Historical biogeography and phenotype-phylogeny of Chroodiscus (lichenized Ascomycota: Ostropales: Graphidaceae)

To analyse the historical biogeography of the lichen genus Chroodiscus using a phenotype-based phylogeny in the context of continental drift and evolution of tropical rain forest vegetation. All tropical regions (Central and South America, Africa, India, Southeast Asia, north-east Australia). We performed a phenotype-based phylogenetic analysis and ancestral character state reconstruction of 14 species of the lichen genus Chroodiscus, using paup* and mesquite; dispersal-vicariance analysis (DIVA) and dispersal-extinction-cladogenesis (DEC) modelling to trace the geographical origin of individual clades; and ordination and clustering by means of pc-ord, based on a novel similarity index, to visualize the biogeographical relationships of floristic regions in which Chroodiscus occurs. The 14 species of Chroodiscus show distinctive distribution patterns, with one pantropical and one amphi-Pacific taxon and 12 species each restricted to a single continent. The genus comprises four clades. DIVA and DEC modelling suggest a South American origin of Chroodiscus in the mid to late Cretaceous (120-100 Ma), with subsequent expansion through a South American-African-Indian-Southeast Asian-Australian dispersal route and late diversification of the argillaceus clade in Southeast Asia. Based on the abundance of extant taxa, the probability of speciation events in Chroodiscus is shown to be extremely low. Slow dispersal of foliicolous rain forest understorey lichens is consistent with estimated phylogenetic ages of individual species and with average lengths of biological species intervals in fungi (10-20 Myr). The present-day distribution of Chroodiscus can be explained by vicariance and mid-distance dispersal through the interconnection or proximity of continental shelves, without the need for recent, trans-oceanic long-distance dispersal. Phylogenetic reconstruction and age estimation for Chroodiscus are consistent with the 'biotic ferry' hypothesis: a South American origin and subsequent eastward expansion through Africa towards Southeast Asia and north-eastern Australia via the Indian subcontinent. The present-day pantropical distributions of many clades and species of foliicolous lichens might thus be explained by eastward expansion through continental drift, along with the evolution of modern rain forests starting 120 Ma, rather than by the existence of a hypothetical continuous area of pre-modern rain forest spanning South America, Africa and Southeast Asia during the mid and late Cretaceous.