A cytochrome-b perspective on Passerina bunting relationships

We sequenced the complete mitochondrial cytochrome-b gene (1,143 nucleotide s) for representatives of each species in the cardinalid genera Passerina ( 6 species), Guiraca (1 species), and Cyanocompsa (3 species), and used a va riety of phylogenetic methods to address relationships within and among gen era. We determined that Passerina, as presently recognized, is paraphyletic . Lazuli Bunting (P amoena) is sister to the much larger Blue Grosbeak (Gui raca caerulea). Indigo Bunting (P. cyanea) and Lazuli Bunting are not siste r taxa as generally thought. In all weighted parsimony trees and for the ga mma-corrected HKY tree, Indigo Bunting is the sister of two sister groups, a "blue" (Lazuli Bunting and Blue Grosbeak) and a "painted" (Rosita's Bunti ng [P. rositae], Orange-breasted Bunting [P. leclancherii], Varied Bunting [P versicolor], and Painted Bunting [P ciris]) clade. The latter two specie s form a highly supported sister pair of relatively more recent origin. Unc orrected (p) distances for ingroup (Passerina and Guiraca) taxa range from 3.0% (P versicolor-P ciris) to 7.6% (P. cyanea-P leclancherii) and average 6.5% overall. Assuming a molecular clock, a bunting "radiation" between 4.1 and 7.3 Mya yielded four lineages. This timing is consistent with fossil e vidence and coincides with a late-Miocene cooling during which a variety of western grassland habitats evolved. A reduction in size at that time may h ave allowed buntings to exploit that new food resource (grass seeds). We sp eculate that the Blue Grosbeak subsequently gained large size and widesprea d distribution as a result of ecological character displacement.