Non-monophyly and deep genetic differentiation across low-elevation barriers in a Neotropical montane bird (Basileuterus tristriatus; Aves: Parulidae).

Most widespread birds of Neotropical cloud forests exhibit phenotypic variation that is partitioned geographically suggesting allopatric divergence, but little is known about the extent to which such phenotypic differentiation is consistent with genetic variation. We studied geographic patterns of genetic differentiation in the Three-striped Warbler (Basileuterus tristriatus), a polytypic and widespread understory bird of the foothills and mid-elevation zone of the tropical Andes and adjacent mountains of Central and South America. We sequenced mitochondrial DNA for 196 samples covering the entire range of B. tristriatus, as well as 22 samples of its putative closest relatives: the Three-banded (B. trifasciatus) and Santa Marta (B. basilicus) warblers. We found deep genetic structure across the range of B. tristriatus, which consisted of ten major clades including B. trifasciatus, a species that was nested within B. tristriatus. In contrast, B. basilicus was not closely related to B. tristriatus but part of a clade of Myiothlypis warblers. Geographic boundaries among clades were clearly related to lowland gaps separating subspecies groups. The subspecies melanotis of the mountains of Central America was sister to a large clade including B. t. tacarcunae, and the rest of South American clades, including B. trifasciatus. Five clades are found in the northern Andes, where no signs of gene flow were found across barriers such as the Táchira Depression or the Magdalena valley. Our study highlights the importance of valleys in promoting and maintaining divergence in a lower montane forest bird. The substantial genetic and phenotypic differentiation, and the paraphyly uncovered in B. tristriatus, may call for revising its species boundaries.