DNA hybridization evidence for the principal lineages of hummingbirds (Aves:Trochilidae)

The spectacular evolutionary radiation of hummingbirds (Trochilidae) hasserved as a model system for many biological studies. To begin to provide ahistorical context for these investigations, we generated a complete matrixof DNA hybridization distances among 26 hummingbirds and an outgroup swift(Chaetura pelagica) to determine the principal hummingbird lineages. FITCHtopologies estimated from symmetrized delta TmH-C values and subjected tovarious validation methods (bootstrapping, weighted jackknifing, branchlength significance) indicated a fundamental split between hermit(Eutoxeres aquila, Threnetes ruckeri; Phaethornithinae) and nonhermit(Trochilinae) hummingbirds, and provided strong support for six principalnonhermit clades with the following branching order: (1) a predominantlylowland group comprising caribs (Eulampis holosericeus) and relatives(Androdon aequatorialis and Heliothryx barroti) with violet-ears (Colibricoruscans) and relatives (Doryfera ludovicae); (2) an Andean-associatedclade of highly polytypic taxa (Eriocnemis, Heliodoxa, and Coeligena); (3)a second endemic Andean clade (Oreotrochilus chimborazo, Aglaiocercuscoelestis, and Lesbia victoriae) paired with thorntails (Popelairiaconversii); (4) emeralds and relatives (Chlorostilbon mellisugus, Amaziliatzacatl, Thalurania colombica, Orthorhyncus cristatus and Campylopterusvillaviscensio); (5) mountain-gems (Lampornis clemenciae and Eugenesfulgens); and (6) tiny bee-like forms (Archilochus colubris, Myrtis fanny,Acestrura mulsant, and Philodice mitchellii). Corresponding analyses on amatrix of unsymmetrized delta values gave similar support for theserelationships except that the branching order of the two Andean clades (2,3 above) was unresolved. In general, subsidiary relationships wereconsistent and well supported by both matrices, sometimes revealingsurprising associations between forms that differ dramatically in plumageand bill morphology. Our results also reveal some basic aspects ofhummingbird ecologic and morphologic evolution. For example, most of thediverse endemic Andean assemblage apparently comprises two geneticallydivergent clades, whereas the majority of North American hummingbirdsbelong a single third clade. Genetic distances separating somemorphologically distinct genera (Oreotrochilus, Aglaiocercus, Lesbia;Myrtis, Acestrura, Philodice) were no greater than among congeneric(Coeligena) species, indicating that, in hummingbirds, morphologicaldivergence does not necessarily reflect level of genetic divergence.