Testing big evolutionary hypotheses with small organisms

Polyploids, organisms that underwent a whole genome duplication (WGD), possess one extra copy of their genome, which is free to evolve new functionality. Many WGDs are accordingly found in very successful eukaryotic lineages characterized by particular biological innovations and/or diversifications. However, the possession of two complete genomes is generally not well tolerated by cells leading to harmful effects on the overall fitness and fertility of the organism. This results in a paradox between the observed immediate negative effects of WGD, and their attributed long-term positive effects. In previous work, we found that many plant polyploids became established during the last mass extinction event. Present-day polyploids are also more abundant in stressful environments such as the Arctic. We therefore hypothesize that stress can enhance polyploid establishment, because their plastic phenotypes and genotypes can enable rapid adaptive changes that allow survival. To test this hypothesis, we propose an evolutionary experiment based on a unicellular green algal model system. First, we will artificially create polyploid strains and subject them to a wide variety of stressors to quantify their survival. Second, we will select the most successful polyploid populations and sequence their complete genomes every few generations to identify the genomic features that allow their success. Such an experiment will significantly contribute to our understanding of polyploid organisms.