Thermal adaptation of Thalassiosira pseudonana using experimental evolution approaches

Schmidt, Katrin (2017) Thermal adaptation of Thalassiosira pseudonana using experimental evolution approaches. Doctoral thesis, University of East Anglia.

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Abstract

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.

Item Type: Thesis (Doctoral)
Faculty \ School: Faculty of Science > School of Environmental Sciences
Depositing User: Katie Miller
Date Deposited: 13 Jun 2017 14:33
Last Modified: 30 Jun 2018 00:38
URI: https://ueaeprints.uea.ac.uk/id/eprint/63741
DOI:

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