The environment and co-infection mediate disease risk in corals through impacts on the microbiome and immunity

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Disease in natural populations depends on the interaction between a host and a parasite, but the environment may also modify this interaction. In this dissertation, I explore how abiotic and biotic components of a host’s environment alter health and disease in the sea fan octocoral, Gorgonia ventalina. As ectotherms, corals are particularly sensitive to the environment and thus a priority for studying broader questions about environmental drivers of disease. The microbiome is an essential component of the holobiont that can shift under stressful conditions and alter host susceptibility. In Chapter 1, I compare sea fan and scleractinian bacterial communities across the warm thermal anomaly of 2010. Bacterial communities shifted in sea fans, but not in the more bleaching-susceptible, reef-building scleractinian, Orbicella faveolata. In Chapter 2, I further explore the role of organisms infecting sea fans by studying co-infecting macroparasites. Co-infection is common in nature and has ecological and evolutionary consequences for disease outbreaks. I surveyed 10 sites in Puerto Rico and determined that one parasite suppressed host immunity, yet did not facilitate a second parasite due to the overriding influence of the environment and host demography. A primary goal at the intersection of eco-immunology and disease ecology is to understand how the environment influences host immunity in multi-parasite systems. I investigate this interplay in Chapter 3 by measuring both cellular immunity and immune gene expression. Laboratory experiments reveal distinct immune responses to two parasites, but immune responses in field populations are dominated by the influence of environment and demography. There were no signs that the parasites influence each other in nature. While disease outbreaks occur even in healthy populations, anthropogenic change may alter disease risk. In Chapter 4, I use field surveys and a laboratory experiment to test how warming and copper pollution influence sea fan immunity and disease. Higher copper and temperature increased disease risk, while also driving nonlinear immune responses to a damaging parasite. This dissertation provides insight into the mechanisms through which biotic and abiotic factors structure disease. Understanding sea fan health is also a look to the future, as octocorals are critical for reef habitat in a changing ocean.

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Co-infection; Coral; Eco-immunology; Gorgonia ventalina; Ecology; environment; disease
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Harvell, Catherine Drew
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Lazzaro, Brian
Power, Alison G.
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Ecology and Evolutionary Biology
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Ph.D., Ecology and Evolutionary Biology
Degree Level
Doctor of Philosophy
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Government Document
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dissertation or thesis
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