DNA HYBRIDIZATION EVIDENCE FOR THE PRINCIPAL LINEAGES OF HUMMINGBIRDS(AVES, TROCHILIDAE)

The spectacular evolutionary radiation of hummingbirds (Trochilidae) h as served as a model system for many biological studies. To begin to p rovide a historical context for these investigations, we generated a c omplete matrix of DNA hybridization distances among 26 hummingbirds an d an outgroup swift (Chaetura pelagica) to determine the principal hum mingbird lineages. FITCH topologies estimated from symmetrized Delta T mH-C values and subjected to various validation methods (bootstrapping , weighted jackknifing, branch length significance) indicated a fundam ental split between hermit (Eutoxeres aquila, Threnetes ruckeri; Phaet hornithinae) and nonhermit (Trochilinae) hummingbirds, and provided st rong support for six principal nonhermit clades with the following bra nching order: (1) a predominantly lowland group comprising caribs (Eul ampis holosericeus) and relatives (Androdon aequatorialis and Heliothr yx barroti) with violet-ears (Colibri coruscans) and relatives (Doryfe ra ludovicae); (2) an Andean-associated clade of highly polytypic taxa (Eriocnemis, Heliadoxa, and Coeligena); (3) a second endemic Andean c lade (Oreotrochilus chimborazo, Aglaiocercus coelestis, and Lesbia vic toriae) paired with thorntails (Popelairia conversii) (4) emeralds and relatives (Chlorostilbon mellisugus, Amazilia tzacatl, Thalurania col ombica, Orthorhyncus cristatus and Campylopterus villaviscensio); (5) mountain-gems (Lampornis clemenciae and Eugeness fulgens); and (6) tin y bee-like forms (Archilochus colubris, Myrtis fanny, Acestrura mulsan t, and Philodice mitchellii). Corresponding analyses on a matrix of un symmetrized Delta values gave similar support for these relationships except that the branching order of the two Andean clades (2, 3 above) was unresolved. In general, subsidiary relationships were consistent a nd well supported by both matrices, sometimes revealing surprising ass ociations between forms that differ dramatically in plumage and bill m orphology. Our results also reveal some basic aspects of hummingbird e cologic and morphologic evolution. For example, most of the diverse en demic Andean assemblage apparently comprises two genetically divergent clades, whereas the majority of North American hummingbirds belong a single third clade. Genetic distances separating some morphologically distinct genera (Oreotrochilus, Aglaiocercus, Lesbia; Myrtis, Acestrur a, Philodice) were no greater than among congeneric (Coeligena) specie s, indicating that, in hummingbirds, morphological divergence does not necessarily reflect level of genetic divergence.