Molecular cytogenetic analyses reveal extensive chromosomal rearrangements and novel B chromosomes in Moenkhausia (Teleostei, Characidae)

Abstract

The cytogenetic characteristics of five fish species of the Moenkhausia are described, based on the analysis of specimens collected in different headwater. All the species analyzed presented 2n=50 chromosomes. The C-banding revealed a similar distribution pattern of heterochromatic blocks in all the species, except Moenkhausia nigromarginata. The 5S rDNA sites were distributed on multiple chromosome pairs in all five species. Single and multiple histone H1 sites were observed in all the species, and histone H1 was shown to be co-located with the 18S rRNA gene in a single chromosome pair. The U2 snDNA gene was distributed at multiple sites in all the Moenkhausia species. The presence of B microchromosomes was confirmed in Moenkhausia forestii, while individuals of the three study populations of Moenkhausia oligolepis presented three morphologically distinct types of B chromosome. The chromosomal mapping of the 18S rDNA sites using the FISH technique revealed signals in the B chromosomes of M. forestii, while clusters of the H1 histone and U2 snDNA genes were found in the B chromosomes of M. forestii and M. oligolepis. The classical and molecular cytogenetic markers used in this study revealed ample variation in the Moenkhausia karyotypes, reflecting the dynamic nature of the chromosomal evolution.

Chromosomal Instability and Origin of B Chromosomes in the Amazonian Glass Tetra <b><i>Moenkhausia oligolepis</i></b> (Günther, 1864) (Characiformes, Characidae)

“…In the case of M. oligolepis, the larger neo-isochromosome must have been eliminated, while the B microchromosome was incorporated into the genome of the species. Presence of homologies between these B microchromosomes was also observed, and the possibility of a joint location of the histone H1 and 18S rDNA sites, reflecting the origin of these B chromosomes from ancestral A chromosomes [Nascimento et al, 2020].…”

Moenkhausia andrica (Characiformes: Characidae): a new species from the rio Tapajós basin, Brazil, with minute fin hooklets in females

“…Accordingly, it was observed low morphological variation between these samples. The populations from Moenkhausia andrica was identified as M. oligolepis (Lima et al, 2007;Nascimento et al, 2020;Pastana & Dagosta, 2014), although these species can now be morphologically differentiated by the diagnostic characters presented herein. Concordant with these findings, the mitochondrial data analysis of this study showed an exceptionally high value of genetic divergence between M. oligolepis from the rio Teles Pires basin and M. andrica (19.6%, Table 3, Figure 5), which strengthens the support for the identity of the new species.…”

B Chromosomes in Psalidodon scabripinnis (Characiformes, Characidae) Species Complex

“…In most cases, B chromosomes are a mixture of DNA sequences acquired from several chromosomes of the standard genome [ 12 , 13 , 14 ] and/or organelles [ 15 ]. Most B chromosomes have a large repetitive DNA content, such as ribosomal DNA, satellite DNAs, U snRNA genes, histone genes, amplified telomeric sequences and transposable elements [ 6 , 16 , 17 , 18 , 19 ]. Even though these elements are frequently heterochromatic, young B chromosomes may show few repetitive DNA sequences, since they are euchromatic [ 7 , 20 ].…”