Comparação citogenética de quatro populações de Astyanax scabripinnis (Pisces, Characibae) da região do Triângulo Mineiro

Abstract

The characidae family is the most complex group among the characiformes and represents a huge group of sweet water fish from South America. The Tetragonopterinae subfamily detaches itself in the characidae family because it has the most species among the fishes. Its geographic distribution goes from the frontiers of México and United State of America to Argentina. The most genus studied cytogenetically within this family is the Astyanax which is popularly known as lambari, piaba and others. Despite the huge karotypic variability observed in the Astyanax scabripinnis specimen, the present work had the purpose to compare cytogenetically four populations this specie from the Triângulo Mineiro region (Uberlândia and Campina Verde town), being three populations from Paranaíba River basin (Jatai, dos Caetano and Cruz da Retirada Bonita Streams) and one from Grande River basin (da Manga Stream). All of them presented a 50 chromosomes diploid number but four male samples from Jatai Stream presented a supernumerary chromosome (2n=50+1B). The silver staining showed a multiple NORs system. The constitutive heterochromatine blocks were localized in the centromeric and pericentromeric regions in some chromosomes beyond an interstitial band in an acrocentric chromosome in the Cruz da Retirada Bonita Stream population. The use of chromomicine A3 (CMA3) in metaphases of individuais from Cruz da Retirada Bonita, dos Caetano and Jatai Streams indicated that the AgNORs sites were CMA3+. The fluorochromes showed other chromosomic regions GC bases rich beyond those NORs regions silver stained. The cytogenetic regions (number and positioning of NORs quantity of heterochromatic sections), observed in the four A. scabripinnis populations probably can be attributed to the environment of this specie. Despites three of the populations are belonged to the same hydrographic basin, the behavior to inhabit preferentially the head of small rivers is a strong sign that justify such differences, because the physical barriers and the distance that separate these populations lead to their isolation and prevent the genic flow favouring establishment of possible alterations.