Local adaptation within a population of Hydrocotyle bonariensis

Local adaptation may occur when selection for heritable traits differs from environment to environment and gene flow among environments is restricted. In this study, we used reciprocal transplants to explore both the existence and possible causes of local adaptation in the clonal plant Hydrocotyle bonariensis at high and low elevations of sand dunes on St. George Island, Florida. Individuals found in high dune areas had substantially longer and more internodes and produced larger leaves than those from low dune areas. Reciprocal transplants used 10 genets from high dunes and 10 from low dunes. Greenhouse-grown, replicate plants from each genet were transplanted to high and low dune sites in the field, with and without the natural vegetation removed. The resulting plant growth was consistent with patterns of local adaptation: plants from high sites grew better in high sites than did plants from low sites and vice versa. A significant source × site interaction was found for final below-ground, but not above-ground, biomass. In plots with surrounding vegetation removed, plants from high and low dunes performed similarly in both environments, suggesting that local adaptation was related to interactions with other plants at each dune height. Small-scale local adaptation may be more likely in clonal plants undergoing little gene flow in spatially heterogeneous environments.