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UBC Theses and Dissertations

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UBC Theses and Dissertations

Host specificity of bacterial communities : natural history, ecology, and conservation Loudon, Andrew Howard


Animals live with a symbiotic community of bacteria, and some of these bacteria affect host biology. Generally, these bacterial communities are diverse and complex. A key question in microbiome research is whether bacteria are specific to a host and affect host biology. In my dissertation, I use observational and experimental approaches to 1) understand the factors that contribute to composition of host-microbiota, 2) determine the core bacteria of a host by comparing the abundance of host bacteria to the bacteria in environmental bacterial communities, 3) determine the phylogenetic and environmental distribution of core bacteria and their close relatives to better understand their natural history, and 4) test whether core bacteria are correlated with aspects of host biology. Across three host species, I found bacterial communities that were populated by a few common and prevalent core bacteria that are absent from the environment; in most cases, these core bacteria belong to host-associated clades of bacteria. In chapter 2, I characterize the microbiota of the keystone sea star Pisaster ochraceus, identify core bacteria, and use phylogenetic trees to assess the distribution of their relatives. In chapter 3, I study the interactions between the skin microbiota and host innate immunity of Columbia spotted frogs and to determine whether they explain the occurrence of the amphibian pathogen, Batrachochytrium dendrobatidis (Bd). In chapter 4, I characterize the microbiota of wild and captive endangered Oregon spotted frogs (OSF) and whether their skin bacteria are associated with Bd intensity. Lastly, I experimentally test the hypothesis environmental reservoirs of bacteria influence the bacteria on the skins of frogs. Understanding the factors that structure captive communities has substantial conservation implications for captive breeding and head start programs. My results differ from previous studies by comparing the host to their environment and focusing on specific core bacteria.

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