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Populations of Astyanax paranae, Astyanax fasciatus and Astyanax altiparanae collected from the Pindorama and Lopei streams (upper Paraná river basin, Brazil) were cytogenetically studied, checking for chromosomal differentiation and the evolutionary trend in the three species. Forty-eight chromosomes (8m + 20sm + 10st + 10a) were observed in both populations of Astyanax paranae. Astyanax fasciatus exhibited 50 chromosomes (8m + 18sm + 10st + 14a, Pindorama stream; 8m + 14sm + 12st + 16a, Lopei stream). The diploid number for A. altiparanae was 50 chromosomes in both populations (6m + 30sm + 4st + 10a). The three studied species exhibited multiple AgNORs with differences among the populations of A. paranae and A. fasciatus. Regarding the heterochromatin distribution, interpopulational differences were observed in the three species. The data of the present study demonstrate that both A. paranae and A. fasciatus exhibit karyotypical interpopulational differences more conspicuous than A. altiparanae populations, probably due to the characteristics that restricted both the A. paranae and the A. fasciatus to the upper portion of the streams, leading to the fixation of different chromosomal rearrangements in the populations. However, the absence of conspicuos interpopulational karyotypical differences in A. altiparanae suggests a gene flow between both populations. In the present study, the role of the streams as an environment which maintains the diversity of fish with different genetic pools became evident.

biologia

Interpopulational comparative cytogenetics analysis among three Astyanax (Characiformes: Incertae Sedis) species of two streams of upper Paraná River basin, Brazil