Limited pollen dispersal and biparental inbreeding in Symphonia globulifera in French Guiana

In this paper, we report a study of the mating system and gene flow of Symphonia globulifera, a hermaphroditic, mainly bird-pollinated tree species with a large geographic distribution in the tropical Americas and Africa.

Using three microsatellites, we analysed 534 seeds of 28 open pollinated families and 164 adults at the experimental site ‘Paracou’ in French Guiana. We observed, compared to other tropical tree species, relatively high values for the effective number of alleles.
Significant spatial genetic structure was detected, with trees at distances up to 150 m more genetically similar than expected at random.

We estimated parameters of the mating system and gene flow by using the mixed mating model and the TwoGener approach.
The estimated multilocus outcrossing rate, tm, was 0.920.
A significant level of biparental inbreeding and a high proportion of full-sibs were estimated for the 28 seed arrays. We estimated mean pollen dispersal distances between 27 and 53 m according to the dispersal models used. Although the adult population density of S. globulifera in Paracou was relatively high, the joint estimation of pollen dispersal and density of reproductive trees gave effective density estimates of 1.6 and 1.3 trees/ha.

The parameters of the mating system and gene flow are discussed in the context of spatial genetic and demographic structures, flowering phenology and pollinator composition and behaviour.