Comparative karyotype analysis and chromosome evolution in the genus Aplastodiscus (Cophomantini, Hylinae, Hylidae)

Abstract

BackgroundThe frogs of the Tribe Cophomantini present, in general, 2n = 24 karyotype, but data on Aplastodiscus showed variation in diploid number from 2n = 24 to 2n = 18. Five species were karyotyped, one of them for the first time, using conventional and molecular cytogenetic techniques, with the aim to perform a comprehensive comparative analysis towards the understanding of chromosome evolution in light of the phylogeny.ResultsAplastodiscus perviridis showed 2n = 24, A. arildae and A. eugenioi, 2n = 22, A. callipygius, 2n = 20, and A. leucopygius, 2n = 18. In the metaphase I cells of two species only bivalents occurred, whereas in A. arildae, A. callipygius, and A. leucopygius one tetravalent was also observed besides the bivalents. BrdU incorporation produced replication bands especially in the largest chromosomes, and a relatively good banding correspondence was noticed among some of them. Silver impregnation and FISH with an rDNA probe identified a single NOR pair: the 11 in A. perviridis and A. arildae; the 6 in A. eugenioi; and the 9 in A. callipygius and A. leucopygius. C-banding showed a predominantly centromeric distribution of the heterochromatin, and in one of the species distinct molecular composition was revealed by CMA3. The telomeric probe hybridised all chromosome ends and additionally disclosed the presence of telomere-like sequences in centromeric regions of three species.ConclusionsBased on the hypothesis of 2n = 24 ancestral karyotype for Aplastodiscus, and considering the karyotype differences and similarities, two evolutionary pathways through fusion events were suggested. One of them corresponded to the reduction of 2n = 24 to 22, and the other, the reduction of 2n = 24 to 20, and subsequently to 18. Regarding the NOR, two conditions were recognised: plesiomorphy, represented by the homeologous small-sized NOR-bearing pairs, and derivation, represented by the NOR in a medium-sized pair. In spite of the apparent uniformity of C-banding patterns, heterogeneity in the molecular composition of some repetitive regions was revealed by CMA3 staining and by interstitial telomeric labelling. The meiotic tetravalent might be due to minute reciprocal translocations or to non-chiasmatic ectopic pairing between terminal repetitive sequences. The comparative cytogenetic analysis allowed to outline the chromosome evolution and contributed to enlighten the relationships within the genus Aplastodiscus.

Chromosome Evolution in Dendropsophini (Amphibia, Anura, Hylinae)

“…The equilocal distribution and colocalization of heterochromatic blocks and ITSs support the idea that ITSs originated from the same evolutionary processes described for heterochromatic blocks [Redi et al, 2001; Ka- [Gruber et al, 2012] that according to our criteria mimic the true telomere resultant from the postulated chromosome fusion.…”

“…At the same time, the presence of centromeric ITSs has only been reported for some species of Aplastodiscus with 2n = 22 (A. albofrenatus , A. arildae and A. eugenioi) and 2n = 18 (A. leucopygius) . However, other species with 2n = 22 (A. ehrhardti) or 2n = 20 (A. callipygius) have no ITS, although the transformations between 2n = 24 and 2n = 22 and those between 2n = 24, 2n = 20 and 2n = 18 are well-supported by the analyses of diverse cytological markers in a phylogenetic context [Carvalho et al, 2009;Gruber et al, 2012]. The only other anuran for which centromeric ITSs were reported is P. cruentus [Schmid et al, 2010].…”

“…In hylids, the heterochromatic blocks are equilocally distributed on the set of heterologous chromosomes, as observed in the 5 genera with karyotypes described in the present contribution. In Aplastodiscus , many of these blocks also colocalize with ITSs [Carvalho et al, 2009;Gruber et al, 2012]. As heterochromatic blocks, ITSs are equilocalized [Wiley et al, 1992, figs.…”

“…Nevertheless, noncentromeric ITSs were not observed in any of the 20 species analyzed with the telomeric probe of the other Hylinae tribes, including 8 taxa with the ancestral 2n = 24 karyotype [Anderson, 1996;Carvalho et al, 2009;Ferro et al, 2012;Gruber et al, 2012;present work]. At the same time, the presence of centromeric ITSs has only been reported for some species of Aplastodiscus with 2n = 22 (A. albofrenatus , A. arildae and A. eugenioi) and 2n = 18 (A. leucopygius) .…”

Comparative cytogenetics of tree frogs of the Dendropsophus marmoratus (Laurenti, 1768) group: conserved karyotypes and interstitial telomeric sequences

“…Aplastodiscus albofrenatus (Lutz, 1924), A. arildae (Cruz & Peixoto, 1987) and A. eugenioi (Carvalho-e-Silva & Carvalhoe-Silva, 2005)-Carvalho et al 2009, Gruber et al 2012a; Hypsiboas faber (WiedNeuwied, 1821)- Schmid and Steinlein 2016]. In the hylid Itapotihyla langsdorffii (Duméril & Bibron, 1841), ITSs were also observed in several centromeres (Gruber et al 2012b), but in this case the het-ITSs are not as large as those previously mentioned.…”