River network rearrangements promote speciation in lowland Amazonian birds

Large Amazonian rivers impede dispersal for many species, but lowland
river networks frequently rearrange, thereby altering the location and
effectiveness of river-barriers through time. These rearrangements may
promote biotic diversification by facilitating episodic allopatry and
secondary contact among populations. We sequenced genome-wide markers to
evaluate histories of divergence and introgression in six Amazonian avian
species-complexes. We first tested the assumption that rivers are barriers
for these taxa and found that even relatively small rivers facilitate
divergence. We then tested whether species diverged with gene flow and
recovered reticulate histories for all species, including one potential
case of hybrid speciation. Our results support the hypothesis that river
dynamics promote speciation and reveal that many rainforest taxa are
micro-endemic, unrecognized and thus threatened with imminent extinction.
We propose that Amazonian hyper-diversity originates in part from
fine-scale barrier displacement processes –including river dynamics– which
allow small populations to differentiate and disperse into secondary
contact.