Multiple Sex Chromosomes and Evolutionary Relationships in Amazonian Catfishes: The Outstanding Model of the Genus (Siluriformes: Loricariidae).

The armored catfishes present great species diversity and remarkable cytogenetic variation, including different sex chromosome systems. Here we analyzed three new species, , and , using both conventional and molecular cytogenetic techniques (Giemsa-staining and C-banding), including the mapping of repetitive DNAs using fluorescence hybridization (FISH) and comparative genomic hybridization (CGH) experiments. Both and have 2n = ♀56/♂55 chromosomes, and an XXXX /XXY sex chromosome system, while a proto or neo-XY system is proposed for (2n = 54♀♂). Single motifs of 5S and 18S rDNA occur in all three species, with the latter being also mapped in the sex chromosomes. The results confirm the general evolutionary trend that has been noticed for the genus: an extensive variation on their chromosome number, single sites of rDNA sequences and the occurrence of multiple sex chromosomes. Comparative genomic analyses with another congeneric species, , reveal that the XXY sex chromosomes of these species share the genomic contents, indicating a probable common origin. The remarkable karyotypic variation, including sex chromosomes systems, makes a suitable model for evolutionary studies focusing on karyotype differentiation and sex chromosome evolution among lower vertebrates.