RESUMO
Approximately 90 species in the genus Leporinus (Characiformes, Anostomidae) are known, and most of them do not present differentiated sex chromosomes. However, there is a group of 7 species that share a heteromorphic ZW sex system. In all of these species, the W chromosome is the largest one in the karyotype and is mostly heterochromatic. We investigated the distribution of several microsatellites in the genome of 4 Leporinus species that possess ZW chromosomes. Our results showed a very large accumulation of mostly microsatellites on the W chromosomes. This finding supports the presence of an interconnection between heterochromatinization and the accumulation of repetitive sequences, which has been proposed for sex chromosome evolution, and suggests that heterochromatinization is the earlier of the 2 processes. In spite of the common origin that has been proposed for W chromosomes in all of the studied species, the microsatellites followed different evolutionary trajectories in each species, which indicates a high plasticity for sex chromosome differentiation.