THE EXTENT, EFFECTS AND DYNAMICS OF AMPHIBIAN CHYTRIDIOMYCOSIS IN AUSTRALIA

Kris Murray (2010). THE EXTENT, EFFECTS AND DYNAMICS OF AMPHIBIAN CHYTRIDIOMYCOSIS IN AUSTRALIA PhD Thesis, School of Biological Science, The University of Queensland.

       
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Author Kris Murray
Thesis Title THE EXTENT, EFFECTS AND DYNAMICS OF AMPHIBIAN CHYTRIDIOMYCOSIS IN AUSTRALIA
School, Centre or Institute School of Biological Science
Institution The University of Queensland
Publication date 2010-05
Thesis type PhD Thesis
Supervisor Robbie Wilson
Hamish McCallum
Rick Speare
Total pages 234
Total colour pages 12
Total black and white pages 122
Subjects 06 Biological Sciences
Abstract/Summary Chytridiomycosis, caused by infection with the pathogenic chytrid fungus Batrachochytrium dendrobatidis (Bd), is an emerging infectious disease implicated in global amphibian declines and extinctions. The origin of Bd remains disputed but the evidence suggests that it has been introduced repeatedly as a novel pathogen to new geographic locations after expansion via trade in wildlife of a single clonal lineage. Impacts have been most severe in stream dwelling species in high altitude, often pristine rainforests in Central/South America and Australia, but infections have been found in a wide variety of habitats on all continents where amphibians occur. Management of the disease in wild settings at this time is limited to restricting spread, with conventional control strategies being unlikely to be effective at broad spatial or temporal scales. Unlike most wildlife pathogens, Bd appears capable of driving populations to extinction because it has a broad host range and can therefore exist in the environment independent of a particular species or life-stage undergoing population declines. For many species, survival will thus be dependent on evolutionary processes leading to resistance to the pathogen as it becomes endemic and positive natural growth rate of populations is restored. Some frog populations and species have persisted and possibly begun to recover post-decline, despite the continued presence of Bd infections in their ecosystems. This indicates that a shift in the host-pathogen relationship favouring host survival may be occurring where the pathogen has become endemic. Studies on chytridiomycosis in the wild, however, have so far been largely restricted to detection and prevalence surveys in areas where die-offs have occurred, and few studies have addressed the effects of infection on individuals outside the laboratory, particularly in populations that may be exhibiting recovery and where the pathogen is well established. Perhaps for the same reason, the distribution and host range of this pathogen remain poorly resolved, both locally and globally. Many critical questions about chytridiomycosis thus remain – what is the evidence linking the establishment and spread of this pathogen to ongoing amphibian declines and extinctions? Are endemic chytridiomycosis infections continuing to impact susceptible amphibian species, despite a seemingly long period since the pathogen’s epidemic invasion? If so, how can we predict the ongoing consequences of this infection, in species, through space, through time? Can we predict future disease distribution, disease outbreaks, population declines, extinctions? And ultimately, how can we use this knowledge to inform the research, management and stewardship of anuran biodiversity in the short-, medium-, and long-term futures? These are some of the questions I address in this dissertation and broadly speaking they relate to the extent, effects and dynamics of chytridiomycosis in Australian amphibians. In order to broach these topics, I have necessarily explored and adopted a range of methodologies. At one end of the scale, I have undertaken my own extensive fieldwork to ask specific questions about the dynamics and effects of this disease in amphibian communities where Bd has become endemic, while at the other end I have collated and compiled afresh existing information to address questions about the extent and effects of this pathogen at a continental scale. Given the diversity of these data sources, I have employed a large range of analysis tools, including individual based mark-recapture modelling, fine scale analyses of infection patterns, geographic information systems (GIS) data and processing techniques, correlative and mechanistic species distribution (spatial) modelling, machine-learning prediction techniques and so on. I thus approached the study of chytridiomycosis at a number of spatial and temporal scales. The underlying objectives of my research are to ask straightforward and practical questions, utilise modern, powerful, flexible, free (generally) and sufficiently generic tools that can be readily adopted to address such questions in other contexts, and to integrate new and existing data sources in order to help guide and inform future management and research activities on chytridiomycosis. Specific summaries of each of the papers presented in this thesis, their contexts, methodologies, results and key conclusions can be found in the respective abstracts included at the beginning of each chapter. The thesis comprises a detailed introduction that represents a general review of the literature relevant to the thesis, four major papers (published or submitted for publication in Conservation Biology, Journal of Applied Ecology, Proceedings of the Royal Society of London B, and one in review), a published data chapter (Ecology) and a published short paper included as an Appendix (Conservation Biology). There is increasing evidence that the incidence of emerging infectious diseases has increased as a result of anthropogenic influences that can favour the growth, dispersal and transmission of pathogens, and that such diseases can have major impacts on populations, species and biodiversity in general. Chytridiomycosis is just one such disease. I hope that the questions that I have addressed in this thesis will be relevant and of some use to ecologists and conservation biologists confronting similar disease-associated challenges both now and into the future.
Keyword Chytridiomycosis
chytrid fungus
Batrachochytrium dendrobatidis
wildlife disease
amphibian decline
extinction
endemic disease
disease dynamics
mark-recapture
survival
epidemiology
species distribution model
Additional Notes colour pages: 1 17 23 96 117 147 149 153 156 158 194 195

 
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Created: Wed, 01 Dec 2010, 19:57:46 EST by Mr Kris Murray on behalf of Library - Information Access Service