Differentiation and evolutionary relationships in Erythrinus erythrinus (Characiformes, Erythrinidae): comparative chromosome mapping of repetitive sequences

Erythrinus erythrinus presents extensive karyotypic diversity, with four karyomorphs (A-D) differing in the number of chromosomes, karyotype structure or sex chromosomes systems. Karyomorph A has 2n = 54 chromosomes in males and females without heteromorphic sex chromosomes, while karyomorph C has 2n = 52 chromosomes in females and 2n = 51 chromosomes in males, due a X1X1X2X2/X1X2Y sex chromosome system. Three allopatric populations of the karyomorph A and one population of the karyomorph C were now in deep investigated by molecular cytogenetic analyses, using repetitive DNAs as probes. The results reinforced the relatedness among populations of the karyomorph A, despite their large geographic distribution. Karyomorph C, however, showed a remarkably difference in the genomic constitution, especially concerning the amount and distribution of the 5S rDNA and Rex3 sequences on chromosomes. In addition, although karyomorphs C and D share several features, exclusive chromosomal markers show the derivative evolutionary pathway between them. Thus, besides the classical chromosomal rearrangements, the repetitive DNAs were useful tools to reveal the biodiversity, relatedness and differentiation of this fish group. The chromosomal set strongly corroborates that E. erythrinus corresponds to a species complex instead of a single biological entity.