The historical connections between the Amazon and the Atlantic Forest revisited

Aim: To assess ancient biotic connections between the Amazon Forest (AmF) and the Atlantic Forest (AtF) based on environmental niche modelling (ENM), palaeobiological, and molecular evidence; to test Por (1992)'s hypothesis of the south-eastern -north-western (SE-NW) route as the most important route in terms of frequency and duration; to evaluate past climatic conditions associated with the routes. Location: South America. Methods: We generated random points in climate space of AmF and AtF and identified two major climatic groups in the shared environmental space (colder and warmer) with a K-means cluster analysis. We modelled each climatic group using eleven algorithms of ENM and selected the best model, projecting the results back to 120 ka. We used published data on South American palaeopalynology, speleothem and travertine chronology for model validation. We also accessed vertebrate molecular studies and extracted the split timing of lineages distributed both in the AmF and the AtF to test Por (1992)'s hypothesis in more ancient times. Results: Palynological and speleothem studies supported the results of our ENM models, indicating expansion of cold-adapted species along the SE-NW and NE routes in the LGM. The SE-NW route was also supported in the LIG, however, involving warm-adapted species. Our results support Por (1992)'s hypothesis and suggest that the SE-NW was established more than once in the past, involving different plant communities each time, adapted to different temperature conditions. Vertebrate molecular studies also support Por (1992)'s hypothesis and suggest that the SE-NW route was established since the Andean uplift. Main Conclusions: The SE-NW route is the most ancient connection route between the AmF and the AtF and probably was established since the Andean uplift and the formation of the South American monsoon system. This route was established many times in the past, alternating by the distribution expansion of coldadapted and warm-adapted plant communities.