Cytogenetic aspects of fish from the Gempylidae and Balistidae families of the São Pedro and São Paulo Archipelago, Meso-Atlantic region
Karyotypic evolution, DNAr, mobile elements, repetitive DNA.
Despite the accumulation of cytogenetic information, which already exceeds 3,000 species, different fish groups, regardless of their diversity, are still lacking useful cytogenetic information in evolutionary inferences. Gempylidae (Scombriformes) with 16 genera and 26 meso or bentopelagic species and relative importance in commercial fishing, has no cytogenetic information. Similarly, the diverse family Balistidae (Tetraodontiformes), with 42 species, has less than half of species with known karyotypes. Aiming to contribute to the mitigation of gaps in the knowledge of cytogenetic aspects of marine fish, especially those that inhabit Brazilian island environments, the Promethichthys prometheus and Ruvettus pretiosus (Gempylidae) and Canthidermis maculata and C. sufflamen (Balistidae) species from Archipelago of St. Peter and St. Paul, Meso-Atlantic region. Cytogenetic analyzes employed conventional methodologies (Giemsa staining, Ag-NORs staining and C-banding), base-specific fluorochrome staining (CMA³ / DAPI) and repetitive DNAr18S, rDNA 5S, microsatellite (CA)15 and (GA)15, and transposable elements Tol2 and Rex3, by fluorescence in situ hybridization (FISH). Promethichthys prometheus and R. pretiosus have 2n = 48 chromosomes, however, differ considerably in karyotype formula (NF = 84 and NF = 50, respectively.) The mapping patterns of the different classes of repetitive DNA, however, suggest a small divergence in microstructure. On the other hand, C. maculata (2n = 46 and NF = 58) and C. sufflamen (2n = 44 and NF = 58) exhibit reduced karyotypes resulted from tandem fusions rearrangements, which contributed to structural and numerical variation of karyotypes, followed by small diversification in the internal organization of chromosomes. The present results corroborate that the remarkable diversity of marine fish groups in some groups is accompanied by particular karyoevolutionary tendencies.