Evidence for ecological divergence across a mosaic of soil types in an Amazonian tropical tree: Protium subserratum (Burseraceae)

Soil gradients are known to be an important driver of divergent natural selection in plant populations. Neotropical trees have the highest diversity on earth and it is not uncommon to find soil specialist congeners distributed parapatrically. Nevertheless very little is known about the role that edaphic heterogeneity plays in the origin and maintenance of tropical tree diversity. We predict that the mosaic of different soils in the lowland Amazon rainforest play a major role in generating and maintaining genetic variation in tropical tree populations through ecological divergence. This study examines genetic and morphological differentiation in the tropical tree Protium subserratum populations growing on the mosaic of white-sand, brown-sand and clay soil types distributed parapatrically throughout the western Amazon basin. We use nuclear microsatellites and vegetative characters to answer four major questions: (1) Are populations phenotypically and genetically differentiated across all...