Karyotypic Diversification in TwoMegaleporinusSpecies (Characiformes, Anostomidae) Inferred fromIn SituLocalization of Repetitive DNA Sequences

Anostomidae species have conserved diploid numbers (2n = 54), although comparative cytogenetic studies have demonstrated chromosomal rearrangements occurrence among them, especially in repetitive DNA rich regions. The location and distribution of ribosomal DNA (rDNA) andsmall nuclear RNAs(snRNAs) multigene families are highly dynamic in the genomes of several organisms. In this study, wein situlocated the rDNA and snRNAsites in two populations ofMegaleporinus obtusidensand a sample ofMegaleporinus reinhardtito infer their chromosomal changes in the evolutionary lineages. Both species ofMegaleporinusshared 2n = 54 chromosomes with the presence of ZZ/ZW sex chromosome system, but they diverged in relationship to the location of 5S and 45S rDNAs as well as the distribution ofsnRNAssites. The characterization of the analyzed sequences revealed the presence of complete rDNA andsnRNAssequences as well assnRNAscontaining transposable elements (TEs) and microsatellite repeats. After chromosomal mapping, the sequences encompassing TEs proved to be dispersed through autosomes and accumulated on sex chromosomes. The data demonstrate that intra- and interspecific chromosomal changes occurred involving the multigene family's sites inMegaleporinuskaryotypes. Furthermore, we detected TE-like sequences in the differentiation of sex chromosome systems inM. obtusidensandM. reinhardti.