Transcriptional plasticity in diploid and tetraploid Biscutella laevigata from lowland and alpine populations across an elevation gradient
Whole genome duplication is pervasive in plants and polyploids have repeatedly been shown to exhibit fitness advantages over diploids across diverse environments. On the other hand, adapting to specific environments should be more difficult for tetraploids since, compared to diploids, newly introduced mutations start at half the frequency. Therefore, fitness advantages of polyploids have often been attributed to increased phenotypic plasticity. However, previous research has often reported no difference in phenotypic plasticity between diploid and polyploid plants, which indicates differences in plasticity on another level, such as gene expression. In a multiple common gardens experiment across an elevation gradient we determine fitness, phenotypic plasticity and transcriptional plasticity in Buckler Mustards (Biscutella laevigata; Brassicaceae). Using diploid and tetraploid subspecies of B. laevigata, from lowland and alpine populations, we gauge adaptation to the elevation the populations originated in and assess differences of adaptation to elevation between ploidy levels. We found consistent phenotypic differences between diploid and tetraploid B. laevigata, but reaction norms across the three investigated elevation levels and phenotypic plasticity in terms of relative trait distances (RDPI), did not consistently differ between ploidy levels. However, tetraploid B. laevigata demonstrated higher fitness at low elevation (585 m), while exhibiting similar fitness compared to diploids in two higher elevation sites (1236 m and 1967 m). Fitness was higher for B. laevigata of lowland compared to alpine origin, indicating adaptation of lowland populations to low elevation, but not alpine populations to high elevation. Such adaptation to elevation appeared similar in diploids and tetraploid B. laevigata. Investigation of gene expression in a common greenhouse environment revealed only a few dozen genes changing their expression based on past growth in low and high elevation, indicative of highly plastic transcriptomes reflecting mostly immediate environmental changes. Transcriptional plasticity measured in this way appeared similar for both diploids and tetraploids, supporting previous conclusions of no differences in plasticity between ploidy levels.
Whole genome duplication is pervasive in plants and polyploids have repeatedly been shown to exhibit fitness advantages over diploids across diverse environments. On the other hand, adapting to specific environments should be more difficult for tetraploids since, compared to diploids, newly introduced mutations start at half the frequency. Therefore, fitness advantages of polyploids have often been attributed to increased phenotypic plasticity. However, previous research has often reported no difference in phenotypic plasticity between diploid and polyploid plants, which indicates differences in plasticity on another level, such as gene expression. In a multiple common gardens experiment across an elevation gradient we determine fitness, phenotypic plasticity and transcriptional plasticity in Buckler Mustards (Biscutella laevigata; Brassicaceae). Using diploid and tetraploid subspecies of B. laevigata, from lowland and alpine populations, we gauge adaptation to the elevation the populations originated in and assess differences of adaptation to elevation between ploidy levels. We found consistent phenotypic differences between diploid and tetraploid B. laevigata, but reaction norms across the three investigated elevation levels and phenotypic plasticity in terms of relative trait distances (RDPI), did not consistently differ between ploidy levels. However, tetraploid B. laevigata demonstrated higher fitness at low elevation (585 m), while exhibiting similar fitness compared to diploids in two higher elevation sites (1236 m and 1967 m). Fitness was higher for B. laevigata of lowland compared to alpine origin, indicating adaptation of lowland populations to low elevation, but not alpine populations to high elevation. Such adaptation to elevation appeared similar in diploids and tetraploid B. laevigata. Investigation of gene expression in a common greenhouse environment revealed only a few dozen genes changing their expression based on past growth in low and high elevation, indicative of highly plastic transcriptomes reflecting mostly immediate environmental changes. Transcriptional plasticity measured in this way appeared similar for both diploids and tetraploids, supporting previous conclusions of no differences in plasticity between ploidy levels.
Christian Parisod