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Oceanic photosynthetic protists such as diatoms contribute at least 20% of global primary production. Yet, how their genomes evolve under conditions of natural selection to cope with environmental change of the upper ocean has barely been investigated. However, this fundamental knowledge is not only essential to identify mechanisms of how they adapt, but it may also be used to investigate and to predict the evolutionary response of important primary producers to global climate change. To address this knowledge gap, this lecture will discuss the concept of adaptive evolution and how it can be applied to identify evolutionary mechanisms that shape the structure and function of protist genomes using model diatoms as a test case. By applying the approach of experimental evolution to wild-type and genetically modified (CRISPR/Cas genome editing) diatom strains
under conditions of natural (temperature change) and artificial selection (DNA mutagen), our work not only revealed mechanisms of adaptive genome evolution in diatoms, but it also has shown that there are hotspots of evolution in the genome depending on the selection pressure imposed. Furthermore, the geography of chromosomes impacts the rise of genetic variants involved in adaptation and population differentiation. If the mechanisms of adaptive evolution in diatoms are conserved across diverse protists and possibly other eukaryotes remains to be identified.
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