Limits to Evolutionary Adaptation of Phytoplankton in the Arctic Ocean

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Global warming is rapidly altering ocean temperature, pH, carbon saturation state, circulation, and oxidation state, and this will impact the community composition of phytoplankton; the primary producers in the world's oceans. Predicting which marine phytoplankton species will persist and dominate under these changing environmental conditions requires an understanding of the adaptive evolutionary potential of these species. With this project, we will improve understanding and predictive capability of the dynamics of polar marine phytoplankton communities, especially diatoms, and the limits of their adaptive capacities in response to environmental change driven by global warming. As single-celled microbes with large population sizes and high replication rates, phytoplankton species have considerable potential to adapt rapidly to changing environmental conditions. This can happen by (i) individual organisms adapting their phenotypes through epigenetic processes (i.e. phenotypic plasticity), (ii) by natural selection acting on individual genotypes, and by (iii) group selection (i.e. lineage and species-sorting). These three fundamental levels of selection result in changes in physiology, population genetic composition and community structure, respectively, which in turn can drive changes in both biogeochemical cycles and higher trophic levels. These adaptive changes already occur in the Arctic Ocean, yet existing climate models fail to capture these combined ecological and evolutionary adaptive responses. This proposal aims to address this fundamental gap in knowledge by studying adaptive evolution at the level of the genome, epigenome and transcriptome of a model species for polar diatoms, Fragilariopsis cylindrus, as well as 10 diatom species from the Arctic Ocean. We will thus address how environmental changes such as the loss of sea ice in the Arctic Ocean will impact the adaptive evolution and diversity of key primary producers with consequences for biogeochemical cycles in an ecosystem that is under extreme threat by global warming.