Biogeography, phylogenetic relationships and morphological analyses of the South American genus Mutisia L.f. (Asteraceae) shows early connections of two disjunct biodiversity hotspots

Abstract

The Andes is recognized as one of the most biodiverse places on Earth, promoting in its uplift process a series of recent rapid diversification events in different biotic groups like birds, mammals, insects and vascular plants. The uplift of the Andes during the Cenozoic acted as a barrier for many biotic groups, as a scenario for radiation processes due to occupancy of different niches and as a corridor for others. Connections between the Andes and the Atlantic Forest showed intermittent phases along the Cenozoic, affecting the distribution patterns and diversification of different biotic groups. Nowadays, the Andes and the Atlantic Forest are both considered globally relevant biodiversity hotspots. Floristic groups thriving in both hotspots are crucial for a better understanding of their biogeographic history, as well as for informing future conservation actions. Mutisia (Asteraceae), a genus comprising 63 perennial shrubs and vines endemic to South America, shows a marked West-East disjunction: Most species occupy almost the whole Andean chain from Colombia to Patagonia, while a second group encompasses four species distributed in eastern Brazil and the surrounding areas of Paraguay, Uruguay and Argentina. We reconstructed the phylogeny of the genus to assess its possible biogeographic history. We analysed three DNA regions, i.e. the chloroplast trnL-trnF intergenic spacer and the nuclear ribosomal internal and external transcribed spacers, ITS and ETS. Using maximum likelihood and Bayesian inference, gene trees were reconstructed, and a concatenated phylogenetic tree was inferred. Divergence times were estimated by means of BEAST, and the ancestral areas were inferred using BioGeoBEARS. An ancestral reconstruction of morphological traits was also performed, as well as maps representing current richness hotspots within the genus. Phylogenetic analyses strongly support the monophyly of Mutisia, with two well-supported main clades: clade A, with presence of Atlantic-central-northern Andes species, and clade B, with central/southern Andes species. Dating analyses suggest that a main clade separation occurred at the early Miocene, followed by the separation of the Atlantic clade A2 by the late Miocene, and more recent radiations occurred in the central, northern and southern Andes during the Pliocene. Results are in tune with other angiosperm taxa that also underwent rapid radiations, possibly related to environmental and pollinator changes. The biogeographic history of Mutisia is related to morphological adaptations, history and geographic factors acting since the Miocene along the Andes and adjacent areas. Threat assessments and conservation actions for the genus shall include the whole distribution range, including low-range northern and southern Andes species, as well as the distinctive Atlantic Forest clade.