Low Interannual Variation of Mating System and Gene Flow of Symphonia globulifera in the Brazilian Amazon

Six microsatellite loci were used to compare the mating system and gene flow in two consecutive years of a natural, unlogged population of Symphonia globulifera in a 500 ha experimental plot in the Brazilian Amazon (Flona Tapaj6s). The species had a low density of reproductive trees per hectare (d = 0.46 trees/ha). We analyzed 205 trees and 261 and 487 open-pollinated seeds from 26 and 30 mother-trees in the years 2002 and 2003, respectively. A significant spatial genetic structure was detected for the adult trees for distances up to 100 m. We observed only small interannual differences in multilocus outcrossing rate (tim(2002) = 1.000, tm(2003) = 0.998), biparental inbreeding (Am - ts(2002) = 0.093, tm - ts(2003) = 0.063), and paternity correlation (rp(2002) = 0.414, ip(2003) = 0.386). The number of pollen donors contributing to mating of each tree in both years was estimated to be low (Siep = 2.4 - 4.0). Using TwOGENER analysis to calculate the density of reproductive trees and the distance of pollen dispersal for normal and exponential models, the lowest error was detected for exponential model. For this model, the estimated density of reproductive trees was lower in 2002 (ae(2002) = 0.03 trees/ha) than 2003 (de(2003) = 0.19 trees/ha), resulting in a higher distance of pollen dispersal in 2002 (3(2002) = 444 m) than 2003 (S(2003) = 154 m), although these changes did not affect the outcrossing and correlated mating rates.