Integração dos estudos cromossômicos e DNA barcoding em Rhamphichthys (Pisces: Gymnotiformes)

Abstract

The Order Gymnotiformes is composed by 219 valid species, which are distributed in five families. The most investigated genera are Eigenmannia and Gymnotus. Our work focused on family Rhamphichthyidae, genus Rhamphichthys that, like other Gymnotiformes, present greater abundance and diversity in the Amazon region. Sampling was carried out in the municipalities of Abaetetuba, Barcarena and Belém (Pará) and Tefé, Ecological Reserve Mamirauá (Amazonas), in order to better define the species, through the integration of classical cytogenetic data, cytogenomic analysis (probes for repetitive DNA sequences) and DNA Barcoding and thus understand the evolution of this fish in the Amazon. A new karyotype was identified for R. rostratus with the presence of B chromosomes and karyotype formula FC = 48m / sm + 2st / a + (5-10) B, as well as a new cytotype from the Amazon region, in Rhamphichthys sp. FC = 44m / sm + 6st / a, and also in R. marmoratus, FC = 46 + 4st / a in the state of Pará. The analysis of repetitive sequences in the new cytotypes demonstrated that probes 18S coincided with the regions of constriction secondary that are marked with silver nitrate in the classical NOR staining technique. The DNA probes 5S mark multiple sites, letting clear that the evolution of the ribosomal gene family is independent, at least in the genus Rhamphichthys. Retroelements REX1 and REX3 marked in a dispersed fashion throughout the genome, as already described in literature for other fishes. The REX1 element also marks the secondary constriction in R. rostratus, which has also been described in other species of fishes that inhabit polluted environments, exposed to environmental stresses and also in hybrid individuals. The barcoding DNA analysis allowed the construction of a Bayesian tree, which is in agreement with the cytogenetic data. Thus, populations of R. rostratus with and without B chromosomes are separate taxa. In turn, the sample from Mamirauá, herein called Rhamphichthys sp., since it was not been formally described, it is more similar in both karyotypic data as the barcoding analysis with R. hanni from southeastern Brazil. Our data let clear that the number of species in Rhamphichthys is underestimated, which reinforces the need for a taxonomic revision of the genus.