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

Abstract

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 <i>(Gallus gallus</i>), Japanese quail <i>(Coturnix coturnix</i>), guineafowl <i>(Numida meleagris</i>), peafowl <i>(Pavo cristatus</i>), Ring-necked pheasant <i>(Phasianus colchicus</i>), turkey <i>(Meleagris gallopavo</i>), Sagegrouse <i>(Centrocercus urophasianus</i>), and Bob-white quail <i>(Colinus virginianus</i>). 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 <i>Gallus </i>most nearly approaching the ancestral karyotype. <i>Gallus, Numida, Coturnix, </i>and <i>Pavo </i>retain the ancestral submetacentric chromosome 2, which also occurs in the cracid, <i>Crax mitu </i>(DeBoer and Belterman, 1981), and certain other bird orders. <i>Coturnix </i>differs from <i>Gallus </i>by four inversions. <i>Numida </i>differs from <i>Gallus </i>by a centric fusion of two microchromosomes which formed a unique new macrochromosome. <i>Pavo </i>differs from <i>Gallus </i>by two centric fusions which result in two unique macrochromosomes. The second major group, <i>Phasianus, Meleagris, Colinus, </i>and <i>Centrocercus </i>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 <i>C</i>. <i>mitu, </i>in place of the modified 4 seen in the <i>Gallus </i>group. <i>Meleagris </i>is similar to <i>Phasianus; </i>it differs mainly by an inversion on the Z chromosome. <i>Colinus </i>differs from <i>Phasianus </i>by an inversion on 1. <i>Centrocercus </i>differs from <i>Phasianus </i>by a centric fusion which produced a unique chromosome. <i>Gallus, Pavo, Numida, </i>and <i>Coturnix </i>are related but distinct lines which are clearly separate from <i>Phasianus</i>. <i>Meleagris, Colinus, </i>and <i>Centrocercus </i>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 <i>Phasianus</i>. Comparison of the data from this study and that of DeBoer and Belterman (1981) for <i>C</i>. <i>mitu </i>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.