Population structure and gene flow of the Brazilian shrub Helicteres brevispira

Helicteres brevispira is a pioneer species of the tropical riparian forest whose populations appear to cycle through episodes of extinction and recolo nization. Therefore, genetic consequences of founding events may strongly a ffect the genetic structure of its populations. An analysis of F-statistics showed that the studied population of N. brevispira is genetically substru ctured with the highest values of F-ST found in areas of high plant densiti es. Spatial autocorrelation analysis showed that genetic patches have diame ters of 3-6 m. Although pollinator movements are usually between plants whi ch are 3-6 m apart, longer flights occur and the neighbourhood area is esti mated to have a diameter of 15 m. This suggests that genetic patches are sm aller than the neighbourhood area. Seed dispersal is limited, mostly less t han 2 m from the mother plants. Thus, short seed dispersal, seed dormancy a nd founder effects in the seed bank may be the most important determinants of genetic structure in populations of H. brevispira. Factors such as drift and inbreeding may also increase the level of substructure in this populat ion, but the equilibrium model of isolation by distance does not fit our da ta.