The Ecology and Functional Significance of Distinct Coral Symbionts
Open Access
- Author:
- Lewis, Allison Michelle
- Graduate Program:
- Biology
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- November 30, 2018
- Committee Members:
- Todd C Lajeunesse, Dissertation Advisor/Co-Advisor
Claude Walker Depamphilis, Committee Chair/Co-Chair
Monica Medina, Committee Member
Todd C Lajeunesse, Committee Member
Timothy Iwao Miyashiro, Outside Member - Keywords:
- Indo-Pacific
Scleractinia
Symbiodiniaceae
Endosymbiosis
Ecological Specialization
Calcification
Physiology
Caribbean
Taxonomy - Abstract:
- Distinct coral symbiont associations have been shown to influence the response of a coral colony to environmental stress. Genetic evidence has revealed the existence of cryptic symbiont species previously masked by similar morphological traits. Thus, there is a pressing need to study the biological and underlying functional diversity of symbionts and their effects on the physiology of the coral host. Chapter 1 introduces the application of molecular genetics to understanding the diversity, evolution, and ecology of nondescript Symbiodiniaceae and how different symbiont associations respond to environmental stresses such as anthropogenic global warming. In Chapter 2, new species of Symbiodiniaceae discovered through this research are resolved. This chapter shows that a presumed symbiont generalist is actually comprised of multiple distinct species, co-evolved with specific coral taxa. These findings support the primary role of niche specialization to particular hosts in the diversification of symbiotic dinoflagellates. Dynamic or shifting symbiont associations have been observed as an adaptive mechanism to alter coral physiology, particularly for corals under acute environmental stress. It is often presumed that shifting symbiont associations is a common phenomenon, yet, few studies have investigated whether the relationship between host colony and resident symbiont is stable or dynamic over time. In Chapter 3, coral symbionts from various Indo-Pacific corals were investigated over multiple years. All colonies harbored and maintained an association with a single dominant species of Symbiodiniaceae belonging to genus Cladocopium (formerly Symbiodinium Clade C). Individual clone genotypes, or strains, of the resident symbionts were diverse across the coral population, and few clones were found in more than one colony. Individual corals consistently maintained stable symbioses dominated by one or two genotypes which likely persist for the life of a colony. Chapter 4 investigates coral species from two habitats that represent extremes in environmental conditions in the Indo-Pacific. In this chapter differences in the physiology of coral with distinct symbiont pairings is investigated and then evaluated in the context of a warming climate. Our evidence shows that an association with the symbiont Durusdinium (formerly Symbiodinium Clade D) trenchii imparts thermal resilience to corals without significant trade-off to overall colony growth and stands in contrast to previous reports for corals with thermally-tolerant symbionts in other regions of the world. Symbioses involving D. trenchii in the Pacific might be better integrated and co-adapted with Pacific corals resulting in a more stable and optimized association. Thus, shifts in host-symbiont pairings to combinations that are better adapted to increasingly stressful conditions constitute an ecological response that may allow reefs to remain viable during global ocean warming.