Phenotypic responses to whole-genome duplication vs post-polyploidy evolution in Biscutella laevigata

Whole-genome duplication (WGD) is a major driver of plant speciation and often considered to promote rapid adaptation to new or changing environmental conditions. However, the extent to which WGD per se fosters phenotypic novelties and the relative contribution of WGD-induced changes vs post-WGD evolution to traits differences between currently established cytotypes remains largely unexplored. In this study, the phenotypic consequences of WGD and post-WGD evolution on 14 physiological and fitness-related traits were investigated in the diploid-autotetraploid Biscutella laevigata species complex by comparing diploid, synthetic tetraploid, and established tetraploid lines. To assess phenotypic plasticity and stress resilience of the different cytotypes, plants were grown either under stable or changing conditions involving daily temperature stress. WGD resulted in reduced specific leaf area and slowed rosette growth but had no significant effects on biomass-related traits or pollen viability. Phenotypic plasticity was similar among all cytotypes, indicating no increase in plasticity following WGD. Post-WGD evolution acted in contrasting directions on WGD-induced changes, either reverting traits to diploid-like values or maintaining them in established tetraploids. Overall, WGD-induced decrease in survival and fitness was mitigated by post-WGD evolution, resulting in established tetraploids with similar or even higher fitness under changing environmental conditions than diploids. Highlighting a complex interplay between WGD-induced and longer-term phenotypic changes, we conclude on a strong role of post-WGD evolution in the differentiation of current cytotypes and potentially adaptive evolution of tetraploids of B. laevigata.