Karyotype relationships among species of subfamily tetragonopterinae (Pisces, Characidae): Cytotaxonomy and evolution aspects

Abstract

Chromosome analyses were carried out on 3 species of fish, Moenkhausia sanctaefilomenae, Moenkhausia intermedia and Hemigrammus marginatus (Tetragonopterinae) from the upper Paraná River floodplain (PR, Brazil). Species showed diploid number 2n=50 chromosomes, with different chromosome formulae. Karyotype of M. sanctaefilomenae was composed of 12M+36SM+2ST, while M. intermedia had 16M+34SM, with FN=100 for both species. Diploid numbers and chromosome formulae presented a predominance of 2-arm chromosomes, similar to that of other species of the genus. Since the chromosome formulae of H. marginatus is 10M+34SM+6A (FN=94), it differed from the previous data on this species. NOR studies for the 3 species revealed a simple system, obtained by silver nitrate staining and CMA3. Whereas M. sanctaefilomenae presented strong heterochromatic blocks in the interstitial and centromeric regions of the chromosomes, heterochromatin of the other 2 species was mainly located in the NOR bearing chromosomes. Evolutionary and cytotaxonomic aspects of these genera are discussed.