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Title: Thermal adaptation of Thalassiosira pseudonana using experimental evolution approaches
Author: Schmidt, Katrin
ISNI:       0000 0004 6351 157X
Awarding Body: University of East Anglia
Current Institution: University of East Anglia
Date of Award: 2017
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Diatoms contribute about 50% of global primary production and are on of the most diverse phytoplankton groups. Additionally, they form the basis of most marine food webs and play an important role in elemental cycles such as carbon and silica. Global warming impacts the diversity and productivity of marine ecosystems as temperature is considered a strong selecting agent underpinning global diversity patterns of marine phytoplankton. In order to gain insights into diatom distribution and diversity in the Atlantic Ocean, we analysed 18S rDNA ribotypes over a broad spatial scale from the Fram Strait to the South Atlantic. Diversity patterns were related to environmental metadata in order to identify main drivers. Our results indicate that salinity had a negative effect on diatom diversity in the Fram Strait transect with stations showing low diversity at high salinities. In contrast, diatom diversity in the Atlantic Ocean was negatively correlated to temperature with high temperature showing low diatom diversity. The order of Coscinodiscales showed a, formerly unknown, cosmopolitan distribution and was the overall most abundant species. With this study we provided an updated estimate of diatom distribution and diversity in the Atlantic Ocean. Phytoplankton physiology is highly temperature dependent and despite the importance of temperature as a major driver of marine phytoplankton evolution, the molecular mechanisms of adaptive evolution under temperature selection are largely unknown but instrumental for predicting how marine phytoplankton will respond to a changing ocean. Here we provide evidence, based on experimental evolution experiments with the marine model diatom Thalassisoria pseudonana that thermal tolerance can rapidly evolve within 300 generations. Our results indicate that upper and lower temperature limits were fixed, however temperature optima for growth shifted towards the selection temperature. Furthermore, temperature had a significant impact on average cell diameter, bSi content and cellular stoichiometry (C:N:P). Physiological adaptation to high temperature was underpinned by differential expression of genes related to protein metabolism (protein binding and folding), and down-regulation of mismatch repair mechanisms potentially causing a high number of SNPs in the genome. Furthermore, several transposable elements showed strong, temperature specific up-regulation suggesting epigenetic enabled genome plasticity. Our results highlight the relation of adaptive pheno- and genotypes driven by temperature selection. This knowledge is key to our understanding of how the environment shapes the evolution of microbes and the biogeochemical processes they drive.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available