Download or read book Environmental Influences on Host pathogen Dynamics of the Amphibian Chytrid Fungus written by Julia C. Buck and published by . This book was released on 2013 with total page 173 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.

Download or read book The Effects of Host and Pathogen Variation on Infection Dynamics in the Amphibian chytrid System written by Trang D. Dang and published by . This book was released on 2017 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: This dissertation uses manipulative experiments to explore amphibian-Bd infection dynamics. Although there has been almost two decades research since the discovery of Bd, many questions still remain regarding what conditions mediate chytridiomycosis virulence. My research shows how certain host and pathogen factors can influence disease virulence. Identifying how host and pathogen factors mediate disease virulence is important in order to understand, predict, and mitigate this infectious amphibian disease. Worldwide biodiversity loss is occurring at unprecedented rates. Numerous factors are contributing to this loss, including infectious disease. Among vertebrate groups, amphibians are experiencing the highest rate of population declines and extinctions and are vulnerable to numerous infectious pathogens that appear to be contributing to amphibian biodiversity loss. A widespread infectious chytrid fungus, Batrachochytrium dendrobatidis (Bd), causing the disease, chytridiomycosis, is implicated in numerous amphibian population declines and extinctions and can induce sublethal effects within individuals. My dissertation research examines host-pathogen factors that mediate infection outcomes in the amphibian-Bd system. The severity of an infectious disease is the result of specific host-pathogen interactions. Thus, there may be large variation in disease outcome depending on host and pathogen related factors. In Chapter 2, I conducted a comparative experimental study in larval amphibians using multiple host species and Bd strains. I showed that host species varied in Bd susceptibility but that susceptibility was also contingent on Bd strain type. Thus, I showed chytridiomycosis virulence depended upon host and pathogen traits and that a sensitive host species could be robust to certain pathogen strains. In Chapter 3, I experimentally investigated multiple pathogen interactions with amphibian three amphibian host species to examine how Bd infection dynamics might change under simultaneous coinfection with a common water mold, Saprolegnia ferax (Sf). Coinfecting pathogens might interact within a host in a synergistic and antagonistic manner. In two host species, Bd infection intensity was slightly higher in hosts that were exposed to both Bd and Sf compared to just Bd alone indicating a small synergistic interaction with Sf. However, the differences were not significant in either host species. Survival differences were only detected in one host species; hosts exposed to Bd only experienced lower survival than those in the coinfected group. Additionally, I found host weight and days survived were predictive of Bd infection level for some hosts species showing species variation in infection response. Lastly, in Chapter 4, I experimentally examined age-dependent differences in Bd infection heterogeneity in two host species. I followed this with another experiment to test whether age-dependent differences in infection intensity of these hosts (‘donors’) influenced subsequent Bd transmission to a naïve conspecific host (‘recipients’). I found Bd infection intensity differences among juvenile and adult donors of both species. However, trend directions were not consistent; in one host species, adults had significantly higher infection levels than juveniles while the opposite was true in the second host species. Regardless of donor infection intensity, recipients had comparable infection levels within each host species. Survival also differed among host species and age groups suggesting Bd susceptibility may change with age and is species specific.

Download or read book Host pathogen Ecology written by Brooke L. Talley and published by . This book was released on 2014 with total page 234 pages. Available in PDF, EPUB and Kindle. Book excerpt: The worldwide decline of amphibians is due to several interacting factors that vary in their involvement and severity according to species, geography, environment, and individual response (Wake and Vredenburg 2008; Gahl et al. 2011). One of those threats has caused population declines globally (Stuart et al. 2004), Batrachochytrium dendrobatidis (Bd ), which is the fungal pathogen that causes chytridiomycosis in amphibians (Berger et al. 1998; Longcore et al. 1999). Bd 's effects are not completely known since some areas of the world have been studied (e.g., Panama, Lips et al. 2006; United States Sierra Nevada, Briggs et al. 2010; Australia, Phillott et al. 2013) while other areas have received little or no attention, often because these systems appear stable or because the effect of threats are not known. In the Midwestern United States, widespread anuran population declines occurred historically and are in some cases ongoing (e.g., Vogt 1981, Oldfield and Moriarty 1995, Brodman and Kilmurry 1998, Casper 1998, Hay 1998, Moriarty 1998, Mossman et al. 1998, Varhegyi et al. 1998, Steiner and Lehtinen 2008, Zippel and Tabaka 2008). Large-scale habitat alterations, chemical contaminations, and other threats have likely caused some Midwestern U.S. amphibian declines (Lannoo, 1998), but the role of Bd in historic and current population declines has been limited to small population surveys or incidental discovery of Bd (e.g., Pessier et al. 1999; Beasley et al. 2005; Steiner and Lehtinen 2008). I investigated the current and historic Bd infection levels among amphibians in Illinois and identified species risk factors associated with likelihood of chytridiomycosis-related death. My research questions focused on which biotic and abiotic factors explained Bd prevalence and intensities among current populations, which species risk factors would make them more likely to suffer severe Bd infection, and what the historic Bd status was in Illinois. Working with Illinois amphibians presented the opportunity to answer these research questions because Bd was already known to occur in Illinois (Pessier et al. 1999), there were a variety of anecdotal examples of historic population declines in Illinois (Beasley et al. 2005; Lannoo 1998), and extensive museum holdings were available to document the spatial and temporal pattern of Bd among Illinois populations. In the chytridiomycosis-amphibian disease system, mortality is driven by intensity of infection. Intensity is affected by many factors, including environmental temperatures, amphibian community composition, and fungal traits. However, the relative importance of biotic and abiotic factors on Bd prevalence and intensity in multispecies, natural communities is unknown for any wild populations. I found that Bd was geographically and taxonomically widespread in Illinois, which suggested an established infection status, perhaps longer than the first report from the 1990s (Pessier et al. 1999). Also, this suggests that population declines from chytridiomycosis might have occurred historically. I used museum holdings to determine spatial and temporal distributions of Bd in Illinois amphibians. I tested 1,008 museum specimens from the vertebrate collections at Southern Illinois University, Illinois Natural History Survey, and the University of Illinois Museum of Natural History to determine the oldest date of anuran Bd infection in Illinois. I detected 110 Bd positive specimens (10.7%, CI: 9.0-12.8%) in four species collected during the 1890s-1980s. The earliest Bd record was from a Lithobates sphenocephalus collected in southern Illinois in 1900. I determined that Illinois amphibians have been living endemically with Bd for at least 113 years, extending the date of the oldest U.S. record of Bd infection by 61 years. The long-term presence of Bd , coupled with multiple anecdotal reports of population declines, suggest that Bd may have been involved in historic population declines in Illinois amphibians. I found widespread taxonomic and geographic distribution of Bd among current and historic populations of Illinois amphibians. I found a surprisingly long history of Bd in Illinois that transforms the way we consider impacts on historic species and potential co-evolution of disease in Midwestern U.S. amphibians. My finding is as old as the oldest records from Brazil, Africa, and Asia (Weldon et al. 2004; Goka et al. 2009; Schloegel et al. 2010, 2012), suggesting a more ancient history of Bd and amphibians. (Abstract shortened by UMI.)

Download or read book Host pathogen Dynamics in a Changing Environment written by Catherine L. Searle and published by . This book was released on 2011 with total page 129 pages. Available in PDF, EPUB and Kindle. Book excerpt: Infectious diseases are a growing concern for both humans and wildlife. The negative effects of infectious disease have been exemplified by the recent global amphibian population declines associated with disease outbreaks. Although multiple pathogens and factors play a role in these declines, the aquatic fungal pathogen, Batrachochytrium dendrobatidis (Bd), has received considerable attention due to its substantial contribution to amphibian population declines around the world. Bd prevalence and severity appears to be increasing worldwide, either from recent anthropogenic spread of the pathogen or from changes in the environment that have altered host-pathogen dynamics. This dissertation explores the factors that affect host susceptibility to Bd. I first tested the effects of hormonal stress on susceptibility to Bd (Chapter 2). Using corticosterone, the major chronic stress hormone in amphibians, I was able to mimic the physiological effects of stress without altering other factors that may affect the host-pathogen relationship. I exposed three species of larval amphibians to corticosterone for two weeks to induce chronic stress before challenging them with exposure to Bd. I found that exposure to corticosterone did not alter infection prevalence or severity in any species, indicating that chronically elevated levels of corticosterone do not affect susceptibility to Bd. I next examined the interactive effects of the ubiquitous stressor, ultraviolet-B radiation (UVB), and host infection by Bd (Chapter 3). UVB can cause lethal and sublethal effects in amphibians, including increased susceptibility to pathogens. In outdoor mesocosms, I used ambient levels of UVB to stress larval amphibians while simultaneously exposing them to Bd. Although exposure to UVB increased mortality, it did not alter infection. To investigate the effects of community structure on infection prevalence and severity, I studied how six anuran species (frogs and toads) differed in susceptibility to Bd (Chapter 4). I experimentally exposed post-metamorphic amphibians native to North America to Bd under identical laboratory conditions. All species tested had higher rates of mortality when exposed to Bd compared to unexposed controls. However, the species differed widely in their rates of Bd-associated mortality, even though there was no difference in infection levels among species. I also found that within species, the relationship between body size and infection varied, indicating physiological differences in the way that amphibian species respond to pathogen infection. Finally, I studied the effects of the amphibian host community on infection. I experimentally exposed larval amphibians to Bd after manipulating host density and species richness in the laboratory (Chapter 5). I recorded five measures of disease risk and found a dilution effect where greater species richness decreased disease risk, even after taking into account changes in density. Together with Chapter 4, this study emphasizes the need to understand the effects of the community on host-pathogen dynamics. This dissertation provides insight into the effects of stress and community structure on disease dynamics. Although there has been a great effort to understand Bd since it was discovered, the ecology of Bd remains relatively unknown. My research represents an important step in understanding the host-pathogen relationship in a changing environment.

Download or read book Emerging Infectious Disease in Lentic Environments written by Tara Chestnut and published by . This book was released on 2015 with total page 167 pages. Available in PDF, EPUB and Kindle. Book excerpt: Biodiversity losses in terrestrial, freshwater, and marine systems are accelerating at a global scale and the most threatened vertebrate taxa are those associated with freshwater habitats. The causes of biodiversity losses are often complex and include synergistic effects of natural and human-induced stressors, such as habitat loss and fragmentation, urbanization, invasive species, contaminants, global climate change, and emerging infectious diseases. In the last 35 years, the amphibian extinction rate has been estimated to exceed 105 times the baseline expected rate for all species and in the USA, the number of occupied amphibian sites has been reported to be declining by 3.7% per year. Among the many threats to amphibians, the role of disease in population declines has been recognized increasingly over the last two decades. Numerous amphibian diseases have been identified and attributed to mass mortality events. Chytridiomycosis, the emerging infectious disease caused by the amphibian chytrid fungus, Batrachochytrium dendrobatidis (Bd), is implicated as a causal agent in many recent global amphibian population declines and extinctions. To understand the pathology and conservation implications of Bd, a greater understanding of its ecology, life history, and distribution in the wild is of paramount importance. Although it has an impact on the persistence of selected amphibian populations around the world, the full scope of the effects of chytridiomycosis on global amphibian population declines are not well understood. Most Bd research efforts have focused on Bd in amphibian hosts per se, with little attention to understand the environmental associations and dynamics of free-living Bd outside of the amphibian host. In particular, information on Bd responses to climatic variation outside of hosts is a research gap. Furthermore, as a microorganism within an aquatic environment, studies are lacking of potential water quality associations, how Bd may interact with other members of their biological communities, and how Bd responses to chemical contaminants found in aquatic environments. My research begins to fill these gaps by studying the basic ecology of free-living Bd in field settings, and investigating factors that may influence its distribution at a landscape scale, occurrence at a regional scale, and detection at a site scale. Herein, I describe spatial and temporal patterns in the detection and density of free-living Bd in aquatic habitats in two different geographic regions of the United States, Alaska (Chapter 2) and Oregon (Chapter 3). The Alaska work examines Bd ecology at the northernmost extent of amphibian occurrence in North America, where climate associations may be particularly relevant and where Bd occurrence may be representative of one of the most novel pathogen-host systems in the world. I also describe (Chapter 2) experimental results of Bd and amphibian response to extreme cold temperatures they may experience in continental settings, at high elevations, and at high latitudes. My Oregon studies (Chapter 3) focus on multivariate associations of free-living Bd occurrences with a suite of aquatic environmental factors, both abiotic and biotic in nature. In Chapter 4, I describe how amphibians and Bd respond to agricultural chemicals (fungicides) that they may be exposed to in field settings. These results are specific to Bd, but might also warrant consideration as fungicidal treatments for a newly described chytrid affecting salamanders; both of these amphibian chytrids have been detected in captive animals and solutions to treat trade animals for the pathogen are gaining relevancy. Finally, in Chapter 5, I reflect upon the journey of conservation biologists and herpetologists for 25 years of amphibian decline research, with global losses becoming widely recognized in 1989. In this context, my research significantly advances understanding of the geographic distribution and ecology of one potential threat factor to amphibian populations on Earth, Batrachochytrium dendrobatidis. The factors that I report to both promote or limit free-living Bd distribution and abundance will further inform pathogen dynamics research.

Download or read book Ecology of Amphibian Microbial Symbioses written by Eria A. Rebollar and published by Frontiers Media SA. This book was released on 2019-08-02 with total page 275 pages. Available in PDF, EPUB and Kindle. Book excerpt: The field of amphibian microbial ecology has greatly advanced in recent years. The work published to date has shown that amphibian skin bacterial communities can be influenced by host species, host life-history stage, environmental conditions, surrounding bacterial communities that serve as reservoirs and external biotic agents such as pathogens. As the ecology of amphibian-microbial symbiosis is a relatively new field, there are still many unanswered questions. The aim of this Research Topic is to highlight recent research on amphibian microbiomes that addresses relevant questions on the ecology of amphibian-microbe interactions. The publications gathered in this Research Topic have expanded our knowledge on the role of microbial symbionts of amphibians and have revealed novel insights that can direct the next set of research questions. We suggest that soon the field will move from the basic (and necessary) descriptions of microbial communities to more experimental approaches that include the use of omics methods and a variety of novel analytic and multivariate approaches. In addition to providing more insights into the microbial and disease ecology of amphibians, these studies may lead to effective ways to manipulate the microbiome to achieve protection from diseases, such as chytridiomycosis.

Download or read book Effects of Biotic and Abiotic Setting on a Host pathogen Relationship written by and published by . This book was released on 2015 with total page 176 pages. Available in PDF, EPUB and Kindle. Book excerpt: The most important factors predicting tadpole body condition varied markedly by species. Tadpole body condition was positively correlated with Bd infection and predator diversity for the introduced Lithobates catesbeiana, negatively correlated with amphibian community diversity for Rana draytonii, and positively correlated with predator diversity index for Pseudacris regilla..

Download or read book Ecology of Chytridiomycosis in Boreal Chorus Frogs Pseudacris Maculata written by Oliver J. Hyman and published by . This book was released on 2012 with total page 146 pages. Available in PDF, EPUB and Kindle. Book excerpt: Infectious diseases have emerged as a significant threat to wildlife. Environmental change is often implicated as an underlying factor driving this emergence. With this recent rise in disease emergence and the acceleration of environmental change, it is important to identify the environmental factors that alter host-pathogen dynamics and their underlying mechanisms. The emerging pathogen Batrachochytrium dendrobatidis (Bd) is a clear example of the negative effects infectious diseases can have on wildlife. Bd is linked to global declines in amphibian diversity and abundance. However, there is considerable variation in population-level responses to Bd, with some hosts experiencing marked declines while others persist. Environmental factors may play a role in this variation. This research used populations of pond-breeding chorus frogs (Pseudacris maculata) in Arizona to test if three rapidly changing environmental factors nitrogen (N), phosphorus (P), and temperature influence the presence, prevalence, and severity of Bd infections. I evaluated the reliability of a new technique for detecting Bd in water samples and combined this technique with animal sampling to monitor Bd in wild chorus frogs. Monitoring from 20 frog populations found high Bd presence and prevalence during breeding. A laboratory experiment found 85% adult mortality as a result of Bd infection; however, estimated chorus frog densities in wild populations increased significantly over two years of sampling despite high Bd prevalence. Presence, prevalence, and severity of Bd infections were not correlated with aqueous concentrations of N or P. There was, however, support for an annual temperature-induced reduction in Bd prevalence in newly metamorphosed larvae. A simple mathematical model suggests that this annual temperature-induced reduction of Bd infections in larvae in combination with rapid host maturation may help chorus frog populations persist despite high adult mortality. These results demonstrate that Bd can persist across a wide range of environmental conditions, providing little support for the influence of N and P on Bd dynamics, and show that water temperature may play an important role in altering Bd dynamics, enabling chorus frogs to persist with this pathogen. These findings demonstrate the importance of environmental context and host life history for the outcome of host-pathogen interactions.

Download or read book All Hosts are Not Created Equal written by Stephanie S. Gervasi and published by . This book was released on 2013 with total page 209 pages. Available in PDF, EPUB and Kindle. Book excerpt: Emerging infectious diseases are increasing globally and are a threat to human, wildlife, and ecosystem health. The emerging fungal pathogen, Batrachochytrium dendrobatidis (Bd), or amphibian chytrid fungus, is associated with worldwide amphibian population declines and extinctions. Bd has been found on every continent where amphibians exist and has been documented to infect hundreds of species. As with other multi-host pathogens, the outcome of infection with Bd appears to vary among individuals, species, and populations. Variation in host responses to infection can lead to changes in the structure and composition of amphibian assemblages and can affect disease dynamics including pathogen persistence or fadeouts in ecological communities. Understanding the feedback between hosts and pathogens requires disentangling the influence of multiple interacting biotic and abiotic factors, yet fundamentally depends on characterizing intrinsic host responses to infection. This thesis broadly examines variation in species-specific susceptibility to the chytrid fungus among amphibians. I have characterized patterns of mortality, quantitative infection load, feeding behavior, and pathogen avoidance behavior of twenty different amphibian species exposed to the fungus or control conditions (Chapter 2). We found a high degree of variation in pathogen-induced responses to chytrid fungus, ranging from zero mortality to 100% mortality after only six days of pathogen exposure. Variation in infection load was also significant at the species level and there was not always a direct relationship between infection load and mortality. Behavior of pathogen exposed animals was significantly different from that of control animals, and reduced feeding behavior of pathogen-exposed animals is likely to be related to the decline in health of pathogen-exposed animals. In Chapter 3, I examined a special case of amphibian susceptibility to chytrid fungus in the American bullfrog (Lithobates catesbeianus). Bullfrogs are widely reported to be a tolerant host and a carrier of Bd that spreads the pathogen to less tolerant hosts. However, this hypothesis has not been rigorously tested using an experimental approach. In Chapter 3, co-authors and I tested whether bullfrogs raised from eggs to metamorphosis in outdoor mesocosms were susceptible to two different strains of Bd (one strain isolated from a "non susceptible" species, the American bullfrog; the second strain isolated from a highly susceptible species, the Western toad (Anaxyrus boreas)). Bullfrogs were susceptible to strain JEL 274, and this is the first documented case of susceptibility to chytrid fungus in this species. Bullfrogs were not susceptible to strain JEL 630, indicating variation in virulence among chytrid fungus strains and important context dependency when considering the effect of infection non individuals, species, and populations of amphibians. In Chapter 4, I examined fine- scale variation in responses of three key amphibian hosts, and examine the evidence for tolerance (the ability to maintain health as infection severity increases) or resistance (the ability to reduce pathogen infection load) of larval and post-metamorphic animals to Bd. I saw pronounced variation in responses to chytrid fungus among species, between life history stages, over time, and found that responses to the fungal inoculate were not dose dependent in two out of the three species examined. In the final data chapter, Chapter 5, I investigated immunological responses that underlie variation in species-specific responses to Bd. I looked at temporal patterns of functional immune responses during a time-course of early and later stage exposure to Bd, spanning 24 hours after experimental inoculation to 15 days post-inoculation. I uncovered patterns in immune responses that were distinctly associated with susceptibility and temporal patterns in infection load associated with susceptibility and immune response. This thesis provides critical information about variation in host responses to a conservation relevant pathogen. Differences in how host hosts acquire, transmit, and persist with infection have important implications for spatiotemporal disease dynamics. Further, understanding host sensitivity to infection allows for predictive risk management of imperiled species.

Download or read book Complexity in Host pathogen Dynamics written by Yang Xie and published by . This book was released on 2015 with total page 164 pages. Available in PDF, EPUB and Kindle. Book excerpt: Emerging infectious diseases impact both human and wildlife populations. Infectious agents, in particular the aquatic fungus Batrachochytrium dendrobatidis (chytrid), have an influential role in driving global amphibian population declines. The emergence of the chytrid fungus has aspects of both geographic spread as well as climate shifts altering environmental conditions and host-pathogen interactions. My dissertation examines the spatial spread of chytrid by host dispersal at the metapopulation level, as well as how spatial risk from chytrid is associated with the climate. In Chapter 2 of my thesis, I examine preexisting conclusions in the wildlife disease literature on the relationship between disease spread mediated by host dispersal and metapopulation persistence. I show how explicit inclusion of local dynamics and dispersal-induced synchronization alters conclusions derived by previous metapopulation disease models. Contrary to existing models that do not include explicit local dynamics, I find that synchronization increases metapopulation extinction risks and regional persistence is optimized at intermediate dispersal levels when disease transmission rate from external sources are low. However, at high rates of external infections, I come to the similar conclusion that increased dispersal monotonically increases metapopulation persistence. In Chapter 3, I use a spatially explicit, individual-based model to simulation disease spread dynamics in a set of connected mountain yellow-legged frog population. I compare the simulated disease forecasts to field data, and test for the sensitivity of these results to assumptions of host dispersal potential. I find that chytrid is able to spread across the majority of the metapopulation even with assumptions of low host dispersal potential and that metapopulation extinction rate increases with increased host dispersal. In Chapter 4, I examine how chytrid distribution is influenced by climatic variables based on the most comprehensive and up-to-date set of global chytrid surveillance data. Using a machine learning algorithm, I generate predictions showing how chytrid distributions might be expected to change according to IPCC projected scenarios of future climate change. I conclude that chytrid distribution is likely to shift to higher altitudes and latitudes with overall increases in environmental suitability in the high latitudes of the Northern Hemisphere. The chosen input climatic variables yields excellent performance when predicting chytrid occurrence at a site, but no single variable has dominant predictive power. My dissertation provides insight into the applicability of conclusions derived from existing metapopulation disease models to specific conservation contexts. Much research has been invested in the chytrid-amphibian system at the individual and population level, yet how disease management might integrate into conservation planning targeted at the metapopulation level remains largely unknown. My research will form an important part in addressing amphibian conservation in spatially-fragmented, pathogen-ridden landscapes, which is especially important in today's changing climate.

Download or read book Wildlife Disease Ecology written by Kenneth Wilson and published by Cambridge University Press. This book was released on 2019-11-14 with total page 693 pages. Available in PDF, EPUB and Kindle. Book excerpt: Introduces readers to key case studies that illustrate how theory and data can be integrated to understand wildlife disease ecology.

Download or read book Interactions Among Bacteria and Batrachochytrium Dendrobatidis written by Carissimi Alissa M and published by LAP Lambert Academic Publishing. This book was released on 2015-05-18 with total page 72 pages. Available in PDF, EPUB and Kindle. Book excerpt: Pathogenic threats to biodiversity contribute significantly to community and species level extinctions, and for amphibians the chytrid fungus, Batrachochytrium dendrobatidis (Bd) is their greatest threat. The host-pathogen dynamics between amphibians and Bd are not fully understood; however, recent studies have shown that the microbial community composition on amphibian epidermal tissues can promote resistance to the disease. Antidermatophyte bacteria can inhibit fungi that require keratin from the epidermis for growth. Two species, Janthinobacterium lividum and Pseudomonas fluorescens, have been found on Bd resistant amphibians. In a series of three individual experiments, Bd susceptible amphibians (i.e. Lithobates shpenocephalus) were exposed to these bacteria both before and after experimental infection by Bd. J. lividum and P. fluorescens mounted a strong immune response, and therefore, can be used to prevent Bd induced mortality. Conversely, neither bacteria proved effective when applied to those frogs with prior Bd exposure. These results can be used to address other aspects of amphibian immunity when Bd and bacteria induce changes of their epidermal community structure.

Download or read book Plant Pathology written by Christian Joseph Cumagun and published by BoD – Books on Demand. This book was released on 2012-04-04 with total page 378 pages. Available in PDF, EPUB and Kindle. Book excerpt: Plant pathology is an applied science that deals with the nature, causes and control of plant diseases in agriculture and forestry. The vital role of plant pathology in attaining food security and food safety for the world cannot be overemphasized.

Download or read book The Effects of an Emerging Pathogen on Amphibian Host Behaviors and Interactions written by Barbara A. Han and published by . This book was released on 2009 with total page 256 pages. Available in PDF, EPUB and Kindle. Book excerpt: Contemporary environmental change encompasses massive biodiversity loss and increasing numbers of emerging diseases worldwide. As part of a global biodiversity crisis, amphibians are disappearing at unprecedented rates. Batrachochytrium dendrobatidis is an emerging infectious pathogen prominently associated with many declines. Chapter 1 reviews the past decade of research on this system and highlights areas where knowledge is notably lacking. Host behavior remains a crucial determinant of host-pathogen dynamics yet studies addressing the effects of Batrachochytrium on amphibian behaviors are virtually nonexistent. Remaining chapters examine behavioral responses of host species to Batrachochytrium. Chapter 2 examines how ancient behaviors that have persisted in amphibians for millions of years change with exposure to Batrachochytrium. I examined thermoregulatory behavior in tadpoles of four species (Pseudacris regilla, Rana aurora, Bufo boreas, Rana cascadae), and aggregation behavior in two species that school as tadpoles (B. boreas, R. cascadae). Results suggest that some amphibians will continue seeking optimal temperatures and continue aggregating regardless of infection risk. I discuss the importance of behavioral plasticity and evolutionary inertia in interpreting host behavioral responses to infection. Chapter 3 examines Batrachochytrium dynamics when multiple host species interact. I manipulated infection status in tadpoles of three naturally co-occurring hosts (P. regilla, B. boreas, R. cascadae) in various combinations and measured growth, survival and infection severity. There were strong interactions between species combinations and infection leading to pathogen-mediated mutualism and competition. Results also suggest that both species richness and species identity may be important factors moderating a dilution effect in this system. Coexisting, interacting hosts must also contend with predators in a community. Chapter 4 explores Batrachochytrium-induced changes in antipredator behaviors in four species (P. regilla, R. aurora, B. boreas, R. cascadae). I also examined whether antipredator behaviors increased survivorship in the presence of lethal predators in R. cascadae, R. aurora. Exposure to Batrachochytrium changed activity rate and refuge use in Bufo, but not in the other species. Nonselective predation of Batrachochytriumexposed prey by susceptible predators adds an unexplored dimension of complexity to this system. Chapter 5 summarizes the ecological implications of studies presented in this dissertation.

Download or read book Environmental Effects on a Host pathogen System written by Robert Puschendorf and published by . This book was released on 2009 with total page 150 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Biotic and Abiotic Factors Influencing Host pathogen Dynamics in a Zooplankton fungus System written by Tad Dallas and published by . This book was released on 2016 with total page 346 pages. Available in PDF, EPUB and Kindle. Book excerpt: Host-pathogen interactions can be influenced by environmental conditions and interactions with other hosts, either directly through the modification of pathogen transmission or development inside of hosts, or indirectly by influencing host or pathogen demography, survival, or functional traits. In this dissertation, I investigate several environmental (e.g. nitrate) and ecological (e.g., competition) factors that could influence host-pathogen interactions, using a model system of Daphnia species infected by an environmentally-transmitted fungal pathogen. I use this system to examine 1) the effect of nitrate pollution on host demography, pathogen survival, and infection dynamics, 2) how host-pathogen interactions respond to variable environments, 3) if a critical host density is present, and predictable, 4) how competition with a non-susceptible competitor influences epidemic dynamics, and 5) how pathogen exposure and infection influences host fitness for a number of host species differing in susceptibility.

Download or read book Spatial and Temporal Patterns of Amphibian Chytrid Fungus Batrachochytrium Dendrobatidis Occupancy in Amphibian Habitats written by and published by . This book was released on 2013 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Chytrid fungi are the most ancestral of the fungi and are global in distribution. There are over 1200 species of Chytridiomycota described from freshwater, marine and terrestrial systems in temperate, tropical and tundra environments. Chytridiales are characterized by a range of morphologies and share the flask- or pot-like shape of the zoosporangia, within which motile zoospores develop. Chytrids function primarily as plant saprobes and parasites, but some also parasitize animals. Chytrids are observed in conjunction with the decline of freshwater and marine algal blooms, they decompose excess pollen, and comprise the fungal flora in gut of herbivores. Some chytrids also parasitize micro-invertebrates, insects and amphibians. The amphibian chytrid fungus, Batrachochytrium dendrobatidis (Bd) is the only chytrid known to infect a vertebrate host. Bd exists free-living in the aquatic environment. Lab experiments have demonstrated Bd survival on sterilized moist sand for up to three months and it remained infective in lake water for up to seven weeks. Bd cultures can be maintained under lab conditions for several months (personal observation), which suggests Bd can survive in the environment without a host as long as nutrients are not limiting. In the aquatic environment, Bd is detected by filtering water samples to capture free-living zoospores and zoosporangia then performing a qPCR analysis. Bd has not been reliably isolated from sediments. The goal of our research was to study free-living Bd in amphibian habitats to better understand its ecology and host-pathogen dynamics.