'Through the looking glass' : diversity and its functional significance in marine benthic microbial eukaryotes

Publication Type:
Thesis
Issue Date:
2018
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Marine microbial eukaryotes are of immense ecological and evolutionary significance in marine ecosystems. Understanding their biodiversity and functional evolutionary traits are key to improving our understanding of marine ecosystem functioning. The East Australian Current (EAC) is a global climate change hotspot, and yet we lack in our understanding of its impact on phytoplankton distribution and dynamics. Ostreopsis species have been reported to cause severe blooms and produce palytoxin (PLTX) – like compounds all around the globe but we do not have basic information on the distribution and dynamics of Ostreopsis species in Australia. In this dissertation, I established the first comprehensive report of Ostreopsis species from Australian waters and explored cryptic diversity and functional traits in this genus. Extensive sampling along a north-south gradient of 1800 km from sub-tropical to temperate waters yielded the identification of three species, including a novel pseudo-cryptic Ostreopsis rhodesae from the Great Barrier Reef, along with Ostreopsis cf. ovata. Ostreopsis cf. siamensis was identified at all locations and its eco-physiological traits and genetic population structure were investigated. The genetic diversity in the northern subtropical locations was greater compared to the more southern locations, reflecting a longstanding divergence and local radiations originating from the ancestral population and a potential southward range expansion, which may be related to the intensification of the EAC over the past century. Intra- and inter-population variations in physiological traits were investigated to understand its range expansion and functional trade-offs. This is the first study to our knowledge to report growth rates, cell size, cellular toxic concentrations and photobiological parameters on fifty-three clones of a marine protist, in order to investigate intra-specific diversity in key functional traits. The toxin biosynthesis pathway in the three species was investigated using de novo transcriptomics and compared to Coolia malayensis. All essential domains needed to synthesize a PLTX-like carbon backbone were identified in the three Ostreopsis species and were also found in the non-PLTX producing C. malayensis. Putative molecules with potential polyketide-like backbone structures were reported in this investigation using non-targeted metabolomics, suggesting a greater diversity of polyketide compounds amongst these species than previously anticipated. Results from this dissertation add to the knowledge of species biodiversity, population structures, eco-physiological traits and toxin biosynthesis mechanisms in marine microbial eukaryotes, and Ostreopsis species in particular.
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