Cytogenetic characterization of three allopatric species of Hypostomus Lacépède (1803) (Teleostei, Loricariidae)

The genus Hypostomus is distributed throughout South America and is one of the most widely studied genera among Loricariidae, with approximately 130 species described. However, correct taxonomic identification is difficult due to subtle morphological differences between species. Thus, cytogenetic data on this genus are fundamental to clarifying the evolutional history of the group. Cytogenetic analyses were carried out on three species of Hypostomus in the state of Paraná, Brazil: one from the Tibagi river basin (Hypostomus aff. ancistroides) and two from the Iguaçu river basin (Hypostomus commersonii and Hypostomus derbyi). Hypostomus aff. ancistroides had 2n = 66 chromosomes (12m; 16sm; 10st; 28a) and number of arms (fundamental number, FN) = 104, with large heterochromatic blocks identified in two chromosome pairs and nucleolar organizing regions (NORs) detected in seven chromosomes of the complement. The H. commersonii population had 2n = 68 chromosomes (12m; 12sm; 8st; 36a) and FN = 100, with low heterochromatin located pericentromerically and NORs detected in only one chromosome pair. The H. derbyi population had 2n = 66 chromosomes (6m; 10sm; 20 st; 30a), with large heterochromatic blocks dispersed throughout the karyotype and multiple sites with NORs. The karyotype markers proved efficient in separating the species studied herein and corroborate the divergent karyotype evolution in the genus Hypostomus.