Molecules vs. morphology in avian evolution: the case of the "pelecaniform" birds.

Abstract

The traditional avian Order Pelecaniformes is composed of birds with all four toes connected by a web. This "totipalmate" condition is found in ca. 66 living species: 8 pelicans (Pelecanus), 9 boobies and gannets (Sula, Papasula, Morus), ca. 37 cormorants (Phalacrocorax), 4 anhingas or darters (Anhinga), 5 frigatebirds (Fregata), and 3 tropicbirds (Phaethon). Several additional characters are shared by these genera, and their monophyly has been assumed since the beginning of modern zoological nomenclature. Most ornithologists classify these genera as an order, although tropicbirds have been viewed as related to terns, and frigatebirds as relatives of the petrels and albatrosses. DNA-DNA hybridization data indicated that the pelicans are most closely related to the Shoebill (Bakniceps rex), a-stork-like bird that lives in the swamps of central Africa; the boobies, gannets, cormorants, and anhingas form a closely related cluster; the tropicbirds are not closely related to the other taxa; and the frigatebirds are closest to the penguins, loons, petrels, shearwaters, and albatrosses (Procellarloidea). Most of these results are corroborated by DNA sequences of the 12S and 16S rRNA mitochondrial genes, and they provide another example of incongruence between classifications derived from morphological versus genetic traits.Until recently, morphological characters have been the principal, and virtually the only, source of evidence for organizing species into larger categories in the construction of classifications. The traditional Order Pelecaniformes (pelicans, cormorants, anhingas and darters, boobies and gannets, frigatebirds, and tropicbirds) has been defined by the totipalmate foot, in which the hallux is turned forward and connected by a web to digit II, in addition to the webs between digits II and III and between III and IV. In other birds with webbed feet only the three front toes (digits II, III, IV) are connected by webs, and the hallux is free or absent; no bird has five toes. Of the totipalmate birds all but the tropicbirds have an obvious gular pouch; the frigatebird's gular pouch is inflatable and used in display, thus differing from those of the other species. The combination of totipalmate feet and gular pouch has seemed so unlikely to evolve more than once that the monophyly of the group has been widely accepted since Linnaeus (1) placed them in the genera Pelecanus (pelicans, cormorants, boobies, anhingas, and frigatebirds) and Phaethon (tropicbirds). They also share the location of the salt-excreting gland within the orbit instead of in a supraorbital groove, and they lack an incubation patch which is present in all other seabirds and waterbirds. However, they vary in pelvic musculature, carotid artery arrangement, and several other anatomical characters. The similarities argue for monophyly; the differences raise the possibility of polyphyly. The palmate avian foot with two webs between the three front toes has evolved in groups with separate origins-e.g., ducks, gulls, flamingos, and albatr...

Old World fruitbat phylogeny: Evidence for convergent evolution and an endemic African clade

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“…This implies the absence of major bottlenecks due to selection or chance effects, and is perhaps an argument for pleiotropy and against rapid convergence. Hedges & Sibley (1994) suggested that when, as here, molecular data produce a robust phylogeny that conflicts with morphology, the morphological characters should be reassessed. Perhaps a detailed morphological study (pace Strauch 1978) would reveal that similarity between the Pomarine skua, S. pomarinus, and other Stercorarius species is only skin-deep.…”

An Update of Wallace’s Zoogeographic Regions of the World

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