Comparative cytogenetics among species of the Astyanax scabripinnis complex. Evolutionary and biogeographical inferences

Karyotype data are presented for distinct species of the genus Astyanax from four rivers belonging to three different hydrographic basins of the State of Parand, Brazil (Verde River - Tibagi basin, Aqungui River - Ribeira basin, and Santo Antonio and Jaguariava Rivers - Jaguariava basin). Three karyotypic forms were identified, here denominated karyotype A (2n = 50 chromosomes, with 8m+1 8sm+10st+14a, and thirteen 18S rDNA sites); karyotype B (2n = 50 chromosomes, with 8m+18sm+10st+14a, and four 18S rDNA sites); and karyotype C (2n = 48 chromosomes, with 10m+16sm+10st+12a, and eight 18S rDNA sites). The pattern of constitutive heterochromatin was similar among the three karyotypic forms, with few differences. The 5S rDNA corresponds to a synapomorphic character regarding its number and chromosomal localization. The karyotypic form A occurs in the distribution center of the type locality of A. paranae, in the proximities of the town of Castro (Tibagi basin), and may have reached the headwaters of the Ribeira River by the breakdown of geographical barriers. The karyotypic forms B and C are sympatric and syntopic, occurring solely in the Jaguariava River basin. Our hypothesis is that the karyotypic form A corresponds to the species A. paranae and forms B and C correspond to other species of the A. scabripinnis complex.