Abstract

Mitochondrial DNA (mtDNA) within a nominal species is often paraphyletic: some individuals have mtDNAs more closely related to those of another species than to other conspecific individuals. Resolution of such discrepancies is an opportunity to uncover interesting biology. If existing taxonomy needs revision, then biological understanding of the taxa involved is immediately improved. If the discrepancy is due to phenomena such as hybridization or very recent divergence from a common ancestor that is not yet 'tracked' in the mtDNA, further, new windows are opened on present and past ecology, and demography. Such discrepancies in the Dusky-capped Flycatcher, Myiarchus tuberculifer (Passeriformes: Tyrannidae), are discussed. Widespread across North, Central and South America with up to 13 recognised subspecies, M. tuberculifer is a taxonomically challenging member of the Myiarchus tyrant-flycatchers, which are in turn among the world's most taxonomically difficult groups of birds because of overall morphological uniformity of the ~22 species. Paraphyly of mtDNA from M. tuberculifer as currently construed should be seen as a stimulus to reassess the morphological diversity within the 'species' and its historical biogeography, which, even for a Myiarchus species, is substantial. Further, integrating the paraphyly of mtDNA within a South American subspecies, M. t. atriceps, with morphological and vocal data, generates the hypothesis that this subspecies comprises at least two taxa, one of which would require naming. A fresh assessment is called for of molecular, morphological and vocal characters in terms of the altitudinal and latitudinal range of the bird.