Abstract
South American frogs of the genus Eupsophus Fitzinger, 1843 comprise 10 species. Two of them, Eupsophus vertebralis Grandison, 1961 and E. emiliopugini Formas, 1989 belong to the Eupsophus vertebralis group, exhibiting 2n = 28. Fundamental number differences between these species have been described using conventional chromosome staining of few specimens from only two localities. Here, classical techniques (Giemsa, C-banding, CMA3/DAPI banding, and Ag-NOR staining), and fluorescence in situ hybridization (FISH, with telomeric and 28S ribosomal probes), were applied on individuals of both species collected from 15 localities. We corroborate differences in fundamental numbers (FN) between E. vertebralis and E. emiliopugini through Giemsa staining and C-banding (FN = 54 and 56, respectively). No interstitial fluorescent signals, but clearly stained telomeric regions were detected by FISH using telomeric probe over spreads from both species. FISH with 28S rDNA probes and Ag-NOR staining confirmed the active nucleolus organizer regions signal on pair 5 for both species. Nevertheless, one E. emiliopugini individual from the Puyehue locality exhibited 28S ribosomal signals on pairs 4 and 5. Interestingly, only one chromosome of each pair showed Ag-NOR positive signals, showing a nucleolar dominance pattern. Chromosomal rearrangements, rRNA gene dosage control, mobile NORs elements, and/or species hybridization process could be involved in this interpopulation chromosomal variation.
Highlights
Eupsophus Fitzinger, 1843 is a South American genus of frogs that currently comprises 10 species (Frost 2019, Suárez-Villota et al 2018a), endemic from the temperate Nothofagus forests from Chile and Argentina (Formas 1978, Ibarra-Vidal et al 2004)
Mitotic plates of E. vertebralis exhibited a telocentric pair 13 presenting fundamental numbers (FN) = 54, while the other karyotypic features were similar to E. emiliopugini (Fig. 2, middle)
We present the first comparative cytogenetic study using classical and molecular cytogenetic techniques among specimens from different localities of E. emiliopugini and E. vertebralis
Summary
Eupsophus Fitzinger, 1843 is a South American genus of frogs that currently comprises 10 species (Frost 2019, Suárez-Villota et al 2018a), endemic from the temperate Nothofagus forests from Chile and Argentina (Formas 1978, Ibarra-Vidal et al 2004). The E. roseus group is composed of eight species: E. calcaratus (Günther, 1881), E. contulmoensis Ortiz, Ibarra-Vidal & Formas, 1989, E. septentrionalis Ibarra-Vidal, Ortiz, & Torres-Pérez, 2004, E. nahuelbutensis Ortiz & Ibarra-Vidal, 1992, E. insularis (Philippi, 1902), E. migueli Formas, 1978, E. roseus (Duméril & Bibron, 1841), and E. altor Nuñez, Rabanal & Formas, 2012 (Suárez-Villota et al 2018a) exhibiting the same diploid number 2n = 30 with some species specific characteristics (e.g. fundamental number, sex chromosomes, secondary constriction location; Iturra and Veloso 1986, Veloso et al 2005, Nuñez et al 2012). The pair 13 is metacentric in E. emiliopugini and telocentric in E. vertebralis, differing in their fundamental number (FN = 56 and FN = 54, respectively). Having in mind the hypothetical ancestrality of telocentric chromosomes in amphibians (Morescalchi 1980), Formas (1991) proposed two alternative hypotheses to explain the origin of the differences on the pair 13 in the E. vertebralis group. The second hypothesis is the addition of heterochromatic segments in the centromeric region of the telocentric pair in E. vertebralis, which leads to a metacentric pair in E. emiliopugini. Formas (1991) considered the first alternative as a reasonable hypothesis because telocentric and metacentric pairs 13 are the same size
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