Effects of variation at flowering and dormancy loci on life history and fitness responses of Arabidopsis thaliana to different precipitation regimes
The timing of germination and flowering greatly determine the survival and reproductive success of an annual plant. The timing of phenological events is determined by a plant’s genotype and its interaction with the environment. For instance, in Arabidopsis thaliana variation in the gene DOG1 affects the duration of primary dormancy, and variation at the major flowering time gene FRI affects the requirement for overwinter vernalization and the seasonal timing of flowering. Moreover, within-season rainfall variability can have drastic effects on a plant’s fitness. The aim of our study is to investigate if plants with different genotypes controlling the timing of germination and flowering display different responses to rainfall variability. For instance, does delayed germination allow plants to avoid an early drought during the rainy season? Are plants that flower early in the spring able to set flower in a short growth season? In order to answer these questions we quantified the effect of simulated rainfall variation on different A. thaliana near isogenic lines (NILs) with introgressed alleles controlling the timing of germination (DOG1), flowering (FRI), or both on life history traits and fitness. Plants were grown under ambient temperature and light conditions in a screen house which allowed manipulation of rainfall events. Simulated rainfall variability conditions included: varying onset and length of precipitation, and an early and late drought period. Timing and percentage of germination, rosette growth rate, bolting, flowering and fruiting dates were recorded, and fruit and seed size and number were also measured to estimate fitness.
Contrary to prediction, allelic variation at DOG1 did not affect germination timing or fitness of plants in early-season rainfall treatments. As expected, the short rainy season treatment selected against late-flowering plants. The late drought had larger effects on plant fitness than the early drought. The strong DOG1 allele did not give a relative advantage to the plants in the early drought treatment, as we did not see differences in pre-drought germination between the different genotypes. Late drought caused high pre-reproductive mortality in genotypes with the late-flowering FRI allele, whereas other genotypes were able to set a small amount of seed. Thus, in natural seasonal environments, different precipitation regimes may affect the relative fitness of different genotypes, but phenological predictions based on controlled environment studies may not be realistic.