B chromosomes: an update about their occurrence in freshwater Neotropical fishes (Teleostei)

Abstract

In freshwater Neotropical fishes, supernumerary chromosomes or B chromosomes have been found in 61 species so far, distributed in 16 families of seven different orders and in distinct hydrographic basins. The order Characiformes is the one that possesses the most species with these chromosomes, including 31 species from six different families. The order Siluriformes has 21 species from five families, with Rhamdia, of the family Heptapteridae, being the most common genus where these chromosomes are found. The order Perciformes has five species with B chromosomes in only one family, Cichlidae, and the orders Beloniformes, Cyprinodontiformes, Gymnotiformes and Synbranchiformes contain only one species each with extra chromosomes. They are found as microchromosomes in Schizodon, Astyanax, Moenkhausia, Cyphocharax, Steindachnerina, Prochilodus, Rhamdia, Iheringichthys and Loricaria, among others, up to supernumerary macrochromosomes as in Astyanax, varying in morphology as well as number, showing evidence of the wide diversity of B chromosomes in Neotropical fishes.

Preferential accumulation of sex and Bs chromosomes in biarmed karyotypes by meiotic drive and rates of chromosomal changes in fishes

“…and Siluriformes (n=21 spp.) (Fenocchio and Bertollo 1990, Dias and Foresti 1993, Venere et al 1999, Carvalho et al 2008. In these orders, the frequency of B chromosomes is the highest found in all fish orders to date, including the large order Perciformes.…”

“…The total number of species analyzed included 52 species with sex chromosome systems and 39 species with MEIOTIC DRIVE AND CHROMOSOMAL CHANGES IN FISHES Bs chromosomes. Diploid numbers and karyotype formulas were obtained from several databases, mainly reviews by Carvalho et al (2008) and Arai (2011). The karyotype formulas were used to calculate the mean percentages of mono-brachial (acrocentric or telocentric) chromosomes for each species.…”

“…In these orders, the frequency of B chromosomes is the highest found in all fish orders to date, including the large order Perciformes. MEIOTIC DRIVE AND CHROMOSOMAL CHANGES IN FISHES More revealing is the fact that both orders show a tendency toward retaining bi-brachial chromosomes, which is also the most frequent morphology in their supernumerary chromosomes (Carvalho et al 2008). Morphologically and numerically, the B chromosomes of fish may range from dot-like elements to large metacentrics close to the size of the larger pairs of the A karyotype (e.g., MoreiraFilho et al 2004).…”

“…Cases of Bs chromosomes in fish have increasingly been identified in recent years, especially in the Neotropical region (Carvalho et al 2008). Supernumerary chromosomes, albeit of independent origins, are notoriously recurrent in Characiformes (n=31 spp.)…”

Chromosomal analyses in Megalonema platanum (Siluriformes: Pimelodidae), an endangered species from South American rivers

“…In Neotropical fishes, 61 species have supernumerary chromosomes or Bs, distributed in 16 families, 33 genera and seven different orders (Carvalho et al, 2008). These chromosomes in the family Pimelodidae were described in Bergiaria westermanni (Lütken, 1874) by Dias & Foresti (1993), Iheringichthys labrosus (Lütken, 1874) by Vissotto et al (1999), Carvalho et al (2004) Borin & MartinsSantos (2004).…”