Diversification of Galianthe species (Rubiaceae) in the Neotropical seasonally dry forests: a case study of a mainly subshrubby genus

Abstract

Aim ‒ To evaluate the current distribution of the species of the genus Galianthe by track analysis, and to establish the distributional patterns based on the available tectonic information and the biogeographical regionalization of the Neotropical region. Methods ‒ A total of 2680 geographical records of 55 species were analysed, representing 100% of the species assigned to Galianthe. Individual tracks were obtained for each species by plotting localities and connecting them by minimum-spanning trees. Generalized tracks and nodes were determined from the spatial overlap among individual tracks. Individual and generalized tracks and nodes were geographically located using DIVA-GIS. Generalized tracks and nodes were superimposed on two layers, one of them with the biogeographical provinces of the Neotropical region, and the other with the distribution of Neotropical seasonally dry forests.Results ‒ Five generalized tracks and four nodes were identified, all located within the Brazilian and Chacoan subregions. These nodes coincide with almost all fragments of Neotropical seasonally dry forests.Main conclusions ‒ Our results demonstrate the intimate relationship of the ancestral biota of Galianthe with the fragments of Neotropical seasonally dry forests, suggesting that they could serve as refugia during unfavourable geological periods and, therefore, actively influence the current distribution of their species. In addition, the early dispersal of the species, along with the various vicariant events such as the rise of the Andes, the cooling and aridification during the Oligocene-Miocene, the formation of the Chacoan subregion, and the alluvial dynamics during the Pliocene-Holocene could favoured adaptive radiation of Galianthe species.