抄録
Cytogenetic studies were conducted in Astyanax scabripinnis (Pisces, Characidae, Tetragonopterinae) species complex, from the Canta Galo brook (Tietê River basin, State of São Paulo, Brazil). Two sympatric cytotypes differing in diploid number and karyotype structure were detected. Almost all specimens presented 2n=50, with a karyotype consisting of 4M+26SM+4ST+16A and a fundamental number FN=84. However, two specimens in this sample-a female and a male-collected syntopically with that cytotype were found to be 2n=48 (6M+22SM+8ST+12A) and to have the same number of chromosome arms (FN=84). The two cytotypes showed some differences in constitutive heterochromatin distribution. The probable events implicated in this divergence and their significance are discussed, together with aspects of the evolutionary process of this species complex.
