Somatic Chromosomes of the Congo Peafowl (Afropavo Congensis) and Their Bearing on the Speices' Affinities
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Condor 83:204-208 0 The Cooprr Ornithological Society 1981 SOMATIC CHROMOSOMES OF THE CONGO PEAFOWL (AFROZAVO’ CONGENSIS) AND THEIR BEARING ON THE SPECIES ’ AFFINITIES LEOBERT E. M. DE BOER AND ROLAND VAN BOCXSTAELE 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 (Pave cristutus) and differs progressively more from those of guineafowl, domestic chicken, and various other gallinaceous birds. This evidence supports Chapins’ 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 werp were made available for chromosome studies, Chapin, the Congo Peafowl (Afropuvo con- Heparinized blood was aseptically drawn from the gensis) and its taxonomic affinities have main brachial vein (V. basilica) and full-blood cultures were prepared according to techniques described by been much discussed. Chapin (1936, 1937) De Boer (1974,1976). Pokeweed mitogen (PKW, Gibco believed the species to be most closely re- 670-5360) and phytohaemagglutinin (PHA, Difco, lated to the Asiatic peafowl (Puvo), as is ex- 0528-56) were used as mitotic stimulators to induce pressed in its generic name. His view that cell division in lymphocytes. Cultures were harvested after three days of incubation at 40°C and 1.5 h of in- Afropuvo represented an unspecialized, cubation in the presence of colchicine (0.0001% final generalized or primitive peacock was adopt- concentration) as a metaphase arresting agent. Slides ed by Lowe (1938) on the basis of the lat- were prepared using the flame-drying technique and ters’ anatomical studies of the skeleton. Ver- chromosomes were stained with acetic orcein (2%) and heyen (1956), however, concluded that it photographed using phase-contrast microscopy. Arm ratios of individual chromosomes were calcu- was more closely related to African guinea lated by dividing the length of the long chromosome fowl (Numididae), while Ghigi (1949) sug- arm by that of the short arm In accordance with Levan gested affinities with the Himalayan Mona1 et al. (1964), chromosomes with arm ratios between 1.0 Pheasant (Lophophorus impejunus). Stud- and 1.6 are designated as metacentric, those with arm ies on the soluble proteins of the eye lens ratios between 1.6 and 3.0 as submetacentric and those with higher arm ratios as (sub)telocentric. and of the skeletal, heart, and stomach mus- cles by Gysels and Rabaye (1962) and stud- RESULTS ies on the hind limb musculature by Hul- selmans (1962) pointed to a rather isolated A total of 60 metaphase plates of Congo Pea- position for the Congo Peafowl. These au- fowl were available for analysis. The dip- thors recommended that this species be loid chromosome number for the species as placed in a monotypic subfamily Afropavon- estimated from these plates is 76. The inae of Phasianidae, remotely allied to karyotype consists of 9 pairs of macrochro- Pave. Finally, Benoits’ (1962) work on Mal- mosomes and of approximately 29 pairs OF lophaga showed the presence of ectopara- microchromosomes. Each of the macrochro- sites on Afropuvo that are related to those mosome pairs can be easily recognized in- of the African guineafowl, as well as species dividually. Pair 1 (see Fig. 1) consists of two related to those of the Asiatic phasianids. large metacentric chromosomes (arm ratio In view of this taxonomic uncertainty, we 1.4) and pair 2 of somewhat smaller sub- readily accepted the opportunity to study metacentrics (arm ratio 1.6). The elements the chromosomes of this species, which was of pairs 3 and 4 are medium-sized subtelo- offered by the Royal Zoological Society of centrics, those of pair 3 having minute short Antwerp. We describe here the chromo- arms (arm ratio 7.9), while the short arms in some complement of the Congo Peafowl pair 4 are clearly longer (arm ratio 3.2). The and discuss its taxonomic implications. chromosomes of pair 5 are also subtelocen- tric (arm ratio 3.5), but they are considerably MATERIALS AND METHODS smaller than the preceding ones. Pairs 6 and Two Congo Peafowls, a cock and a hen, from the 7 consist of small metacentric elements (arm breeding stock of the Royal Zoological Society of Ant- ratios 1.5 and 1.2, respectively) which, in ~2041 SOMATIC CHROMOSO.MES OF THE CONGO PEAFOWL 205 properties (Bloom 1974). However, since we applied only routine staining techniques on our material of Aft-opaoo congensis the W chromosome cannot be detected with any certainty because in this case it is in- distinguishable from the microchromo- somes. There are approximately 58 of the latter, all of which are subtelocentric or tel- acentric without apparent short arms. They gradually decrease in size until the smallest are barely visible using standard tech- niques. One of the largest microchromo- somes was tentatively chosen as the possi- ble female W chromosome. In Figure 1 representative male and fe- male karyograms are shown, while a sche- matic representation of morphology and rel- ative lengths of the macrochromosomes is given in Figure 2. DISCUSSION . - 37 In contrast to the situation in many of the other avian orders, the chromosome com- plements of the gallinaceous birds have been studied extensively. The karyotypes of almost 30 species have been described (for a review of avian chromosome cytology see De Boer 1981). In Figure 2, the macrochro- mosome pairs of Afropavo congensis are compared to those of some other galliform species which are relevant to the Congo Peafowls’ taxonomic relationships. As far as the macrochromosomes are con- 6 7 8 zw cerned, the karyotype of Afropavo is vir- tually identical to that of the Blue Peafowl FIGURE 1. Representative male (top) and female (Puuo cristutus; Ray-Chaudhuri et al. 1969; karyograms of the Congo Peafowl. Of the female chro- Sasaki et al. [1968] studied the karyotype of mosome set, only the macrochromosomes and the sex chromosomes are shown. Bar indicates 5 p of absolute a P. cristatus x P. muticus hybrid). The only length. possible differences seem to be that the Z chromosome of the Congo Peafowl is some- what smaller and more metacentric, while plates with more condensed chromosomes, the Blue Peafowls’ W chromosome is some- cannot always be individualized with cer- what larger. tainty. Finally, pair 8 consists of two small The karyotypes of Helmeted Guineafowl subtelocentrics with short arms of minute (Numida meleagris) and Vulturine Guinea- size (arm ratio 6.6). These elements are con- fowl (Acr!yllium vulturinum; Piccini and siderably longer than the longest micro- Stella 1970, Takahasi and Hirai 1974, Omu- chromosomes, so that they can be recognized ra 1976) clearly differ from those of Afro- without difficulty. pauo. They lack a chromosome pair com- The 2 chromosome belongs to the macro- parable to pair 5 in the Congo Peafowl and chromosomes as well. It is metacentric (arm possess only one pair of small metacentric ratio 1.1) and of medium size, somewhat macrochromosomes. This pair possibly cor- longer than the metacentrics of pairs 6 and responds to pair 6 of Afropwo, while Af- 7. As in all bird species with the possible ropavos’ pair 7 possibly is present as two exception of the ratites, two Z chromosomes separate telocentric chromosome arms are found in the male, only one in the fe- among the larger microchromosomes of male. Instead of the second 2, the female both guineafowl (indicated as 7q and 7p in chromosome complement carries a W chro- Fig. 2). mosome. The avian W chromosome often The chromosome complement of the do- can be identified by its specific staining mestic fowl (Gallus gullus var. domesticus) 206 LEOBERT E. M. DE BOER AND ROLAND VAN BOCXSTAELE i-25 O/,TCL._ differs from that of Afropmo by the same features as do those of the guineafowl, no- -20 tably the absence of pair 5 and the occur- rence of the arms of the chromosomes of pair 7 as independent elements (e.g., Ohno 1961, Wang and Shoffner 1974, Stock and Afropavo congensis 10 Mengden 1975). In addition, the second pair of small metacentric macrochromo- 5 somes of Afropmo (pair 6) is also absent in the domestic fowl. Possibly the chromo- !15 Iii illi I I some arms of this pair are also present as 12345678 2 w independent elements among the larger microchromosomes of its karyotype (indi- cated as 6q and 6p in Fig. 2). Finally, the W chromosome of Gallus is metacentric in- stead of telocentric. Pavo cristatus The karyotypes of the pheasants that have been studied so far are all identical and dif- fer still more from those of Afropavo. As an example, the chromosomes of the Ring- necked Pheasant (Phasianus colchicus) are shown in Figure 2 (e.g., Stenius et al. 1963, 12345678 z w Krishan and Shoffner 1966, Takagi and Sa- saki 1974). As with domestic fowl, the pheasant karyotypes lack pairs 5,6, and 7 of the Congo Peafowl but, in addition, pairs 2 and 4 are absent. Instead of these, three ad- ditional pairs of medium-sized telocentric Numida meleagris chromosomes are present in the pheasants, which probably correspond to the long and short arms of pair 2 and the long arms of pair 4 of Afropavo (indicated as 2q, 2p, and 4q in Fig. 2). The short arms of pair 4 (4~) 1 2 3 4 5 6 7a 8 z w may be found among the pheasants’ micro- chromosomes. These comparisons show that in the se- ries “peafowl, guineafowl, domestic chick- en, and pheasants” there is a gradual in- crease in the numbers of karyotypic Gallus domesticus differences relative to Afropavo.