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Braz. J. Genet. vol. 20 no. 4 Ribeirão Preto Dec. 1997
Chromosome study in two Aratinga species (A. guarouba and A. acuticaudata) (Psittaciformes)
Beatriz Goldschmidt 1, Denise M. Nogueira 1, Denise W. Monsores 2 and Lúcia M. Souza 1
1Faculdade de Veterinária, Universidade Federal Fluminense, Rua Vital Brasil Filho, 64, 24230-340 Rio de Janeiro, RJ, Brasil. Send correspondence to B.G.
2Fundação Rio-Zoo, Rio de Janeiro, RJ, Brasil.
The karyotypes of two species of Psittacidae of the genus Aratinga, Aratinga guarouba and A. acuticaudata were studied for the first time. The metaphases were obtained using a short term culture of feather pulp. These karyotypes are compared with others of the genus and their karyological relationships in the Psittaciformes are discussed.
Cytogenetic studies of birds are relatively rare as compared with similar studies in other vertebrate classes. The most complete revision on this matter was made by De Lucca and Rocha (1992). There are approximately 9021 species of birds, 1590 of them living in Brazil. According to the authors, 165 species were citogenetically analyzed. In 1995, Duarte and Caparroz analyzed eight more species totalling 173 species of birds for which karyotypes are known.
The order Psittaciformes presently has 41 species analyzed belonging to 15 different genera (Manfredi and Ferrari, 1979; De Lucca, 1980, 1985; De Lucca and Marco, 1983; Aquino, 1987; De Lucca et al., 1991; Duarte and Caparroz, 1995).
The genus Aratinga includes species with habitat from South América to Mexico. Forshaw (1977) described 19 species in this genus, 10 of which are found in Brazilian territory.
De Lucca (1984) studied the karyotype of 5 species of Aratinga (A. aurea, A. auricapilla, A. cactorum, A. leucophtalmus, A. solstitialis) using bone marrow cells. De Lucca et al. (1991) studied the species A. jandaya, mentioning a great similarity between its karyotype and that of A. aurea.
We analyzed the karyotypes of A. acuticaudata and A. guarouba, the latter one threatened by extinction, using a short term culture of feather pulp aiming at a better knowledge of genus Aratinga and its evolutionary processes.
MATERIAL AND METHODS
Young feathers of two males and two females of Aratinga acuticaudata and three males and three females of Aratinga guarouba, belonging to the Rio-Zoo Foundation in Rio de Janeiro State, were collected.
From each species, forty metaphases were analyzed by conventional staining method.
The cytogenetic preparations were made following the direct method with young feather pulp, described by Giannoni et al. (1986) with slight modifications. The technique consisted of removing three to four primary feathers and approximately 15 days later, taking out the young bulbs and transporting them to the laboratory on ice.
The material extracted from the young bulbs was cultured for 40 min in 10 ml McCoys medium with five drops of a 0,0016% colchicine solution at 37oC. After centrifugation at 1000 rpm for 10 min, the material was hypotonized at 37oC for 30 min with a 0.075 M KCl solution and fixed in a 3:1 methanol/acetic acid solution following the usual standard for chromosome analysis.
Sex determination was easily obtained since Z and W chromosomes in Psittaciformes are clearly visualized. It was possible to obtain a sufficient number of metaphases in order to establish the karyotypic pattern of the two species.
Both species presented 2n = 70 chromosomes like other Aratinga species (De Lucca, 1984 and De Lucca et al., 1991), and a very sharp boundary was observed between the microchromosomes and the ten pairs of macrochromosomes.
Figure 1 shows metaphase and karyotype of a female Aratinga acuticaudata. The first pair consisted of large metacentrics, and the second pair of subtelocentrics almost of the same shape of the first pair. The third pair was submetacentric and the 4th, 5th and 6th were subtelocentrics having a remarkable reduction of size from the 4th to the 5th pair. The 7th pair was submetacentric, and the 8th and 9th were formed by little metacentric chromosomes. The Z chromosome was metacentric corresponding to the 5th pair in shape and the W was a small submetacentric corresponding to the 8th in shape. Figure 2 shows a male metaphase of A. acuticaudata and the arrows indicate the Z chromosomes.
Figure 3 shows metaphase and karyotype of a female Aratinga guarouba. This species showed similar karyotypic characteristics to A. acuticaudata except the 2nd and 4th pairs which were submetacentrics, the 7th pair which was metacentric, and the 8th and 9th which were submetacentrics in this species. Figure 4 shows the metaphase of a male A. guarouba and the arrows indicate the Z chromosomes.
The species A. guarouba and A. acuticaudata had the first pair of chromosomes classified as metacentric. This is a distinctive characteristic of Psittaciformes, occurring also in genus Ara, Loriculus, Psittacula, Nestor, Psittriches, Electrus, Forpus, Poicephalus, and Polytelis of family Psittacidae and in genus Lorius of family Loriidae.
The karyotype of both Aratinga species showed to be rather similar, with differences in the 2th and 4th pairs which were subtelocentrics in A. acuticaudata and submetacentrics in A. guarouba, and in the 7th pair which was submetacentric in A. guarouba and metacentric in A. acuticaudata. The 8th and 9th pairs were metacentrics in A. acuticaudata and submetacentrics in A. guarouba.
The karyotypic results found in A. acuticaudata showed to be very similar to those described by De Lucca (1984) for species A. cactorum, with differences in pair 8, which was metacentric in the first and submetacentric in the second, and in W chromosome, submetacentric in A. acuticaudata and metacentric in A. cactorum.
According to Sick (1990), A. guarouba differs from other Aratinga species in regard to behavior, vocalization and reproduction. Therefore, the author suggested it to represent a monotypic genus Guarouba and to be named Guarouba guarouba.
However, the species A. guarouba showed similar cytogenetic results to those obtained in other Aratinga species. The 5th pair in A. guarouba was subtelocentric, similar to A. solstitialis and A. acuticaudata, differing from the other species analyzed where it is submetacentric. Among the species already studied of this genus, the one that presented greatest karyotypic similarity with A. guarouba was A. jandaya (De Lucca et al., 1991), including the 7th pair, which is metacentric in both. As no female karyotype of A. jandaya has been published, the W chromosome of this species remains unknown.
Within the genus Aratinga, it is possible to observe several differences in centromeric position between the same chromosome pair of each species but the shape of these chromosomes remains always the same. So, we hypothesize that pericentric inversions are responsible for these variations.
The authors thank the Rio-Zoo Foundation for its cooperation and Universidade Federal Fluminense for its support.
Foram estudados pela primeira vez os cariótipos de duas espécies do gênero Aratinga, A. guarouba e A. acuticaudata. As metáfases foram obtidas utilizando-se o método de cultura de curta duração de polpa de penas jovens. Estes cariótipos foram comparados com outros do mesmo gênero. Interpretações cariológicas na ordem Psittaciformes são discutidas.
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(Received May 9, 1997)
Figure 1 - Metaphase and karyotype of a female Aratinga acuticaudata.
Figure 2 - Metaphase of a male Aratinga acuticaudata. The arrows indicate the sexual pair.
Figure 3 - Metaphase and karyotype of a female Aratinga guarouba.
Figure 4 - Metaphase of a male Aratinga guarouba. The arrows indicate the sexual pair.