Identifying the Distinct Adaptive and Plastic Gene Expression Patterns and Microbial Indicators that Mediate Coral Disease Resistance

Abstract

Infectious diseases are an increasing threat to coral reefs, resulting in altered community structure and hindering the functional contributions of disease susceptible species. While forecasting disease outbreaks based on environmental factors has progressed, we still lack a comparative understanding of susceptibility among coral species that would help predict disease impacts on coral communities. This dissertation compared the phenotypic, microbial, and coral host gene expression responses of seven diverse Caribbean coral species after exposure to white plague disease. Disease incidence and lesion progression rates were evaluated over a seven-day exposure. Coral microbiomes and RNA were sampled after lesion appearance or at the end of the experiment if no disease signs appeared. A spectrum of disease susceptibility was observed among the coral species that corresponded to microbial dysbiosis. This experimental exposure also determined gene expression processes involved in (i) lesion progression, (ii) within species gene expression plasticity, and (iii) expression-level adaptation among species that lead to differences in disease risk. Finally, phylosymbiotic bacteria, which are hypothesized to provide stabilizing and probiotic contributions to the host were identified and associated with community-level microbial dysbiosis, an emerging hypothesis in coral disease etiology. Collectively, this dissertation offers insight into the adaptive constraints and plasticity of coral host gene expression patterns and microbial indicators involved in disease lesion progression and within and between species dynamics that lead to differences in disease risk that is evident on current Caribbean reefs.