Does experience with competition matter? Effects of source competitive environment on mean and plastic trait expression in Erodium cicutarium

Interspecific competition is likely to act as an agent for selection on local scales, although evidence in plants is sparse so far. We hypothesize that in annual shade-avoiding grassland species, heterogeneity in the intensity of aboveground competition for light may shape patterns of genetic variation and induce phenotypic plasticity in traits affecting competitive ability. We collected maternal seed families of Erodium cicutarium from replicated high and low competition environments and exposed them to different levels of aboveground competition in a glasshouse. We examined effects of seed source and competition treatment on expression of plant traits related to competitive ability and fitness. Source environments with high levels of competition were significantly more heterogeneous in competition intensity at both intermediate (approx. 10 m) and small (approx. 0.1 m) spatial scales. Seed source and competition treatment both had highly significant effects on trait expression. Greater intensity of competition experienced by maternal plants was coupled with lower vegetative biomass production and slower growth rates, and at the same time lower abortion rates in the offspring. We interpret these findings as an indication of greater reproductive efficiency in the next generation, in response to competition experienced by parents. There was higher total phenotypic variability in the plants from high competition source sites, but equivalent levels of phenotypic plasticity across source-site competition levels; no costs of phenotypic plasticity were detected. We concluded that differences in competition intensity can lead to trait differentiation in the next generation. For E. cicutarium, experience with competition matters: it leads to substantial phenotypic differences and more total variability in the offspring generation.