Cytogenetic analyses performed in populations of the Neotropical freshwater fish Leporinus elongatus of the Upper Paraná River basin showed a chromosome polymorphism involving heterochromatic segments of the nucleolar organizing pair in this species. The NOR-bearing chromosome pair was characterized by two phenotypes identified by the absence (C¹) or presence (C²) of a heterochromatic segment located in an interstitial position of the long arm in this pair. The meiotic segregation of these variations results in three distinct cytotypes, C¹C¹, C¹C² and C²C². Both populations were in Hardy-Weinberg equilibrium. Sex-related cytotype divergence was identified and multivariate analyses revealed that the C²C² individuals presented morphometric differentiation relative to body height in relation to the other cytotypes. A chromosome differentiation and a cytotype proportion difference observed between both populations suggest the occurrence of population subdivision within this species along the Upper Paraná River basin. These findings might contribute to the knowledge of the population biology of this fish and for its conservation.
Characiformes; Anostomidae; heterochromatin; chromosome polymorphism
