Adaptive value and costs of physiological plasticity to soil moisture limitation in recombinant inbred lines of Avena barbata.

Costs are hypothesized to constrain the evolution of adaptive phenotypic plasticity, but they have been difficult to quantify because strong selection should eliminate costly genotypes from natural populations. However, recent studies suggest that crosses between natural populations can recover these genotypes. We determined the adaptive value and costs of, as well as the genetic variation for, physiological and morphological plasticity to soil water limitation in Avena barbata recombinant inbred lines (RILs) created by crossing mesic and xeric ecotypes. All traits were plastic, and plasticity in stomatal limitation of photosynthesis and photosynthetic rate before and at reproduction was adaptive. However, we detected a significant cost of plasticity only for stomatal conductance at reproduction, and the mean cost for all traits of A. barbata RILs was at least 50% smaller than costs previously estimated using RILs. In addition, heritabilities for plasticity were <0.1 and were significant only for photosynthesis at reproduction and leaf mass per unit area. Our results suggest that costs are less likely to constrain the evolution of adaptive plasticity in A. barbata than genetic variation for plasticity.