The Evolutionary History of Pagamea (Rubiaceae), a White‐sand Specialist Lineage in Tropical South America

Abstract

AbstractThe flora of the Guiana Shield contains several plant lineages that are restricted to white‐sand vegetation, some of which are widespread in tropical South America. Here, the history of diversification of one of these lineages, the genus Pagamea (Rubiaceae), is reconstructed through phylogenetic hypotheses. Data from chloroplast (rps16 and rpl20‐rps12) and nuclear (ITS) markers were incongruent, with ITS found to be more consistent with morphological criteria to delimit species. Reconstruction of the ancestral area for the genus was ambiguous, with both the western Guiana Shield and the Atlantic coastal areas containing early divergent lineages, but most speciation events appeared to have happened in the western Guiana Shield where most extant diversity is present. Dispersal events into the western Amazon and the Andes (1.5–4.5 Ma) and the eastern Guiana Shield (0.4–2.2 Ma) were followed by speciation events in these regions. Dispersal events between the Amazon and Atlantic rain forest occurred at least three times independently. However, dispersals into new areas were limited, and most regions were found to be phylogenetically clustered. Altitudinal and habitat shifts happened multiple times independently, but ecological traits were found to be phylogenetically conserved, implying that such shifts were not the cause of lineage divergence. The result that most speciation events happened in the western Guiana Shield, where white‐sand habitats predominate in both lowlands and highlands, and which has been less affected by Pleistocene climatic change, coupled with the result that ecological traits are phylogenetically conserved, suggests that the diversification of Pagamea may have been related primarily to the patchy distribution of white‐sand vegetation.