Constitutive Heterochromatin and Ag-NOR Polymorphisms in the Small Characid Fish Astyanax scabripinnis (Jenyns, 1842)

Abstract

Summary Studies on different populations of the Characidae fish Astyanax scabripinnis, a species complex, have shown the occurrence of many levels of cytogenetic polymorphisms, such as in the positioning and amount of constitutive heterochromatins, and in the localization of nucleolar rDNA sites. The present paper describes the wide polymorphisms and the differences in location and quantity of heterochromatins in 2 A. scabripinnis populations, which are isolated from each other by waterfalls along the Canta Galo stream (São Paulo State, Brazil). Samples from both populations presented the same karyotype formulae. The specimens from the population located at 980 m of altitude revealed few variations in heterochromatins and NORs sites. On the other hand, those specimens collected from 720 m showed high variability in positioning and number of C-bands and rDNA loci. Events of transposition between telomeric segments, preferential positioning of the nucleolar rDNA clusters and the presence of GC-rich heterochromatins are also discussed.

Molecular cytogenetics and its contribution to the understanding of the chromosomal diversification in Hoplias malabaricus (Characiformes)

“…The band pattern produced by CMA 3 is coincident with some heterochromatic blocks, especially those associated with Ag‐NORs. In this population, the observed Ag‐NORs are coincident with the C‐bands and are CMA (possibly rich in GC base pairs), as in other populations of H. malabaricus (Vicari et al , 2005), and several other groups of Characiformes, such as Characinae and Cynopotaminae (Venere et al , 1997), the genera Leporinus (Artoni et al , 1999; Margarido & Galetti, 2000), Astyanax (Souza et al , 2007) and Salminus (Souza et al , 2008).…”

Downstairs gene flow: the effects of a linear sequence of waterfalls on the only population of the endangered minnow Astyanax xavante

“…This type of migration pattern and population differentiation due to waterfalls has been previously described in the literature, reflecting limited and unidirectional gene-flow and increased genetic diversity in populations from upper distributions (Hernandez-Martich & Smith, 1990;Castric et al, 2001;Souza et al, 2007;Tatarenkov et al, 2010). This pattern can also be observed in another species of the Astyanax genus, Astyanax scabripinnis (Jenyns 1842).…”

“…In particular, a unidirectional gene flow pattern was observed in populations sampled from two sites isolated by a waterfall with c . 100 m of free fall in Canta‐Galo Brook in south‐eastern Brazil, where individuals located at an altitude of 980 m exhibited lower genetic diversity (measured as the variability in the nucleolus organizer regions) compared with individuals located at an altitude of 720 m (Souza et al , ). The distribution pattern and ecological–biological characteristics of A. xavante are very similar to those of the A. scabripinnis complex, despite occupying distinct regions (Venere & Garutti, ).…”

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

“…While the "scabripinnis complex" has been characterized by a preferential centromeric and telomeric pattern of C-bands (Fernandes and Martins-Santos, 2005;Souza et al, 2007;Santos et al, 2012), the "bimaculatus group" has shown mainly interstitial heterochromatic blocks on the chromosomes (Domingues et al, 2007;Hashimoto et al, 2008;Ferreira Neto et al, 2009;Kavalco et al, 2011). The species now analyzed show that the distribution of heterochromatin falls, in general, among the above cases.…”