The importance of trace metals in coral-algal symbiosis
Open Access
- Author:
- Reich, Hannah Gallogly
- Graduate Program:
- Biology
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- February 26, 2020
- Committee Members:
- Todd C Lajeunesse, Dissertation Advisor/Co-Advisor
Iliana Brigitta Baums, Committee Chair/Co-Chair
Roberto Iglesias-Prieto, Committee Member
Erin L Connolly, Outside Member
Tracy Langkilde, Program Head/Chair - Keywords:
- coral-algal symbiosis
Symbiodiniaceae
Trace metals
Metal quota
Iron limitation
Coral bleaching
genomics
Algal culturing
Dinoflagellate
Micronutrients
Physiology - Abstract:
- From an ecological standpoint, iron, among other trace metals, limits primary productivity in many ocean basins and is important to food web dynamics. On a cellular level, trace metals are required for all biochemical processes, making them key for organismal function. Meeting the metabolic demands of abiotic stressors often necessitates fulfilling elevated trace metal demands. Our understanding of trace metal quotas in coral-algal symbiosis and how it pertains to climate change is poorly understood. Understanding how trace metals important to reef building corals in light of climate change requires comparative (i.e., research comparing lineages representative of multiple niches) experimentation and research at multiple levels of organization (i.e., algal culturing, physiology, genomics, transcriptomics, oceanography, enzymology). My dissertation creates a comprehensive understanding of the importance of trace metals in coral-algal symbiosis using these techniques. In chapter two, I exposed five Symbiodiniaceae cultures to iron concentrations ranging from starvation to replete conditions to investigate their metal profiles (content, quotas). The free-living capability of Symbiodiniaceae enabled me to investigate their iron demand while living outside of the coral host (in algal culture media) and compare lineages with different symbiosis capabilities, geographic ranges, and temperature tolerances. My results showed substantial differences between the metal profiles of pairs of closely related species. The distinct trace metal requirements of each lineage may allow closely-related species to co-exist in the same habitat. Despite the broad range of specialties, exposure to iron starvation always resulted in cell death. This implies a lack of iron availability may exacerbate coral bleaching outbreaks and subsequent coral death. The third chapter examines how host coral identity, symbiont identity, and reef thermal history influence the trace metal profiles of the coral holobiont. Corals hailing from warm water habitats had elemental profiles that were distinct from their cool-water conspecifics. Additionally, inter- and intraspecific variation in metal content of the heat tolerant coral symbiont Durusdinium spp. was driven by host coral and corroborated strategies of heat stress resistance. The fourth chapter consisted of experimentation to determine how iron availability influences Breviolum spp. survival to heat stress. Without access to sufficient iron supply, Breviolum spp. were unable to persist during heat stress while their counterparts with sufficient iron supply were able to survive. Moreover, one species that actively acquired more metals had a greater capacity to withstand heat stress. My findings indicate that maintaining sufficient metal reserves is critically important to the health of the algal symbiont and contributes to the stability of their mutualisms during ocean warming. The fifth chapter uncovers the genomic basis of Symbiodinium ‘fitti’ intraspecific diversity. Genome-wide data of an S. ‘fitti’ revealed Single Nucleotide Polymorphisms (SNPs) unique to the strains residing in each of its three acroporid hosts. These SNPs likely facilitate adaptation to the subtly different lifestyles dictated by different light environments in addition to putative biochemical and nutritional demands of each acroporid host. Overall, my dissertation demonstrates that trace metals underlie many facets of the biology of coral-algal symbiosis. Most importantly, my research reveals how trace metals are important to niche specialization of coral-algal symbiosis and survival to heat stress. Furthermore, trace metal availability may dictate the distribution of different Symbiodiniaceae lineages and in particular heat tolerant ones. The importance of trace metal availability and how it relates to bleaching outbreaks deserves considerably more research.