Mapeamento físico dos genes ribossomais 5S e 18S em diferentes populações de Astyanax bimaculatus (Characiformes, Characidae)

Abstract

The physical mapping by fluorescent in situ hybridization (FISH) of 5S and 18S ribosomal genes has been used with great frequency in cytogenetic studies of Neotropical fishes, to assist in the resolution of taxonomic, biogeographic and phylogenetic problems. In this way, the present work aimed to carry out a physical mapping by FISH of 5S and 18S ribosomal genes in populations of Astyanax bimaculatus from tributaries and piscicultures of the region of influence of Itaipú Lake, region of Santa Helena - PR. The specimens were collected with the aid of nets and containers, and transported alive to the Laboratory of Ichthyology and Limnology of the Universidade Tecnológica Federal do Paraná - Santa Helena Campus, where they were kept in aquariums until they were euthanized to obtain the cellular suspension. For the preparation and obtaining of mitotic chromosomes, the technique of "in vitro" treatment was used, which consists in obtaining mitotic metaphases from fragments of the cephalic kidney, since this one has hematopoietic function. The cistrons of 5S rDNA and 18S rDNA were mapped on chromosomes using double fluorescence in situ hybridization (Double-FISH), under 77% stringency. Simple 5S rDNA markings were observed in the population of Santa Helena, Córrego São Gabriel and Piscicultura Cerâmica, in the pericentromeric position of the metacentric pair 3. In the population of Córrego Sanepar 5S rDNA markings were evidenced in the pericentromeric position of metacentric pair 3 and subtelocentric pair 18. The 18S rDNA probe tags revealed markings in the terminal regions of the short arm of the subtelocentric pair 18 of the populations Piscicultura Cerâmica, Córrego Sanepar and Córrego São Gabriel. In the population Piscicultura Santa Helena, in the terminal region of the short arm of the subtelocentric pair 15. In the Córrego Sanepar population there was an overlap of the cistrons in the terminal position of the short arm of the subtelocentric pair 18. The results revealed that the 5S rDNA is an excellent genetic marker for Astyanax but new analyzes should be carried out to confirm if the variations found refer to the population polymorphisms or they are characteristics of distinct biological units, since A. bimaculatus is considered a complex of species.