Chromosome polymorphism of heterochromatin and nucleolar regions in two populations of the fish Astyanax bockmanni (Teleostei: Characiformes)

Fábio Porto-Foresti,Diogo Teruo Hashimoto

doi:10.1590/s1679-62252010000400016

Abstract

Karyotype and other chromosomal markers as revealed by C-banding and silver (Ag) impregnation in two Astyanax bockmanni populations (Barra Seca Stream and Campo Novo River) were examined. The diploid chromosome number 2n = 50 and nearly identical karyotypes were documented. C-banding revealed heterochromatic blocks on the terminal regions of some chromosomes, with high frequencies of polymorphisms. The Ag-impregnation showed that the nucleolus organizer regions (NORs) varied in number, location and organization. Astyanax bockmanni revealed chromosome characteristics similar those of the species complex "A. scabripinnis". Mechanisms that may be responsible for the high degree of polymorphism are discussed.

Highlights

The family Characidae, order Characiformes, is one of the most numerous and diverse families of freshwater fishes in South America (Nelson, 2006), consisting of approximately 597 recognized species (Buckup et al, 2007)
The diploid chromosome number of 2n = 50 described in the present study is in accordance with data previously reported for other populations of Astyanax bockmanni (Kavalco et al, 2009)
Our results indicate a stable 2n for A. bockmanni in contrast to the species complexes A. fasciatus and A. scabripinnis that show variable diploid chromosome numbers in different individuals, some of which live in sympatry (Moreira-Filho & Bertollo, 1991; Artoni et al, 2006)

Summary

Introduction

The family Characidae, order Characiformes, is one of the most numerous and diverse families of freshwater fishes in South America (Nelson, 2006), consisting of approximately 597 recognized species (Buckup et al, 2007). The genus Astyanax, a speciose group of Neotropical characids, comprises about 86 valid species (Lima et al, 2003) that occur in diverse habitats within freshwater drainages from the southern United States to central Argentina. According to Mirande (2009), the nominal species currently assigned to Astyanax represent a nonmonophyletic assemblage. An example is Astyanax scabripinnis, which was first characterized as a “species complex” by Moreira-Filho & Bertollo (1991) based on chromosomal and morphological characters. It currently contains 15 valid species (Bertaco & Lucena, 2006)

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Conclusion