The Significance of Compatibility in Scleractinian Corals and Applications for Environmental Bioengineering in a Warming Ocean
Restricted (Penn State Only)
- Author:
- Osborne, Cornelia
- Graduate Program:
- Biology
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- June 07, 2024
- Committee Members:
- Elizabeth Mcgraw, Program Head/Chair
David Toews, Major Field Member
Manuel Llinas, Outside Unit & Field Member
Valerie Chamberland, Special Member
Roberto Iglesias-Prieto, Major Field Member
Todd Lajeunesse, Chair of Committee
Iliana B Baums, Special Member
Zachary Szpiech, Dissertation Advisor - Keywords:
- Coral
Climate change
Gene expression
Hybridization
Chimerism
Reproduction
Thermal stress
Acropora
Diploria
Spawning
Restoration
Conservation
Marine biology
Gamete recogntion - Abstract:
- Scleractinian corals face unprecedented decline from disease and anthropogenic stressors that affect their reproduction, early development, and adult survival. Caribbean reefs in particular have experienced devastating losses over recent decades, with many key reef-building species declining by up to 95% throughout their range. The recent marine heatwaves of 2023-2024 have further intensified this crisis, highlighting the urgent need for novel interventions. This dissertation investigates how bioengineering approaches – such as selective breeding, assisted hybridization, and manipulation of genetic exchange - can enhance coral survival and resilience across multiple biological scales. Through a series of experiments spanning different life stages in Caribbean corals, I examined how “compatibility” influences coral survival and resilience, with implications for reef restoration. My first chapter (Chapter 2) focuses on compatibility at the gamete level, where variable fertilization success between coral genotypes may create barriers to recruitment in declining populations. Through studies of sperm-egg interactions in Diploria labyrinthiformis, I found that while eggs chemically attract sperm, confirming a role of chemoattraction in their fertilization, this mechanism does not ultimately moderate fertilization success between compatible and incompatible genets. Chapter 3 addresses compatibility in < 1 year old Acropora at the tissue level, where the high mortality of juvenile corals creates a critical bottleneck in coral restoration. I demonstrated that chimerism resulted in high survival rates of 97.3% compared to 42.4% in single-genet settlers. Similarly, hybrid offspring between A. palmata and A. cervicornis showed 63% lower mortality risk than purebred settlers, indicating that both tissue fusion and hybridization can substantially enhance early-life performance. Examining genetic compatibility at broader scales, Chapter 4 focuses on the population level testing assisted gene flow (AGF) between geographically distinct A. palmata populations from Florida, Puerto Rico, and Curaçao as a strategy to enhance local thermal tolerance while maintaining genetic diversity in severely reduced populations. Our results showed that AGF crosses maintained heat stress performance comparable to local Florida genets while successfully introducing novel genetic diversity. Finally, at the species level (Chapter 5), I investigated the thermal resilience of the natural hybrid A. 'prolifera' to understand the mechanisms underlying hybrid vigor in adult coral colonies and assess the potential of hybridization as a tool for developing climate-resilient corals. The hybrid demonstrated superior thermal tolerance compared to parental species, achieved through frontloaded gene expression and reduced transcriptional responses under heat. Taken together, the findings in this dissertation indicate that manipulating genetic diversity through fusion, hybridization, and assisted gene flow can significantly enhance coral survival across life stages, though benefits may be context-dependent. These bioengineering approaches provide promising new tools for coral restoration at multiple points of a coral’s life cycle, starting at the gametic level, through to the adult phase. However, the long-term success of these approaches will require careful consideration of environmental context and life-stage specific effects. Ultimately, this work advances our understanding of coral reproductive biology and development and provides practical strategies for enhancing the resilience of restored populations in a rapidly changing climate.