Human activity since the Industrial Revolution has increased global greenhouse gas concentrations resulting in rapid climate change, which now threatens terrestrial and marine ecosystems. Tropical coral reefs, along with the biodiversity and communities they support, are particularly threatened by these changes in climate. Corals are a consortium of organisms, with the coral host along with its photosynthetic endosymbiont (Family Symbiodiniaceae) and diverse community of microorganisms (bacteria, archaea, fungi, and viruses) together forming the ‘coral holobiont’. However, the symbiosis between tropical corals and Symbiodiniaceae algae is sensitive to even small changes in temperature and ‘coral bleaching’ events – the loss of symbiosis – are now occurring with increased frequency and severity. These bleaching events can result in coral mortality and loss of entire reefs if stressful conditions do not subside. While research efforts have increased our ability to understand and predict coral bleaching events, fundamental questions remain surrounding how genetic diversity of the coral holobiont and interactions with its environment can drive coral resilience or resistance under climate change. The overarching goal of my dissertation is to understand how various abiotic (i.e., stress duration, spatiotemporal variation on the reef) and biotic (i.e., holobiont diversity, symbiosis) factors determine a coral’s response to environmental change at the level of phenotype and genotype. To achieve this goal, I first tested how environmental history and stress duration modulated the physiological responses of two reef-building corals under combined ocean warming and ocean acidification conditions. I found that one species was more stress-resistant (Siderastrea siderea), but that both duration of stress exposure and environmental history (inshore vs. offshore reef origin) modulated coral physiology. Next, I investigated the importance of holobiont genetic identity and abiotic environment in driving phenotypic responses of S. siderea exposed to a diel temperature variability (DTV) and subsequent heat challenge experiment. I found that while DTV increased coral growth, cryptic host diversity and their unique pairings with algal symbiont strains were the strongest predictors of holobiont physiology and response to heat challenge. Lastly, I leveraged genome-wide gene expression profiling and the facultative symbiosis between the subtropical coral Oculina arbuscula and its symbiont Breviolum psygmophilum to disentangle the independent responses of both partners to heat and cold challenges in and out of symbiosis. I found that O. arbuscula host gene expression was more plastic under temperature challenges relative to B. psygmophilum when in symbiosis, and that symbionts exhibited more gene expression plasticity in culture compared to in symbiosis. Taken together, this dissertation provides valuable insights into the phenotypic and genotypic mechanisms that contribute to coral success in a changing climate.
| Identifer | oai:union.ndltd.org:bu.edu/oai:open.bu.edu:2144/46804 |
| Date | 13 September 2023 |
| Creators | Aichelman, Hannah Elise |
| Contributors | Davies, Sarah W. |
| Source Sets | Boston University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
| Rights | Attribution-NonCommercial-NoDerivatives 4.0 International, http://creativecommons.org/licenses/by-nc-nd/4.0/ |
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