Distribution, abundance and life cycle of free-living Symbiodinium

Publication Type:
Thesis
Issue Date:
2018
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01front.pdf403.11 kB
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02whole.pdf10.07 MB
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03appendix E2.1.pdf207.62 kB
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03appendix E2.2.pdf321.9 kB
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03appendix E2.3.pdf321.65 kB
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03appendix E2.4.pdf300.99 kB
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03appendix E2.5.pdf193.29 kB
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03appendix E3.1.pdf209.74 kB
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03appendix E3.2.pdf210.08 kB
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03appendix E3.3.pdf303.01 kB
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03appendix E3.4.pdf196.87 kB
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03appendix E3.5.pdf303.21 kB
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03appendix E3.6.pdf420.41 kB
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03appendix E4.1A.mp4380.02 kB
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03appendix E4.1B.mp4479.81 kB
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03appendix E4.1C.mp4496.23 kB
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03appendix E4.1D.mp4530.81 kB
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03appendix E6.1.xlsx38.97 kB
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03appendix E6.2.xlsx15.3 kB
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Symbiodinium are endosymbiotic microalgae of reef-building corals. Photosynthesis by these algae fuels the productivity of corals and ultimately the growth of entire reef systems. However, a critical phase of Symbiodinium’s life history is existence as “free-living” cells prior to acquisition by their host. Free-living populations are essential for establishing symbiosis for many corals that propagate larval generation without algal symbionts, but also for recombination of host-symbiont associations recovering from stress. Despite the importance of free-living populations, their underlying biodiversity and ecology remains a black box. For example, how they distribute spatially, temporally and regionally, and contribute to coral reef ecosystems as they currently face an era of “ecological crisis”, are largely unknown. To unlock the distribution, abundance and life cycle of free-living Symbiodinium, I applied novel dual NGS- (eDNA metabarcoding using next generation sequencing) and qPCR-based (using clade-specific primers) approaches to first explore the qualitative and quantitative distribution and abundance of free-living Symbiodinium for tropical (Heron Island) (Chapter 2) and temperate (Sydney Harbour) (Chapter 3) east coast Australian coral communities that are periodically connected by the Eastern Australian Current. To further evaluate how such diversity (which is only a snap shot of population dynamics over time) is sustained as a result of individual population turnover, I analysed the Symbiodinium cell cycle to establish a novel baseline for how population turnover is regulated by cell cycle dynamics across species and under alternate conditions (light and temperature) (Chapter 4). This thesis highlights the importance of habitat variety in sustaining diverse free-living Symbiodinium communities, functional plasticity and hence resistance to disturbance (Chapter 5). For example, I provide new insight of macroalgae habitats as key reservoirs of symbiont availability to hosts via local supply but also wider dispersal. In the latter case, I discuss that dispersal of Symbiodinium is critical to support paradigms of high-latitude temperate reefs acting as refugia for tropical corals under climate change, since temperate and tropical Symbiodinium communities are currently geographically separated. Cell cycle dynamics differed between genetically different types (species), and results in specific types proliferating faster under certain environmental conditions thereby supporting shifts in community structure. As such, cell cycle dynamics comprises a key functional trait that is still overlooked but warrants further targeted investigation, not only amongst free-living populations, but also in hospite to clarify how functional equilibrium under steady-state symbioses is maintained as reef environments continue to be subjected to stressors into the future.
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