Constitutive heterochromatin and Ag-NOR polymorphisms in the small characid fish Astyanax scabripinnis (Jenyns, 1842)

Abstract

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. © 2007 The Japan Mendel Society.