High resolution microsatellite based analysis of the mating system allows the detection of significant biparental inbreeding in Caryocar brasiliense, an endangered tropical tree species

Abstract

In this work we investigate the mating system of four populations of the endangered tropical tree species Caryocar brasiliense, using genetic data from 10 microsatellite loci. Eight to 10 open-pollinated progeny arrays of 16 individuals, together with their mother tree, were sampled per population. Mating system parameters were estimated under the mixed mating model, implemented by the software MLTR. The single-locus outcrossing rate (ts) varied among loci and populations, but multilocus outcrossing rates (tm) were equal to one for all four populations. Nevertheless, biparental inbreeding (tm - ts) was different from zero for all populations, indicating that outcrossing events may occur between relatives. Our results also indicate that the high polymorphism of microsatellite markers provide an extraordinary resolution to discriminate precisely selfing events from outcrossing events between close relatives. Our results indicate that, although highly outcrossed, C. brasiliense shows high levels of biparental inbreeding, most likely due to the limited flight range of pollinators and restriction in seed dispersal. Furthermore, these results suggest that Cerrado fragmentation could limit gene flow by isolating seed dispersers and territorial small sized bat pollinators inside fragments, increasing the rate of mating between close relatives. The conservation of nonisolated populations in large preserved areas may be necessary to foster outcrossing events between unrelated individuals and thus maintain species viability.