Time calibrated tree of Dioscorea (Dioscoreaceae) indicates four origins of yams in the Neotropics since the Eocene

Abstract

The yam genus Dioscorea comprises circa 650 species of tropical vines with starch rich tubers, usefull as energy source and prospection of secondary metabolites. The Neotropical Region holds the highest diversity of species and morphology of yams. We generated a time-calibrated tree for Dioscorea using, for the first time, a dense sampling of Neotropical species to trace the biogeography of these plants in this region. Four origins of Dioscorea in the neotropics were estimated since Eocene. The two most diverse lineages originated between Eocene and Oligocene,respectively in Southern Andes and eastern South America.They occupied the South American Dry Diagonal after the Miocene, but clade II remained associated to forest habitats. Several exchanges between Dry Diagonal and adjacent forested biomes occurred, corroborating the interchange between these vegetation types. Dispersals to Central America occurred before the closure of the Panama Isthmus by long distance dispersal. We highlight two important events of long distance dispersal, the colonization of Central American before the closure of Isthmus of Panama and the dispersal of D. antally lineage to Madagascar. In addition, our phylogenetic tree evidenced the unnatural nature of the classical infrageneric classification of Dioscorea. The taxonomic implications of our results is also discussed.