The hylid tribe Cophomantini is a diverse clade of Neotropical treefrogs composed of the genera Aplastodiscus, Boana, Bokermannohyla, Hyloscirtus, and Myersiohyla. The phylogenetic relationships of Cophomantini have been comprehensively reviewed in the literature, providing a suitable framework for the study of chromosome evolution. Employing different banding techniques, we studied the chromosomes of 25 species of Boana and 3 of Hyloscirtus; thus providing, for the first time, data for Hyloscirtus and for 15 species of Boana. Most species showed karyotypes with 2n = 2x = 24 chromosomes; some species of the B. albopunctata group have 2n = 2x = 22, and H. alytolylax has 2n = 2x = 20. Karyotypes are all bi-armed in most species presented, with the exception of H. larinopygion (FN = 46) and H. alytolylax (FN = 38), with karyotypes that have a single pair of small telocentric chromosomes. In most species of Boana, NORs are observed in a single pair of chromosomes, mostly in the small chromosomes, although in some species of the B. albopunctata, B. pulchella, and B. semilineata groups, this marker occurs on the larger pairs 8, 1, and 7, respectively. In Hyloscirtus, NOR position differs in the three studied species: H. alytolylax (4p), H. palmeri (4q), and H. larinopygion (1p). Heterochromatin is a variable marker that could provide valuable evidence, but it would be necesserary to understand the molecular composition of the C-bands that are observed in different species in order to test its putative homology. In H. alytolylax, a centromeric DAPI+ band was observed on one homologue of chromosome pair 2. The band was present in males but absent in females, providing evidence for an XX/XY sex determining system in this species. We review and discuss the importance of the different chromosome markers (NOR position, C-bands, and DAPI/CMA₃ patterns) for their impact on the taxonomy and karyotype evolution in Cophomantini.

Recently, Physalaemus albifrons (Spix, 1824) was relocated from the P. cuvieri group to the same group as P. biligonigerus (Cope, 1861), P. marmoratus (Reinhardt & Lütken, 1862) and P. santafecinus Barrio, 1965. To contribute to the analysis of this proposition, we studied the karyotypes of P. albifrons, P. santafecinus and three species of the P. cuvieri group. The karyotype of P. santafecinus was found to be very similar to those of P. biligonigerus and P. marmoratus, which were previously described. A remarkable characteristic that these three species share is a conspicuous C-band that extends from the pericentromeric region almost to the telomere in the short arm of chromosome 3. This characteristic is not present in the P. albifrons karyotype and could be a synapomorphy of P. biligonigerus, P. marmoratus and P. santafecinus. The karyotype of P. santafecinus is also similar to those of P. marmoratus and P. biligonigerus owing to the presence of several terminal C-bands and the distal localization of the NOR in a small metacentric chromosome. In contrast, the P. albifrons karyotype has no terminal C-bands and its NOR is located interstitially in the long arm of submetacentric chromosome 8. The NOR-bearing chromosome of P. albifrons very closely resembles those found in P. albonotatus (Steindachner, 1864), P. cuqui Lobo, 1993 and some populations of P. cuvieri Fitzinger, 1826. Additionally, the P. albifrons karyotype has an interstitial C-band in chromosome 5 that has been exclusively observed in species of the P. cuvieri group. Therefore, we were not able to identify any chromosomal feature that supports the reallocation of P. albifrons.

Oreobates Jiménez de la Espada, 1872 is a large group of South American frogs with terrestrial reproduction and direct development, located in the superfamily Brachycephaloidea. About 260 brachycephaloidean species have been cytogenetically studied so far, at least with standard techniques. However, this information represents fewer than 17% species of the family Craugastoridae Hedges, Duellman & Heinicke, 2008, where the genus Oreobates is included. In the present work, using a diversity of standard and molecular techniques, we describe the karyotype of O. barituensis Vaira & Ferrari, 2008, O. berdemenos Pereyra, Cardozo, Baldo & Baldo, 2014 and O. discoidalis (Peracca, 1895), from northwestern Argentina. The three species analyzed showed a diploid karyotype with 2n = 22 biarmed chromosomes, fundamental number (FN) = 44, nucleolus organizer regions (NORs) located pericentromerically on pair 7, and a centromeric and pericentromeric C-banding pattern. We observed variations in the chromosome number in O. barituensis due the presence of two morphs of B chromosomes, one medium-sized telocentric (BT) and another subtelocentric and smaller (Bst). Both B chromosomes are mitotically stable and were recorded in all somatic and germinal cells analyzed. The BT chromosome occurred at a maximum of one per individual (2n = 22+BT), and the other one was observed single (2n = 22 + Bst) or as a pair in two doses (2n = 22 + 2BT). We additionally observed other supernumerary chromosomes in the three species analyzed, all of them euchromatic, small, dot-shaped and with instability during mitoses, showing a frequency of occurrence below 50% in studied specimens. The occurrence of polymorphic and spontaneous chromosomal rearrangements and supernumerary chromosomes is a recurrent feature reported in frogs with terrestrial habits (Brachycephaloidea and Hemiphractidae Peters, 1862), which suggests that Brachycephaloidea may be a promising group for studying the origin and maintenance of B chromosomes in anurans.

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.