Chromosomal Characterization of Armored CatfishHarttialongipinna(Siluriformes, Loricariidae): First Report of B Chromosomes in the Genus

Abstract

The B chromosomes are accessory elements that are widely distributed among eukaryotic genomes and often show non-Mendelian inheritance. They are considered dispensable for the growth, development, and reproduction of organisms. Some studies have suggested that these elements may affect sex determination. Harttia is a small armored catfish genus that shows sexual dimorphism, including hypertrophied odontodes on the pectoral fin spines and along the margins of the snout in mature males. They exhibit considerable karyotypic diversity with diploid number (2n) variation and heteromorphic sex system in H. carvalhoi. To date, no occurrences of B chromosomes in the Harttia genus were detected and no relation to sexual differentiation in Neotropical fish has been determined. To determine the validity of this claim, the present paper characterized specimens of Harttia longipinna by classical and molecular cytogenetic methods. The 2n found was 58 (16m + 12sm + 16st + 14a), but of the 50 specimens analyzed (30 male and 20 female), 23 specimens (16 males and seven females) show an intra-individual from 0 to 2 micro B chromosomes. The B chromosomes were completely heterochromatic. The single NORs were shown in the first acrocentric pair with silver staining and 18S rDNA probing. FISH performed with 5S rDNA probe showed a single cistron in the proximal region of the short arm of a small metacentric pair. Thus, the cytogenetic data obtained in this study of H. longipinna highlight the karyotypic diversity found within the genus Harttia, and represent the first description of B chromosomes for this genus.

Twenty Years of Physical Mapping of Major Ribosomal RNA Genes across the Teleosts: A Review of Research

“…In contrast, in Loricariinae, evolution diversified karyotypes by centric fissions, centric fusions, as well as pericentric inversions in both number and chromosome morphology. In the genus Harttia , rDNA sites are located at either termini of distinct acro-/subtelocentric chromosomes, but interstitial locations have been also revealed in some species by other techniques [Kavalco et al, 2005a;Blanco et al, 2012]. The dislocation of rDNA sites from the plesiomorphic position most likely follows from overall chromosome rearrangements in this genus.…”

Chromosomal distribution of the retroelements Rex 1, Rex 3 and Rex 6 in species of the genus Harttia and Hypostomus (Siluriformes: Loricariidae)

“…In H. longipinna, there is a conspicuous heterochromatic block allocated in the acrocentric pair 23 (Blanco et al, 2012a), in which it was not detected the presence of any of the retroelements tested, as well as in the supernumerary chromosomes of this species. The absence of the elements Rex in the B chromosomes of H. longipinna discards the role of these retrotransposons in the origin of these accessory chromosomes.…”

“…Harttia is a genus of the subfamily Loricariinae that has 26 valid species (Fricke et al, 2019). Of these, only eight species present cytogenetic data (Alves et al, 2003;Kavalco et al, 2005;Centofante et al, 2006;Rodrigues, 2010;Blanco et al, 2012aBlanco et al, , 2013Blanco et al, , 2014Blanco et al, , 2017. The genus Harttia has conspicuous karyotype diversity, with diploid numbers (2n) ranging from 52 chromosomes in Harttia carvalhoi Miranda Ribeiro, 1939 females (Centofante et al, 2006) to 62 chromosomes in Harttia absaberi Oyakawa, Fichberg & Langeani, 2013 (cited as Harttia sp.…”

First report of B chromosomes in three neotropical thorny catfishes (Siluriformes, Doradidae)

“…In Neotropical fish, the mechanisms responsible for the origin and evolution of B chromosomes remain unclear, as several theories were proposed (Lui et al 2009, Blanco et al 2012, and others). The B microchromosomes were described in distinct neotropical fishes, including Schizodon Agassiz, 1829, Astyanax Baird et Girard, 1854, Moenkhausia Eigenmann, 1903, Cyphocharax Fowler, 1906, Steindacnerina Fowler, 1906, Prochilodus Agassiz, 1829, Rhamdia , Bleeker, 1858 Iheringichthys Eigenmann et Norris, 1900, Callichthys Scopoli, 1777, Megalonema Eigenmann, 1912, Pimelodella , Eigenmann et Eigenmann, 1888 and Loricaria Linnaeus, 1758 (Carvalho et al 2008, Lui et al 2009).…”