Strong genetic differentiation on a small geographic scale in the Neotropical rainforest understory tree Paypayrola blanchetiana (Violaceae)

Self-incompatible plants as well as common plant species are expected to be especially vulnerable to the deleterious effects of fragmentation on genetic diversity. Paypayrola blanchetiana (Violaceae) is a common, self-incompatible understory tree in the East Brazilian Atlantic forest. Its autochorous seed dispersal and occurrence in dense, well-separated clusters makes it an interesting model for studies of gene flow and genetic structuring on a small geographic scale. A previous study has found remarkably low fruit set and frequent seed abortions in this species in several populations situated in forest fragments. We tested the hypothesis that P. blanchetiana is affected by inbreeding and loss of genetic diversity in a fragmented landscape. Nine nuclear and three plastid microsatellite loci were genotyped for 285 individuals (149 adult trees and 136 saplings) across seven populations in five forest fragments in a 240-km(2) sugarcane-rainforest matrix. We found a low to moderate genetic diversity in nuclear loci of P. blanchetiana, population structuring on a small geographical scale and high levels of inbreeding. Haplotype distributions confirmed that seed dispersal is very limited. There were, however, no signs for lower genetic diversity or higher inbreeding in populations situated in the smallest forest fragments. Furthermore, genetic diversity was not lower in the sapling cohort, which was created in post-fragmentation condition. Therefore, we may be witnessing the genetic consequences of this species' biology, rather than immediate effects of fragmentation.