Cytogenetic analysis in three species from genus Astyanax (Pisces; Characiformes) with a new occurrence of B chromosome in Astyanax paranae

Abstract

Cytogenetic studies were carried out in three species from genus Astyanax: Astyanax paranae (Tagaçaba Stream and Tauá Stream), Astyanax altiparanae (Iguaçu River and Maringá Stream) and Astyanax fasciatus (Maringá Stream). Both populations of A. paranae featured 2n = 50 chromosomes, although with different karyotype formulae and Ag-nucleolar organizer regions systems. Using the FISH technique in the Tagaçaba population, it was possible to detect rDNA genes in 14 chromosomes and bitelomeric marking in one chromosome. The constitutive heterochromatin pattern also showed differences between the two populations. Moreover, the Tagaçaba population showed macrochromosome B in 50% of analyzed females. Both A. altiparanae populations featured 2n = 50 chromosomes, but also differed in karyotype formula. Both populations featured multiple-NOR systems and quite similar constitutive heterochromatin patterns. For the A. fasciatus population from Maringá Stream, the diploid number was 2n = 46 chromosomes with karyotype formulae 14m, 10sm, 12st and 10a (fundamental number = 82), with single-NOR system and heterochromatin pattern showing evident markers in the telomeric regions of several subtelocentric and acrocentric chromosomes. The data presented for this species differ from some previously analyzed populations with regard to diploid number (2n = 48 chromosomes) and karyotype formula for those with the same diploid number. The present data strengthen the accentuated cytogenetical variability of the genus Astyanax. © 2014 © 2014 Dipartimento di Biologia Evoluzionistica, Università di Firenze.