Patterns of ribosomal DNA distribution in hylid frogs from the Hypsiboas faber and H. semilineatus species groups

Abstract

We performed a comparative analysis of the nucleolus organizer region (NOR) distribution in the karyotypes of hylid frogs from two different taxonomic groups, Hypsiboas faber and H. semilineatus. Silver nitrate staining of NORs (Ag-NORs) and fluorescence in situ hybridization (FISH) with a rDNA probe were used to investigate the chromosomal location of rDNA loci in two species. The karyotype of H. semilineatus and the Ag-NORs distribution of the four species are presented herein for the first time. After conventional staining, the four species presented very similar karyotypes with 2n = 24, but Ag-NORs analyses revealed species-specific characteristics. H. albomarginatus, H. faber and H. semilineatus had one pair of interstitial Ag-NORs in the short arm of pairs 2, 11, and in the long arm of pair 7, respectively. H. pardalis presented telomeric NORs in the long arm of pair 11. Ag-NORs were heteromorphic in three of the species (H. pardalis, H. semilineatus and H. albomarginatus) and FISH confirmed the differential activity of rDNA genes in H. semilineatus. In the present study, 2n = 24 karyotypes could be distinguished by their Ag-NORs distribution. Our results further the knowledge about the cytogenetics of hylids from Brazil.

Dynamics of chromosomal evolution in the genus Hypsiboas (Anura: Hylidae)

“…On the other hand, NORs in species and populations of Hypsiboas are variable, although most species presented single NORs located interstitially on long arms of mediumsized to small chromosomes (pairs 7, 10, and 11; present study; Ananias et al, 2004;Gruber et al, 2006;Nunes and Fagundes, 2008). Besides interspecific variation, 2 populations of H. crepitans (present study; Gruber et al, 2006) also differed in relation to the NOR-bearing pair.…”

“…After the chromosomal measurements were standardized, 8 karyotype groups could be defined, many of which were shared by distinct species (Table 2 and Figure 3). (Nunes and Fagundes, 2008); C. H. albopunctatus (Gruber et al, 2006); D. H. crepitans (Gruber et al, 2006); E. H. crepitans (present study); F. H. raniceps (Gruber et al, 2006); G. H. bischoffi (Raber et al, 2004); H. H. guentheri (Raber et al, 2004); I. H. marginatus ; J. H. pardalis (Nunes and Fagundes, 2008); K. H. semiguttatus ; L. H. sp aff semiguttatus ; M. H. semilineatus (Nunes and Fagundes, 2008); N. H. semilineatus (present study); O. H. pombali (present study); P. H. faber (Carvalho et al, 2009); Q. H. faber (Nunes and Fagundes, 2008); R. H. polytaenius (Nunes and Fagundes, 2008); S. H. atlanticus (present study). Table 1.…”

“…These data indicate that NORs are weak chromosomal markers for species identification of the genus Hypsiboas when used separately from other techniques or, alternatively, they might indicate the presence of cryptic species. Nonetheless, NORs located on the largest chromosomes (pairs 1 and 2) or terminal NORs were restricted to certain groups, serving as species-specific markers, such as in H. albomarginatus and Hypsiboas semiguttatus Nunes and Fagundes, 2008).…”

“…The available phylogenetic studies in Hypsiboas suggest that interstitial single NORs are likely a plesiomorphic trait (Nunes and Fagundes, 2008), while variant conditions would be apomorphic.…”

“…Within Hypsiboas, cytogenetic data have been shown for only 16% of the species, most of which have been derived based on conventional karyotype descriptions, and thus, some inferences about their chromosomal evolution that need to be determined using banding techniques are missing (Raber et al, 2004;Ananias et al, 2004;Gruber et al, 2006;Nunes and Fagundes, 2008;Carvalho et al, 2009). …”