Naturally fragmented and isolated distribution in subtropical grassland patches affects genetic diversity and structure at different spatial scales: The case of Tibouchina hatschbachii , an endemic shrub from Brazil.

PREMISE OF THE STUDY: The genetic structure of organisms results from the interactions between life history traits and the ecological and demographic characteristics of the landscape that shape the intra- and interpopulation genetic variation in space and time. In this study, we used a species restricted to islands of grassland vegetation in southern Brazil to investigate the effects of its naturally fragmented distribution on diversity and genetic structure patterns.

METHODS: Diversity and intra- and interpopulational genetic structure were analyzed using polymorphisms of eight nuclear microsatellite markers in 205 individuals of T. hatschbachii and Bayesian and multivariate methods.

KEY RESULTS: At the intrapopulation level, populations presented low genetic diversity and strong spatial genetic structure, indicating a greater spatial autocorrelation until ∼50-500 m. At the interpopulation level, genetic variation partitioned into two geographically structured genetic clusters. Gene flow through pollen was more efficient than gene flow by seeds.

CONCLUSIONS: Genetic structure was influenced locally by seed and pollen dispersal dynamics and regionally by fragmentation of the grassland landscape. This study highlights the importance of geological barriers, and potentially a role for genetic drift, in influencing diversification of species in subtropical grasslands of southern Brazil.