VARIATION IN SEXUAL AND ASEXUAL REPRODUCTION AMONG YOUNG AND OLD POPULATIONS OF THE PERENNIAL MACROPHYTE SPARGANIUM-ERECTUM

We examined how population age affects the relative importance of clon al propagation and sexual reproduction in the aquatic macrophyte Sparg anium erectum. Plants were collected from two newly established popula tions and four successionally mature populations. The comparison of li fe history traits associated with sexual reproduction and clonal multi plication was carried out in a controlled environment experiment. We f ound that several physiological trade-offs occurred between sexual rep roduction and clonal propagation. Moreover, we Found a higher investme nt in sexual reproduction in newly established populations than in old er populations. These results suggest that clonal propagation is favou red at the population level while, because seeds produced by sexual re production are the only means for long distance dispersal, selection w ill favour sexual reproduction at the metapopulation level. This discr epancy between selective pressures at different spatial scales could f avour the maintenance of a mixed sexual-asexual reproductive system in Sparganium erectum.