From southern Africa and beyond: historical biogeography of the Ledebouriinae (Scilloideae, Asparagaceae)

Abstract

AimWithin sub-Saharan Africa, plants inhabiting more seasonal and arid landscapes showcase unique distributional patterns that hint at fascinating evolutionary histories. The Ledebouriinae (Scilloideae, Asparagaceae) are widespread throughout such climates in sub-Saharan Africa, and Madagascar, the Middle East, India, and Sri Lanka. Long-distance dispersal has been hypothesized as leading to such a widespread distribution; however, low taxon sampling and taxonomic uncertainties have made uncovering the history of the Ledebouriinae difficult. Here, using the most comprehensive sampling of the lineage to date, we hypothesize that both vicariance and dispersal events impacted the biogeographical history of these bulbous monocots within and outside of Africa. LocationSub-Saharan Africa, Madagascar, Asia TaxonLedebouriinae (Scilloideae, Asparagaceae) MethodsWe infer age estimates using penalized likelihood as implemented in treePL. Capitalizing on our broad geographic sampling, we use BioGeoBEARS to reconstruct ancestral ranges and investigate the role of vicariance and dispersal. ResultsOur results suggest the Ledebouriinae originated within the past [~]30 myr in southeastern sub-Saharan Africa, with the major subclades arising soon thereafter. Although long-distance dispersal cannot be fully ruled out, our results lead us to hypothesize vicariance was the major process responsible for the current distribution of Ledebouria in Eurasia. We recover two distinct Ledebouria groups that overlap in eastern Africa, but are divided into mostly northern and southern clades with divergent biogeographical histories, and each showing an independent dispersal to Madagascar. A similar north-south split is seen in Drimiopsis. Additionally, we recover a complex biogeographic history in the predominantly sub-Saharan African Ledebouria clade, with a rapid radiation estimated at [~]14 mya. Main conclusionsWe recover evidence to suggest that the expansion of seasonal rainfall and aridity in sub-Saharan Africa, coupled with orogeny, may have fostered the diversification of the Ledebouriinae and many subclades. Miocene-driven aridification may have caused fragmentation of a once widespread distribution that led to their occurrence in Eurasia.