A new multiple sex chromosome system X1X1X2X2/X1Y1X2Y2 in Siluriformes: cytogenetic characterization of Bunocephalus coracoideus (Aspredinidae)

Abstract

We analyzed one Bunocephalus coracoideus population from the Negro River basin using cytogenetic techniques. The results showed a diploid number of 42 chromosomes in both sexes, with the karyotypic formula 4m + 14sm + 24a and fundamental number (FN) = 60 for females and the formula 5m + 14sm + 23a and FN = 61 for males, constituting an XXXX/XYXY multiple sex chromosome system. The constitutive heterochromatin is distributed in the pericentromeric regions of most of the chromosomes, except for the sex chromosomes, of which the X, X, and Y chromosomes were euchromatic and the Y chromosome was partially heterochromatic. 18S rDNA mapping confirmed the presence of nucleolar organizer regions on the short arms of the fifth chromosomal pair for both sexes. The 5S rDNA is present in the terminal regions of the short arms on the 2nd, 10th, and 12th pairs and on the X chromosome of both sexes; however, we observed variations in the presence of these ribosomal cistrons on the Y chromosome, on which the cistrons are pericentromeric, and on the Y chromosome, on which these cistrons are present in the terminal portions of the short and long arms. Telomeric sequences are located in the terminal regions of all of the chromosomes, particularly conspicuous blocks on the 10th and 12th pairs and internal telomeric sequences in the centromeric regions of the 1st, 6th, and 9th pairs for both sexes. This work describes an new sex chromosomes system for the Siluriformes and increases our genetic knowledge of the Aspredinidae family.

The Bunocephalus coracoideus Species Complex (Siluriformes, Aspredinidae). Signs of a Speciation Process through Chromosomal, Genetic and Ecological Diversity

“…In this sense, the other ESUs share a synapomorphic condition by presenting karyotypes mostly composed by acrocentric chromosomes, where pericentric inversions and/or centric fissions may have played a role. Such feature is also found in other Bunocephalus species, such as B. doriae ( Fenocchio and Swarça, 2012 ) and B. coracoideus population from the Negro River ( Ferreira et al, 2016 ), in which acrocentric chromosomes are also mainly composing the karyotype. Thus, taking in account the Oliveira and Gosztonyi (2000) proposition, it can be considered that the Bunocephalus ESUs A, B, and D presents a trend toward the reduction of the chromosome number in relation to other Siluriformes, while ESU-C maintained the probable ancestral 2n = 56 chromosomes.…”

“…Up to now, only two Bunocephalus species had cytogenetic studies already conducted, B. doriae and B. coracoideus . While the first one has 2n = 50 chromosomes, the later presents 2n = 42, in addition to a multiple X 1 X 1 X 2 X 2 /X 1 Y 1 X 2 Y 2 sex chromosome system ( Fenocchio and Swarça, 2012 ; Ferreira et al, 2016 ).…”

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

“…Meaningly, a close association between microsatellites, rDNAs and multiple sex chromosomes has been reported for many fish taxa [ 55 , 56 , 57 , 58 , 59 ], which highlights the probable role of these sequences in the genesis of such systems. Despite our CGH data do not reveal any conspicuous Y-specific region, neither in both Y chromosomes of H. duriventris and H. villasboas , nor in the proto/neo-Y of H. rondoni , a slight binding preference for the male-derived probe occur at the pericentromeric region of all these chromosomes ( Figure 5 ).…”

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

“…5S rDNA is an important cytotaxonomic and evolutionary marker, since it helps provide a better understanding of fish chromosomal diversity (Bellafronte et al 2005;Teixeira et al 2009;Vicari et al 2010). For instance, a study by Ferreira et al (2016), mapping of 5S rDNA sequences in Bunocephalus coracoideus Cope, 1874, revealed an association between this rDNA site and a multiple sex chromosome system previously unknown in Siluriformes (X 1 X 1 X 2 X 2 /X 1 Y 1 X 2 Y 2 ). Repetitive 5S and 18S rDNA sequences are the most well-studied in fish, and have been gaining prominence mainly in studies of between-species evolutionary relationships, population characterization and genome structure (Martins et al 2004;Terencio et al 2012;Schneider et al 2013).…”