http://hdl.handle.net/1957/17891 2013-06-20T05:26:37Z http://hdl.handle.net/1957/39420 Environmental influences on host-pathogen dynamics of the amphibian chytrid fungus Buck, Julia C. The causes of the global biodiversity crisis are varied and complex. Anthropogenic threats may act in isolation, or interact additively or synergistically with each other or with natural stressors to affect sensitive taxa. The recent emergence of many infectious diseases in wildlife has brought attention to the role of disease in population declines and species extinctions. Both abiotic and biotic components of the environment may mitigate or exacerbate effects of pathogens on their hosts through direct or indirect mechanisms. The effects of the environment on host-pathogen dynamics are complex, context-dependent, and in need of further examination. One particularly sensitive group, amphibians, is at the leading edge of the sixth mass extinction. The emerging infectious disease (EID) chytridiomycosis, caused by the fungal pathogen Batrachochytrium dendrobatis (Bd), is implicated in population declines and extinctions of amphibians globally. My disseration addresses questions pertaining to environmental influences on disease dynamics of Bd. As described in chapter 1, various abiotic and biotic components of the environment may affect host-pathogen dynamics of Bd, resulting in changes to the dynamics of Bd transmission and spread. Chapter 2 examines the influence of an abiotic factor, the insecticide (carbaryl) and three different assemblages of larval Pacific treefrogs (Pseudacris regilla) and Cascades frogs (Rana cascadae) on host-pathogen dynamics of Bd within a community context. I found separate effects of each treatment on amphibian growth and development, but no interactive effects among the treatments. However, Bd appeared to reduce phytoplankton abundance and increase periphyton biomass, an unexpected result that merited further investigation. One possible explanation for the results described in chapter 2 is that zooplankton might consume Bd zoospores, the infective stage of the pathogen, a hypothesis that I examine in chapter 3. I conducted laboratory experiments and confirmed the presence of Bd zoospores in the gut of Daphnia sp. through quantitative PCR and visual inspection. I discuss conservation implications of this finding. To determine whether predation on Bd zoospores by zooplankton could reduce infection in amphibians, I conducted a mesocosm experiment, which is described in chapter 4. I found complex effects on species interactions: competition between larval Cascades frogs and zooplankton for phytoplankton resources reduced phytoplankton concentration, zooplankton abundance, and survival of amphibians. These effects were diminished in the presence of Bd, suggesting that zooplankton may have at least partially substituted Bd zoospores for phytoplankton in their diet, thus stimulating competitive release. However, competitive effects between zooplankton and larval amphibians overshadowed indirect positive benefits of zooplankton predation on Bd zoospores. In chapter 4, competitive effects between zooplankton and larval amphibians for phytoplankton suggested that host-pathogen dynamics might be affected by the host’s supply of resources. Chapter 5 describes a mesocosm experiment that examined how eutrophication might affect Bd-infected Pacific treefrogs and other members of the aquatic community. Nutrient additions caused increased algal growth, which benefitted herbivorous larval amphibians. Larvae exposed to Bd altered their growth, development, and diet, and allocated resources differently than unexposed individuals. However, nutrient supplementation did not alter the response of larval amphibians to Bd. As described in chapter 6, consideration of hosts and pathogens as functional members of the ecological communities in which they exist can lead to important insights in host-pathogen dynamics. My PhD research may contribute to control measures for the emerging infectious disease chytridiomycosis. Graduation date: 2013; Access restricted to the OSU Community at author's request from June 17, 2013 - June 17, 2015 2013-05-17T00:00:00Z http://hdl.handle.net/1957/37548 Response to Hypoxia in the staghorn sculpin, (Leptocottus armatus) Wagner, Sara Anne Long-term subae lal survival has been anecdotally noted in the staghorn sculpin, Leptocottus armatus. In this study, I quantified this phenomenon physiologically by examining the following parameters: standard metabolic rate and indications of reduced standard metabolic rate during subaerial exposure; capacity for and mechanism(s) of oxygen consumption in air; capacity for anaerobic production of lactate and/or ethanol; and blood pH. The staghorn sculpin appears well-suited for the subaerial exposure it experiences in nature. Mean subaerial survival time was 6 hours which would enable fish to survive intertidal stranding. Staghorns breathe air through well-supported gills and supplement depressed rates of subaerial aerobiosis by anaerobic production of lactic acid. Most remarkably, the staghorn sculpin may also substantially reduce minimal energy expenditure requirements during periods of hypoxia by reducing resting metabolic rate. Graduation date: 1991 1990-11-02T00:00:00Z http://hdl.handle.net/1957/37344 The role of gonadotropin-releasing hormone in the regulation of courtship behavior in the male red-sided garter snake, Thamnophis sirtalis parietalis Smith, Mitchell Todd Graduation date: 1994 1994-04-14T00:00:00Z http://hdl.handle.net/1957/37322 The symbiotic relationships and morphology of Paravortex sp. nov. (Turbellaria, Rhabdocoelida) a parasite of Macoma nasuta Conrad, 1837 Hanson, Alfred Warren Rhabdocoels of the genus Paravortex are parasites of marine molluscs. The bent-nosed clams, Macoma nasuta(Conrad, 1837) of Yaquina Bay, Lincoln County, Oregon are commonly infected with a new species of Paravortex. The morphology of the adult worm has been described and it has been compared to the other three species of this genus. The percent infection increased as the size of the clams increased. Analysis of the size frequency distribution of the clam population suggests at least two age classes. Incidence of infection was substantially lower in the younger of these two classes. Clams less than 14 mm in length were not infected. Possible reasons for this distribution of the parasite population were discussed. A peak in the percent of infection, in the incidence of multiple infection, and in the abundance of immature worms was found during April, May, and June, 1968. These data suggest a seasonal periodicity in the reproduction of Paravortex sp. nov. A correlation between the sex of the bent-nosed clams and the incidence and degree of infection could not be established. Paravortex sp. nov. was found only in the pericardial cavity of Macoma nasuta. It is postulated that the rhabdocoel enters this cavity from the suprabranchial space by passing through the kidney. Possible methods by which this endoparasitic rhabdocoel obtains food were discussed. Physical damage to the host clam could not be shown to be the result of parasitic infections. Multiple infections of as many as 28 worms did not appear to physically impair the clam. Observations of the morphology and behavior of living worms were made and conclusions were reached concerning the nature of the symbiotic relationship between Paravortex sp. nov. and its host. Examination of collections of Macoma nasuta made in Coos Bay, Oregon, and Puget Sound, Washington,produced no rhabdocoels. Graduation date: 1970 1969-12-11T00:00:00Z