Fine-scale genetic structure in Tibouchina papyrus (Pohl) Toledo (Melastomataceae), an endemic and habitat-restricted species from Central Brazil

Spatial genetic structure (SGS) is the non-random distribution of genotypes in space, which is usually correlated with life history traits and is driven by ecological and demographic processes. This study aimed to use spatial statistical analysis methods to assess genetic diversity and spatial genetic structure in three known disjunct localities where Tibouchina papyrus occurs, varying in aggregation and density of individuals and in landscape characteristics. This small tree species is endemic to the "Cerrado" (savannas) region of Central Brazil and is also restricted to elevation rock fields ("campo rupestre"). Therefore, it can be considered a model species to help guide studies on Cerrado endemic plants that are isolated with geographic distributions restricted to this highland habitat. The analyses were based on the polymorphisms at ten microsatellite loci. Our working hypothesis was that wind-dispersed species, such as T. papyrus, present no or low SGS because of the long distance seed gene flow. The spatial genetic structure was indeed weak for two of the three populations. The intensity and shape of the SGS are related to density and aggregation (defined by Ripley's K statistic of spatial aggregation) of individuals in the three localities. Low SGS occurs in populations with aggregation patterns, corroborating the overall hypothesis, although in this species, this pattern depends on the landscape characteristics of each local population.