Contrasting evolutionary histories in Neotropical birds: Divergence across an environmental barrier in South America.

Avian diversity in the Neotropics has been traditionally attributed to the effect of vicariant forces promoting speciation in allopatry. Recent studies have shown that phylogeographical patterns shared among codistributed species cannot be explained by a single vicariant event, as species responses to a common barrier depend on the biological attributes of each taxon. The open vegetation corridor (OVC) isolates Amazonia and the Andean forests from the Atlantic Forest, creating a notorious pattern of avian taxa that are disjunctly codistributed in these forests. Here, we studied and compared the evolutionary histories of Ramphotrigon megacephalum and Pipraeidea melanonota, two passerines with allopatric populations east and west of the OVC that represent different subspecies. These species differ in their biological attributes: R. megacephalum is a sedentary, forest specialist mostly confined to bamboo understorey, whereas P. melanonota is a seasonal migrant and generalist species that ranges in a variety of closed and semi-open environments. We performed genetic and genomic analyses, complemented with the study of coloration and behavioural differentiation, to assess population divergence across the OVC. We found that the evolutionary histories of both R. megacephalum and P. melanonota have been shaped by this environmental barrier. However, these species responded in different and asynchronous manners to the establishment of the OVC and to past connections between the currently isolated South American forests, which can be mostly explained by their distinct ecologies and dispersal abilities. Our results support the fact that the biological attributes of species can make their evolutionary histories idiosyncratic.