Citogenetica comparativa de especies de aplastodiscus e do grupo de Hyla albomarginata (Hylidae, Anura) / Comparative cytogenetics of aplastodiscus species and Hyla albomarginata group (Hylidae, Anura)

AUTOR(ES)
DATA DE PUBLICAÇÃO

2005

RESUMO

The Hylidae family includes four subfamilies, with Hylinae comprising 27 genera. The Hyla genus has many species divided into related groups. The Hyla albomarginata group, as known as "green Hylas" is subdivided into 3 complexes: "albomarginata","albosignata" and "albofrenata". The Aplastodiscus genus has been the object oftaxonomic discussion since its description, having been synonymyzed to and removed from Hyla more than once. Since there are great morphological and behavioral similarities between the species of the H albomarginata group and the species of Aplastodiscus, the phylogenetic and taxonomic relationships of these genera are still under discussion. In the present research, a cytogenetic study was carried out evaluating two species of Aplastodiscus (A.perviridis and A. cochranae), three populations of H albomarginata ("albomarginata" complex), H albosignata and H leucopygia ("albosignata" complex) and H albofrenata, H arildae, H ehrhardti and Hyla eugenioi ("albofrenata" complex), as well as H faber, a very closely related species not pertaining to the group. The aim of this research was to contribute to the systematics of this group and to the understanding of the intra- and intergeneric relationships of Aplastodiscus. Mitotic and meiotic metaphases were obtained from suspension of intestinal epithelial cells, stained with Giemsa and submitted to the techniques of C-banding, silver impregnation and in situ hybridization with probes of ribosomal DNA and telomeric sequence. The diploid number of 2n=24 was found in the two species of Aplastodiscus, Hyla albomarginata and Hyla faber, while Hyla albosignata had 2n=20 and Hyla leucopygia had 2n=18. The four species of the complex "albofrenata" had 2n=22 chromosomes. The two species of Aplastodiscus had the same heterochromatin pattern, but they differ from the Hyla species. The nucleolus organizing region (NOR) was located on the telomeric regions or pair 12 in both species of Aplastodiscus, in pair 09 of H albosignata and H leucopygia, in pair 11 in H faber, and intersticially on the short arms of pair 02, with size heteromorphism in H albomarginata. In two of the eight individuals of Hyla albofrenata, the NOR was present in the telomeric region on the long arm in pair 07 and, in six of these individuals, a interesting pattern for Anura was found. The NOR was found in the pairs 01 and 07, but in only one of the homologues of each pair. In H ehrhardti, the Ag-NOR technique marked the pairs 06 and 10, but only that on pair 06 was confirmed by in situ hybridization. In H arildae, the NOR was located in the 10 pair and in Hyla eugenioi in the pair 07, also in the telomeric regions. In H albofrenata and H arildae multivalent rings were observed in the prophase I of meiosis, constituted of 4 to 6 bivalents, being one of them the NOR-bearing chromosomes. Translocation events during the evolution of H albofrenata and H arildae could be responsible for the ring formation in meiosis. The participation of the NOR bearing chromosomes in the multivalente rings could have facilitated the occurrence of polymorphism of NOR, as observed in H albofrenata. The telomeric sequence probe marked the telomeric region in all species studied as well as the centromeric regions of the chromosomes of H albofrenata and H arildae, at the centromeric heterochromatin. In amphibians, telomeric sequences located outside the telomeric regions had only been detected in interstitial regions. The presence of these sequences in centromeric regions may have been originated by the amplification of the (TTAGGG)n sequences related to heterochromatic amplification. The data of the present work a11ow the conc1usion that A. perviridis and A. cochranae could not be differentiated. The NOR bearing chromosomes 9 of H leucopygia and H albosignata are very similar in size, morphology (metacentric) and NOR localization (telomeric region) to the pair 12 of the species Aplastodiscus and also to the pair 11 of H faber, suggesting that these are homologous chromosomes. Although Hyla albomarginata differs from all species analyzed for NOR localization on pair 2, it presented the same diploid number and chromosome morphology of Aplastodiscus. The conserved chromosomal morphology, mainly in the first seven pairs, between the species of "alboftenata" (present work), "albosignata" and "albomarginata" complexes and Aplastodiscus, suggests that one ancestral karyotype in common must have originated all these current species. The chromosomal rearrangements could lead to the differentiation of these karyotypes, with changes in diploid number, involving mainly the short chromosome group and the dispersion of heterochromatin and NOR

ASSUNTO(S)

nucleolar organizing region região organizadora do nucleolo cytogenetics citogenetica cromossomos chormosomes

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