Cytogenetic patterns in representatives of two fish species complexes occurring in neotropical semiarid ecosystems: Astyanax bimaculatus (Characidae) and Gymnotus carapo (Gymnotidae).
Chromosomal evolution, allopapinous speciation, cytotypes, genetic evolution, cytogenetics
Cytogenetic studies have revealed an expressive diversity, which has not yet been identified in many fish families. There are considerably those with great diversity, such as Characiformes and also those with low diversity such as Gymnotiformes, but both have species of difficult morphological characterization, often diagnosed through cariotypic analyses, in which they reveal marked interspecific variations in the number and chromosomal structure. Thus, the present work intends to contribute from analyses, using classical cytogenetic methods, in specimens of Astyanax bimaculatus from the hydrographic basin, in the municipality of Parnamirim, in Rio Grande do Norte and compare them with species already described in the literature, in order to assist in an interdisciplinary way with other areas. For cytogenetic characterization, conventional staining by Giemsa and silver nitrate impregnation (Ag NORs) were used. The analyses showed that for Astyanax bimaculatus was characterized the diploid number of 50 chromosomes without the presence of sex chromosome system, caryotypic formula: 10m + 12sm + 18st + 10a, NF=90 (Pium River), and for Gymnotus carapo, diploid number equal to 44 chromosomes, with caryotypic formula 12m + 8sm + 8st + 16a, NF=74 (Rio Pium). The populations presented simple RONs in the short arms of subtelocentric chromosomes 12 and 7, respectively. This study helps to understand the group considered A. bimaculatus and the group considered G. carapo, enabling a better understanding for a future identification of species due to the genetic differences found, their conservation and protection.