Phylogeography of the Chestnut-tailed Antbird (Myrmeciza hemimelaena, Thamnophilidae) in lowland Amazonia: evidence for river-mediated cryptic diversification centered on the Pleistocene

Patterns of molecular phylogeography and population genetic structure are essential to understanding the historical processes affecting diversity in the Amazon. Here, we examined the patterns of spatial and temporal diversification of Mymeciza hemimelaena, a polytypic species endemic to the Amazon. Sequences of the mitochondrial ND2 and cytochrome b genes of 63 individuals distributed throughout the entire range of M. hemimelaena were investigated, including both of the currently valid subspecies: M. hemimelaena hemimelaena and M. hemimelaena pallens. Based on a combination of phylogeographic tools, molecular dating, and population genetics methods we reconstructed the spatio-temporal scenario of diversification of M. hemimelaena in the Amazon. The genetic data revealed three well-supported reciprocally monophyletic groups in M. hemimelaena separated by high genetic distances, which can also be distinguished by a combination of morphological and vocal characters. Two of these clades correspond to the already named taxa hemimelaena and pallens and are separated by the upper Madeira River, a main Amazonian tributary. The third clade is distributed between the middle reaches of the Madeira River and the much smaller tributaries Jiparaná and Aripuanã and is currently treated as pallens, even though it clearly constitutes an independent evolutionary lineage deserving separate species status. Molecular clock and population genetics analyses indicate that diversification in this group occurred throughout the Pleistocene, with demographic fluctuations inferred for M. h. hemimelaena and M.h. pallens. Our findings provide support for a complex diversification scenario, whereby paleo-drainage changes could have acted in creating opportunities for cladogenesis in the M. hemimelaena complex.