Cytogenetics studies in two populations of Astyanax scabripinnis with 2n=48 chromosomes (Teleostei, Characidae)

Abstract

Cytogenetic analysis in 2 populations of Astyanax scabripinnis from São Domingos and Tamboara streams, affluents of the Ivaí river basin, was carried out. Both populations presented same diploid of 2n=48 chromosomes, although they might be differentiated by karyotypic formulae (10M, 20SM, 8ST, 10A and 10M, 24SM, 6ST, 8A, respectively) and number of nucleolar organizer chromosomes (3 and 7 NORs, respectively). Besides the population from São Domingos showed 1 metacentric B microchromosome restricted to females. Low frequency of this B microchromosome suggests a recent origin in populations of Astyanax scabripinnis and its adaptive function remains unknown. Aspects related to karyotype diversity of this "species complex" are discussed, contributing to the understanding of the mechanisms involved in the diversity and speciation on the group.