Low levels of pollen and seed flow in a riparian forest fragment of the dioecious tropical tree Genipa Americana L

Abstract

The intense process of deforestation in tropical regions has resulted in the fragmentation of most native forests. The effects of fragmentation on genetic diversity and effective population size of tree species depends in large part on the level of gene flow among remnant populations. The main objective of this study was to use microsatellite loci to investigate the impact of spatial isolation caused by forest fragmentation on pollen and seed flow in a population of the tropical tree Genipa americana. We also investigate the genetic diversity, inbreeding, and spatial genetic structure (SGS) in adults, regenerants, and open-pollinated seeds. In the studied fragment, all adult trees were mapped, sexed, and sampled. We also mapped and sampled regenerants and collected open-pollinated seeds during two reproductive events. Using parentage analysis, we detected a minimum immigration of pollen at 6% and seeds at 4% and pollen and seeds were dispersed in a pattern of isolation by distance. We found variation in female and male fertility, with the largest females mothering more regenerants and the largest males fathering more seeds. We found significant SGS for adults and regenerants; the SGS in adults resulted in regenerants and seeds produced through mating among relatives (20-40%), which explains the inbreeding detected in all samples. Our results indicate genetic connectivity between the fragment and other populations, possibly due to insect pollination and seed dispersal vectors (barochory, hydrochory, and zoochory by mammals). We discuss our results in terms of in and ex situ conservation.