A comparison of cytochrome b and DNA hybridization data bearing on the phylogeny of swallows (Aves: Hirundinidae).

Cytochrome b sequence data from 17 species representing 16 genera of swallows (Aves: Hirundinidae) were compared with DNA-DNA hybridization data from the same species in a taxonomic congruence assessment of swallow phylogeny. In the process, subsets (partitions) of the cytochrome b sequence data were examined in light of the DNA hybridization distances to assess their potential phylogenetic informativeness. When the sequence data were weighted-with or without reference to the DNA hybridization data-they produced parsimony and maximum likelihood (but not distance) trees that were largely congruent with the DNA hybridization tree. To this extent, the cytochrome b data supported many of the phylogenetic conclusions based on the DNA hybridization tree and vice versa. However, the cytochrome b data produced largely unresolved trees when branch robustness was tested by bootstrapping and other methods. This poor resolution appeared to be caused by a lack of hierarchical structure in the cytochrome b distances, which were confined to a narrow range (between 10-13%), compressed by saturation, and noisy. Partition analysis by codon sites and protein domains yielded typical avian cytochrome b patterns, except for idiosyncrasies attributable to the genetic divergence level of swallows in comparison to other groups of birds whose cytochrome b sequences have been analyzed.