Somatic Chromosomes of the Congo Peafowl (Afropavo congensis) and Their Bearing on the Species' Affinities

Abstract

-The Congo Peafowl has an estimated diploid chromosome number of 76: nine pairs of macrochromosomes and approximately 29 pairs of microchromosomes. As far as the macrochromosomes are concerned, the karyotype closely resembles that of the Blue Peafowl (Pavo cristatus) and differs progressively more from those of guineafowl, domestic chicken, and various other gallinaceous birds. This evidence supports Chapin's view that Afropavo and Pavo are more closely related to each other than to any of the other galliform species. Karyotypic evolution within the order is discussed. Since its remarkable discovery by James Chapin, the Congo Peafowl (Afropavo congensis) and its taxonomic affinities have been much discussed. Chapin (1936, 1937) believed the species to be most closely related to the Asiatic peafowl (Pavo), as is expressed in its generic name. His view that Afropavo represented an unspecialized, generalized or primitive peacock was adopted by Lowe (1938) on the basis of the latter's anatomical studies of the skeleton. Verheyen (1956), however, concluded that it was more closely related to African guinea fowl (Numididae), while Ghigi (1949) suggested affinities with the Himalayan Monal Pheasant (Lophophorus impejanus). Studies on the soluble proteins of the eye lens and of the skeletal, heart, and stomach muscles by Gysels and Rabaye (1962) and studies on the hind limb musculature by Hulselmans (1962) pointed to a rather isolated position for the Congo Peafowl. These authors recommended that this species be placed in a monotypic subfamily Afropavoninae of Phasianidae, remotely allied to Pavo. Finally, Benoit's (1962) work on Mallophaga showed the presence of ectoparasites on Afropavo that are related to those of the African guineafowl, as well as species related to those of the Asiatic phasianids. In view of this taxonomic uncertainty, we readily accepted the opportunity to study the chromosomes of this species, which was offered by the Royal Zoological Society of Antwerp. We describe here the chromosome complement of the Congo Peafowl and discuss its taxonomic implications. MATERIALS AND METHODS Two Congo Peafowls, a cock and a hen, from the breeding stock of the Royal Zoological Society of Antwerp were made available for chromosome studies, Heparinized blood was aseptically drawn from the main brachial vein (V. basilica) and full-blood cultures were prepared according to techniques described by De Boer (1974, 1976). Pokeweed mitogen (PKW, Gibco 670-5360) and phytohaemagglutinin (PHA, Difco, 0528-56) were used as mitotic stimulators to induce cell division in lymphocytes. Cultures were harvested after three days of incubation at 400C and 1.5 h of incubation in the presence of colchicine (0.0001% final concentration) as a metaphase arresting agent. Slides were prepared using the flame-drying technique and chromosomes were stained with acetic orcein (2%) and photographed using phase-contrast microscopy. Arm ratios of individual chromosomes were calculated by dividing the length of the long chromosome arm by that of the short arm. In accordance with Levan et al. (1964), chromosomes with arm ratios between 1.0 and 1.6 are designated as metacentric, those with arm ratios between 1.6 and 3.0 as submetacentric and those with higher arm ratios as (sub)telocentric.