Invasion, dispersion and hybridization of fish associated to river transposition: karyotypic evidence in Astyanax "bimaculatus group" (Characiformes: Characidae)

Author(s)

Moreira Peres, Wellington Adriano ; Carlos Bertollo, Luiz Antonio ; Buckup, Paulo Andreas ; Blanco, Daniel Rodrigues ; Zanella Kantek, Daniel Luis ; Moreira-Filho, Orlando

• Document type: Journal article
• Source: Reviews in Fish Biology and Fisheries; v. 22, n. 2, p. 8-pg., 2012-06-01.

Abstract

The Astyanax species of the bimaculatus group include morphologically similar representatives that share the same color pattern, corresponding to at least 20 species. Specimens from the So Francisco River basin and from the Grande River (Upper Parana basin) are included in this group. In the early 1960's, the Piumhi River, an original tributary of the Grande River, was transposed to the So Francisco River basin due to the construction of the Furnas Hydroelectric Power, in the state of Minas Gerais, Brazil. In this context, we characterized representatives of the group from both basins and from the transposition region of the Piumhi River, using chromosome characteristics obtained by conventional analyzes and fluorescence in situ hybridization with rDNA probes. All the analyzed specimens presented 2n = 50 chromosomes and similar localization of the nucleolus organizer regions (Ag-NORs), 18S rDNA and 5S rDNA sites. However, diagnostic chromosome differences were detected concerning the number of submetacentric and acrocentric chromosomes in the karyotypes, making possible the characterization of five distinct karyotypes (Cytotypes A-E), where the specimens from the So Francisco and from the Grande River correspond to Cytotypes A and B, respectively. In addition, these two Cytotypes were sympatrically found in the Piumhi River with specimens carrying a clear intermediate karyotype (Cytotype C), as well as with others harboring different karyotypes (Cytotypes D and E). Our data indicate that Cytotypes A and B probably diverged from each other during the prior geographic isolation. However, despite their chromosomal differentiations, they still maintain a close relationship which allows interbreeding and the formation of a secondary hybrid zone, due to the breakdown of the geographic isolation. (AU)