Estudo citogenetico comparativo de Edalorhina perezi e Physalaemus petersi (Amphibia, Anura, Leptodactylidae)

AUTOR(ES)
DATA DE PUBLICAÇÃO

1996

RESUMO

Sixty one specimens of Physalaemus petersi and seven of Edalorhina perezi (Leptodactylidae, Anura) from Acre State, Brazil, were studied, to contribute to phylogenetic relationship studies between these two neotropical genera. Chromosome preparations were obtained from cellular suspensions of testis and intestinal epithelium. These cytological preparations were conventionally stained by Giemsa or submitted to Ag-NOR and C-banding techniques. Morphometric analyses of twenty nine mitotic metaphases chromosomes from the specimens of E. perezi (two females and five males), showed that ali these individuais present 2n=22. The eleven chromosome pairs of this karyotype are homomorphic, being six metacentric (pairs 1, 5, 6, 9, 10 and 11), four submetacentric (pairs 2, 4, 7 and 8) and one subacrocentric (pair 3). Only one pair of NOR per diploid genome of chromosome preparations obtained from six specimens was detected and this was located interstitially in the long arm of pair 8. The C-banding techniques, applied to cells from two of these specimens, showed that this NOR is surrounded by constitutive heterochromatin blocks, also present at the centromere of ali the chromosomes. Gray heterochromatic bands were detected in the short arm of chromosome pair 1 and in the long arm of pair 2. Analyses of meiotic chromosomes of two males detected multivalent chains in spermatocytes I, apparently formed by three long chromosome pairs, indicating the ocurrence of heterozygous translocations in this karyotype. Ali the specimens of P. petersi studied present 2n=22, but two distinct karyotypes were detected among them. These findings suggest a re-evaluation of the taxon P. petersi. The most commom karyotype presents four metacentric (1, 5, 6 and 10), four submetacentric (2, 4, 7 and 9), two subacrocentric chromosome pair (3 and 8) and one pair of sex chromosomes xx/XY. Among the groups of specimens with this kind of karyotype, a big interindividual variability of NOR and heterochromatic band patterns was observed. The analysis of spermatocytes I bivalents showed that chromosome pairs which are heterozygous to non-centromeric heterochromatic bands do not present chiasma at these chromosome regions. The other karyotype was observed in only three males, whose call also differs from that of most commom specimens of P. petersi. This karyotype is formed by six metacentric (2, 3, 4, 7, 8 and 10), two submetacentric (5 and 9), two subacrocentric (1 and 6) and one heteromorphic chromosome pairo The relation of this pair with sex determination could not be elucidated, because no female with this karyotype was found. The Ag-NOR method showed two patterns of NOR distribution, which involve two chromosome pairs (8 and 9). The Cbanding technique applied to material obtained from one of these specimens showed the presence of constitutive heterochromatin at ali the centromeres of this karyotype, in the telomeres of the chromosomes of the pairs 4 and 8 and at one of the telomeres of one pair 9 chromosomes. Multivalent configurations were observed in meiotic prophase I of both karyological groups of P. petersi, suggesting the involvement of translocations in the evolution of these karyotypes. This kind of rearrangement can be involved in the origin of different NOR patterns and heterochromatic band distribution

ASSUNTO(S)

cromossomos polimorfismo heterocromatina anuro herpetologia anfibio nucleolo citogenetica

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