Intraspecific crosses resulting in the first occurrence of eight and nine B chromosomes in Prochilodus lineatus (Characiformes, Prochilodontidae)

B chromosomes are supernumerary elements present in about 15% of eukaryotic species and are most frequently heterochromatic, behave parasitically, show a transmission rate higher than standard (A) chromosomes, and can provoke harmful effects on carriers. In the current work, Prochilodus lineatus individuals carrying eight and nine B chromosomes were obtained by induced crossing performed involving breeders with different B chromosome numbers in their cells. The high B chromosome numbers found in the offspring were recorded for the first time in this species. The use of cytogenetic techniques applied in the present study revealed that regardless of the increase in number of B chromosomes in the genome of these individuals, those elements did not presented active genes, and showed their normal heterochromatic characteristic

Cytogenetic and Molecular Data Demonstrate that the Bryconinae (Ostariophysi, Bryconidae) Species from Southeastern Brazil Form a Phylogenetic and Phylogeographic Unit

<div><p><i>Brycon</i> spp. occur in Neotropical watersheds to the west and east of the Andes, and as they are sensitive to anthropogenic changes, many these species are endangered in southeastern Brazil. Coastal rivers in southeastern Brazil are characterized by the presence of relatively few freshwater fish species and high endemism of this fauna. The objective of this study was to examine whether <i>Brycon</i> spp. occurring in the coastal basins of southeastern Brazil are monophyletic, using cytogenetic data, mitochondrial, and nuclear molecular markers. All the species showed a diploid number of 50 chromosomes, a conserved number within the subfamily Bryconinae. However, the karyotypic formulas were unique to most species, including <i>Brycon devillei</i> (26m+22sm+2st), <i>Brycon ferox</i> (26m+12sm+12st), <i>Brycon insignis</i> (22m+20sm+8st), <i>Brycon opalinus</i>, and <i>Brycon vermelha</i> (24m+20sm+6st), indicating the prevalence of pericentric and paracentric inversions in the chromosomal evolution of these species. All of them had nucleolar organizer regions in the first pair of subtelocentric chromosomes and no equilocal distribution of heterochromatin in the first pair of chromosomes of the karyotype. These two features, not seen in any other <i>Brycon</i> spp. examined to date, indicate that Bryconinae species from the Brazilian southeastern coastal basins, including the monotypic genus <i>Henochilus</i>, are monophyletic. Also, this is the first study that reports NOR location and C-banding patterns as synapomorphies for a Neotropical fish species group. The monophyly was also supported by a phylogenetic analysis of <i>16S</i> rDNA (<i>16S</i>), cytochrome oxidase subunit I (<i>COI</i>), alpha-myosin (<i>MYH6</i>) genes and <i>S72</i> intron molecular data. Our results partially corroborate the “<i>Brycon acuminatus</i>” group proposed by Howes in 1982: our proposed clade keeps <i>B</i>. <i>devillei</i>, <i>B</i>. <i>ferox</i>, and <i>B</i>. <i>insignis;</i> but it also includes <i>B</i>. <i>opalinus</i>, <i>B</i>. <i>vermelha</i>, and <i>H</i>. <i>weatlandii</i> whereas it excludes <i>B</i>. <i>nattereri</i>. The phylogeographic unit formed by Bryconinae species in southeastern Brazil reflects the long and isolated paleohydrological history of these coastal basins relative to the continental watersheds.</p></div