Straight-billed Woodcreeper (Xiphorhynchus picus) Science Article 1
Among those few hypotheses amenable to falsification by phylogenetic methods concerning the diversification of the Amazonian biota, three can be singled out because of their verifiable predictions: the riverine barrier, the gradient, and the basal trichotomy hypotheses. I used phylogenetic and population genetics methods to reconstruct the diversification history of the genus Xiphorhynchus (aves: Dendrocolaptidae) in Amazonia. First, I estimated the phylogeny of the entire genus Xiphorhynchus to test a key prediction of the gradient hypothesis; secondly, I documented phylogeographies of a superspecies associated with upland forest (X. spixii / elegans) and two species linked to floodplain forest (X. kienerii and X. obsoletus) to evaluate predictions of the riverine barrier and basal trichotomy hypotheses. The phylogeny estimated for the genus Xiphorhynchus falsified an anticipated sister relationship between floodplain and upland forest species, as predicted by the gradient hypothesis. Phylogeographic and population genetics analyses of the upland forest superspecies (X. spixii / elegans), and floodplain forest species (X. kienerii and X. obsoletus) indicated that predictions of the riverine barrier hypothesishold only for populations of the upland forest superspecies separated by rivers located on the Brazilian shield; in contrast, rivers located in western Amazonia did not represent areas of primary divergence for populations of X. spixii / elegans.
Alexandre Aleixo, Dissertation submitted to the Graduate Faculty of theLouisiana State University