Mating system and population genetic structure of two shrub species of Helicteres from Brazi

Mating systems strongly influence the distribution of genetic diversity within and among plant populations. Thus, in order to understand microevolution in plant populations, it is important to characterize their mating systems. Mating systems are influenced by a number of genetic and ecological factors, such as compatibility system, genetic structure of population, plant density, number of flowers per plant and pollinator movements. I investigated the simultanous effects of these factors on the mating system of two self-compatible Brazilian shrub species: Helicteres brevispira and H. sacarolha.;Outcrossing rate and plant density had a positive correlation for both species. This result can be explained by the effect of plant density on pollinator movements among plants. Plants in high density have fewer flowers visited per plant during each pollinator visit than plants in low density. Also, pollinators in high density visit many plants several times. These factors increase the chances of pollen exchange among plants in high density.;Temporal and spatial variation in outcrossing rate were detected in H. sacarolha. The variation was related to changes in plant density and number of flowers per plant. The year when number of flowering plants and number of flowers per plant were high, outcrossing rate was also high. The mating system in H. sacarolha is also influenced by pollinator movements. However, factors such as high pollen carry-over and abortion against selfed progeny also affect the outcrossing rate of this species.;The population of H. brevispira is substructured at fine scale as shown by F-statistics and spatial autocorrelation analysis. There is a positive correlation between plant density and substructuring. Substructuring is mainly caused by limited seed dispersal. Although H. sacarolha also has limited seed dispersal, this species shows very little population substructure. This contrast may be explained by differences between the fecundity of these two species.