Chromosomal Analysis of Eighteen Species ofAnura

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Abstract
Karyotypes of eighteen species of Anura from Brazil have been studied (Bufonidae, Leptodactylidae, Hylidae, and Pseudidae). Leptodactylidae show a variation of chromosomal number from 2 n = 18 to 2 n = 26. Hylidae presents also variations from 2 n = 22 to 2 n = 30. These differences were correlated to morphological alterations of the karyotypes. Bufonidae, however, disclosed a great chromosomal uniformity, showing the same diploid number, 2 n = 22. In Pseudidae one species showed 2 n = 24 chromosomes. Pseudopaludicola falcipes has 2 n = 18. It seems to be the lowest chromosome number described in Anura. Variation of number and shape of chromosomes in Hylidae and Leptodactylidae suggests that the mechanism of centric fusion played a role in karyotype differentiation. This mechanism could not be evidenced in the Bufonidae. Centric fusion however is not the only mechanism in amphibian evolution. Indeed, the occurence of natural bisexual polyploid species in the family Ceratophrydidae (BEÇAK M. L. et al. 1966, 1967; BEÇAK W. et al. 1967), shows that duplication of the whole genome is another mechanism of differentiation in Anura. Heteromorphic sex chromosomes, were not observed in any species, and no bivalents with characteristic morphology and behavior of sex bivalent during male meiosis was observed.