Análise biogeográfica do gênero gymnotus (gymnotidae, gymnotiformes), por meio de marcadores cariotípicos e moleculares

Abstract

The family Gymnotidae of electric fishes is composed by two genera: Electrophorus, popularly known as “poraquê” and Gymnotus, commonly known as “sarapós” or “tuviras”. Unique by their capacity of producing electric potential, which they use to electrolocation and environmental interaction, this group has evolved within South American continent. While E. electricus is restricted to the Amazon region, Gymnotus presents a greater dispersion. Nowadays, it has 39 described species, which were separated in five distinct clades: G1, Pantherinus clade; G2, Cylindricus clade and the Carapo clade. Concerning to cytogenetics, this group presents a great chromosomal plasticity, especially Carapo clade, with diploid numbers varying from 34 to 54 chromosomes. In the present work, we analyzed the karyotypes of nine species of Gymnotidae family from Central Amazon, by cytogenetic and molecular markers. We described the karyotypes of E. electricus, Gymnotus ucamara, G. mamiraua, G. carapo “Catalão”, G. cf. coropinae, G. cf. stenoleucus, G. cf. pedanopterus, G.ymnotus sp. “Negro” and G. carapo “Maranhão. The presence of sex chromosomes is remarkable within this genus and three new systems of turnover type were described, with low amounts of heterochromatin, recent and independent origin in: G. carapo “Catalão” (XX/XY); Gymnotus sp. “Negro” and G. coropinae (X1X1X2X2/X1X2Y). Chromosome painting in G. carapo “Catalão” revealed three pairs involved in the formation of the sexual pair. Ribosomal DNA location is conserved in relation to the 18S rDNA for Gymnotus species and for E. electricus, we confirmed the presence of a single pair bearing the major rDNA. For 5S rDNA, the trend in the family is of unique sites in basal clades, but with substantial increase in the species composing the Carapo clade. A special case was found in G. mamiraua. They presented 13 sites with this sequence, which were co-located with a transposition element TC1/mariner. This feature of numerous sites is shared by species from the Paraná-Paraguay River basin. The proximity between G. mamiraua (2n=54) from Amazon basin and G. inaequilabiatus (2n=54) was confirmed by the DNA barcode technique, suggesting that the expansion of the 5S ribosomal sites occurred in an ancestor, still in Amazon region. Gymnotus presents itself as a model group for evolution and chromosomal differentiation, being the 5S rDNA an excellent cytotaxonomic tool and the species as biogeographic indicators.