Diversidade morfológica e cariotípica de Astyanax bifasciatus (Teleostei, Characidae) frente à morfofisionomia do Rio Iguaçu

Abstract

The geomorphological processes that occur in the formation of environments affect the evolutionary history of the species, which in the case of freshwater is even more effective, and can refer to the connection or separation of the hydrographic basins in the past. Since these processes affect the distribution, abundance and diversification of fish in these geographical regions. In this regard, the objective of the present work was to infer the diversity and variability of Astyanax bifasciatus along the Iguaçu river basin. For this, was used morphometric analyzes related to the body and head size of the individuals of the upper, middle and lower regions of the Iguaçu river basin. And cytogenetic analyzes, including conventional staining with Giemsa, localization of nucleolar organizer regions by impregnation with silver nitrate, detection of constitutive heterochromatin by C-banding method and fluorescent in situ hybridization using rDNA probes 5S and 18S, snDNA U2 gene and telomeric DNA sequences. The results of the morphological analyzes indicated a significant differentiation between the populations of A. bifasciatus of the three regions of the Iguaçu river basin, the location of the flippers being the most variable character. The cytogenetics revealed the same diploid number of chromosomes (50) for the populations of the middle and upper regions of the Iguaçu river, as well as the same fundamental number (86) and karyotype formula (6m+24sm+6st+14a). Already the population of the lower region of the Iguaçu river had a diploid number of 48 chromosomes, NF=82 and FC=6a+22sm+6st+14a. The Ag-NORs were multiple for the medium population of the Iguaçu river, and simple for those upper and lower populations of the Iguaçu river, with their locations coincident with 18S rDNA. The C-banding demonstrated centromeric and pericentromeric markers for the three populations of the Iguaçu river, as well as heterogeneous telomeric markers between them. The 5S and 18S markers were variable for the populations of the Iguaçu river, with 5S markers coincident with heterochromatic sites in all populations. The U2 snDNA sites were variable between the populations, with their location in one chromosomal pair in the population of the middle region of the Iguaçu river and only one homologous in the other populations. The mapping of telomeric DNA in the lower population of the Iguaçu river revealed markers in the telomeric region of the most of chromosomes, as well as in the centromeric region of a chromosomal pair. These different levels of analysis showed a great differentiation between the populations of A. bifasciatus of the medium and lower regions of the Iguaçu river, probably arising to tectonic events that occurred in the region.