Species delimitation, phylogeny and evolutionary demography of co-distributed, montane frogs in the southern Brazilian Atlantic Forest

• The Brazilian Atlantic Forest (BAF) is a biodiversity hotspot, yet the origins of its diversity are still poorly understood.
• We investigate two co-distributed frog genera associated with montane areas of southern BAF.
• Species delimitation and species-tree analyses indicate concordant patterns of diversification.
• These results are consistent with the existence of a montane refugium in southern BAF during the Quaternary.

The Brazilian Atlantic Forest (BAF) is recognized as one of the world’s biodiversity hotspots, with even more species per unit of area than the Amazon, however the mechanisms that led to such astonishing diversity are yet to be fully understood. In this study, we investigate the diversification of two co-distributed frog genera associated with montane areas of southern BAF: Melanophryniscus (Bufonidae) and Brachycephalus (Brachycephalidae). Species delimitation methods using mitochondrial and nuclear loci supported the existence of a remarkable number of highly endemic species in each genus, most of which occupy only one or a few adjacent mountaintops. Their timing of diversification was highly congruent, supporting recent speciation events within the past 600 thousand years. Extended Bayesian skyline plots indicate that most populations have remained relatively stable in size across the evolutionary past, with recent growth after 0.15 My, suggesting that the drastic changes found in previous studies on lowland frog species were not shared by these montane taxa. These results are consistent with the existence of a montane refugium in southern BAF, allowing species persistence through the climatic shifts experienced along the BAF during the Quaternary.

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