Polyploidy has important ecological effects, including ploidy-mediated effects on morphology, breeding system and ecological tolerances. However, there is still little comprehensive research available to test its adaptive significance and its role in driving distributional patterns. This work aimed to assess the contribution of genome duplications to ecological divergence using an experimental approach with the diploid-tetraploid Jasione maritima polyploid complex. We explored if individuals with different ploidy differ in their tolerance to water deficit and if this may contribute to explaining the distribution patterns along a latitudinal gradient in the northwest Iberian Peninsula. For that, we used three cytogenetic entities: diploids and established tetraploids collected in natural populations along a latitudinal gradient, and neotetraploids synthesized from diploid populations after treatments with colchicine. Thirty plants from each of the nine populations were grown under controlled conditions with half randomly assigned to the water deficit treatment, and half used as control. We determined experimental plants’ response by measuring fitness-related parameters, such as above and belowground biomass, plant water status, photosynthetic efficiency and pigments, membrane stability, antioxidant capacity and sugars content. Our data shows that biomass, chlorophyll content, photochemical quenching (qP) and non-photochemical quenching (NPQ) in neotetraploids and established tetraploids were significantly higher than in diploids and that these differences could be attributed to genome duplications. In response to the water deficit, diploids seem to use a strategy of avoidance, whereas tetraploids seem to employ the strategy of tolerance to overcome water deficit stress, which appears equally efficient. Additionally, we did not observe a response pattern along the latitudinal gradient of the distributional range of the J. maritima complex. The results indicate that the response to water deficit is population dependent. Further studies are necessary to understand the role of ploidy in explaining the distribution patterns of the J. maritima complex.

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Polyploidy is a pervasive phenomenon in nature and has significantly contributed to the adaptive evolution of plants. The conditions necessary for the spread of neopolyploids in populations of the diploid progenitor are limited; however, the superior competitive ability of neopolyploids may promote its establishment. Here, we assess the contribution of polyploidisation to the divergence of plant traits affecting competitive response, which could explain the successful establishment and current geographic distribution of polyploids. We conducted an intraspecific competition experiment using diploids, neotetraploids and established tetraploids of Jasione maritima var. maritima to determine whether cytotypes differ in phenological, growth and physiological traits and competitive response. Cytotypes respond differently under different competition scenarios with implications for cytotype establishment and distribution. Competition impacted all cytotypes, but neotetraploids were least affected by competition, and the tetraploids were the most impacted. Thus, competitive advantage may have contributed to the displacement of diploid populations and colonisation of new areas by neotetraploids but might have been lost afterwards. Evolutionary changes after polyploidisation have also been detected, and tetraploids invested more in belowground biomass, suggesting that root development might also play a role in colonising southernmost locations. Interestingly, diploids and both tetraploids seem to have different life strategies, the first investing in growth while the latter investing in reserves for the next season. Overall, polyploidisation seems to provide immediate changes that confer an advantage under competition that, together with other factors, may have allowed the establishment of neotetraploids.