The biogeography of the Andean-Atlantic Forests connection: a multilocus study with passerines

We have studied the biogeographic history of the connection between the Andean and the Atlantic rainforests by studying the phylogeographic structure of the forest passerines Syndactyla rufosuperciliata and Arremon flavirostris. In addition, we evaluated the molecular systematics of the species’ intraspecific lineages. The central Andean rainforests are isolated from the Atlantic forest by dry and open biomes (Chaco and Cerrado). Despite of this isolation, both rainforests share closely related lineages, which denotes a recent biogeographic connection. Both regions could have been linked through gallery forests in the Cerrado, or alternatively, by gallery forest along the main rivers of the Chaco. We performed conventional phylogenetic analyses using DNA sequences, and population analyses with genomic data collected by double digestion and random sequencing (ddRadSeq) of 18 to 30 samples per species (about 4000 loci each). We evaluated population structure with STRUCTURE and performed coalescent analyses to estimate gene flow in GPHOCS. Results indicated for both species that the major phylogeographic disjunction occurred between the Andean and the Atlantic regions, during the Mid-Pleistocene. The STRUCTURE and gene flow analyses supported for both species that the Cerrado was the main route of connection between regions, rejecting any important recent link through Chaco. This study, combined with our previous analyses, suggests that the biodiversity of the Andean and of the Atlantic forests have been impacted by cycles of connections through the Cerrado. This study also supports to split the Andean and Atlantic forest lineages of both species into full species.