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- All Subjects: Chytridiomycosis
- All Subjects: Social archaeology
- 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
Exchange is fundamental to human society, and anthropologists have long documented the large size and complexity of exchange systems in a range of societies. Recent work on the banking system of today's world suggests that complex exchange systems may become systemically fragile and in some types of complex exchange systems that involve feedbacks there exists a fundamental trade-off between robustness (stability) and systemic fragility. These properties may be observable in the archaeological record as well. In southern Arizona, the Hohokam system involved market-based exchange of large quantities of goods (including corn, pottery, stone, and shell) across southern Arizona and beyond, but after a few generations of expansion it collapsed rapidly around A.D. 1070. In this case, increasing the scale of a pre-existing system (i.e., expanding beyond the Hohokam region) may have reduced the efficacy of established robustness-fragility trade-offs, which, in turn, amplified the fragility of the system, increasing its risk of collapse. My research examines (1) the structural and organizational properties of a transregional system of shell exchange between the Hohokam region and California, and (2) the effect of the presence and loss of a very large freshwater lake (Lake Cahuilla) in southeastern California on the stability of the Hohokam system. I address these issues with analysis of ethnographic, ethnohistoric, and archaeological data, and with mathematical modeling. My study (1) produced a simple network model of a transregional system of interaction that links the Hohokam region and California during the centuries from A.D. 700 to 1100; (2) uses network and statistical analysis of the network model and archaeological data to strongly suggest that the transregional exchange system existed and was directional and structured; (3) uses network and other analysis to identify robustness-fragility properties of the transregional system and to show that trade between Lake Cahuilla fishers and the Hohokam system should be included in a mathematical model of this system; and (4) develops and analyzes a mathematical model of renewable resource use and trade that provides important insights into the robustness and systemic fragility of the Hohokam system (A.D. 900-1100).
ContributorsMerrill, Michael (Author) / Hegmon, Michelle (Thesis advisor) / Anderies, John M (Thesis advisor) / Brandt, Elizabeth, (Committee member) / Arizona State University (Publisher)
Created2014
Description
My dissertation contributes to a body of knowledge useful for understanding the evolution of subsistence economies based on agriculture from those based on hunting and gathering, as well as the development of formal rules and norms of territorial ownership in hunter-gatherer societies. My research specifically combines simple formal and conceptual models with the empirical analysis of large ethnographic and environmental data sets to study feedback processes in coupled forager-resource systems. I use the formal and conceptual models of forager-resource systems as tools that aid in the development of two alternative arguments that may explain the adoption of food production and formal territorial ownership among hunter-gatherers. I call these arguments the Uncertainty Reduction Hypothesis and the Social Opportunity Hypothesis. Based on the logic of these arguments, I develop expectations for patterns of food production and formal territorial ownership documented in the ethnographic record of hunter-gatherer societies and evaluate these expectations with large ethnographic and environmental data sets. My analysis suggests that the Uncertainty Reduction Hypothesis is more consistent with the data than the Social Opportunity Hypothesis. Overall, my approach combines the intellectual frameworks of evolutionary ecology and resilience thinking. The result is a theory of subsistence change that integrates elements of three classic models of economic development with deep intellectual roots in human ecology: The Malthusian, Boserupian and Weberian models. A final take home message of my study is that evolutionary ecology and resilience thinking are complementary frameworks for archaeologists who study the transition from hunting and gathering to farming.
ContributorsFreeman, Jacob (Author) / Anderies, John M (Thesis advisor) / Nelson, Margaret C. (Thesis advisor) / Barton, C Michael (Committee member) / Arizona State University (Publisher)
Created2014
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