Physiological ecology and functional genomics of symbiotic corals: The effect of light exposure
Restricted (Penn State Only)
- Author:
- Gomez Campo, Kelly
- Graduate Program:
- Biology
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- December 11, 2021
- Committee Members:
- Sally Mackenzie, Major Field Member
James Marden, Major Field Member
David Hughes, Outside Unit & Field Member
Roberto Iglesias-Prieto, Major Field Member & Dissertation Advisor
Iliana Baums, Chair of Committee
Elizabeth Mcgraw, Program Head/Chair - Keywords:
- Symbiotic corals
Photoacclimation
Light-stress
Coral bleaching
Heat-stress
Phenotypic plasticity
DNA methylation
Gene expression
Biological networks - Abstract:
- Tropical coral reefs are biodiversity reservoirs that protect our coastlines from tsunamis and hurricanes, supply food for 1 billion people, and create millions of jobs in the tourism and fishing industries, generating billions of dollars annually. Symbiotic corals support the formation of these reefs by significantly contributing to the net accumulation of structural calcium carbonate over space and time. However, these ecosystem engineers are threatened by the impacts of climate change; thermal anomalies expose coral species to heat-stress levels well past most tolerance limits, and lead to the disruption of coral-algal symbioses, in some cases, to coral mass mortality and subsequent ecosystem collapse. To predict how corals will respond to present and future environmental challenges and best prepare conservationists to act, a detailed understanding of their acclimatory mechanisms is required. In this dissertation, (1) I first map the cascade of cellular events triggered by thermal stress in symbiotic corals. Based on existing knowledge, I propose a model that maps coral responses from the initial stimulus in the algal symbiont chloroplast to the complex cascade of events leading to seasonal phenotypic changes (i.e. seasonal acclimation), and to the downstream coral bleached phenotype if stress progresses (i.e. when the coral’s capacity to acclimate is overwhelmed by heat stress). (2) I then use an experimental approach to quantify the implications of photoacclimation and light-stress in protein turnover. By characterizing these responses, we were able to discuss the variable energetic costs of maintenance of symbionts in hospite (higher metabolic costs in shallow high light environments), which may explain the variable energy balance of the coral holobiont across depth (and light) gradients. This prompted to (3) combine experimental data with theoretical concepts to build a bio-optical model capable of testing hypotheses by predicting changes in symbiotic coral calcification. The model describes and hindcasts ‘bio-optical states’, namely energy available for coral calcification (EAC) as a function of depth (or light). This model was implemented using available published data, resolving changes in calcification rates in depth gradients and future global warming conditions. In order to understand strategies that corals use to thrive in shallow – costly – environments, (4) I use an experimental approach to induce light-mediated phenotypic responses and investigate underlying molecular mechanisms, such as, DNA methylation, accompanied with transcriptional responses, potentially responsible for the well-known plasticity in symbiotic corals. Results show that coral plasticity is a colony trait emerging from comprehensive morphological and physiological changes at the module level. These changes optimize light harvesting and utilization and were initiated by differentially methylated and expressed coral genes that together altered biological networks. These findings fundamentally rewire our understanding of how cnidarian invertebrates repattern the methylome to affect the phenotype and uncover an important role of light sensing by the coral animal to optimize photosynthetic performance of the symbionts.