Diversification of Antbirds Associated with Amazonian Flooded Forest Habitats

Rivers represent one of the few geographic barriers that bisect, and promote allopatric speciation, in an otherwise continuous landscape of the Amazon basin. In contrast to Amazonian understory forests birds, which replace each other across river barriers, a strong barrier effect has not been reported for flooded forest species, which may experience rivers as dispersal corridors rather than as barriers. The apparent lack of geographic barriers for flooded forest birds raises the possibility that parapatric rather than allopatric speciation, might drive divergence in this habitat. Parapatric speciation usually involves gradual divergence across a species range, frequently involving divergence across geographically structured ecological gradients. Here I used morphometrics, plumage and genome-wide SNP datasets to uncover clinal patterns in three species of flooded forest antbirds at different stages of divergence. I found weak phylogeographic structure in Hypocnemoides maculicauda and H. melanopogon and much stronger structure in Sclateria naevia. While the clinal patterns uncovered in H. maculicauda and H. melanopogon could be consistent with either parapatric divergence or secondary contact, Sclateria exhibited strongly concordant cline centres across nuclear loci, mitochondrial DNA and female plumage, consistent with secondary contact between an eastern and western lineage that diverged in allopatry. I also applied coalescent modelling to distinguish between allopatric, parapatric or mixed allo-parapatric models in driving the diversification of Hypocnemoides from their common ancestor. The parapatric model of diversification was rejected in favor of one including an allopatric phase followed by secondary contact prior to the completion of speciation. Thus, while parapatry may have played a role in speciation, an initial allopatric phase is supported by this model. I proposed that the main drivers of genetic differentiation in flooded forest birds were climatic fluctuations caused by glacial and interglacial cycles. These species probably suffered multiple cycles of population expansion and retraction that resulted in the current phylogeographic structure. Repeated episodes of secondary contact during interglacials might explain why speciation in flooded forest birds is rare. Allopatric barriers have rarely persisted long enough to cause speciation, and cycles of expansion of populations erased part of the accumulated genetic divergence, impeding the completion of reproductive isolation.Ph.D.2021-07-19 00:00:0