Non-monophyletic taxa and cryptic species--evidence from a molecular phylogeny of leaf-warblers (Phylloscopus, Aves)

The avian taxa Cryptigata and Acanthopneuste have been treated either as subgenera within Phylloscopus (leaf-warblers), or as a distinct genus and an informal group, respectively. The circumscriptions of these taxa have varied between authors. We estimated the phylogeny, based on the mitochondrial cytochrome b and 12S genes and the nuclear myoglobin intron II, of all except two of the species placed in the Cryptigata and Acanthopneuste groups, as well as two recently described species and representatives of all subgenera and major clades in Phylloscopus and Seicercus recognized by previous studies. Neither Cryptigata nor Acanthopneuste is found to be monophyletic. The polytypic species P. reguloides and P. davisoni show deep divergences between some of their respective subspecies, and the latter species is non-monophyletic. We propose that the former be split into three species and the latter into two species. Seicercus xanthoschistos is nested in a clade that includes only Phylloscopus, and we recommend that it be placed in Phylloscopus. The rate of morphological divergence varies considerably among the taxa in this study. Our results emphasize the importance of dense taxon sampling in intrageneric phylogenetic studies.