Cytogenetic analysis of four central Amazonian species of Colostethus (Anura - Dendrobatidae) with a diploid complement of 22 chromosomes

Chromosome evolution in Lophyohylini (Amphibia, Anura, Hylinae)

The hyline tribe Lophyohylini includes 87 species of treefrogs, of which cytogenetics aspects have been studied in less than 20% of them. In order to evaluate the evolution of some of its chromosome characters (NOR position, C-bands, and DAPI/CMA₃ bands), we studied the karyotypes of 21 lophyohylines, 16 of them for the first time, and analyzed them in a phylogenetic context. Most species showed similar karyotypes regarding chromosome number (2n = 24) and morphology (FN = 48), excepting Phyllodytes edelmoi and Osteocephalus buckleyi with 2n = 22 (FN = 44) and 2n = 28 (FN = 50), respectively. The NOR location was variable among species and provided valuable phylogenetic information. This marker was located in pair 11 in all species of Trachycephalus, Itapotihyla langsdorffii, and Nyctimantis arapapa, representing the plesiomorphic condition of Lophyohylini. Besides, other apomorphic states were recovered for the clades comprising N. rugiceps and N. siemersi (NOR in pair 5), and Dryaderces pearsoni, Osteocephalus, and Osteopilus (NOR in pair 9). Phyllodytes presented variation for NORs position; they were in pair 2 in P. edelmoi, pair 7 in P. melanomystax, and pair 8 in P. gyrinaethes and P. praeceptor. Polymorphisms in size, number, and activity of this marker were observed for N. siemersi, Osteocephalus fuscifacies, and some species of Trachycephalus. Remarkably, in N. siemersi NORs were detected on a single chromosome in the two specimens studied by this technique, raising the question of how this complex polymorphism is maintained. Interstitial telomeric sequences were found in P. edelmoi, P. melanomystax, and Osteocephalus buckleyi, and their presence seems to be not related to the chromosome reorganization events. Finally, some species showed spontaneous rearrangements, possibly as a consequence of an uncommon phenomenon in anuran cytogenetics: the presence of fragile sites or secondary constrictions not associated with NORs. We propose that this rare feature would have played an important role in the evolution of this group of frogs. From the evidence obtained in this and previous studies, we conclude that Lophyohylini presents a complex chromosome evolution.

Cytogenetic analysis of four species of Pseudis (Anura, Hylidae), with the description of ZZ/ZW sex chromosomes in P. tocantins

Pseudis paradoxa paradoxa, P. p. platensis, P. bolbodactyla, P. fusca and P. tocantins were analyzed cytogenetically by conventional chromosomal staining, C-banding, silver staining and fluorescent in situ hybridization with an rDNA probe. Pseudis tocantins chromosomes were also stained with distamycin A/DAPI. All of the species had a diploid number of 2n = 24 chromosomes and the nucleolar organizer region (NOR) was located on pair 7. However, the karyotypes could be differentiated based on the morphology of chromosomal pairs 2 and 8, the region that the NORs occupied on the long arms of the homologous of pair 7, and the pattern of heterochromatin distribution. The subspecies P. p. paradoxa and P. p. platensis had identical karyotypes. Heteromorphism in NOR size was seen in P. p. paradoxa, P. p. platensis, P. bolbodactyla and P. fusca. Heteromorphic sex chromosomes (ZZ/ZW) were identified in P. tocantins. The W chromosome was subtelocentric and larger than the metacentric Z chromosomes. The differences observed in the C-banding pattern and in the position of the NOR on the sex chromosomes suggested that inversions and heterochromatinization were responsible for the morphological differentiation of these chromosomes.

Chromosomal Study of Colostethus brunneus from the Type Locality and Two Related Species (Anura – Dendrobatidae)

In this paper, we report a chromosomal study of three Brazilian species of Colostethus, C. brunneus from the type locality, Colostethus sp. (aff. trilineatus), and Colostethus sp., which is morphologically similar to C. brunneus. The diploid number for C. brunneus was 2n = 24 chromosomes, in agreement with that previously described for specimens from Peru. Colostethus sp. (aff. trilineatus) and Colostethus sp. showed a very similar karyotype with 22 chromosomes. The NOR was located on pair 3 in C. brunneus, on pair 4 in Colostethus sp. (aff. trilineatus), and on pair 2 in Colostethus sp. In one specimen of Colostethus sp., an additional NOR site was located on pair 7 in only one of the homologs. This extra Ag-NOR site was confirmed by FISH using an rDNA probe. In addition to the NOR location, the C-banding pattern was also species-specific, despite the similar chromosomal morphology of the species. These results indicate that although these species may be closely related, there is a clear dichotomy in their chromosome number.