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- All Subjects: Chytridiomycosis
- All Subjects: Water resources management
- Creators: Anderies, John M
Description
Epidemiological theory normally does not predict host extinction from infectious disease because of a host density threshold below which pathogens cannot persist. However, host extinction can occur when a biotic or abiotic pathogen reservoir allows for density-independent transmission. Amphibians are facing global population decline and extinction from the emerging infectious disease chytridiomycosis, caused by the fungus Batrachochytrium dentrobatidis (Bd). I use the model species Eleutherodactylus coqui to assess the impact of Bd on terrestrial direct-developing frog species, a common life history in the tropics. I tested the importance of two key factors that might influence this impact and then used laboratory experiments and published field data to model population-level impacts of Bd on E. coqui. First, I assessed the ontogenetic susceptibility of E. coqui by exposing juvenile and adult frogs to the same pathogen strain and dose. Juveniles exposed to Bd had significantly lower survival rates compared with control juveniles, while adult frogs often cleared infection. Second, I conducted experiments to determine whether E. coqui can become infected with Bd indirectly from contact with zoospores shed onto vegetation by an infected frog and from direct exposure to an infected frog. Both types of transmission were observed, making this the first demonstration that amphibians can become infected indirectly in non-aquatic habitats. Third, I tested the hypothesis that artificially-maintained cultures of Bd attenuate in pathogenicity, an effect known for other fungal pathogens. Comparing two cultures of the same Bd strain with different passage histories revealed reduced zoospore production and disease-induced mortality rates for a susceptible frog species (Atelopus zeteki) but not for the less-susceptible E. coqui. Finally, I used a mathematical model to project the population-level impacts of chytridiomycosis on E. coqui. Model analysis showed that indirect transmission, combined with either a high rate of zoospore production or low rate of zoospore mortality, is required for Bd to drive E. coqui populations below an extinction threshold. High rates of transmission plus frequent re-infection could lead to poor recruitment of infected juveniles and population decline. My research adds further insight into how emerging infectious disease is contributing to the loss of amphibian biodiversity.
ContributorsLanghammer, Penny F. (Author) / Collins, James P. (Thesis advisor) / Brooks, Thomas M (Committee member) / Burrowes, Patricia A. (Committee member) / Anderies, John M (Committee member) / Escalante, Ananias A (Committee member) / Smith, Andrew T. (Committee member) / Arizona State University (Publisher)
Created2013
Description
Batrachochytrium dendrobatidis (Bd), the amphibian chytrid fungus causing chytridiomycosis, is the cause of massive amphibian die-offs. As with any host-pathogen relationship, it is paramount to understand the growth and reproduction of the pathogen that causes an infectious disease outbreak. The life-cycle of the pathogen, Bd, is strongly influenced by temperature; however, previous research has focused on Bd isolated from limited geographic ranges, and may not be representative of Bd on a global scale. My research examines the relationship between Bd and temperature on the global level to determine the actual thermal maximum of Bd. Six isolates of Bd, from three continents, were incubated at a temperature within the thermal range (21°C) and a temperature higher than the optimal thermal range (27°C). Temperature affected the growth and zoosporangium size of all six isolates of Bd. All six isolates had proliferative growth at 21°C, but at 27°C the amount and quality of growth varied per isolate. My results demonstrate that each Bd isolate has a different response to temperature, and the thermal maximum for growth varies with each isolate. Further understanding of the difference in isolate response to temperature can lead to a better understanding of Bd pathogen dynamics, as well as allow us the ability to identify susceptible hosts and environments before an outbreak.
ContributorsWoodland, Laura Elizabeth (Author) / Collins, James (Thesis director) / Davidson, Elizabeth (Committee member) / Roberson, Robert (Committee member) / School of Politics and Global Studies (Contributor) / School of Molecular Sciences (Contributor) / Barrett, The Honors College (Contributor)
Created2016-12
Description
In many social-ecological systems, shared resources play a critical role in supporting the livelihoods of rural populations. Physical infrastructure enables resource access and reduces the variability of resource supply. In order for the infrastructure to remain functional, institutions must incentivize individuals to engage in provision and maintenance. The objective of my dissertation is to understand key formal and informal institutions that affect provision of shared infrastructure and the policy tools that may improve infrastructure provision. I examine these questions in the context of irrigation systems in India because infrastructure maintenance is a persistent challenge and system function is critical for global food production.
My first study investigates how the presence of private infrastructure, such as groundwater pumps, affects the provision of shared infrastructure, such as shared tanks or surface reservoirs. I examine whether formal institutions, such as water pricing instruments, may prevent under-provision of the shared tanks. My findings suggest that in the absence of rules that coordinate tank maintenance, the presence of private pumps will have a detrimental effect on system productivity and equality. On the other hand, the combination of a fixed groundwater fee and a location-based maintenance fee for tank users can improve system productivity and equality.
The second study examines the effect of power asymmetries between farmers, caused by informal institutions such as caste, on the persistence of political institutions that govern infrastructure provision. I examined the effect of policy tools, such as non-farm wage employment and informational interventions, on the persistence of two types of political institutions: self-governed and nested. Results suggest that critical regime shifts in political institutions can be generated by either intervening in formal institutions, such as non-farm wage employment, or informal institutions, such as knowledge transmission or learning mechanisms.
The third study investigates how bureaucratic and political corruption affect public good provision. I examine how institutional and environmental factors affect the likelihood of corruption and infrastructure provision. I demonstrate that cracking down on corruption is only beneficial when infrastructure provision is poor. I also show that bureaucratic wages play an important role in curbing extralegal transactions and improving infrastructure provision.
My first study investigates how the presence of private infrastructure, such as groundwater pumps, affects the provision of shared infrastructure, such as shared tanks or surface reservoirs. I examine whether formal institutions, such as water pricing instruments, may prevent under-provision of the shared tanks. My findings suggest that in the absence of rules that coordinate tank maintenance, the presence of private pumps will have a detrimental effect on system productivity and equality. On the other hand, the combination of a fixed groundwater fee and a location-based maintenance fee for tank users can improve system productivity and equality.
The second study examines the effect of power asymmetries between farmers, caused by informal institutions such as caste, on the persistence of political institutions that govern infrastructure provision. I examined the effect of policy tools, such as non-farm wage employment and informational interventions, on the persistence of two types of political institutions: self-governed and nested. Results suggest that critical regime shifts in political institutions can be generated by either intervening in formal institutions, such as non-farm wage employment, or informal institutions, such as knowledge transmission or learning mechanisms.
The third study investigates how bureaucratic and political corruption affect public good provision. I examine how institutional and environmental factors affect the likelihood of corruption and infrastructure provision. I demonstrate that cracking down on corruption is only beneficial when infrastructure provision is poor. I also show that bureaucratic wages play an important role in curbing extralegal transactions and improving infrastructure provision.
ContributorsVallury, Sechindra (Author) / Abbott, Joshua K (Thesis advisor) / Anderies, John M (Thesis advisor) / Leonard, Bryan (Committee member) / Arizona State University (Publisher)
Created2019
Description
My research is motivated by a rule of thumb that no matter how well a system is designed, some actors fail to fulfill the behavior which is needed to sustain the system. Examples of misbehavior are shirking, rule infraction, and free riding. With a focus on social-ecological systems, this thesis explored the effectiveness of social feedback mechanisms driven by the two available individual options: the exit option is defined as any response to escape from an objectionable state of affairs; and the voice option as any attempt to stay put and improve the state. Using a stylized dynamic model, the first study investigates how the coexistence of participatory and groundwater market institutions affects government-managed irrigation systems. My findings suggest that patterns of bureaucratic reactions to exit (using private tubewells) and voice (putting pressure on irrigation bureaus) are critical to shaping system dynamics. I also found that the silence option – neither exit nor voice – can impede a further improvement in public infrastructure, but in some cases, can improve public infrastructure dramatically. Using a qualitative comparative analysis of 30 self-governing fishing groups in South Korea, the second study examines how resource mobility, group size, and Ostrom’s Design Principles for rule enforcement can co-determine the effectiveness of the voice option in self-controlling rule infractions. Results suggest that the informal mechanism for conflict resolution is a necessary condition for successful self-governance of local fisheries and that even if rules for monitoring and graduated sanctions are not in use, groups can be successful when they harvest only stationary resources. Using an agent-based model of public good provision, the third study explores under what socioeconomic conditions the exit option – neither producing nor consuming collective benefits – can work effectively to enhance levels of cooperation. The model results suggest that the exit option contributes to the spread of cooperators in mid- and large-size groups at the moderate level of exit payoff, given that group interaction occurs to increase the number of cooperators.
ContributorsShin, Hoon Cheol (Author) / Anderies, John M (Thesis advisor) / Abbott, Joshua K (Committee member) / Janssen, Marcus A (Committee member) / Arizona State University (Publisher)
Created2020