Paleotemperatures and recurrent habitat shifts drive diversification of treefrogs across distinct biodiversity hotspots in sub-Amazonian South America

Aim We investigate the biogeographical history and diversification in a treefrog lineage distributed in contrasting (open and forested) ecoregions of South America, including three biodiversity hotspots. We evaluate the role of dispersal and whether other factors such as diversity-dependence or paleotemperatures could explain the diversification pattern for this group. Especially focusing on the savanna endemics, we illuminate the processes governing the species assembly and evolution of the Cerrado savanna. Location South American ecoregions south of the Amazon (i.e. Atlantic Forest, Cerrado, Araucaria Forest, Pampas, Central and Southern Andes). Taxon Boana pulchella group. Methods We built the most complete time-calibrated phylogeny for the group to date. We then reconstructed ancestral ranges using the dispersal-extinction-cladogenesis (DEC) model comparing different dispersal scenarios considering distance, adjacency and ecological similarity among regions. Centre-of-origin hypotheses in forest and open ecoregions were also tested. Using biogeographical stochastic mapping, we additionally estimated the contribution of range shifts across different biomes. Lastly, we evaluated several diversification models, including the effect of time, diversity-dependence and temperature-dependence on speciation and extinction rates. Results The Boana pulchella group originated during the Early Miocene (similar to 17.5 MYA) and underwent high speciation rates during the Middle Miocene Climatic Optimum, with a decreasing trend following the Miocene Climatic Transition. We found no support for a single ecoregion acting as a centre of origin and diversification; instead, we inferred recurrent range shifts with dispersal among dissimilar adjacent ecoregions. Speciation linearly dependent on paleotemperatures, with either no or very low constant extinction rates, best explained the slowdown diversification pattern. Main conclusions Our results support a species assembly of Cerrado savanna in South America during the Miocene with intermittent interchange with rain forest habitats. Past climate changes impacted the rate new species originated with apparently no impact on extinction. Finally, the repeated habitat shifts among open/dry and forested/humid ecoregions, rather than long-term in-situ diversification in single areas, highlights the very dynamic historical interchange between contrasting habitats in South America, possibly contributing to its high species diversity.

Automated summary

This study investigates the biogeographical history and diversification of a treefrog lineage in contrasting ecoregions of South America. The research found no support for a single ecoregion acting as a center of origin and diversification, instead inferring recurrent range shifts among dissimilar adjacent ecoregions.