Caracterização cromossômica de espécies de acarás da subfamília Cichlasomatinae (Perciformes: Cichlidae) da Amazônia Central

Abstract

Cytogenetic studies were performed on 13 species of acarás in the family Cichlidae, subfamily Cichlasomatinae, collected from different locations in the Amazon basin. Of these, two exhibited 2n=50, one 2n=42, two 2n=46, and eight 2n=48 chromosomes. Different karyotypic formulae were found in this subfamily, with the number of arms varying from 50 to 60. This degree of variation in diploid number and karyotypic formulae within the family suggests the presence of both Robertsonian (fission and fusion) and non-Robertsonian (inversions and translocations) rearrangements. Robertsonian rearrangements increase or decrease the diploid number, while non-Robertsonian rearrangements modify the karyotypic formula. The nucleolar organizing regions, an excellent chromosomal marker among fish, varied in their chromosomal locations, as well as in their karyotypic positions. Nine species had simple NORs, with three on the first pair of the complement. Two species had multiple NORs, but never in more than two chromosome pairs. Constitutive heterochromatin was present in the centromeric region of all chromosomes in all species; however some exhibited quite evident blocks, while others were paler. The cytogenetic data obtained for the subfamily Cichlasomatinae during this study corroborates its derived position in the Cichlidae family, most notably the diversity of diploid numbers and karyotypic formulae and the species-specific location and position of the NOR and heterochromatin blocks. This diversity may be considered, without a doubt, as consequence of the chromosome rearrangements.