Selection analyses
Selection on several traits differed between low and high watering in the greenhouse (Fig. 2). As in the field experiment, days to flowering and leaf number at flowering experienced stronger directional selection under low water availability (water availability × days to flowering: χ2=13.6, df=1, p<0.001, blow=-0.3, bhigh=-0.08; water availability × leaf number at flowering: χ2=9.4, df=1, p=0.002, blow=-0.24, bhigh=-0.1). The third trait showing rapid evolution, reproductive allocation, was generally under strong selection due to its close correlation with relative fitness (Fig. 2); yet a significant interaction with water availability indicated that high reproductive allocation was more favored under low than under high watering (χ2=114.6, df=1, p<0.001, blow=0.7, bhigh=0.35).
Among traits without significant rapid evolution, vegetative biomass was stronger selected against under low water availability than under high water availability (χ2=17.1, df=1, p<0.001, Fig. 2). Because this negative correlation with relative fitness (b=-0.24) disappeared (b=0.01) when reproductive allocation was added to the model, this may be an indirect effect driven by the observed selection for high reproductive allocation. No differential selection was found for stomata density (χ2=2.16, df=1, p=0.14, Fig. 2) and for plant height, where tall plants were favored alike under low and high water availability (Fig. 2, χ2=0.21, df=1, p=0.65).