B chromosomes in the fish <i>Astyanax scabripinnis</i> (Characidae, Tetragonopterinae): An overview in natural populations

Abstract

Astyanax scabripinnis, a small neotropical freshwater fish, is a headwater species living in small tributaries of many Brazilian rivers, where they form isolated populations. This species harbors a B chromosome system in several populations. Among the several kinds of Bs reported in this species, the B_M variant, a large metacentric of a similar size to the largest A chromosome, is the most widespread in natural populations. It probably corresponds to the ancestral B type in this species and a very similar B chromosome is also found in other Astyanax species. Strong evidence suggests that this B is an isochromosome showing structural and functional homology between its two arms, as shown by satellite DNA localization and the formation of a ring B univalent during meiosis. The B_SM and B_m variants, a large submetacentric and a small metacentric, respectively, represent rare variants and may be derived from structural rearrangements of the B_M chromosome. In addition, B microchromosomes (B_micro) were found in some populations. Frequency analyses in mountain populations have shown that B chromosomes are found in populations located at high altitude, but are absent in populations at low altitude, which is consistent with their parasitic nature, given the ecological peculiarities of both kinds of populations.

First report of a B chromosome in a natural population of Astyanax altiparanae (Characiformes, Characidae)

“…Nevertheless, there are no reports about B chromosomes in Astyanax altiparanae, and this represents the first occurrence reported for this species. Although A. scabripinnis reveals B chromosomes of different morphology and size, a metacentric B macrochromosome (B M ) has been found to be a common feature in most of the analyzed populations with supernumerary chromosomes (Moreira-Filho et al, 2004). Additionally, a similar B M chromosome has been found in other three species of the same genus (A. eigenmanniorum, A. fasciatus, and A. schubarti), suggesting that this B M variant might have preceded the differentiation of these species (Moreira-Filho et al, 2001).…”

B chromosomes in a population of Astyanax eigenmanniorum (Characiformes, Characidae) from the Araguari River Basin (Uberlândia, MG, Brazil)

“…However, although very common, these characteristics are not present in all B chromosomes (Beukeboom, 1994). Among fishes, the most studied species is A. scabripinnis, which presents macro-and micro-supernumerary chromosomes with a frequency that varies between males and females and according to the altitude at which populations occur (Salvador and Moreira-Filho, 1992;Vicente et al, 1996;Néo et al, 2000;Mestriner et al, 2000;Ferro et al, 2003;Moreira-Filho et al, 2004;Araujo and Morelli, 2006). This paper gives the description of a large metacentric supernumerary chromosome in A. eigenmanniorum from the Caetano Stream (18°44' 56" S/ 048°18' 39" W, Uberlândia, MG, Brazil).…”

Karyotypic diversity among three species of the genus Astyanax (Characiformes: Characidae)

“…The first approach on the probable origin of this chromosome was performed by Salvador and Moreira-Filho (1992), who considered that a non-disjunction, followed by heterochromatinization, could be associated with its emergence. However strong evidence that this supernumerary is an isochromosome was given by some additional mitotic and meiotic studies, which also indicated that its heterochromatic nature is related with the amplification and dispersion of highly repetitive sequences (Mestriner et al, 2000;Moreira-Filho et al, 2004;Vicari et al, 2011).…”