Análisis citogenético del ratón de montaña saccodon wagneri (characiformes; paradontidae) kner, 1863 mediante métodos convencionales y moleculares.

Abstract

The Parodontidae is a relatively small group of Neotropical fishes belonging to the Characiformes that consists of three genera (Apaeirodon, Parodon and Saccodon) with 32 valid species. The genus Saccodon contains only three valid species: Saccodon dariensis (Meek & Hildebrand 1913) distributed in Colombia and Panama, Saccodon wagneri (Kner 1863) distributed in the coastal basins of Ecuador and more northern coastal basins of Peru and Saccodon terminalis (Eigenmann & Henn 1914) in the Daule River Basin in Ecuador. This study present, the first cytogenetic data for Saccodon wagneri, including the standard karyotype, C bands and repetitive DNA mapping by fluorescent in situ hybridization (FISH). Males and females shares a diploid chromosome number 2n = 54. In females, the karyotype consisted of 31 metacentric (m), 16 submetacentric (sm) and 7 subtelocentric (st), with a fundamental number FN = 101, whereas in males the karyotype presented 32 m, 16 sm and 6 st, FN = 102, revealing the presence of heteromorphic sex chromosomes of the ZZ / ZW type. Impregnation with Silver Nitrate revealed a single pair of Ag-NORs bearing chromosomes located in the secondary constriction on the distal tip in the short arm of a small metacentric pair (N°14). C banding revealed regions of centromeric heterochromatin in most chromosomes, as well as interstitial and terminal bands and a remarkably large distal block, of heteromorphic size, which fully corresponded to Ag-NORs sites on the chromosomal pair N° 14. The ZZ pair did not appear heterochromatic, while in females the W chromosome has a terminal heterochromatin band in the long arm, occupying approximately half of the long arm of the W chromosome, being approximately half the size of the Z chromosome. FISH assay showed hybridization signals with the 18S-rDNA probe coinciding with the Ag-NOR signals in the pair number 14 confirming the presence of a single group of main ribosomal genes whereas the 5S-rDNA probe revealed only a pair of minor ribosomal genes located on the same chromosome No. 14, just below the 18 S rDNA signal. Hybridization with the probe (TTAGGG)n revealed fluorescent signals only on the telomeric regions of all chromosomes, without interstitial telomeric sites (ITSs). Results here obtained and its comparison with those of other species of the family, allows generalizing that the presence of simple Ag-NOR is the most frequent condition in the majority of the species and, therefore, a simplesiomorphy in the Parodontidae. Although the family has a conserved diploid number, at the macro and microstructural level, the species so far analyzed show several cytogenetic differences that suggest the occurrence of reorganization processes during diversification in the group. Since this study constitutes the first report on cytogenetic characteristics in species of the genus Saccodon, the need to perform additional analyzes in other species of the genus is highlighted in order to obtain a more complete picture of the chromosomal evolution within the Saccodon and, therefore, in the Parodontidae.