Estudos cromossômicos em anuros das famílias Hylidae rafinesque, 1815 e Leptodactylidae werner, 1896 (Amphibia: Anura)

Abstract

Although there exists a large variety of chromosomal complements in Leptodactylidae (2n = 18 to 2n = 26) and Hylidae (2n = 20 to 2n = 32), the high fragmentation of data limits the access to the information about the origins and underlying mechanisms of its diversity. This, probably, had influence on the use of cytogenetic data on the characterization of species status more than been widely included in phylogenetic analyses. This work approaches, through cytogenetic data, some evolutionary aspects of three maior groups of anurans widely distributed in the Neotropical region. The genus Leptodactylus is clustered with Hydrolaetare, Paratelmatobius and Scythrophrys in the family Leptodactylidae. The chromosomal background in the genus indicates variation of the diploid numbers from 2n = 18 to 2n = 26, as well as, variation on the fundamental numbers (number of autosomic arms, FN) and on the position of Nucleolus Organizer Regions (NOR). Results of the analysis of 26 species of Leptodactylus, using several techniques, probably represents the most inclusive cytogenetic analyses on the genus Leptodactylus until now and its results provides appropriate bases to establish consistent relationships of chromosomal evolution on the genus Leptodactylus. Actually the Lophyiohylini tribe cluster 81 species distributed in 10 genera. The cytogenetic information is scarce and restrict to only 12 species. In the present study, are presented, comparatively, cytogenetic data of species from Argenteohyla, Itapotihyla, Phyllodytes, Trachycephalus and Osteocephalus genera. With exception of O. buckleyi (2n = 26; NF = 50) and P. edelmoi (2n = 22; NF = 44), the results indicate that all the others analyzed species coincide with cytogenetic data available, that indicates 2n = 24 (NF = 48) on the majority of karyotyped species, with NOR and secondary constrictions (SC) located on the 11 pair. However, in Phyllodytes edelmoi and Argentohyla siemersi pederseni, these regions are located on pairs 2 and 5, respectively. Heterochromatic blocks were associated to additional SC (fragile sites) in Osteocephalus, but not in Trachycephalus. Cytogenetic data on the Nyctimantis and Tepuihyla genera, techniques with techniques with higher resolution and more inclusive studies are necessary to better comprehend the chromosomal evolution of the tribe. The Dendropsophini tribe actually clusters the Scinax, Pseudis, Scarthyla, Sphaenorhynchus, Xenohyla and Dendropsophus genera. The registered cytogenetic data of all the genera revealed high karyotype diversity with great variation on the diploid numbers (2n = 22 in Scarthyla; 2n = 24 in Scinax and Xenohyla; 2n = 24, 24 +1- 2B e 26 in Sphaenorhynchus; 2n = 24 and 28 in Pseudis; and, 2n = 30 in Dendropsophus). The 2n=24 observed in X. truncata indicates that 2n=30 constitute a synapomorphy of the Dendropsophus genus. The NOR localization on the pair 7 is a characteristic shared by species of Scarthyla, Xenohyla, Pseudis and Sphenorhynchus, with some exceptions in the last two genera (P. caraya and S. carneus). However, the Dendropsophus genus displays an interesting diversity related to the number and its localization. On the other hand, the heterochromatin distribution presented standard variables, particularly on genus Pseudis. Although there is an exceptional chromosome variation in this group, fragmentary information in some genera made difficult to formulate consistent hypotheses about the role of chromosomes in the evolution of the group.