Evolutionary Processes and the Origin of Plant Biodiversity in Old Neotropical Sky-Islands: a Genomic and Model-Based Approach

A large proportion of the world’s plant biodiversity is concentrated on the Neotropics and mountains have been shown to play an important role on this pattern. The Espinhaco/Chapada-Diamantina chain harbors the highly diverse campos rupestres, a sky-island herbaceous-shrubby vegetation mosaic, that occurs above 900 m on nutrient poor, rocky and sandy soils. In this study we used two groups occurring in the campos rupestres and presenting contrasting ecological characteristics (Bulbophyllum sect. Didactyle, Orchidaceae, and Vellozia auriculata, Velloziaceae) to understand the evolutionary process leading to the high species and endemic diversity observed on this vegetation. We observed geographical structure, and this structure was stronger for the less vagile V. auriculata. For Bulbophyllum involutum the gene flow between Espinhaco localities was high, corroborating the notion that the small and light seeds of orchids are able of long-range dispersion. However, our data also support that environment or past demographic events might be important factors driving population differentiation. Overall, the distribution of the genetic variability of B. sect. Didactyle reflects the population geography, but some species have not been recovered as monophyletic. Beyond the importance of disjunction and environmental variability for population differentiation, here we demonstrate that hybridization might be and critical engine for the origin and maintenance of the campos rupestres biodiversity.