We used a generalized parsimony model to estimate the phylogeny of 47 species in the avian subfamily Icterinae using restriction enzyme cleavage sites in mitochondrial DNA (mtDNA). Deep branches in the tree are poorly resolved, either because blackbirds radiated rapidly after the origin of the clade or because substitutions have saturated sites in the mtDNA. Our tree is similar to one published by Lanyon (1994, Evolution 48:679-693) based on mtDNA sequences, which suggests that lack of basal resolution might be attributable to closely spaced speciation events. Both data sets had similar consistency and retention indices, suggesting comparable information content in these two types of data. Neither the restriction-site tree nor the sequence tree support the monophyly of the genus Agelaius. The restriction-site tree suggests that several traditional taxonomic rearrangements are likely based on phenotypic resemblance rather than phylogeny and that the feature viewed as a key innovation of blackbirds (gaping) might not be the basal condition; gaping might be a composite of characters rather than a single homologous condition. The restriction-site tree suggests that the brood-parasitic cowbird species are not monophyletic, contra the sequence data. A combined analysis of sequences and restriction sites for cowbirds supports the sequence tree of Lanyon (1994); however, we suggest an alternative view of the evolution of brood parasitism that is also consistent with the combined data tree. Polygyny appears to be independently derived within blackbirds. Icterus galbula and I. bullockii, which hybridize and are therefore currently considered a single biological species, are not sister taxa; these are likely phylogenetic species.
Bibliographical noteFunding Information:
Financial support for this study was provided by the American Ornithologists' Union, the American Museum of Natural History, the Burke Museum, the Field Museum of Natural History, the Graduate School of the University of Washington, Charles Laird, the National Museum of Natural History, the National Science Foundation, the Parrett Foundation, the Society of Sigma Xi, the University of Washington Department of Zoology, and the Wilson Ornithological Society. Tissue donations were provided by A. Espinosa, W. Jackson, O. Kovacs, W. Post, C. Thompson, M. Webster, and the staffs of the Burke Museum (S. Rohwer, C. Wood) and the Louisiana State University Museum of Natural Science (S. Cardiff). A study this comprehensive would have been impossible without the resources of the LSU frozen tissue collection. J. Felsenstein provided source codes for the PHYLIP computer package, W Ellis customized a Macintosh version of PHYLIP, D. Swofford installed the UNIX version of PAUP, and D. McElroy provided a Pascal program for computing genetic distances. E. Bermingham provided technical help. Discussions with J. Felsenstein and S. Rohwer helped guide the research, and comments from A. Fry, K. Johnson, J. Klicka, S. Lanyon, K. de Queiroz, J. Weckstein, and S. Weller improved the manuscript.
- Brood parasitism
- Generalized parsimony
- Mating systems
- Maximum likelihood
- Phylogenetic species concept