The evolutionary implications of chromosome banding pattern homologies in the bird order Galliformes

The chromosome banding patterns of eight species of birds of the order Galliformes have been compared to determine their degree of chromosomal homology. The species studied were domestic chicken (Gallus gallus), Japanese quail (Coturnix coturnix), guineafowl (Numida meleagris), peafowl (Pavo cristatus), Ring-necked pheasant (Phasianus colchicus), turkey (Meleagris gallopavo), Sagegrouse (Centrocercus urophasianus), and Bob-white quail (Colinus virginianus). These species were selected as key genera in a preliminary study of evolutionary relationships in the order Galliformes.The chromosome banding patterns defined two major groups, with Gallus most nearly approaching the ancestral karyotype. Gallus, Numida, Coturnix, and Pavo retain the ancestral submetacentric chromosome 2, which also occurs in the cracid, Crax mitu (DeBoer and Belterman, 1981), and certain other bird orders. Coturnix differs from Gallus by four inversions. Numida differs from Gallus by a centric fusion of two microchromosomes which formed a unique new macrochromosome. Pavo differs from Gallus by two centric fusions which result in two unique macrochromosomes. The second major group, Phasianus, Meleagris, Colinus, and Centrocercus all lack the submetacentric 2 and have two separate chromosomes in its place as a result of a centric fission event. All of these species also possess the unmodified 4 seen in C. mitu, in place of the modified 4 seen in the Gallus group. Meleagris is similar to Phasianus; it differs mainly by an inversion on the Z chromosome. Colinus differs from Phasianus by an inversion on 1. Centrocercus differs from Phasianus by a centric fusion which produced a unique chromosome. Gallus, Pavo, Numida, and Coturnix are related but distinct lines which are clearly separate from Phasianus. Meleagris, Colinus, and Centrocercus represent closely related lines that developed in the new world from an early North American phasianid. Chromosome banding patterns indicate that the ancestral stock was karyotypically similar to Phasianus. Comparison of the data from this study and that of DeBoer and Belterman (1981) for C. mitu indicates a close relationship of the cracids to other galliform birds, in contrast to the opinion of Prager and Wilson (1979) based on studies of lysozymes and other proteins. The chromosome data supports the conclusions from several other lines of investigation that challenge the taxonomic treatment of the Galliformes which regards the turkey, guinea fowl, and grouse as belonging to separate families, yet unites divergent lines such as Old World quail, New World quail, peafowl, and true pheasants into a single family, Phasianidae. Treatment of each of the major lines indicated in this study at the subfamily level seems more consistent with the available data.