Chromosome characterization and biogeographic relations among three populations of the driftwood catfish Parauchenipterus galeatus (Linnaeus, 1766) (Siluriformes: Auchenipteridae) in Brazil

The present study employed basic and molecular cytogenetic methods to characterize three populations of Parauchenipterus galeatus from the basins of the Paraná and São Francisco Rivers, and a region of connection between the two basins. Although the diploid number was equal to 58 chromosomes, variations in karyotype formula were detected among the populations. B chromosomes were detected only in the population from the São Francisco River. Heterochromatin was located in the terminal position in almost all the chromosomes and in the pericentromeric position in some acrocentric chromosomes in the three populations. A single nucleolus organizer region was detected by silver nitrate and 18S rDNA‐fluorescent in situ hybridization in the short arm of one subtelocentric pair in the three populations, varying only in the chromosome pair bearing this site. The 5S rDNA sites were located in two submetacentric chromosome pairs in the three populations, varying only in the chromosome pairs bearing these sequences. Classic and molecular chromosome markers, along with the context of the natural history of the formation of hydrographic basins, ecological aspects, and the geographic isolation of populations between hydrographic basins and within the same basin, were important contributions to the discussion on possible biogeographic relations among the populations of Parauchenipterus galeatus. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 99 , 648–656.