Genus Leporinus Research Articles

Cytogenetics of the genus Leporinus (Pisces, Anostomidae). II. Molecular cytogenetics, organization and evolutionary conservation of a chromosome-specific satellite DNA from Leporinus obtusidens.

A chromosome-specific satellite DNA from the South American fish species Leporinus obtusidens has been isolated and characterized. Sequence analysis and Southern hybridization studies indicate that the cloned 483-bp fragment is 60% AT rich and appears to comprise two diverged monomers. A highly variable low-copy number polymorphism was detected and, thus, this satellite DNA may serve as a valuable genetic marker. Using a Southern blot approach, the cloned satellite DNA cross-hybridized strongly to the DNA of Leporinus elongatus but failed to detect homologous sequences in the genomes of other closely related Leporinus species and higher vertebrates. Using fluorescence in situ hybridization to mitotic metaphase spreads of L. obtusidens and L. elongatus, this satellite DNA was located to the (peri)centromeric region of one single chromosome pair in both species. As the cloned satellite DNA sequence clearly evolved along a chromosomal lineage and is highly variable, it may serve as a very useful marker in further genetic, molecular and cytogenetic studies of the genus Leporinus.

Heterochromatin and NORs variability inLeporinusfish (Anostomidae, Characiformes)

SUMMARYC-banding studies in four species of Characiformes fish of the genus Leporinus (Anostomidae) identified interspecific differences despite the strict similarity in karyotype macrostructure among them. A perceptible reduction in centromeric heterochromatin observed in L. piau seems to be a derived condition. L. amblyrhyncus and L. taeniatus exhibit a centromeric and telomeric heterochromatin pattern which is possibly basic in the group, and L. striatus shows a few exclusive intercalary blocks probably derived from inversions and/or transpositions. The nucleolar organizer regions, which were always found to be associated with heterochromatin segments, appear in different chromosomes or chromosome sites in the species studied, also indicating the occurrence of modifications during karyotype evolution in these fish.

Heteromorphic sex chromosomes in three species of the genus Leporinus (Pisces, Anostomidae).

The present paper describes three cases of heteromorphic sex chromosomes in fishes of the genus Leporinus (Anostomidae). An XX/XY type was found in Leporinus lacustris and a ZZ/ZW type in L. silvestrii and L. obtusidens. These facts agree with the observations of Ebeling and Chen (1970), who suggested that heterogamety evolved not once but many times among the teleosts.