Genetic differentiation of life-history traits within populations of the clonal plant Ranunculus reptans

We tested the hypothesis that environmental heterogeneity can maintain gene tic variation in life-history traits within populations of the clonal plant Ranunculus reptans. This may be important for the further evolution and po tential adaptation to environmental change. Moreover, we asked to what exte nt environmental heterogeneity can also reveal trade-offs among fitness com ponents, in particular between sexual reproduction and clonal growth. In th e natural habitat of R. reptans two distinct types of environment can often be found within 10 m distance: vegetation-sparse zones close to the water ("lake") and zones of competition with grasses (mostly Agrostis stolonifera ) more inland ("land"). We grew vegetative offspring of 16 land genotypes a nd 16 take genotypes from four populations in a plant room. Cuttings from e ach genotype were grown with and without competition by the grass A. stolon ifera and on two different substrates, sand and gravel. We found considerable environmental (E) and genetic (G) variation in life-h istory traits. Competition strongly reduced growth, branching, flowering, a nd final biomass. Lake genotypes invested mere into sexual reproduction (me asured as proportion of ramets that flowered) whereas land genotypes invest ed more into vegetative reproduction (proportion of rooted ramets). Signifi cant G x E interactions were consistent with a home-away effect: land-genot ypes performed better if grown under competition, lake-genotypes without co mpetition. These results indicate that genetic variation and phenotypic pla sticity in life-history traits of R. reptans are maintained in a heterogene ous environment, thereby supporting the main hypothesis stated above. They further demonstrate that genetic differentiation occurs even over very shor t distances (10 m). We also found a significant genetic trade-off between s exual and vegetative reproduction (negative genetic correlation between the proportion of flowering ramets and the proportion of rooted ramets). in re sponse to the supplementary question posed above, this suggests that the en vironmental heterogeneity finds its correspondence in the "genetic integrat ion" of life-history traits within the phenotype of R. reptans.