From the Neotropics to the Namib: evidence for rapid ecological divergence following extreme long-distance dispersal

Extreme long-distance dispersal is an important process in plant biogeography. Such events can lead to rapid diversification due to founder effects, genetic drift and novel selection in recipient environments. Balloon vines (Cardiospermum spp.) are mainly Neotropical, but include two native southern African species, the endemic desert-adapted C.pechuelii and the moist subtropical C.corindum (which also occurs in the Neotropics). We used phylogenetic approaches (internal transcribed spacer (ITS), rpl32 and trnL-trnF DNA sequencing data) and population genetics (amplified fragment length polymorphism (AFLP) analyses) to confirm the long-distance dispersal of C.corindum to southern Africa and to reveal the subsequent divergence of the morphologically and ecologically extreme but genetically close C.pechuelii. We could not judge whether incongruences between ecological requirements and morphology and gene trees for the African species resulted from ongoing gene flow or incomplete lineage sorting, but our findings do support recent divergence of C.pechuelii from C.corindum in Africa following transoceanic dispersal of the lineage.