Eocene origin, Miocene diversification and intercontinental dispersal of the genus Drosera (Droseraceae)

Abstract

Resolving the evolutionary history of plant carnivory is of great interest to biologists throughout the world. Among the carnivorous plants, Genus Drosera (Droseraceae) is highly diverse with a wide pantropical distribution. Despite being a group of interest for evolutionary biology studies since the time of Charles Darwin, the historical biogeography of this group remains poorly understood. In this study, with an improved species sampling from Genbank, we present a reanalyzed phylogenetic hypothesis of the genus Drosera. We developed a dated molecular phylogeny of Drosera from DNA sequences of nuclear ITS and chloroplast rbcL genes. Divergence times were estimated on the combined dataset using an uncorrelated lognormal relaxed clock model and a known fossil calibration implemented in BEAST. The maximum clade credibility tree was then used for ancestral range estimations using DEC+J model implemented in BioGeoBEARS. Our analysis suggests that Drosera evolved during the Mid Eocene 36 Ma [95% HPD: 49.5-26] and have diversified and dispersed from the late Miocene onwards. Ancestral areas estimated using the DEC+J models suggest an African origin followed major radiation within Australia. Diversification in Drosera is temporally congruent with the prevailing drier conditions during the Miocene. From Miocene, grasslands and open habitats dominated across continents and might have provided ecological opportunities for their dispersal and diversification. Several long-distance dispersals and range extensions and in situ radiations coinciding with the evolution of drier conditions can explain their extant distribution across continents. Overall our data set provides fresh insights into the biogeographic factors that shaped the origin and evolution of the genus Drosera.