Conservadorismo cromossômico e mapeamento in situ do DNAr em Pareques acuminatus (Perciformes, Sciaenidae) do litoral do Rio Grande do Norte

Abstract

Molecular cytogenetics has proved to be a dynamic and necessary tool to help get closer to the real evolutionary histories of organisms, solve problems in groups - especially fish - and help in the recognition of biodiversity. The order Perciformes constitutes one of the most diverse of the vertebrates, although, the cytogenetic data of its species are still scarce, in particular, those referring to the dynamics of important repetitive sequences through fluorescence in situ hybridization (FISH). Perciformes consists of 66 families, among them the family Sciaenidae, with 36 species known for the Brazilian coast. One of these, Pareques acuminatus is widely distributed in reef coastal regions of the Western Atlantic. In order to contribute with cytogenetic data that can estimate patterns of chromosome evolution of the family, the cytogenetic characterization of the species was performed through conventional cytogenetic techniques (conventional staining by Giemsa, Ag-RONs and band C), staining with base-specific fluorochromes DAPI/CMA3) and fluorescence in situ hybridization (FISH) with 18S and 5S rDNA probes. The specimens were collected at Santa Rita Beach / Extremoz-RN and placed in the laboratory, where they were submitted to cytogenetic techniques. The species presents 2n = 48 chromosomes with a karyotype formed exclusively by acrocentric elements. Heterochromatic blocks are distributed in the centromeric regions of the chromosomes. Ag-RONs / CMA + / DAPI- sites occur exclusively in the pericentromeric region of the par 2 long arm, coincident with the 18S rDNA sites. The 5S rDNA sites, located in par 1, presented a unique heterozygous condition, where in one of the homologues it occupied centromeric position, while in the other it was located in a pericentromeric position in the long arm. The obtained cytogenetic patterns are coincident with other species of the family and indicate conditions considered simpleiomórficas and widely shared between the groups of Perciformes. The structural variation of 5S rDNA sites suggests a transient condition derived from a paracentric inversion event. Additional analyzes in this and other populations of the species will allow to estimate the structural polymorphism involving the 5 rDNA sites and their possible evolutionary consequences.