Pre-Pleistocene differentiation among chat-tyrants

Most species of chat-tyrants (Ochthoeca, Silvicultrix) are widespread along the length of the Andes, with broadly overlapping ranges, but segregated in different altitudinal zones or habitats. We used mitochondrial DNA sequences to study their phylogenetic relationships. Our data show considerable divergence and multiple base substitutions at some positions between geographically overlapping species. Such divergence probably predates the period of marked ecoclimatic changes in the Pleistocene, whereas vicariance patterns may reflect events in the lower Pleistocene. Only some of the boundaries between allospecies correspond to marked topographic barriers, and we suggest that sharp species-replacements indicate secondary contact zones. An evolutionary dynamic scenario is suggested where divergence of isolated populations is followed by establishment of sharp geographical replacements and, with development of full ecological compatibility, establishment of broad overlap along the Andes cordillera. The phylogeny suggests a series of adaptive shifts from the ancestral habitat of scrub and river margins in tropical lowlands to bushy highlands and elfin forest, then colonization of edge habitats in the humid montane forest and finally interior montane and submontane forest. However, the adaptive redistribution has obscured the early vicariance events in the group. The results support the monophyly of all chattyrants, but with a distinctive internal structure, where Silvicultrix is a monophyletic internal branch within Ochthoeca. Support also is given for a close relationship between Tumbezia salvini and Ochthoeca. We suggest keeping Tumbezia as a separate genus, merging Silvicultrix with Ochthoeca, and elevating O. frontalis and spodionota, and O. cinnamomeiventris and thoracica to species rank.