Comparative cytogenetic of six species of Amazonian Peacock bass (, Cichlinae): intrachromosomal variations and genetic introgression among sympatric species.

Cytogenetic data for the genus Bloch et Schneider, 1801 are still very limited, with only four karyotype descriptions to date. The sum of the available cytogenetic information for species, points to a maintenance of the diploid number of 48 acrocentric chromosomes, considered a typical ancestral feature in cichlids. In the current study, we performed molecular and classical cytogenetic analyses of the karyotype organization of six species of , the earliest-diverging genus of Neotropical cichlids. We cytogenetically analysed Kullander et Ferreira, 2006, Agassiz, 1831, Kullander et Ferreira, 2006, Humboldt, 1821, Kullander et Ferreira, 2006 and Kullander et Ferreira, 2006, including three individuals that showed mixed morphological characteristics, likely from different species, suggesting they were hybrid individuals. All individuals analysed showed 2n = 48 acrocentric chromosomes, with centromeric heterochromatic blocks on all chromosomes and a terminal heterochromatic region on the arm of the 2 pair. Mapping 18S rDNA gave hybridization signals, correlated with the nucleolus organizer regions, on the 2 pair for all analyzed individuals. However, we found distinct patterns for 5S rDNA: interstitially at the proximal position on 6 pair of four species (, , and ), and on the distal of the 4 pair in two ( and ). Accordingly, we present here new data for the genus and discuss the evolutionary trends in the karyotype of this group of fish. In addition, we provide data that supports the occurrence of hybrid individuals in the Uatumã River region, mainly based on 5S rDNA mapping.