Cytogenetic comparison of tree frogs of the genus Aplastodiscus and the Hypsiboas faber group (Anura, Hylidae).

Four species of Aplastodiscus and two species of Hypsiboas were cytogenetically compared. Aplastodiscus perviridis, A. cochranae, H. albomarginaus, and H. faber had 2n = 24 chromosomes, while A. albosignatus and A. leucopygius had 2n = 20 and 2n = 18 chromosomes, respectively. Aplastodiscus perviridis and A. cochranae had identical karyotypes, as indicated by their chromosomal morphology, the location of the nucleolus organizer region (NOR) on chromosome pair 12, and the heterochromatin pattern. The NOR-bearing chromosomes of A. albosignatus and A. leucopygius (pair 9) were very similar in size and morphology (metacentric) when compared to A. perviridis and A. cochranae (pair 12) and to H. faber (pair 11); the NOR of these chromosomes also occurred in the same region, suggesting that these chromosomes are homologous. Although H. albomarginatus differs from the other species with regard to the location of its NOR on pair 2, this species had the same diploid number and a chromosomal morphology similar to that of A. perviridis and A. cochranae. Chromosomal differentiation among the species appears to have occurred by reduction in chromosome number.