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).