Recente dispersão através do Rio Amazonas promoveu forte isolamento genético no Formigueiro-ferrugem Myrmoderus ferrugineus (Aves: Thamnophilidae)

Abstract

One of the most debated hypotheses to explain the origin of such a rich Amazonian biota is the "river-barrier" hypothesis, which advocates that main Amazonian rivers acted as powerful barriers promoting isolation and species diversification. Herein, we used an statistical phylogeography approach to study the Ferruginous-backed Antbird species Myrmoderus ferrugineus, an Amazonian upland terra-firme forest endemic species with two known morphologically little differentiated subspecies separated by the mid-Amazon River (M. f. ferrugineus and M. f. elutus). We used the phylogeographic data to address the following alternative scenarios of diversification for M. ferrugineus: 1) the Amazon River does not coincide with major phylogeographic breaks separating M. ferrugineus populations; 2) the Amazon River is correlated with ancient phylogeographic structure within M. ferrugineus, probably resulting from the river's establishment during the Plio-Pleistocene or before that; and 3) the Amazon River correlates with a recent divergence between M. ferrugineus populations, probably due to recent dispersal and isolation after the river's establishment during the Plio-Pleistocene. We sequenced 2 MtDNA and 2 nuclear genes from 13 individuals of M. f. ferrugineus and 15 individuals of M. f. elutus to estimate concatenated and time-calibrated coalescent multilocus phylogenies. We also tested for the occurrence of past population bottlenecks, gene flow and effective population size fluctuations in M. f. ferrugineus and M. f. elutus. Our results retrieved with strong statistical support the monophyly between M. f. ferrugineus and M. f. elutus, and pointed to a scenario of strong population structure and absence of gene flow between these subspecies. However, according to two independent coalescent dating methods, M. f. ferrugineus and M. f. elutus diverged between 2.5 and 75,000 years ago, therefore well after the modern establishment of the Amazon River. Our results demonstrate that even upland terra-firme forest taxa with low dispersal abilities such as antbirds, have been have able to establish populations across the Amazon River after its modern course became established. Whether these events were caused by active or passive dispersal mediated by drainage capture events remain to be determined, although the second scenario is more likely considering the Ferruginous-backed Antbird ecological attributes. Therefore, we anticipate that important drainage capture events involving the middle Amazon River course could have taken place between the Late Pleistocene and as recent as the Holocene, favoring the crossing of several lineages previously isolated on opposite river banks.