyses of A. maculatum s. l. and A. maculatum s. s. to further test for conspecificity between the two. I also investigated the genetic relationships within geographically distinct R. parkeri strains through development and implementation of a multi-locus sequence typing analysis. I showed that while there is no consistent genetic delineation of strains isolated from A. maculatum s. l. versus A. maculatum s. s., there is a subset of R. parkeri strains from A. maculatum s. l. that appear to represent an intermediate genotype between the North and South American strains. While the biological causes for these results are not immediately clear, coevolution of R. parkeri and A. maculatum s. l. may account for the detection of the intermediate genotype only found in association with A. maculatum s. l.